Patent Application
20210155959
Mammalian oocytes are capable of reprogramming somatic cells into a totipotent state through somatic cell nuclear transfer (SCNT). SCNT is used in therapeutic cloning which involves the generation of tissues from a donor organism that is genetically identical to or similar to the intended host. SCNT also enables cloning of animals. This technique has great potential in agro-biotechnology, as well as in the conservation of endangered species. However, the extremely low success rate of cloning makes the actual use of this technique difficult. For example, in the case of mouse, only about 30% of SCNT embryos develop to blastocysts and only 1-2% of embryos transferred to surrogate mothers can reach term. Furthermore, in the surviving embryos, abnormalities are frequently observed in extraembryonic tissues, such as placenta and umbilical cord in almost all cloned mammalian species. These observations suggest that SCNT reprogramming has some deficiencies that impede the embryo developmental process. Various epigenetic abnormalities in DNA methylation, histone modifications, and genomic imprinting have been implicated in the low success rate of SCNT. There is a significant need for improving the efficiency of cloning.
The invention provides methods for improving cloning efficiency. The invention provides methods for improving cloning efficiency. In particular embodiments, the invention provides methods for improving somatic cell nuclear transfer efficiency that involve Kdm4d overexpression is an Xist knockout donor cell.
In one aspect, the invention provides a method for obtaining a cloned blastocyst is provided that includes transferring a donor nucleus obtained from a somatic cell lacking Xist activity into an enucleated oocyte, and expressing in the oocyte Kdm4d, thereby obtaining a cloned blastocyst. In some embodiments of the method, the oocyte is injected with a Kdm4d mRNA. In some embodiments, the donor cell nucleus is obtained from an embryoic fibroblast comprising a deletion in Xist or comprising an inactive form of Xist. In some embodiments, the donor nucleus is obtained from a human, cat, cow, dog, pig, or horse. In some embodiments, the method also includes transferring the blastocyst into a host uterus for gestation. In some embodiments, the method increases the rate of live births relative to conventional somatic cell nuclear transfer by at least about 10-20%. Some aspects of the invention include a blastocyst produced by the method described above. Some aspects of the invention include a cloned organism produced by implanting the blastocyst produced by the method described above.
In another aspect, the invention provides a method for obtaining a cell or tissue for transplantation into a subject, the method comprising inactivating Xist or reducing Xist activity or expression in a cultured cell obtained from a subject; transferring the nucleus from the cultured cell into an enucleated oocyte, thereby activating the oocyte; and injecting the activated oocyte with a Kdm4d mRNA and culturing the resulting cell, thereby obtaining a cell or tissue suitable for transplantation into the subject. In some aspects of the invention, a cell or tissue produced by this method is provided. In some embodiments, Xist is inactivated by genome editing. For example, in some embodiments, a CRISPR system is used to introduce a deletion or inactivating mutation in a genomic Xist polynucleotide. In other embodiments of the method, Xist polynucleotide expression or activity is reduced using siRNA or shRNA.
In other aspects of the invention, a cell is provided that has a deletion in Xist or a reduced level of Xist expression and has a heterologous polynucleotide encoding Kdm4d.
Additional aspects include an oocyte comprising a donor nucleus obtained from a somatic cell lacking Xist activity and expressing an increased level of Kdm4d relative to a conventional oocyte.
Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs. The following references provide one of skill with a general definition of many of the terms used in this invention: Singleton et al., Dictionary of Microbiology and Molecular Biology (2nd ed. 1994); The Cambridge Dictionary of Science and Technology (Walker ed., 1988); The Glossary of Genetics, 5th Ed., R. Rieger et al. (eds.), Springer Verlag (1991); and Hale & Marham, The Harper Collins Dictionary of Biology (1991). As used herein, the following terms have the meanings ascribed to them below, unless specified otherwise.
By “KDM4D polypeptide” is meant a polypeptide or fragment thereof having at least about 85% amino acid sequence identity to NCBI Reference No. Q6B0I6 and having demethylase activity. An exemplary KDM4D amino acid sequence is provided below:
By “KDM4D polynucleotide” is meant a nucleic acid molecule encoding a KDM4D polypeptide. An exemplary KDM4D nucleic acid is provided below:
By “EZH1 polypeptide” (histone-lysine N-methyltransferase EZH1) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: NP_001982, or a fragment thereof, and having methyltransferase activity. An exemplary H3K27 methyltransferase amino acid sequence is provided below:
By “EZH1 polynucleotide” is meant a nucleic acid molecule encoding the EZH1 polypeptide. An exemplary EZH1 polynucleotide sequence is provided at NM 001991.4 and reproduced below:
By “EZH2 polypeptide” (histone-lysine N-methyltransferase EZH2) is meant a protein having at least about 85% amino acid identity to the sequence provided at UniProtKB/Swiss-Prot: Q15910.2, or a fragment thereof, and having methyltransferase activity. An exemplary H3K27 methyltransferase amino acid sequence is provided below:
By “EZH2 polynucleotide” is meant a nucleic acid molecule encoding an EZH2 polypeptide. An exemplary EZH2 polynucleotide sequence is provided at NM_001203248.1 and is provided below:
By “KDM6A polypeptide” (lysine-specific demethylase 6A, also referred to as histone demethylase UTX) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: 015550.2, or a fragment thereof, and having demethylase activity. An exemplary KDM6A amino acid sequence is provided below:
By “KDM6A polynucleotide” is meant a nucleic acid molecule encoding a KDM6A polypeptide. An exemplary KDM6A polynucleotide sequence is provided at NM_001291415.1.
By “KDM6B polypeptide” (lysine-specific demethylase 6, also referred to as JmjC domain-containing protein 3) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: 015054.4, or a fragment thereof, and having demethylase activity. An exemplary KDM6B amino acid sequence is provided below:
By “KDM6B polynucleotide” is meant a nucleic acid molecule encoding a KDM6B polypeptide. An exemplary KDM6B polynucleotide sequence is provided at NM_001080424.2 and reproduced below:
By “KDM6C polypeptide” (histone demethylase UTY, also referred to as ubiquitously-transcribed TPR protein on the Y chromosome) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: 014607.2, or a fragment thereof, and having demethylase activity. An exemplary KDM6C amino acid sequence is provided below:
By “KDM6C polynucleotide is meant a nucleic acid molecule encoding a KDM6C polypeptide. An exemplary KDM6A polynucleotide sequence is provided at NM_001258249.1, which sequence is reproduced below:
By “Gab 1 polypeptide” (GRB2-associated-binding protein 1) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: NP_997006.1, or a fragment thereof. An exemplary Gab1 amino acid sequence is provided below:
By “Gab1 polynucleotide” is meant a nucleic acid molecule encoding a Gab1 polypeptide. An exemplary Gab1 polynucleotide sequence is provided at NM_002039.3, which is reproduced below:
By “Sfmbt2 polypeptide” (scm-like with four MBT domains protein 2) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: NP_001018049.1, or a fragment thereof. An exemplary Sfmbt2 amino acid sequence is provided below:
By “Sfmbt2 polynucleotide” is meant a polypeptide encoding an Sfmbt2 polypeptide. An exemplary Sfmbt2 polynucleotide sequence is provided at NM_001018039.1, which is reproduced below:
By “Smoc1 polypeptide” (SPARC related modular calcium binding 1) is meant a protein having at least about 85% amino acid identity to the sequence provided at NCBI Reference Sequence: NP_001030024, or a fragment thereof. An exemplary Smoc1 amino acid sequence is provided below:
By “Smoc1 polynucleotide” is meant a nucleic acid molecule encoding a Smoc1 polypeptide. An exemplary Smoc1 polynucleotide sequence is provided at XM_005267995.1, which is reproduced below:
By “tri-methylated histone H3 at lysine 27 (H3K27me3)” is meant the trimethylation of lysine 27 on histone H3 protein subunit. The H3K27me3 modification is generally associated with gene repression.
By “agent” is meant a peptide, nucleic acid molecule, or small compound.
By “allele” is meant one of two or more alternative forms of a gene that are found at the same place on a chromosome.
By “alteration” is meant a change (increase or decrease) in the expression levels or activity of a gene or polypeptide as detected by standard art known methods such as those described herein. As used herein, an alteration includes a 10% change in expression levels, preferably a 25% change, more preferably a 40% change, and most preferably a 50% or greater change in expression levels.”
By “ameliorate” is meant decrease, suppress, attenuate, diminish, arrest, or stabilize the development or progression of a disease.
In this disclosure, “comprises,” “comprising,” “containing” and “having” and the like can have the meaning ascribed to them in U.S. patent law and can mean “includes,” “including,” and the like; “consisting essentially of” or “consists essentially” likewise has the meaning ascribed in U.S. patent law and the term is open-ended, allowing for the presence of more than that which is recited so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments.
“Detect” refers to identifying the presence, absence or amount of the analyte to be detected.
By “disease” is meant any condition or disorder that damages, or interferes with the normal function of a cell, tissue, or organ. Examples of disorders include those associated with undesirable repression of an allele by H3K27me3-dependent imprinting. Microphthalmia exemplary disorder associated with H3K27me3-dependent imprinting relating to imprinting disorders.
By “DNA” is meant deoxyribonucleic acid. In various embodiments, the term DNA refers to genomic DNA, recombinant DNA, or cDNA. In particular embodiments, the DNA comprises a “target region.” DNA libraries contemplated herein include genomic DNA libraries, and cDNA libraries constructed from RNA, e.g., an RNA expression library. In various embodiments, the DNA libraries comprise one or more additional DNA sequences and/or tags.
By “effective amount” is meant the amount of a required to ameliorate the symptoms of a disease relative to an untreated patient. The effective amount of active compound(s) used to practice the present invention for therapeutic treatment of a disease varies depending upon the manner of administration, the age, body weight, and general health of the subject. Ultimately, the attending physician or veterinarian will decide the appropriate amount and dosage regimen. Such amount is referred to as an “effective” amount.
By “fragment” is meant a portion of a polypeptide or nucleic acid molecule. This portion contains, preferably, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the entire length of the reference nucleic acid molecule or polypeptide. A fragment may contain 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 nucleotides or amino acids.
The terms “isolated,” “purified,” or “biologically pure” refer to material that is free to varying degrees from components which normally accompany it as found in its native state. “Isolate” denotes a degree of separation from original source or surroundings. “Purify” denotes a degree of separation that is higher than isolation. A “purified” or “biologically pure” protein is sufficiently free of other materials such that any impurities do not materially affect the biological properties of the protein or cause other adverse consequences. That is, a nucleic acid or peptide of this invention is purified if it is substantially free of cellular material, viral material, or culture medium when produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Purity and homogeneity are typically determined using analytical chemistry techniques, for example, polyacrylamide gel electrophoresis or high performance liquid chromatography. The term “purified” can denote that a nucleic acid or protein gives rise to essentially one band in an electrophoretic gel. For a protein that can be subjected to modifications, for example, phosphorylation or glycosylation, different modifications may give rise to different isolated proteins, which can be separately purified.
By “isolated polynucleotide” is meant a nucleic acid (e.g., a DNA) that is free of the genes which, in the naturally-occurring genome of the organism from which the nucleic acid molecule of the invention is derived, flank the gene. The term therefore includes, for example, a recombinant DNA that is incorporated into a vector; into an autonomously replicating plasmid or virus; or into the genomic DNA of a prokaryote or eukaryote; or that exists as a separate molecule (for example, a cDNA or a genomic or cDNA fragment produced by PCR or restriction endonuclease digestion) independent of other sequences. In addition, the term includes an RNA molecule that is transcribed from a DNA molecule, as well as a recombinant DNA that is part of a hybrid gene encoding additional polypeptide sequence.
By an “isolated polypeptide” is meant a polypeptide of the invention that has been separated from components that naturally accompany it. Typically, the polypeptide is isolated when it is at least 60%, by weight, free from the proteins and naturally-occurring organic molecules with which it is naturally associated. Preferably, the preparation is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight, a polypeptide of the invention. An isolated polypeptide of the invention may be obtained, for example, by extraction from a natural source, by expression of a recombinant nucleic acid encoding such a polypeptide; or by chemically synthesizing the protein. Purity can be measured by any appropriate method, for example, column chromatography, polyacrylamide gel electrophoresis, or by HPLC analysis.
Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of 1 to 50 is understood to include any number, combination of numbers, or sub-range from the group consisting 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50.
By “reduces” is meant a negative alteration of at least 10%, 25%, 50%, 75%, or 100%.
By “reference” is meant a standard or control condition.
A “reference sequence” is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset of or the entirety of a specified sequence; for example, a segment of a full-length cDNA or gene sequence, or the complete cDNA or gene sequence. For polypeptides, the length of the reference polypeptide sequence will generally be at least about 16 amino acids, preferably at least about 20 amino acids, more preferably at least about 25 amino acids, and even more preferably about 35 amino acids, about 50 amino acids, or about 100 amino acids. For nucleic acids, the length of the reference nucleic acid sequence will generally be at least about 50 nucleotides, preferably at least about 60 nucleotides, more preferably at least about 75 nucleotides, and even more preferably about 100 nucleotides or about 300 nucleotides or any integer thereabout or therebetween.
Nucleic acid molecules useful in the methods of the invention include any nucleic acid molecule that encodes a polypeptide of the invention or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid molecule. Nucleic acid molecules useful in the methods of the invention include any nucleic acid molecule that encodes a polypeptide of the invention or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid molecule. By “hybridize” is meant pair to form a double-stranded molecule between complementary polynucleotide sequences (e.g., a gene described herein), or portions thereof, under various conditions of stringency. (See, e.g., Wahl, G. M. and S. L. Berger (1987) Methods Enzymol. 152:399; Kimmel, A. R. (1987) Methods Enzymol. 152:507).
For example, stringent salt concentration will ordinarily be less than about 750 mM NaCl and 75 mM trisodium citrate, preferably less than about 500 mM NaCl and 50 mM trisodium citrate, and more preferably less than about 250 mM NaCl and 25 mM trisodium citrate. Low stringency hybridization can be obtained in the absence of organic solvent, e.g., formamide, while high stringency hybridization can be obtained in the presence of at least about 35% formamide, and more preferably at least about 50% formamide. Stringent temperature conditions will ordinarily include temperatures of at least about 30° C., more preferably of at least about 37° C., and most preferably of at least about 42° C. Varying additional parameters, such as hybridization time, the concentration of detergent, e.g., sodium dodecyl sulfate (SDS), and the inclusion or exclusion of carrier DNA, are well known to those skilled in the art. Various levels of stringency are accomplished by combining these various conditions as needed. In a preferred: embodiment, hybridization will occur at 30° C. in 750 mM NaCl, 75 mM trisodium citrate, and 1% SDS. In a more preferred embodiment, hybridization will occur at 37° C. in 500 mM NaCl, 50 mM trisodium citrate, 1% SDS, 35% formamide, and 100·mu·g/ml denatured salmon sperm DNA (ssDNA). In a most preferred embodiment, hybridization will occur at 42° C. in 250 mM NaCl, 25 mM trisodium citrate, 1% SDS, 50% formamide, and 200 μg/ml ssDNA. Useful variations on these conditions will be readily apparent to those skilled in the art.
For most applications, washing steps that follow hybridization will also vary in stringency. Wash stringency conditions can be defined by salt concentration and by temperature. As above, wash stringency can be increased by decreasing salt concentration or by increasing temperature. For example, stringent salt concentration for the wash steps will preferably be less than about 30 mM NaCl and 3 mM trisodium citrate, and most preferably less than about 15 mM NaCl and 1.5 mM trisodium citrate. Stringent temperature conditions for the wash steps will ordinarily include a temperature of at least about 25° C., more preferably of at least about 42° C., and even more preferably of at least about 68° C. In a preferred embodiment, wash steps will occur at 25° C. in 30 mM NaCl, 3 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will occur at 42 C in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will occur at 68° C. in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. Additional variations on these conditions will be readily apparent to those skilled in the art. Hybridization techniques are well known to those skilled in the art and are described, for example, in Benton and Davis (Science 196:180, 1977); Grunstein and Hogness (Proc. Natl. Acad. Sci., USA 72:3961, 1975); Ausubel et al. (Current Protocols in Molecular Biology, Wiley Interscience, New York, 2001); Berger and Kimmel (Guide to Molecular Cloning Techniques, 1987, Academic Press, New York); and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York.
By “substantially identical” is meant a polypeptide or nucleic acid molecule exhibiting at least 50% identity to a reference amino acid sequence (for example, any one of the amino acid sequences described herein) or nucleic acid sequence (for example, any one of the nucleic acid sequences described herein). Preferably, such a sequence is at least 60%, more preferably 80% or 85%, and more preferably 90%, 95% or even 99% identical at the amino acid level or nucleic acid to the sequence used for comparison.
Sequence identity is typically measured using sequence analysis software (for example, Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, Wis. 53705, BLAST, BESTFIT, GAP, or PILEUP/PRETTYBOX programs). Such software matches identical or similar sequences by assigning degrees of homology to various substitutions, deletions, and/or other modifications. Conservative substitutions typically include substitutions within the following groups: glycine, alanine; valine, isoleucine, leucine; aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine; lysine, arginine; and phenylalanine, tyrosine. In an exemplary approach to determining the degree of identity, a BLAST program may be used, with a probability score between e−3 and e−100 indicating a closely related sequence.
By “Somatic Cell Nuclear Transfer” or “SCNT” is meant the transfer of a donor nucleus from a somatic cell into an enucleated oocyte. The process can be used in either reproductive or therapeutic cloning and may be accomplished by fusion of the somatic cell with the enucleated oocyte, injection of the nucleus into the enucleated oocyte, or by any other method.
The nucleus of the somatic cell provides the genetic information, while the oocyte provides the nutrients and other energy-producing materials that are necessary for development of an embryo. Once fusion has occurred, the cell is totipotent, and eventually develops into a blastocyst, at which point the inner cell mass is isolated.
The term “nuclear transfer” as used herein refers to a gene manipulation technique allowing an identical characteristics and qualities acquired by artificially combining an enucleated oocytes with a cell nuclear genetic material or a nucleus of a somatic cell. In some embodiments, the nuclear transfer procedure is where a nucleus or nuclear genetic material from a donor somatic cell is transferred into an enucleated egg or oocyte (an egg or oocyte from which the nucleus/pronuclei have been removed). The donor nucleus can come from a somatic cell.
The term “nuclear genetic material” refers to structures and/or molecules found in the nucleus which comprise polynucleotides (e.g., DNA) which encode information about the individual. Nuclear genetic material includes the chromosomes and chromatin. The term also refers to nuclear genetic material (e.g., chromosomes) produced by cell division such as the division of a parental cell into daughter cells. Nuclear genetic material does not include mitochondrial DNA.
The term “SCNT embryo” refers to a cell, or the totipotent progeny thereof, of an enucleated oocyte which has been fused with the nucleus or nuclear genetic material of a somatic cell. The SCNT embryo can develop into a blastocyst and develop post-implantation into living offspring. The SCNT embryo can be a 1-cell embryo, 2-cell embryo, 4-cell embryo, or any stage embryo prior to becoming a blastocyst.
The term “donor human cell” or “donor human somatic cell” refers to a somatic cell or a nucleus of human cell which is transferred into a recipient oocyte as a nuclear acceptor or recipient.
The term “somatic cell” refers to a plant or animal cell which is not a reproductive cell or reproductive cell precursor. In some embodiments, a differentiated cell is not a germ cell. A somatic cell does not relate to pluripotent or totipotent cells. In some embodiments the somatic cell is a “non-embryonic somatic cell”, by which is meant a somatic cell that is not present in or obtained from an embryo and does not result from proliferation of such a cell in vitro. In some embodiments the somatic cell is an “adult somatic cell”, by which is meant a cell that is present in or obtained from an organism other than an embryo or a fetus or results from proliferation of such a cell in vitro.
The term “oocyte” as used herein refers to a mature oocyte which has reached metaphase II of meiosis. An oocyte is also used to describe a female gamete or germ cell involved in reproduction, and is commonly also called an egg. A mature egg has a single set of maternal chromosomes (23, X in a human primate) and is halted at metaphase II.
A “hybrid oocyte” refers to an enucleated oocyte that has the cytoplasm from a first human oocyte (termed a “recipient”) but does not have the nuclear genetic material of the recipient oocyte; it has the nuclear genetic material from another human cell, termed a “donor.” In some embodiments, the hybrid oocyte can also comprise mitochondrial DNA (mtDNA) that is not from the recipient oocyte, but is from a donor cell (which can be the same donor cell as the nuclear genetic material, or from a different donor, e.g., from a donor oocyte).
The term “enucleated oocyte” as used herein refers to an human oocyte which its nucleus has been removed.
The term “enucleation” as used herein refers to a process whereby the nuclear material of a cell is removed, leaving only the cytoplasm. When applied to an egg, enucleation refers to the removal of the maternal chromosomes, which are not surrounded by a nuclear membrane. The term “enucleated oocyte” refers to an oocyte where the nuclear material or nuclei is removed.
The “recipient human oocyte” as used herein refers to a human oocyte that receives a nucleus from a human nuclear donor cell after removing its original nucleus.
The term “fusion” as used herein refers to a combination of a nuclear donor cell and a lipid membrane of a recipient oocyte. For example, the lipid membrane may be the plasma membrane or nuclear membrane of a cell. Fusion may occur upon application of an electrical stimulus between a nuclear donor cell and a recipient oocyte when they are placed adjacent to each other or when a nuclear donor cell is placed in a perivitelline space of a recipient oocyte.
The term “living offspring” as used herein means an animal that can survive ex utero. Preferably, it is an animal that can survive for one second, one minute, one day, one week, one month, six months or more than one year. The animal may not require an in utero environment for survival.
The term “prenatal” refers to existing or occurring before birth. Similarly, the term “postnatal” is existing or occurring after birth.
The term “blastocyst” as used herein refers to a preimplantation embryo in placental mammals (about 3 days after fertilization in the mouse, about 5 days after fertilization in humans) of about 30-150 cells. The blastocyst stage follows the morula stage, and can be distinguished by its unique morphology. The blastocyst consists of a sphere made up of a layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel or blastocyst cavity), and a cluster of cells on the interior (the inner cell mass, or ICM). The ICM, consisting of undifferentiated cells, gives rise to what will become the fetus if the blastocyst is implanted in a uterus. These same ICM cells, if grown in culture, can give rise to embryonic stem cell lines. At the time of implantation the mouse blastocyst is made up of about 70 trophoblast cells and 30 ICM cells.
The term “blastula” as used herein refers to an early stage in the development of an embryo consisting of a hollow sphere of cells enclosing a fluid-filled cavity called the blastocoel. The term blastula sometimes is used interchangeably with blastocyst.
The term “blastomere” is used throughout to refer to at least one blastomere (e.g., 1, 2, 3, 4, etc.) obtained from a preimplantation embryo. The term “cluster of two or more blastomeres” is used interchangeably with “blastomere-derived outgrowths” to refer to the cells generated during the in vitro culture of a blastomere. For example, after a blastomere is obtained from a SCNT embryo and initially cultured, it generally divides at least once to produce a cluster of two or more blastomeres (also known as a blastomere-derived outgrowth). The cluster can be further cultured with embryonic or fetal cells. Ultimately, the blastomere-derived outgrowths will continue to divide. From these structures, ES cells, totipotent stem (TS) cells, and partially differentiated cell types will develop over the course of the culture method.
The term “cloned (or cloning)” as used herein refers to a gene manipulation technique for preparing a new individual unit to have a gene set identical to another individual unit. In the present invention, the term “cloned” as used herein refers to a cell, embryonic cell, fetal cell, and/or animal cell has a nuclear DNA sequence that is substantially similar or identical to the nuclear DNA sequence of another cell, embryonic cell, fetal cell, differentiated cell, and/or animal cell. The terms “substantially similar” and “identical” are described herein. The cloned SCNT embryo can arise from one nuclear transfer, or alternatively, the cloned SCNT embryo can arise from a cloning process that includes at least one re-cloning step.
The term “transgenic organism” as used herein refers to an organism into which genetic material from another organism has been experimentally transferred, so that the host acquires the genetic traits of the transferred genes in its chromosomal composition.
The term “implanting” as used herein in reference to SCNT embryos as disclosed herein refers to impregnating a surrogate female animal with a SCNT embryo described herein. This technique is well known to a person of ordinary skill in the art. See, e.g., Seidel and Elsden, 1997, Embryo Transfer in Dairy Cattle, W. D. Hoard & Sons, Co., Hoards Dairyman. The embryo may be allowed to develop in utero, or alternatively, the fetus may be removed from the uterine environment before parturition.
By “subject” is meant a mammal, including, but not limited to, a human or non-human mammal, such as an agriculturally significant mammal (e.g., bovine, equine, ovine, porcine), a pet (e.g., canine, feline), or a rare or endangered mammal (e.g., panda).
As used herein, the terms “treat,” treating,” “treatment,” and the like refer to reducing or ameliorating a disorder and/or symptoms associated therewith. It will be appreciated that, although not precluded, treating a disorder or condition does not require that the disorder, condition or symptoms associated therewith be completely eliminated.
Unless specifically stated or obvious from context, as used herein, the term “or” is understood to be inclusive. Unless specifically stated or obvious from context, as used herein, the terms “a”, “an”, and “the” are understood to be singular or plural (i.e., at least one). By way of example, “an element” means one element or more than one element.
Unless specifically stated or obvious from context, as used herein, the term “about” is understood as within a range of normal tolerance in the art, for example within 2 standard deviations of the mean. About can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear from context, all numerical values provided herein are modified by the term about.
The recitation of a listing of chemical groups in any definition of a variable herein includes definitions of that variable as any single group or combination of listed groups. The recitation of an embodiment for a variable or aspect herein includes that embodiment as any single embodiment or in combination with any other embodiments or portions thereof.
Any compositions or methods provided herein can be combined with one or more of any of the other compositions and methods provided herein.
The invention provides methods for improving cloning efficiency. In particular embodiments, the invention provides methods for improving somatic cell nuclear transfer efficiency that involve Kdm4d overexpression is an Xist knockout donor cell.
The invention is based, at least in part, on the discovery that Xist knockout donor cells coupled with Kdm4d mRNA injection can improve somatic cell nuclear transfer efficiency. This combined approach resulted in the highest efficiency ever reported in mouse cloning using differentiated somatic donor cells. However, many of the SCNT embryos still exhibit postimplantation developmental arrest and the surviving embryos have abnormally large placenta, suggesting some reprogramming defects still persist. Comparative methylome and transcriptome analysis revealed abnormal DNA methylation and loss of H3K27me3-dependent imprinting in SCNT blastocyst embryos, which are likely the cause of the observed developmental defects.
Mammalian sperm and oocytes have different epigenetic landscapes and are organized in different fashion. Following fertilization, the initially distinct parental epigenomes become largely equalized with the exception of certain loci including imprinting control regions (ICRs). How parental chromatin becomes equalized and how ICRs escape from this reprogramming is largely unknown. Here parental allele-specific DNase I hypersensitive sites (DHSs) was characterized in mouse zygotes and morula embryos, and the epigenetic mechanisms underlying allelic DHSs was investigated. Integrated analyses of DNA methylome and H3K27me3 ChIP-seq data sets revealed 76 genes (Table 1) with paternal allele-specific DHSs that were devoid of DNA methylation, but harbored maternal allele-specific H3K27me3.
Interestingly, these genes are paternally expressed in preimplantation embryos, and ectopic removal of H3K27me3 induced maternal allele expression. H3K27me3-dependent imprinting was largely lost in the embryonic cell lineage, but at least 5 genes maintained their imprinting in the extra-embryonic cell lineage. The 5 genes include all previously identified DNA methylation-independent imprinted autosomal genes. Maternal H3K27me3 is a DNA methylation-independent imprinting mechanism. In one embodiment, the methods of the invention involve the use of an H3K27me3 selective methylase.
In females of certain therian mammals including rodents, one of the two X chromosomes is inactivated to achieve gene dosage compensation. This phenomenon, called X chromosome inactivation (XCI), provides an excellent model for understanding mechanisms of epigenetic silencing. During development, XCI can take place in either imprinted or random manners. For imprinted XCI, the paternal X chromosome (Xp) is selectively inactivated during preimplantation development. Although imprinted XCI is maintained in the extra-embryonic cell lineage, it is lost in the inner cell mass (ICM) of late blastocysts. At peri-implantation stage, epiblast cells undergo random XCI resulting in the silencing of either Xp or maternal X chromosome (Xm). Previous studies have demonstrated a critical role of Xist, an X-linked long non-coding RNA, in both imprinted and random XCI. The Xist RNA participates in XCI by coating and inactivating X chromosome in cis.
Genomic imprinting allows parent-of-origin specific gene regulation. To selectively silence the Xp during imprinted XCI, the Xist gene is imprinted for silencing in the Xm with a long sought-after, but yet-to-be-identified, mechanism. Previous studies using nuclear transfer approaches have suggested that genomic imprinting of Xist is established during oogenesis, like that of autosomal imprinted genes. In mouse preimplantation embryos and extra-embryonic cells, only the paternal X chromosome (Xp) is inactivated. Central to the imprinted paternal X chromosome inactivation (XCI) is a long non-coding RNA, Xist, which is expressed from Xp and acts in cis to coat and silence the entire Xp. To achieve Xp-specific inactivation, the maternal Xist gene must be silenced, yet the silencing mechanism is not yet clear. As reported herein, the Xist locus is coated with a broad H3K27me3 domain in mouse oocytes, which persists through preimplantation development. Ectopic removal of H3K27me3 induces maternal Xist expression and maternal XCI. Thus, maternal H3K27me3 serves as the imprinting mark of Xist.
In some embodiments, the methods of the invention involve administering a pharmaceutical composition comprising a selective H3K27me3 demethylase inhibitor.
Histone H3 lysine 9 trimethylation (H3K9me3) in donor somatic cells is an epigenetic barrier for SCNT reprogramming. H3K9me3 in donor cells prevents transcriptional activation of the associated regions at zygotic genome activation and leads to developmental arrest of SCNT embryos at preimplantation stages in both mouse and human. Importantly, removal of the H3K9me3 barrier by overexpressing a H3K9me3-specific demethylase, Kdm4d, allows SCNT embryos to develop to the blastocyst stage at a rate similar to that of IVF. Consequently, the overall cloning efficiency for term rate is increased 8-9 fold. Although the use of Kdm4d in SCNT results in an implantation rate comparable to that of IVF, less than 15% of the implanted SCNT embryos develop to term. Moreover, abnormally large placentas are still observed in Kdm4d-injected SCNT embryos. These results suggest that the H3K9me3 reprogramming barrier mainly impedes preimplantation development and other barriers affect postimplantation development.
Xist is important for postimplantation development of mouse SCNT embryos. Abnormal expression of Xist from maternal X chromosome leads to ectopic X chromosome inactivation (XCI) and global transcriptional alteration in preimplantation embryos, resulting in postimplantation developmental failure of SCNT embryos. Importantly, this developmental failure caused by ectopic Xist expression can be overcome by using Xist knockout (KO) somatic cells as donor cells or by injecting small interfering RNA against Xist into 1-cell male SCNT embryos leading to an 8-10 fold increase of term rate.
Inhibitory nucleic acid molecules are those oligonucleotides that inhibit the expression or activity of a polypeptide or polynucleotide (e.g., an Xist polynucleotide). Such oligonucleotides include single and double stranded nucleic acid molecules (e.g., DNA, RNA, and analogs thereof) that bind a nucleic acid molecule that encodes an Xist polynucleotide (e.g., antisense molecules, siRNA, shRNA).
siRNA
Short twenty-one to twenty-five nucleotide double-stranded RNAs are effective at down-regulating gene expression (Zamore et al., Cell 101: 25-33; Elbashir et al., Nature 411: 494-498, 2001, hereby incorporated by reference). The effectiveness of an siRNA approach in mammals was demonstrated in vivo by McCaffrey et al. (Nature 418: 38-39.2002).
Given the sequence of a target gene, siRNAs may be designed to inactivate that gene. Such siRNAs, for example, could be administered directly to an affected tissue, or administered systemically. The nucleic acid sequence of a gene can be used to design small interfering RNAs (siRNAs). The 21 to 25 nucleotide siRNAs may be used, for example, to reduce Xist expression.
The inhibitory nucleic acid molecules of the present invention may be employed as double-stranded RNAs for RNA interference (RNAi)-mediated knock-down of expression. In one embodiment, expression of an Xist gene is reduced in a somatic cell. RNAi is a method for decreasing the cellular expression of specific proteins of interest (reviewed in Tuschl, Chembiochem 2:239-245, 2001; Sharp, Genes & Devel. 15:485-490, 2000; Hutvagner and Zamore, Curr. Opin. Genet. Devel. 12:225-232, 2002; and Hannon, Nature 418:244-251, 2002). The introduction of siRNAs into cells either by transfection of dsRNAs or through expression of siRNAs using a plasmid-based expression system is increasingly being used to create loss-of-function phenotypes in mammalian cells.
In one embodiment of the invention, a double-stranded RNA (dsRNA) molecule is made that includes between eight and nineteen consecutive nucleobases of a nucleobase oligomer of the invention. The dsRNA can be two distinct strands of RNA that have duplexed, or a single RNA strand that has self-duplexed (small hairpin (sh)RNA). Typically, dsRNAs are about 21 or 22 base pairs, but may be shorter or longer (up to about 29 nucleobases) if desired. dsRNA can be made using standard techniques (e.g., chemical synthesis or in vitro transcription). Kits are available, for example, from Ambion (Austin, Tex.) and Epicentre (Madison, Wis.). Methods for expressing dsRNA in mammalian cells are described in Brummelkamp et al. Science 296:550-553, 2002; Paddison et al. Genes & Devel. 16:948-958, 2002. Paul et al. Nature Biotechnol. 20:505-508, 2002; Sui et al. Proc. Natl. Acad. Sci. USA 99:5515-5520, 2002; Yu et al. Proc. Natl. Acad. Sci. USA 99:6047-6052, 2002; Miyagishi et al. Nature Biotechnol. 20:497-500, 2002; and Lee et al. Nature Biotechnol. 20:500-505 2002, each of which is hereby incorporated by reference.
Small hairpin RNAs (shRNAs) comprise an RNA sequence having a stem-loop structure. A “stem-loop structure” refers to a nucleic acid having a secondary structure that includes a region of nucleotides which are known or predicted to form a double strand or duplex (stem portion) that is linked on one side by a region of predominantly single-stranded nucleotides (loop portion). The term “hairpin” is also used herein to refer to stem-loop structures. Such structures are well known in the art and the term is used consistently with its known meaning in the art. As is known in the art, the secondary structure does not require exact base-pairing. Thus, the stem can include one or more base mismatches or bulges. Alternatively, the base-pairing can be exact, i.e. not include any mismatches. The multiple stem-loop structures can be linked to one another through a linker, such as, for example, a nucleic acid linker, a miRNA flanking sequence, other molecule, or some combination thereof.
As used herein, the term “small hairpin RNA” includes a conventional stem-loop shRNA, which forms a precursor miRNA (pre-miRNA). While there may be some variation in range, a conventional stem-loop shRNA can comprise a stem ranging from 19 to 29 bp, and a loop ranging from 4 to 30 bp. “shRNA” also includes micro-RNA embedded shRNAs (miRNA-based shRNAs), wherein the guide strand and the passenger strand of the miRNA duplex are incorporated into an existing (or natural) miRNA or into a modified or synthetic (designed) miRNA. In some instances the precursor miRNA molecule can include more than one stem-loop structure. MicroRNAs are endogenously encoded RNA molecules that are about 22-nucleotides long and generally expressed in a highly tissue- or developmental-stage-specific fashion and that post-transcriptionally regulate target genes. More than 200 distinct miRNAs have been identified in plants and animals. These small regulatory RNAs are believed to serve important biological functions by two prevailing modes of action: (1) by repressing the translation of target mRNAs, and (2) through RNA interference (RNAi), that is, cleavage and degradation of mRNAs. In the latter case, miRNAs function analogously to small interfering RNAs (siRNAs). Thus, one can design and express artificial miRNAs based on the features of existing miRNA genes.
shRNAs can be expressed from DNA vectors to provide sustained silencing and high yield delivery into almost any cell type. In some embodiments, the vector is a viral vector. Exemplary viral vectors include retroviral, including lentiviral, adenoviral, baculoviral and avian viral vectors, and including such vectors allowing for stable, single-copy genomic integrations. Retroviruses from which the retroviral plasmid vectors can be derived include, but are not limited to, Moloney murine leukemia virus, spleen necrosis virus, Rous sarcoma virus, Harvey sarcoma virus, avian leukosis virus, gibbon ape leukemia virus, human immunodeficiency virus, myeloproliferative sarcoma virus, and mammary tumor virus. A retroviral plasmid vector can be employed to transduce packaging cell lines to form producer cell lines. Examples of packaging cells which can be transfected include, but are not limited to, the PE501, PA317, R-2, R-AM, PA12, T19-14x, VT-19-17-H2, RCRE, RCRIP, GP+E-86, GP+envAm12, and DAN cell lines as described in Miller, Human Gene Therapy 1:5-14 (1990), which is incorporated herein by reference in its entirety. The vector can transduce the packaging cells through any means known in the art. A producer cell line generates infectious retroviral vector particles which include polynucleotide encoding a DNA replication protein. Such retroviral vector particles then can be employed, to transduce eukaryotic cells, either in vitro or in vivo. The transduced eukaryotic cells will express a DNA replication protein.
Catalytic RNA molecules or ribozymes that include an antisense sequence of the present invention can be used to inhibit expression of a nucleic acid molecule in vivo (e.g., Xist). The inclusion of ribozyme sequences within antisense RNAs confers RNA-cleaving activity upon them, thereby increasing the activity of the constructs. The design and use of target RNA-specific ribozymes is described in Haseloff et al., Nature 334:585-591. 1988, and U.S. Patent Application Publication No. 2003/0003469 A1, each of which is incorporated by reference.
Accordingly, the invention also features a catalytic RNA molecule that includes, in the binding arm, an antisense RNA having between eight and nineteen consecutive nucleobases. In preferred embodiments of this invention, the catalytic nucleic acid molecule is formed in a hammerhead or hairpin motif. Examples of such hammerhead motifs are described by Rossi et al., Aids Research and Human Retroviruses, 8:183, 1992. Example of hairpin motifs are described by Hampel et al., “RNA Catalyst for Cleaving Specific RNA Sequences,” filed Sep. 20, 1989, which is a continuation-in-part of U.S. Ser. No. 07/247,100 filed Sep. 20, 1988; Hampel and Tritz, Biochemistry, 28:4929, 1989; and Hampel et al., Nucleic Acids Research, 18: 299, 1990. These specific motifs are not limiting in the invention and those skilled in the art will recognize that all that is important in an enzymatic nucleic acid molecule of this invention is that it has a specific substrate binding site which is complementary to one or more of the target gene RNA regions and that it have nucleotide sequences within or surrounding that substrate binding site which impart an RNA cleaving activity to the molecule.
Essentially any method for introducing a nucleic acid construct into cells can be employed. Physical methods of introducing nucleic acids include injection of a solution containing the construct, bombardment by particles covered by the construct, soaking a cell, tissue sample or organism in a solution of the nucleic acid, or electroporation of cell membranes in the presence of the construct. A viral construct packaged into a viral particle can be used to accomplish both efficient introduction of an expression construct into the cell and transcription of the encoded shRNA. Other methods known in the art for introducing nucleic acids to cells can be used, such as lipid-mediated carrier transport, chemical mediated transport, such as calcium phosphate, and the like. Thus the shRNA-encoding nucleic acid construct can be introduced along with components that perform one or more of the following activities: enhance RNA uptake by the cell, promote annealing of the duplex strands, stabilize the annealed strands, or otherwise increase inhibition of the target gene.
For expression within cells, DNA vectors, for example plasmid vectors comprising either an RNA polymerase II or RNA polymerase III promoter can be employed. Expression of endogenous miRNAs is controlled by RNA polymerase II (Pol II) promoters and in some cases, shRNAs are most efficiently driven by Pol II promoters, as compared to RNA polymerase III promoters (Dickins et al., 2005, Nat. Genet. 39: 914-921). In some embodiments, expression of the shRNA can be controlled by an inducible promoter or a conditional expression system, including, without limitation, RNA polymerase type II promoters. Examples of useful promoters in the context of the invention are tetracycline-inducible promoters (including TRE-tight), IPTG-inducible promoters, tetracycline transactivator systems, and reverse tetracycline transactivator (rtTA) systems. Constitutive promoters can also be used, as can cell- or tissue-specific promoters. Many promoters will be ubiquitous, such that they are expressed in all cell and tissue types. A certain embodiment uses tetracycline-responsive promoters, one of the most effective conditional gene expression systems in in vitro and in vivo studies. See International Patent Application PCT/US2003/030901 (Publication No. WO 2004-029219 A2) and Fewell et al., 2006, Drug Discovery Today 11: 975-982, for a description of inducible shRNA.
Naked polynucleotides, or analogs thereof, are capable of entering mammalian cells and inhibiting expression of a gene of interest. Nonetheless, it may be desirable to utilize a formulation that aids in the delivery of oligonucleotides or other nucleobase oligomers to cells (see, e.g., U.S. Pat. Nos. 5,656,611; 5,753,613; 5,785,992; 6,120,798; 6,221,959; 6,346,613; and 6,353,055; each of which is hereby incorporated by reference).
At least two types of oligonucleotides induce the cleavage of RNA by RNase H: polydeoxynucleotides with phosphodiester (PO) or phosphorothioate (PS) linkages. Although 2′-OMe-RNA sequences exhibit a high affinity for RNA targets, these sequences are not substrates for RNase H. A desirable oligonucleotide is one based on 2′-modified oligonucleotides containing oligodeoxynucleotide gaps with some or all internucleotide linkages modified to phosphorothioates for nuclease resistance. The presence of methylphosphonate modifications increases the affinity of the oligonucleotide for its target RNA and thus reduces the IC50. This modification also increases the nuclease resistance of the modified oligonucleotide. It is understood that the methods and reagents of the present invention may be used in conjunction with any technologies that may be developed, including covalently-closed multiple antisense (CMAS) oligonucleotides (Moon et al., Biochem J. 346:295-303, 2000; PCT Publication No. WO 00/61595), ribbon-type antisense (RiAS) oligonucleotides (Moon et al., J. Biol. Chem. 275:4647-4653, 2000; PCT Publication No. WO 00/61595), and large circular antisense oligonucleotides (U.S. Patent Application Publication No. US 2002/0168631 A1).
As is known in the art, a nucleoside is a nucleobase-sugar combination. The base portion of the nucleoside is normally a heterocyclic base. The two most common classes of such heterocyclic bases are the purines and the pyrimidines. Nucleotides are nucleosides that further include a phosphate group covalently linked to the sugar portion of the nucleoside. For those nucleosides that include a pentofuranosyl sugar, the phosphate group can be linked to either the 2′, 3′ or 5′ hydroxyl moiety of the sugar. In forming oligonucleotides, the phosphate groups covalently link adjacent nucleosides to one another to form a linear polymeric compound. In turn, the respective ends of this linear polymeric structure can be further joined to form a circular structure; open linear structures are generally preferred. Within the oligonucleotide structure, the phosphate groups are commonly referred to as forming the backbone of the oligonucleotide. The normal linkage or backbone of RNA and DNA is a 3′ to 5′ phosphodiester linkage.
Specific examples of preferred nucleobase oligomers useful in this invention include oligonucleotides containing modified backbones or non-natural internucleoside linkages. As defined in this specification, nucleobase oligomers having modified backbones include those that retain a phosphorus atom in the backbone and those that do not have a phosphorus atom in the backbone. For the purposes of this specification, modified oligonucleotides that do not have a phosphorus atom in their internucleoside backbone are also considered to be nucleobase oligomers.
Nucleobase oligomers that have modified oligonucleotide backbones include, for example, phosphorothioates, chiral phosphorothioates, phosphorodithioates, phosphotriesters, aminoalkyl-phosphotriesters, methyl and other alkyl phosphonates including 3′-alkylene phosphonates and chiral phosphonates, phosphinates, phosphoramidates including 3′-amino phosphoramidate and aminoalkylphosphoramidates, thionophosphoramidates, thionoalkylphosphonates, thionoalkylphosphotriesters, and boranophosphates having normal 3′-5′ linkages, 2′-5′ linked analogs of these, and those having inverted polarity, wherein the adjacent pairs of nucleoside units are linked 3′-5′ to 5′-3′ or 2′-5′ to 5′-2′. Various salts, mixed salts and free acid forms are also included. Representative United States patents that teach the preparation of the above phosphorus-containing linkages include, but are not limited to, U.S. Pat. Nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5,177,196; 5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455,233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563,253; 5,571,799; 5,587,361; and 5,625,050, each of which is herein incorporated by reference.
Nucleobase oligomers having modified oligonucleotide backbones that do not include a phosphorus atom therein have backbones that are formed by short chain alkyl or cycloalkyl internucleoside linkages, mixed heteroatom and alkyl or cycloalkyl internucleoside linkages, or one or more short chain heteroatomic or heterocyclic internucleoside linkages. These include those having morpholino linkages (formed in part from the sugar portion of a nucleoside); siloxane backbones; sulfide, sulfoxide and sulfone backbones; formacetyl and thioformacetyl backbones; methylene formacetyl and thioformacetyl backbones; alkene containing backbones; sulfamate backbones; methyleneimino and methylenehydrazino backbones; sulfonate and sulfonamide backbones; amide backbones; and others having mixed N, O, S and CH.sub.2 component parts. Representative United States patents that teach the preparation of the above oligonucleotides include, but are not limited to, U.S. Pat. Nos. 5,034,506; 5,166,315; 5,185,444; 5,214,134; 5,216,141; 5,235,033; 5,264,562; 5,264,564; 5,405,938; 5,434,257; 5,466,677; 5,470,967; 5,489,677; 5,541,307; 5,561,225; 5,596,086; 5,602,240; 5,610,289; 5,602,240; 5,608,046; 5,610,289; 5,618,704; 5,623,070; 5,663,312; 5,633,360; 5,677,437; and 5,677,439, each of which is herein incorporated by reference.
In other nucleobase oligomers, both the sugar and the internucleoside linkage, i.e., the backbone, are replaced with novel groups. The nucleobase units are maintained for hybridization with an Xist gene listed. One such nucleobase oligomer, is referred to as a Peptide Nucleic Acid (PNA). In PNA compounds, the sugar-backbone of an oligonucleotide is replaced with an amide containing backbone, in particular an aminoethylglycine backbone. The nucleobases are retained and are bound directly or indirectly to aza nitrogen atoms of the amide portion of the backbone. Methods for making and using these nucleobase oligomers are described, for example, in “Peptide Nucleic Acids: Protocols and Applications” Ed. P. E. Nielsen, Horizon Press, Norfolk, United Kingdom, 1999. Representative United States patents that teach the preparation of PNAs include, but are not limited to, U.S. Pat. Nos. 5,539,082; 5,714,331; and 5,719,262, each of which is herein incorporated by reference. Further teaching of PNA compounds can be found in Nielsen et al., Science, 1991, 254, 1497-1500.
In particular embodiments of the invention, the nucleobase oligomers have phosphorothioate backbones and nucleosides with heteroatom backbones, and in particular —CH2.NH—O—CH2—, —CH2—N(CH3)—O—CH2— (known as a methylene (methylimino) or MMI backbone), —CH2—O—N(CH3)—CH2—, —CH2—N(CH3)—N(CH3)—CH2—, and —O—N(CH3)—CH2—CH2—. In other embodiments, the oligonucleotides have morpholino backbone structures described in U.S. Pat. No. 5,034,506.
Nucleobase oligomers may also contain one or more substituted sugar moieties. Nucleobase oligomers comprise one of the following at the 2′ position: OH; F; O-, S-, or N-alkyl; O-, S-, or N-alkenyl; O-, S- or N-alkynyl; or O-alkyl-O-alkyl, wherein the alkyl, alkenyl, and alkynyl may be substituted or unsubstituted C1 to C10 alkyl or C2 to C10 alkenyl and alkynyl. Particularly preferred are O[(CH2)nO]nCH3, O(CH2)nOCH3, O(CH2)nNH2, O(CH2)nCH3, O(CH2)nONH2, and O(CH2)nON[(CH2)nCH3)]2, where n and m are from 1 to about 10. Other preferred nucleobase oligomers include one of the following at the 2′ position: C1 to C10 lower alkyl, substituted lower alkyl, alkaryl, aralkyl, O-alkaryl, or O-aralkyl, SH, SCH3, OCN, Cl, Br, CN, CF3, OCF3, SOCH3, SO2CH3, ONO2, NO2, NH2, heterocycloalkyl, heterocycloalkaryl, aminoalkylamino, polyalkylamino, substituted silyl, an RNA cleaving group, a reporter group, an intercalator, a group for improving the pharmacokinetic properties of a nucleobase oligomer, or a group for improving the pharmacodynamic properties of an nucleobase oligomer, and other substituents having similar properties. Preferred modifications are 2′-O-methyl and 2′-methoxyethoxy (2′-O—CH2CH2OCH3, also known as 2′-O-(2-methoxyethyl) or 2′-MOE). Another desirable modification is 2′-dimethylaminooxyethoxy (i.e., O(CH2)2ON(CH3) 2), also known as 2′-DMAOE. Other modifications include, 2′-aminopropoxy (2′-OCH2CH2CH2NH2) and 2′-fluoro (2′-F). Similar modifications may also be made at other positions on an oligonucleotide or other nucleobase oligomer, particularly the 3′ position of the sugar on the 3′ terminal nucleotide or in 2′-5′ linked oligonucleotides and the 5′ position of 5′ terminal nucleotide. Nucleobase oligomers may also have sugar mimetics such as cyclobutyl moieties in place of the pentofuranosyl sugar. Representative United States patents that teach the preparation of such modified sugar structures include, but are not limited to, U.S. Pat. Nos. 4,981,957; 5,118,800; 5,319,080; 5,359,044; 5,393,878; 5,446,137; 5,466,786; 5,514,785; 5,519,134; 5,567,811; 5,576,427; 5,591,722; 5,597,909; 5,610,300; 5,627,053; 5,639,873; 5,646,265; 5,658,873; 5,670,633; and 5,700,920, each of which is herein incorporated by reference in its entirety.
Nucleobase oligomers may also include nucleobase modifications or substitutions. As used herein, “unmodified” or “natural” nucleobases include the purine bases adenine (A) and guanine (G), and the pyrimidine bases thymine (T), cytosine (C) and uracil (U). Modified nucleobases include other synthetic and natural nucleobases, such as 5-methylcytosine (5-me-C), 5-hydroxymethyl cytosine, xanthine, hypoxanthine, 2-aminoadenine, 6-methyl and other alkyl derivatives of adenine and guanine; 2-propyl and other alkyl derivatives of adenine and guanine; 2-thiouracil, 2-thiothymine and 2-thiocytosine; 5-halouracil and cytosine; 5-propynyl uracil and cytosine; 6-azo uracil, cytosine and thymine; 5-uracil (pseudouracil); 4-thiouracil; 8-halo, 8-amino, 8-thiol, 8-thioalkyl, 8-hydroxyl and other 8-substituted adenines and guanines; 5-halo (e.g., 5-bromo), 5-trifluoromethyl and other 5-substituted uracils and cytosines; 7-methylguanine and 7-methyladenine; 8-azaguanine and 8-azaadenine; 7-deazaguanine and 7-deazaadenine; and 3-deazaguanine and 3-deazaadenine. Further nucleobases include those disclosed in U.S. Pat. No. 3,687,808, those disclosed in The Concise Encyclopedia Of Polymer Science And Engineering, pages 858-859, Kroschwitz, J. I., ed. John Wiley & Sons, 1990, those disclosed by Englisch et al., Angewandte Chemie, International Edition, 1991, 30, 613, and those disclosed by Sanghvi, Y. S., Chapter 15, Antisense Research and Applications, pages 289-302, Crooke, S. T. and Lebleu, B., ed., CRC Press, 1993. Certain of these nucleobases are particularly useful for increasing the binding affinity of an antisense oligonucleotide of the invention. These include 5-substituted pyrimidines, 6-azapyrimidines, and N-2, N-6 and 0-6 substituted purines, including 2-aminopropyladenine, 5-propynyluracil and 5-propynylcytosine. 5-methylcytosine substitutions have been shown to increase nucleic acid duplex stability by 0.6-1.2° C. (Sanghvi, Y. S., Crooke, S. T. and Lebleu, B., eds., Antisense Research and Applications, CRC Press, Boca Raton, 1993, pp. 276-278) and are desirable base substitutions, even more particularly when combined with 2′-O-methoxyethyl or 2′-O-methyl sugar modifications. Representative United States patents that teach the preparation of certain of the above noted modified nucleobases as well as other modified nucleobases include U.S. Pat. Nos. 4,845,205; 5,130,302; 5,134,066; 5,175,273; 5,367,066; 5,432,272; 5,457,187; 5,459,255; 5,484,908; 5,502,177; 5,525,711; 5,552,540; 5,587,469; 5,594,121, 5,596,091; 5,614,617; 5,681,941; and 5,750,692, each of which is herein incorporated by reference.
Another modification of a nucleobase oligomer of the invention involves chemically linking to the nucleobase oligomer one or more moieties or conjugates that enhance the activity, cellular distribution, or cellular uptake of the oligonucleotide. Such moieties include but are not limited to lipid moieties such as a cholesterol moiety (Letsinger et al., Proc. Natl. Acad. Sci. USA, 86:6553-6556, 1989), cholic acid (Manoharan et al., Bioorg. Med. Chem. Let, 4:1053-1060, 1994), a thioether, e.g., hexyl-S-tritylthiol (Manoharan et al., Ann. N.Y. Acad. Sci., 660:306-309, 1992; Manoharan et al., Bioorg. Med. Chem. Let., 3:2765-2770, 1993), a thiocholesterol (Oberhauser et al., Nucl. Acids Res., 20:533-538: 1992), an aliphatic chain, e.g., dodecandiol or undecyl residues (Saison-Behmoaras et al., EMBO J., 10:1111-1118, 1991; Kabanov et al., FEBS Lett., 259:327-330, 1990; Svinarchuk et al., Biochimie, 75:49-54, 1993), a phospholipid, e.g., di-hexadecyl-rac-glycerol or triethylammonium 1,2-di-O-hexadecyl-rac-glycero-3-H-phosphonate (Manoharan et al., Tetrahedron Lett., 36:3651-3654, 1995; Shea et al., Nucl. Acids Res., 18:3777-3783, 1990), a polyamine or a polyethylene glycol chain (Manoharan et al., Nucleosides & Nucleotides, 14:969-973, 1995), adamantane acetic acid (Manoharan et al., Tetrahedron Lett., 36:3651-3654, 1995), a palmityl moiety (Mishra et al., Biochim. Biophys. Acta, 1264:229-237, 1995), or an octadecylamine or hexylamino-carbonyl-oxycholesterol moiety (Crooke et al., J. Pharmacol. Exp. Ther., 277:923-937, 1996. Representative United States patents that teach the preparation of such nucleobase oligomer conjugates include U.S. Pat. Nos. 4,587,044; 4,605,735; 4,667,025; 4,762,779; 4,789,737; 4,824,941; 4,828,979; 4,835,263; 4,876,335; 4,904,582; 4,948,882; 4,958,013; 5,082,830; 5,109,124; 5,112,963; 5,118,802; 5,138,045; 5,214,136; 5,218,105; 5,245,022; 5,254,469; 5,258,506; 5,262,536; 5,272,250; 5,292,873; 5,317,098; 5,371,241, 5,391,723; 5,414,077; 5,416,203, 5,451,463; 5,486,603; 5,510,475; 5,512,439; 5,512,667; 5,514,785; 5,525,465; 5,541,313; 5,545,730; 5,552,538; 5,565,552; 5,567,810; 5,574,142; 5,578,717; 5,578,718; 5,580,731; 5,585,481; 5,587,371; 5,591,584; 5,595,726; 5,597,696; 5,599,923; 5,599,928; 5,608,046; and 5,688,941, each of which is herein incorporated by reference.
The present invention also includes nucleobase oligomers that are chimeric compounds. “Chimeric” nucleobase oligomers are nucleobase oligomers, particularly oligonucleotides, that contain two or more chemically distinct regions, each made up of at least one monomer unit, i.e., a nucleotide in the case of an oligonucleotide. These nucleobase oligomers typically contain at least one region where the nucleobase oligomer is modified to confer, upon the nucleobase oligomer, increased resistance to nuclease degradation, increased cellular uptake, and/or increased binding affinity for the target nucleic acid. An additional region of the nucleobase oligomer may serve as a substrate for enzymes capable of cleaving RNA:DNA or RNA:RNA hybrids. By way of example, RNase H is a cellular endonuclease which cleaves the RNA strand of an RNA:DNA duplex. Activation of RNase H, therefore, results in cleavage of the RNA target, thereby greatly enhancing the efficiency of nucleobase oligomer inhibition of gene expression. Consequently, comparable results can often be obtained with shorter nucleobase oligomers when chimeric nucleobase oligomers are used, compared to phosphorothioate deoxyoligonucleotides hybridizing to the same target region.
Chimeric nucleobase oligomers of the invention may be formed as composite structures of two or more nucleobase oligomers as described above. Such nucleobase oligomers, when oligonucleotides, have also been referred to in the art as hybrids or gapmers. Representative United States patents that teach the preparation of such hybrid structures include U.S. Pat. Nos. 5,013,830; 5,149,797; 5,220,007; 5,256,775; 5,366,878; 5,403,711; 5,491,133; 5,565,350; 5,623,065; 5,652,355; 5,652,356; and 5,700,922, each of which is herein incorporated by reference in its entirety.
The nucleobase oligomers used in accordance with this invention may be conveniently and routinely made through the well-known technique of solid phase synthesis. Equipment for such synthesis is sold by several vendors including, for example, Applied Biosystems (Foster City, Calif.). Any other means for such synthesis known in the art may additionally or alternatively be employed. It is well known to use similar techniques to prepare oligonucleotides such as the phosphorothioates and alkylated derivatives.
The nucleobase oligomers of the invention may also be admixed, encapsulated, conjugated or otherwise associated with other molecules, molecule structures or mixtures of compounds, as for example, liposomes, receptor targeted molecules, oral, rectal, topical or other formulations, for assisting in uptake, distribution and/or absorption. Representative United States patents that teach the preparation of such uptake, distribution and/or absorption assisting formulations include U.S. Pat. Nos. 5,108,921; 5,354,844; 5,416,016; 5,459,127; 5,521,291; 5,543,158; 5,547,932; 5,583,020; 5,591,721; 4,426,330; 4,534,899; 5,013,556; 5,108,921; 5,213,804; 5,227,170; 5,264,221; 5,356,633; 5,395,619; 5,416,016; 5,417,978; 5,462,854; 5,469,854; 5,512,295; 5,527,528; 5,534,259; 5,543,152; 5,556,948; 5,580,575; and 5,595,756, each of which is herein incorporated by reference.
Gene editing is a major focus of biomedical research, embracing the interface between basic and clinical science. The development of novel “gene editing” tools provides the ability to manipulate the DNA sequence of a cell at a specific chromosomal locus, without introducing mutations at other sites of the genome. This technology effectively enables the researcher to manipulate the genome of a subject's cells in vitro or in vivo. In the context of SCNT, cells comprising a KO in Xist are generated using CRISPR.
In one embodiment, gene editing involves targeting an endonuclease (an enzyme that causes DNA breaks internally within a DNA molecule) to a specific site of the genome and thereby triggering formation of a chromosomal double strand break (DSB) at the chosen site. If, concomitant with the introduction of the chromosome breaks, a donor DNA molecule is introduced (for example, by plasmid or oligonucleotide introduction), interactions between the broken chromosome and the introduced DNA can occur, especially if the two sequences share homology. In this instance, a process termed “gene targeting” can occur, in which the DNA ends of the chromosome invade homologous sequences of the donor DNA by homologous recombination (HR). By using the donor plasmid sequence as a template for HR, a seamless knock out of the gene of interest can be accomplished. Importantly, if the donor DNA molecule includes a deletion within the target gene (e.g., Xist), HR-mediated DSB repair will introduce the donor sequence into the chromosome, resulting in the deletion being introduced within the chromosomal locus. By targeting the nuclease to a genomic site that contains the target gene, the concept is to use DSB formation to stimulate HR and to thereby replace the functional target gene with a deleted form of the gene. The advantage of the HR pathway is that it has the potential to generate seamlessly a knockout of the gene in place of the previous wild-type allele.
Current genome editing tools use the induction of double strand breaks (DSBs) to enhance gene manipulation of cells. Such methods include zinc finger nucleases (ZFNs; described for example in U.S. Pat. Nos. 6,534,261; 6,607,882; 6,746,838; 6,794,136; 6,824,978; 6,866,997; 6,933,113; 6,979,539; 7,013,219; 7,030,215; 7,220,719; 7,241,573; 7,241,574; 7,585,849; 7,595,376; 6,903,185; and 6,479,626; and U.S. Pat. Publ. Nos. 20030232410 and US2009020314, which are incorporated herein by reference), Transcription Activator-Like Effector Nucleases (TALENs; described for example in U.S. Pat. Nos. 8,440,431, 8,440,432, 8,450,471, 8,586,363, and 8,697,853, and U.S. Pat. Publ. Nos. 20110145940, 20120178131, 20120178169, 20120214228, 20130122581, 20140335592, and 20140335618, which are incorporated herein by reference), and the CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas9 system (described for example in U.S. Pat. Nos. 8,697,359, 8,771,945, 8,795,965, 8,871,445, 8,889,356, 8,906,616, 8,932,814, 8,945,839, 8,993,233, and 8,999,641, and U.S. Pat. Publ. Nos. 20140170753, 20140227787, 20140179006, 20140189896, 20140273231, 20140242664, 20140273232, 20150184139, 20150203872, 20150031134, 20150079681, 20150232882, and 20150247150, which are incorporated herein by reference). For example, ZFN DNA sequence recognition capabilities and specificity can be unpredictable. Similarly, TALENs and CRISPR/Cas9 cleave not only at the desired site, but often at other “off-target” sites, as well. These methods have significant issues connected with off-target double-stranded break induction and the potential for deleterious mutations, including indels, genomic rearrangements, and chromosomal rearrangements, associated with these off-target effects. ZFNs and TALENs entail use of modular sequence-specific DNA binding proteins to generate specificity for ˜18 bp sequences in the genome.
RNA-guided nucleases-mediated genome editing, based on Type 2 CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat)/Cas (CRISPR Associated) systems, offers a valuable approach to alter the genome. In brief, Cas9, a nuclease guided by single-guide RNA (sgRNA), binds to a targeted genomic locus next to the protospacer adjacent motif (PAM) and generates a double-strand break (DSB). The DSB is then repaired either by non-homologous end joining (NHEJ), which leads to insertion/deletion (indel) mutations, or by homology-directed repair (HDR), which requires an exogenous template and can generate a precise modification at a target locus (Mali et al., Science. 2013 Feb. 15; 339(6121):823-6). Unlike other gene therapy methods, which add a functional, or partially functional, copy of a gene to a patient's cells but retain the original dysfunctional copy of the gene, this system can remove the defect. Genetic correction using engineered nucleases has been demonstrated in tissue culture cells and rodent models of rare diseases.
CRISPR has been used in a wide range of organisms including bakers yeast (S. cerevisiae), zebra fish, nematodes (C. elegans), plants, mice, and several other organisms. Additionally CRISPR has been modified to make programmable transcription factors that allow scientists to target and activate or silence specific genes. Libraries of tens of thousands of guide RNAs are now available.
Since 2012, the CRISPR/Cas system has been used for gene editing (silencing, enhancing or changing specific genes) that even works in eukaryotes like mice and primates. By inserting a plasmid containing cas genes and specifically designed CRISPRs, an organism's genome can be cut at any desired location.
CRISPR repeats range in size from 24 to 48 base pairs. They usually show some dyad symmetry, implying the formation of a secondary structure such as a hairpin, but are not truly palindromic. Repeats are separated by spacers of similar length. Some CRISPR spacer sequences exactly match sequences from plasmids and phages, although some spacers match the prokaryote's genome (self-targeting spacers). New spacers can be added rapidly in response to phage infection.
CRISPR-associated (cas) genes are often associated with CRISPR repeat-spacer arrays. As of 2013, more than forty different Cas protein families had been described. Of these protein families, Cas1 appears to be ubiquitous among different CRISPR/Cas systems. Particular combinations of cas genes and repeat structures have been used to define 8 CRISPR subtypes (Ecoli, Ypest, Nmeni, Dvulg, Tneap, Hmari, Apern, and Mtube), some of which are associated with an additional gene module encoding repeat-associated mysterious proteins (RAMPs). More than one CRISPR subtype may occur in a single genome. The sporadic distribution of the CRISPR/Cas subtypes suggests that the system is subject to horizontal gene transfer during microbial evolution.
Exogenous DNA is apparently processed by proteins encoded by Cas genes into small elements (about 30 base pairs in length), which are then somehow inserted into the CRISPR locus near the leader sequence. RNAs from the CRISPR loci are constitutively expressed and are processed by Cas proteins to small RNAs composed of individual, exogenously-derived sequence elements with a flanking repeat sequence. The RNAs guide other Cas proteins to silence exogenous genetic elements at the RNA or DNA level. Evidence suggests functional diversity among CRISPR subtypes. The Cse (Cas subtype Ecoli) proteins (called CasA-E in E. coli) form a functional complex, Cascade, that processes CRISPR RNA transcripts into spacer-repeat units that Cascade retains. In other prokaryotes, Cas6 processes the CRISPR transcripts. Interestingly, CRISPR-based phage inactivation in E. coli requires Cascade and Cas3, but not Cas1 and Cas2. The Cmr (Cas RAMP module) proteins found in Pyrococcus furiosus and other prokaryotes form a functional complex with small CRISPR RNAs that recognizes and cleaves complementary target RNAs. RNA-guided CRISPR enzymes are classified as type V restriction enzymes.
See also U.S. Patent Publication 2014/0068797, which is incorporated by reference in its entirety.
Cas9
Cas9 is a nuclease, an enzyme specialized for cutting DNA, with two active cutting sites, one for each strand of the double helix. The team demonstrated that they could disable one or both sites while preserving Cas9's ability to home located its target DNA. Jinek et al. (2012) combined tracrRNA and spacer RNA into a “single-guide RNA” molecule that, mixed with Cas9, could find and cut the correct DNA targets. It has been proposed that such synthetic guide RNAs might be able to be used for gene editing (Jinek et al., Science. 2012 Aug. 17; 337(6096):816-21).
Cas9 proteins are highly enriched in pathogenic and commensal bacteria. CRISPR/Cas-mediated gene regulation may contribute to the regulation of endogenous bacterial genes, particularly during bacterial interaction with eukaryotic hosts. For example, Cas protein Cas9 of Francisella novicida uses a unique, small, CRISPR/Cas-associated RNA (scaRNA) to repress an endogenous transcript encoding a bacterial lipoprotein that is critical for F. novicida to dampen host response and promote virulence. Coinjection of Cas9 mRNA and sgRNAs into the germline (zygotes) generated mice with mutations. Delivery of Cas9 DNA sequences also is contemplated.
gRNA
As an RNA guided protein, Cas9 requires a short RNA to direct the recognition of DNA targets. Though Cas9 preferentially interrogates DNA sequences containing a PAM sequence NGG it can bind here without a protospacer target. However, the Cas9-gRNA complex requires a close match to the gRNA to create a double strand break. CRISPR sequences in bacteria are expressed in multiple RNAs and then processed to create guide strands for RNA. Because Eukaryotic systems lack some of the proteins required to process CRISPR RNAs the synthetic construct gRNA was created to combine the essential pieces of RNA for Cas9 targeting into a single RNA expressed with the RNA polymerase type 21 promoter U6). Synthetic gRNAs are slightly over 100 bp at the minimum length and contain a portion which is targets the 20 protospacer nucleotides immediately preceding the PAM sequence NGG; gRNAs do not contain a PAM sequence.
In one approach, one or more cells of a subject are altered to delete or inactivate Xist using a CRISPR-Cas system. Cas9 can be used to target an Xist gene. Upon target recognition, Cas9 induces double strand breaks in the Xist target gene. Homology-directed repair (HDR) at the double-strand break site can allow insertion of an inactive or deleted form of the Xist sequence.
The following US patents and patent publications are incorporated herein by reference: U.S. Pat. No. 8,697,359, 20140170753, 20140179006, 20140179770, 20140186843, 20140186958, 20140189896, 20140227787, 20140242664, 20140248702, 20140256046, 20140273230, 20140273233, 20140273234, 20140295556, 20140295557, 20140310830, 20140356956, 20140356959, 20140357530, 20150020223, 20150031132, 20150031133, 20150031134, 20150044191, 20150044192, 20150045546, 20150050699, 20150056705, 20150071898, 20150071899, 20150071903, 20150079681, 20150159172, 20150165054, 20150166980, and 20150184139.
Agents modulating H3K27me3 imprinting present in an imprinting control region are useful in generating cloned full term organisms using SCNT. Agents that add H3K27me3 imprinting can be used in combination with an Xist KO cell injected with a Kdm4d polynucleotide.
In one approach, an agent that inhibits H3K27me3 demethylase is used in combination with SCNT. The dosage of the administered agent depends on a number of factors, including the size and health of the individual patient. For any particular subject, the specific dosage regimes should be adjusted over time according to the individual need and the professional judgement of the person administering or supervising the administration of the compositions.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the assay, screening, and therapeutic methods of the invention, and are not intended to limit the scope of what the inventors regard as their invention.
Somatic cell nuclear transfer (SCNT) is a technique that may be used, for example, for the reproductive cloning of livestock (e.g., cows, horses, sheep, goats, pigs) or for therapeutic cloning, in which desired tissues are produced for cell replacement therapy. Unfortunately cloned animals suffer from certain defects arising from improper imprinting, such as a deficiency in trimethylation of lysine 27 on histone H3 protein subunit. This deficiency can be remedied by providing an mRNA encoding an enzyme that carries out the trimethylation event during the SCNT procedure. In one embodiment, an mRNA encoding an enzyme capable of carrying out the trimethylation event (e.g., EZH1, EZH2, PRC2) is injected into the recipient cell or the nuclear donor cell prior to or during the SCNT procedure.
Somatic cell nuclear transfer involves obtaining a nuclear donor cell, then fusing this nuclear donor cell into an enucleated recipient cell, most preferably an enucleated oocyte, to form a nuclear transfer embryo, activating this embryo, and finally culturing the embryo or transferring this embryo into a maternal host. During nuclear transfer a full complement of nuclear DNA from one cell is introduced to an enucleated cell. Nuclear transfer methods are well known to a person of ordinary skill in the art. See, U.S. Pat. No. 4,994,384 to Prather et al., entitled “Multiplying Bovine Embryos,” issued on Feb. 19, 1991; U.S. Pat. No. 5,057,420 to Massey, entitled “Bovine Nuclear Transplantation,” issued on Oct. 15, 1991; U.S. Pat. No. 5,994,619, issued on Nov. 30, 1999 to Stice et al., entitled “Production of Chimeric Bovine or Porcine Animals Using Cultured Inner Cell Mass Cells; U.K. Patents Nos. GB 2,318,578 GB 2,331,751, issued on Jan. 19, 2000 to Campbell et al. and Wilmut et al., respectively, entitled “Quiescent Cell Populations For Nuclear Transfer”; U.S. Pat. No. 6,011,197 to Strelchenko et al., entitled “Method of Cloning Bovines Using Reprogrammed Non-Embryonic Bovine Cells,” issued on Jan. 4, 2000; and in U.S. patent application Ser. No. 09/753,323 entitled “Method of Cloning Porcine Animals (attorney docket number 030653.0026.CIP1, filed Dec. 28, 2000), each of which are hereby incorporated by reference in its entirety including all figures, tables and drawings. Nuclear transfer may be accomplished by using oocytes that are not surrounded by a zona pellucida.
In a nuclear transfer procedure, a nuclear donor cell, or the nucleus thereof, is introduced into a recipient cell. A recipient cell is preferably an oocyte and is preferably enucleated. However, the invention relates in part to nuclear transfer, where a nucleus of an oocyte is not physically extracted from the oocyte. It is possible to establish a nuclear transfer embryo where nuclear DNA from the donor cell is replicated during cellular divisions. See, e.g., Wagoner et al., 1996, “Functional enucleation of bovine oocytes: effects of centrifugation and ultraviolet light,” Theriogenology 46: 279-284. In addition, nuclear transfer may be accomplished by combining one nuclear donor and more than one enucleated oocyte. Also, nuclear transfer may be accomplished by combining one nuclear donor, one or more enucleated oocytes, and the cytoplasm of one or more enucleated oocytes. The resulting combination of a nuclear donor cell and a recipient cell can be referred to as a “hybrid cell.”
The term “nuclear donor” as used herein refers to any cell, or nucleus thereof, having nuclear DNA that can be translocated into an oocyte. A nuclear donor may be a nucleus that has been isolated from a cell. Multiple techniques are available to a person of ordinary skill in the art for isolating a nucleus from a cell and then utilizing the nucleus as a nuclear donor. See, e.g., U.S. Pat. Nos. 4,664,097, 6,011,197, and 6,107,543, each of which is hereby incorporated by reference in its entirety. Any type of cell can serve as a nuclear donor. Examples of nuclear donor cells include, but are not limited to, cultured and non-cultured cells isolated from an embryo arising from the union of two gametes in vitro or in vivo; embryonic stem cells (ES cells) arising from cultured embryonic cells (e.g., pre-blastocyst cells and inner cell mass cells); cultured and non-cultured cells arising from inner cell mass cells isolated from embryos; cultured and non-cultured pre-blastocyst cells; cultured and non-cultured fetal cells; cultured and non-cultured adult cells; cultured and non-cultured primordial germ cells; cultured and non-cultured germ cells (e.g., embryonic germ cells); cultured and non-cultured somatic cells isolated from an animal; cultured and non-cultured cumulus cells; cultured and non-cultured amniotic cells; cultured and non-cultured fetal fibroblast cells; cultured and non-cultured genital ridge cells; cultured and non-cultured differentiated cells; cultured and non-cultured cells in a synchronous population; cultured and non-cultured cells in an asynchronous population; cultured and non-cultured serum-starved cells; cultured and non-cultured permanent cells; and cultured and non-cultured totipotent cells. See, e.g., Piedrahita et al., 1998, Biol. Reprod. 58: 1321-1329; Shim et al., 1997, Biol. Reprod. 57: 1089-1095; Tsung et al., 1995, Shih Yen Sheng Wu Hsueh Pao 28: 173-189; and Wheeler, 1994, Reprod. Fertil. Dev. 6: 563-568, each of which is incorporated herein by reference in its entirety including all figures, drawings, and tables. In addition, a nuclear donor may be a cell that was previously frozen or cryopreserved.
Hybrid cells made by the process of nuclear transfer may be used, for example, in reproductive cloning or in regenerative cloning.
SCNT experiments showed that nuclei from adult differentiated somatic cells can be reprogrammed to a totipotent state. Accordingly, a SCNT embryo generated using the methods as disclosed herein can be cultured in a suitable in vitro culture medium for the generation of totipotent or embryonic stem cell or stem-like cells and cell colonies. Culture media suitable for culturing and maturation of embryos are well known in the art. Examples of known media, which may be used for bovine embryo culture and maintenance, include Ham's F-10+10% fetal calf serum (FCS), Tissue Culture Medium-199 (TCM-199)+10% fetal calf serum, Tyrodes-Albumin-Lactate-Pyruvate (TALP), Dulbecco's Phosphate Buffered Saline (PBS), Eagle's and Whitten's media. One of the most common media used for the collection and maturation of oocytes is TCM-199, and 1 to 20% serum supplement including fetal calf serum, newborn serum, estrual cow serum, lamb serum or steer serum. A preferred maintenance medium includes TCM-199 with Earl salts, 10% fetal calf serum, 0.2 Ma pyruvate and 50 ug/ml gentamicin sulphate. Any of the above may also involve co-culture with a variety of cell types such as granulosa cells, oviduct cells, BRL cells and uterine cells and STO cells.
In particular, epithelial cells of the endometrium secrete leukemia inhibitory factor (LIF) during the preimplantation and implantation period. Therefore, in some embodiments, the addition of LIF to the culture medium is encompassed to enhancing the in vitro development of the SCNT-derived embryos. The use of LIF for embryonic or stem-like cell cultures has been described in U.S. Pat. No. 5,712,156, which is herein incorporated by reference.
Another maintenance medium is described in U.S. Pat. No. 5,096,822 to Rosenkrans, Jr. et al., which is incorporated herein by reference. This embryo medium, named CR1, contains the nutritional substances necessary to support an embryo. CR1 contains hemicalcium L-lactate in amounts ranging from 1.0 mM to 10 mM, preferably 1.0 mM to 5.0 mM. Hemicalcium L-lactate is L-lactate with a hemicalcium salt incorporated thereon. Also, suitable culture medium for maintaining human embryonic stem cells in culture as discussed in Thomson et al., Science, 282:1145-1147 (1998) and Proc. Natl. Acad. Sci., USA, 92:7844-7848 (1995).
In some embodiments, the feeder cells will comprise mouse embryonic fibroblasts. Means for preparation of a suitable fibroblast feeder layer are described in the example which follows and is well within the skill of the ordinary artisan.
Methods of deriving ES cells (e.g., NT-ESCs or hNT-ESCs) from blastocyst-stage SCNT embryos (or the equivalent thereof) are well known in the art. Such techniques can be used to derive ES cells (e.g., hNT-ESCs) from SCNT embryos, where the SCNT embryos used to generate hNT-ESCs have a reduced level of H3K9me3 in the nuclear genetic material donated from the somatic donor cell, as compared to SCNTs which were not treated with a member of the KDM4 demethylase family and/or an inhibitor of the histone methyltransferase SUV39h1/SUV39h2. Additionally or alternatively, hNT-ESCs can be derived from cloned SCNT embryos during earlier stages of development.
In certain embodiments, blastomeres generated from SCNT embryos generated using the methods, compositions and kits as disclosed herein can be dissociated using a glass pipette to obtain totipotent cells. In some embodiments, dissociation may occur in the presence of 0.25% trypsin (Collas and Robl, 43 BIOL. REPROD. 877-84, 1992; Stice and Robl, 39 BIOL. REPROD. 657-664, 1988; Kanka et al., 43 MOL. REPROD. DEV. 135-44, 1996).
In certain embodiments, the resultant blastocysts, or blastocyst-like clusters from the SCNT embryos can be used to obtain embryonic stem cell lines, eg., nuclear transfer ESC (ntESC) cell lines. Such lines can be obtained, for example, according to the culturing methods reported by Thomson et al., Science, 282:1145-1147 (1998) and Thomson et al., Proc. Natl. Acad. Sci., USA, 92:7544-7848 (1995), incorporated by reference in their entirety herein.
Pluripotent embryonic stem cells can also be generated from a single blastomere removed from a SCNT embryo without interfering with the embryo's normal development to birth. See U.S. application Nos. 60/624,827, filed Nov. 4, 2004; 60/662,489, filed Mar. 14, 2005; 60/687,158, filed Jun. 3, 2005; 60/723,066, filed Oct. 3, 2005; 60/726,775, filed Oct. 14, 2005; Ser. No. 11/267,555 filed Nov. 4, 2005; PCT application no. PCT/US05/39776, filed Nov. 4, 2005, the disclosures of which are incorporated by reference in their entirety; see also Chung et al., Nature, Oct. 16, 2005 (electronically published ahead of print) and Chung et al., Nature V. 439, pp. 216-219 (2006), the entire disclosure of each of which is incorporated by reference in its entirety). In such a case, an SCNT embryo is not destroyed for the generation of pluripotent stem cells.
In one aspect of the invention, the method comprises the utilization of cells derived from the SCNT embryo in research and in therapy. Such pluripotent stem cells (PSCs) or totipotent stem cells (TSC) can be differentiated into any of the cells in the body including, without limitation, skin, cartilage, bone, skeletal muscle, cardiac muscle, renal, hepatic, blood and blood forming, vascular precursor and vascular endothelial, pancreatic beta, neurons, glia, retinal, inner ear follicle, intestinal, or lung cells.
In another embodiment of the invention, the SCNT embryo, or blastocyst, or pluripotent or totipotent cells obtained from a SCNT embryo (e.g., NT-ESCs), can be exposed to one or more inducers of differentiation to yield other therapeutically-useful cells such as retinal pigment epithelium, hematopoietic precursors and hemangioblastic progenitors as well as many other useful cell types of the ectoderm, mesoderm, and endoderm. Such inducers include but are not limited to: cytokines such as interleukin-alpha A, interferon-alpha A/D, interferon-beta, interferon-gamma, interferon-gamma-inducible protein-10, interleukin-1-17, keratinocyte growth factor, leptin, leukemia inhibitory factor, macrophage colony-stimulating factor, and macrophage inflammatory protein-1 alpha, 1-beta, 2, 3 alpha, 3 beta, and monocyte chemotactic protein 1-3, 6kine, activin A, amphiregulin, angiogenin, B-endothelial cell growth factor, beta cellulin, brain-derived neurotrophic factor, C10, cardiotrophin-1, ciliary neurotrophic factor, cytokine-induced neutrophil chemoattractant-1, eotaxin, epidermal growth factor, epithelial neutrophil activating peptide-78, erythropoietin, estrogen receptor-alpha, estrogen receptor-beta, fibroblast growth factor (acidic and basic), heparin, FLT-3/FLK-2 ligand, glial cell line-derived neurotrophic factor, Gly-His-Lys, granulocyte colony stimulating factor, granulocytemacrophage colony stimulating factor, GRO-alpha/MGSA, GRO-beta, GRO-gamma, HCC-1, heparin-binding epidermal growth factor, hepatocyte growth factor, heregulin-alpha, insulin, insulin growth factor binding protein-1, insulin-like growth factor binding protein-1, insulin-like growth factor, insulin-like growth factor II, nerve growth factor, neurotophin-3,4, oncostatin M, placenta growth factor, pleiotrophin, rantes, stem cell factor, stromal cell-derived factor 1B, thromopoietin, transforming growth factor—(alpha, beta 1,2,3,4,5), tumor necrosis factor (alpha and beta), vascular endothelial growth factors, and bone morphogenic proteins, enzymes that alter the expression of hormones and hormone antagonists such as 17B-estradiol, adrenocorticotropic hormone, adrenomedullin, alpha-melanocyte stimulating hormone, chorionic gonadotropin, corticosteroid-binding globulin, corticosterone, dexamethasone, estriol, follicle stimulating hormone, gastrin 1, glucagons, gonadotropin, L-3,3′,5′-triiodothyronine, leutinizing hormone, L-thyroxine, melatonin, MZ-4, oxytocin, parathyroid hormone, PEC-60, pituitary growth hormone, progesterone, prolactin, secretin, sex hormone binding globulin, thyroid stimulating hormone, thyrotropin releasing factor, thyroxin-binding globulin, and vasopressin, extracellular matrix components such as fibronectin, proteolytic fragments of fibronectin, laminin, tenascin, thrombospondin, and proteoglycans such as aggrecan, heparan sulphate proteoglycan, chontroitin sulphate proteoglycan, and syndecan. Other inducers include cells or components derived from cells from defined tissues used to provide inductive signals to the differentiating cells derived from the reprogrammed cells of the present invention. Such inducer cells may derive from human, non-human mammal, or avian, such as specific pathogen-free (SPF) embryonic or adult cells.
Blastomere Culturing. In one embodiment, the SCNT embryos can be used to generate blastomeres and utilize in vitro techniques related to those currently used in pre-implantation genetic diagnosis (PGD) to isolate single blastomeres from a SCNT embryo, generated by the methods as disclosed herein, without destroying the SCNT embryos or otherwise significantly altering their viability. As demonstrated herein, pluripotent embryonic stem (hES) cells and cell lines can be generated from a single blastomere removed from a SCNT embryo as disclosed herein without interfering with the embryo's normal development to birth.
The discoveries of Wilmut et al. (Wilmut, et al, Nature 385, 810 (1997) in sheep cloning of “Dolly”, together with those of Thomson et al. (Thomson et al., Science 282, 1145 (1998)) in deriving hESCs, have generated considerable enthusiasm for regenerative cell transplantation based on the establishment of patient-specific hESCs derived from SCNT-embryos or SCNT-engineered cell masses generated from a patient's own nuclei. This strategy, aimed at avoiding immune rejection through autologous transplantation, is perhaps the strongest clinical rationale for SCNT. By the same token, derivations of complex disease-specific SCNT-hESCs may accelerate discoveries of disease mechanisms. For cell transplantations, innovative treatments of murine SCID and PD models with the individual mouse's own SCNT-derived mESCs are encouraging (Rideout et al, Cell 109, 17 (2002); Barberi, Nat. Biotechnol. 21, 1200 (2003)). Ultimately, the ability to create banks of SCNT-derived stem cells with broad tissue compatibility would reduce the need for an ongoing supply of new oocytes.
In certain embodiments of the invention, pluripotent or totipotent cells obtained from a SCNT embryo (e.g., hNT-ESCs) can be optionally differentiated, and introduced into the tissues in which they normally reside in order to exhibit therapeutic utility. For example, pluripotent or totipotent cells obtained from a SCNT embryo can be introduced into the tissues. In certain other embodiments, pluripotent or totipotent cells obtained from a SCNT embryo can be introduced systemically or at a distance from a cite at which therapeutic utility is desired. In such embodiments, the pluripotent or totipotent cells obtained from a SCNT embryo can act at a distance or may hone to the desired cite.
In certain embodiments of the invention, cloned cells, pluripotent or totipotent cells obtained from a SCNT embryo can be utilized in inducing the differentiation of other pluripotent stem cells. The generation of single cell-derived populations of cells capable of being propagated in vitro while maintaining an embryonic pattern of gene expression is useful in inducing the differentiation of other pluripotent stem cells. Cell-cell induction is a common means of directing differentiation in the early embryo. Many potentially medically-useful cell types are influenced by inductive signals during normal embryonic development including spinal cord neurons, cardiac cells, pancreatic beta cells, and definitive hematopoietic cells. Single cell-derived populations of cells capable of being propagated in vitro while maintaining an embryonic pattern of gene expression can be cultured in a variety of in vitro, in ovo, or in vivo culture conditions to induce the differentiation of other pluripotent stem cells to become desired cell or tissue types.
The pluripotent or totipotent cells obtained from a SCNT embryo (e.g., ntESCs) can be used to obtain any desired differentiated cell type. Therapeutic usages of such differentiated cells are unparalleled. As discussed herein, the donor cell, or the recipient oocyte, the hybrid oocyte or SCNT embryo can be treated with a KDM4 histone dimethylase activator and/or H3K9 methyltransferase inhibitor according to the methods as disclosed herein.
Alternatively, the donor cells can be adult somatic cells from a subject with a disorder, and the generated SCNT embryos can be used to produce animal models of disease or disease-specific pluripotent or totipotent cells which can be cultured under differentiation conditions to produce cell models of disease. The great advantage of the present invention is that by increasing the efficiency of SCNT, it provides an essentially limitless supply of isogenic or syngeneic ES cells, particularly pluripotent that are not induced pluripotent stem cells (e.g., not iPSCs). Such NT-ESCs have advantages over iPSCs and are suitable for transplantation, as they do not partially pluripotent, and do not have viral transgenes or forced expression of reprogramming factors to direct their reprogramming.
In some embodiments, the NT-ESCs generated from the SCNTs are patient-specific pluripotent obtained from SCNT embryos, where the donor cell was obtained from a subject to be treated with the pluripotent stem cells or differentiated progeny thereof. Therefore, it will obviate the significant problem associated with current transplantation methods, i.e., rejection of the transplanted tissue which may occur because of host-vs-graft or graft-vs-host rejection. Conventionally, rejection is prevented or reduced by the administration of anti-rejection drugs such as cyclosporin. However, such drugs have significant adverse side-effects, e.g., immunosuppression, carcinogenic properties, as well as being very expensive. The present invention should eliminate, or at least greatly reduce, the need for anti-rejection drugs, such as cyclosporine, imulan, FK-506, glucocorticoids, and rapamycin, and derivatives thereof.
The practice of the present invention employs, unless otherwise indicated, conventional techniques of molecular biology (including recombinant techniques), microbiology, cell biology, biochemistry and immunology, which are well within the purview of the skilled artisan. Such techniques are explained fully in the literature, such as, “Molecular Cloning: A Laboratory Manual”, second edition (Sambrook, 1989); “Oligonucleotide Synthesis” (Gait, 1984); “Animal Cell Culture” (Freshney, 1987); “Methods in Enzymology” “Handbook of Experimental Immunology” (Weir, 1996); “Gene Transfer Vectors for Mammalian Cells” (Miller and Calos, 1987); “Current Protocols in Molecular Biology” (Ausubel, 1987); “PCR: The Polymerase Chain Reaction”, (Mullis, 1994); “Current Protocols in Immunology” (Coligan, 1991). These techniques are applicable to the production of the polynucleotides and polypeptides of the invention, and, as such, may be considered in making and practicing the invention. Particularly useful techniques for particular embodiments will be discussed in the sections that follow.
The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the assay, screening, and therapeutic methods of the invention, and are not intended to limit the scope of what the inventors regard as their invention.
The inactive X chromosome is marked by its punctate staining with an anti-H3K27me3 antibody. Consistently, such punctate staining is detectable only in female (XX) cells but not in male (XY) cells in in vitro fertilized (IVF) embryos. In contrast, such punctate staining was observed in SCNT embryos when male Sertoli cells were used as donor cells (
The fact that the two reprogramming barriers are independent of each other prompted the question of whether a combined approach of using Xist KO donor cells and injecting Kdm4d will have a synergistic or additive effect to achieve increased cloning efficiency. SCNT was attempted using cumulus cells as donors. In wildtype control with B6D2F1 background, only 1.2% of embryos transferred to surrogate mothers reached term (
Kdm4d mRNA injection increased the pup rate to 8.4%, consistent with previous observations (Matoba et al., Proc. Natl. Acad. Sci. U.S.A. 108, 20621-20626, 2014). When cumulus cells derived from Xist heterozygous mice were used as donor cells and combined with Kdm4d mRNA injection, the pup rate increased to 18.7% (
The above results indicate that the invention provides the highest mouse cloning efficiency by using the combined approach. However, even the highest cloning efficiency of 23.5% is still less than half of the IVF pup rate, which is more than 50% of transferred embryos. Indeed, 65% (37 out of 57) of the implanted embryos arrested during postimplantation development in the combined Sertoli cell SCNT group (Table 2). A careful morphological examination at different embryonic stages revealed that the embryo arrest starts just after implantation and gradually increases as development proceeds (
Since the combinational reprogrammed SCNT embryos begin to exhibit developmental defects right after implantation (
DNA methylation information of 20.6 and 20.9 million CpG sites from IVF and SCNT blastocysts, respectively (Table 3).
For comparison, WGBS datasets were also obtained for MEF (Yu et al., Proc. Natl. Acad. Sci. U.S.A. 111, 5890-5895, 2014), sperm and oocyte (Wang et al., Cell 157, 979-991, 2014) from public database. First, the average DNA methylation level of all covered CpGs was calculated. It was found that the average methylation levels in sperm and oocyte are 82.2% and 58.8%, respectively. The average methylation level of sperm and oocyte, which serves as the starting methylation level of IVF zygotes, is 70.5% (
Next, the DNA methylation levels of MEF cells and SCNT blastocysts of the commonly covered CpGs was calculated, and it was found that the donor MEF cells are highly methylated (78.0%), but the SCNT blastocysts were lowly methylated with a methylation level (15.6%) similar to that of the IVF blastocysts (19.1%) indicating successful global reprogramming of DNA methylation state (
These results indicate that DNA methylation and transcriptome are largely reprogrammed by SCNT at the blastocyst stage.
Despite successful global reprogramming of the DNA methylome, the mean methylation level of SCNT blastocysts (15.6%) was slightly but significantly lower (p value<2.2e-16) than that of the IVF blastocysts (19.1%) (
To understand how these DMRs are formed and whether they could contribute to the post-implantation developmental failure of the SCNT embryos, the analysis focused on the hypoDMRs. In sperm, the methylation level at hypoDMRs was significantly higher than the flanking regions (˜90% vs ˜80%) (
Next, the hyperDMRs were analyzed. The methylation levels at hyperDMRs and flanking regions are similar (˜50%) in oocytes, while it is significantly lower than the flanking regions (˜55% vs ˜80%) in sperm (
Defective placental development is a central feature in SCNT embryos. Previous studies have established that genomic imprinting plays a critical role in placental development. Therefore, besides the identified DRMs that can potentially contribute to the post-implantation defects of the SCNT embryos, it is important to evaluate the impact of a combinatorial approach on genomic imprinting. To this end, the DNA methylation level of the 23 known imprinting control regions (ICRs) was analyzed as allelic expression of imprinted genes is largely controlled by allelic ICR methylation. Comparative DNA methylation analysis revealed that although DNA methylation levels are slightly reduced at most ICRs, 21 out of the 23 ICRs maintained at least half that of the IVF blastocysts level (
To further evaluate the potential role of DNA methylation-mediated genomic imprinting in the SCNT defects, RNAseq datasets were analyzed focusing on the 126 known imprinted genes. Of the 45 imprinted genes reliably detectable in IVF blastocysts (FPKM>1), only 6 were significantly upregulated in SCNT blastocysts compared to that in IVF blastocysts (FC>1.5) (
The analysis focused on the H3K27me3-dependent imprinted genes that were recently identified, but that are not included in the above analysis. Among the 76 genes that exhibit H3K27me3-dependent imprinted expression in the morula embryos (Inoue et al., Nature 547, 419-424, 2017), 26 are expressed at a reliably detectable level (FPKM>1) in IVF blastocysts. Interestingly, the majority of them (15/26) are significantly upregulated in SCNT blastocysts (FC>1.5) (
Why do these H3K27me3-dependent imprinted genes lose imprinting in SCNT blastocysts? Since imprinting status of these genes is regulated by maternal allele-specific H3K27me3 domains deposited during oogenesis, it is possible that the H3K27me3 pattern in donor MEFs may differ from that in oocytes. Analysis of available H3K27me3 ChIP-seq datasets of fully grown oocyte and MEF cells revealed that the H3K27me3 domains at these imprinted genes in oocyte were completely absent in MEF cells (
Despite successful cloning of more than 20 mammalian species by SCNT=, the cloning efficiency is uniformly low and developmental abnormalities including placenta overgrowth are observed in essentially all cloned mammalian species. It has been speculated that epigenetic abnormalities are responsible for the developmental failure of the cloned animals. In this study, two approaches were combined to overcome two previously identified reprogramming barriers that impede development of mouse SCNT embryos. The combinatorial use of Xist KO donor somatic cells and Kdm4d mRNA injection indeed increased the overall cloning efficiency (term rate) by 20-fold to generate the highest pup rate (e.g., 23% using Sertoli cells) ever reported in mouse reproductive cloning using somatic donor cells. This efficiency is remarkable as it is close to that of intra-cytoplasmic sperm- or round spermatid-injection (ICSI/ROSI) where similar nuclear injection is involved (Ogonuki et al., PLoS One 5, 2010; Ogura et al., International Review of Cytology, pp. 189-2292005). This achievement clearly demonstrates that H3K9me3 in donor cells and abnormal activation of Xist represent two major barriers for successful cloning, and therefore establishes a foundation for understanding the molecular mechanisms of SCNT-mediated reprogramming.
Despite the remarkable improvement, many of the SCNT embryos generated using the combinational approach failed to develop after implantation. Moreover, placental overgrowth was still observed regardless of the donor cell types indicating additional barriers exist for high efficiency animal cloning. To identify these additional reprogramming barriers, w the time when the developmental failure begins was identified and the first WGBS dataset was generated from SCNT blastocysts right before the developmental phenotype appears. Comparative DNA methylome analysis revealed successful global DNA methylome reprogramming by SCNT, indicating that the DNA demethylation machineries in ooplasm and cleavage embryos are similarly functional in SCNT embryos compared to that in IVF embryos. Nevertheless, detailed comparative analysis of DNA methylomes revealed many DMRs across the genome between IVF and SCNT blastocysts. Interestingly, hyperDMRs are enriched in genomic regions demethylated in germline, which is consistent with the fact that germ cell-specific genes are demethylated by Teti during germ cell development, particularly at the primordial germ cell (PGC) stage. Yet SCNT bypasses this demethylation processes. The list of hyperDMR-associated genes does not include a few germline genes reported to be quickly demethylated at 1 cell SCNT embryos, indicating that some germline genes, but not the majority, are subjected to demethylation after SCNT. On the other hand, hypoDMRs mainly overlap with regions that are methylated in oocytes. Maternal DNA methylation at these regions appears to escape the demethylation processes particularly before the 8-cell stage in IVF embryos. The underlying mechanism for the maternal allele-specific maintenance of DNA methylation before the 8-cell stage is of interest for future study. Collectively, it appears that the SCNT specific DMRs, either high or low, are formed due to the unique feature of gametogenesis which are inherited to the blastocysts through normal fertilization. Maternal DNA methylation passed down from oocyte to embryos through fertilization has been shown to play important roles in early stage trophoblast development (Branco et al., Dev. Cell 36, 152-163, 2016). Therefore, loss of oocyte-like DNA methylation pattern in SCNT blastocysts may contribute to developmental phenotypes of SCNT embryos.
As reported herein, DNA methylation and transcriptome analysis of DNA methylation-imprinted genes revealed that most ICRs largely maintain their normal imprinting status and that most canonical imprinted genes indeed maintain allelic expression pattern in SCNT blastocysts. In contrast, the recently discovered H3K27me3-mediated non-canonical imprinted genes (Inoue et al., 2017) are totally dysregulated and exhibit biallelic expression in SCNT blastocysts. The list of dysregulated non-canonical imprinted genes in SCNT blastocysts included Slc38a4, Sfmbt2 and Gab1, consistent with a previous report of loss-of-imprint (LOI) of these three genes in placenta of E13.5 SCNT embryos (Okae et al., Hum. Mol. Genet. 23, 992-1001, 2014). Given all of the three genes have been shown to play important roles in placental growth, LOI of these genes likely contribute to the placenta overgrowth phenotype of SCNT embryos. Moreover, Runx1, Otx2 and Etv6 have been shown to play critical roles in mouse early embryonic development, therefore LOI of these genes at the blastocyst stage may contribute to embryonic lethality phenotype of postimplantation SCNT embryos. The causes of LOI of non-canonical imprinted genes in SCNT are most likely due to the absence of H3K27me3 at these loci in the donor somatic cells. Further detailed analysis on the regulatory mechanisms of the H3K27me3-imprinted genes will provide clues for improving SCNT embryo development.
In summary, in addition to establishing the most efficient mouse cloning method by combining Kdm4d mRNA injection with the use of Xist KO donor cells, H3K27me3 imprinting was uncovered as a potential barrier preventing efficient animal cloning. Without intending to be bound by theory, based on the clear association of LOI at the H3K27me3-dependent imprinted genes in mouse SCNT blastocysts and their critical functions in embryonic development, LOI at the H3K27me3-imprinted genes most likely accounted for the postimplantation phenotypes of SCNT embryos, although the possibility of potential contribution of abnormal DNA methylation identified in this study cannot be excluded. Given that defective postimplantation development and abnormal placental phenotypes in SCNT embryos are commonly observed in mammalian species, investigation of H3K27me3-dependent imprinting status in cloned embryos of other species may warrant future investigation.
The results described were obtained using the following methods and materials.
Isolation of Maternal and Paternal Pronuclei from PN5 Stage Zygotes
All animal studies were performed in accordance with guidelines of the Institutional Animal Care and Use Committee at Harvard Medical School. MII-stage oocytes were collected from 8 week-old B6D2F1/J (BDF1) females superovulated by injecting 7.5 I.U. of PMSG (Millipore) and hCG (Millipore). For in vitro fertilization (IVF), MII oocytes were inseminated with activated spermatozoa obtained from the caudal epididymis of adult BDF1 male mice in HTF medium supplemented with 10 mg/ml bovine serum albumin (BSA; Sigma-Aldrich). Spermatozoa capacitation was attained by 1 h incubation in the HTF medium. Zygotes were cultured in a humidified atmosphere with 5% CO2/95% air at 37.8° C. At 10 hours post-fertilization (hpf), zygotes were transferred into M2 media containing 10 μg/ml cytochalasin B (Sigma-Aldrich). Zona pellucidae were cut by a Piezo impact-driven micromanipulator (Prime Tech Ltd., Ibaraki, Japan) and the pronuclei were isolated from the zygotes. At 12 hpf (PN5-stage), isolated pronuclei were washed with 0.2% BSA/PBS, transferred into Eppendorf LoBind 1.5 ml tubes, and placed on ice until DNase I treatment. For each experiment, 150-200 pronuclei were collected and prepared for liDNase-seq. The parental pronuclei were distinguished by (1) the distance from the second polar body and (2) the size of the pronucleus.
MII oocytes were collected from 8 week-old superovulated BDF1 females and inseminated with BDF1 sperm. At 7 hpf, zygotes were transferred into M2 media containing 5 μg/ml cytochalasin B, and parental pronuclei were exchanged by using a Piezo impact-driven micromanipulator. The sendai virus (HVJ, Cosmo-bio) was used for fusing karyoplasts with cytoplasms as previously described. After reconstruction, embryos were cultured in KSOM.
When collecting embryos for RNA-seq or/and liDNase-seq, zona pellucida (ZP) was removed by a brief exposure to Acid tyrode's solution (Sigma-Aldrich), then the embryos were washed with M2 media, and then 0.2% BSA/PBS. For liDNase-seq, 10 morula embryos were transferred into an Eppendorf LoBind 1.5 ml tube, and placed on ice until DNase I treatment. For RNA-seq, seven to ten embryos were transferred into a thin-walled RNase-free PCR tubes (Ambion). The 2-cell and morula embryos were collected at 30 and 78 hpf, respectively. When preparing a-amanitin treated 2-cell embryos, 5 hpf zygotes were transferred into KSOM containing 25 μg/ml α-amanitin (Sigma-Aldrich) and cultured in the presence of α-amanitin until collection (30 hpf). ICM and TE were isolated. Briefly, AG and GG embryos at 120 hpi were treated with Acid tyrode's solution to remove ZP. After being washed in M2 media, the embryos were incubated in KSOM containing rabbit anti-mouse lymphocyte serum (Cedarlane, 1:8 dilution) for 45 min at 37° C. After being washed in M2 media, they were transferred into KSOM containing guinea pig complement (MP Biomedicals, 1:3.3 dilution). After incubation for 30 min at 37° C., lysed TE cells were removed by pipetting with a glass capillary. The remaining ICM clumps were incubated in 0.25% Trypsin/EDTA (Thermo Fisher, 25200) for 10 min at 37° C., and then dissociated into single cells to avoid contamination of lysed TE cells. 100-200 cells were collected for RNA-seq.
Isolation of GV Nuclei from Fully-Grown Oocytes
Fully-grown GV-stage oocytes were obtained from 3-week-old BDF1 mice 44-48 h after injection with 5 I.U. PMSG. The ovaries were transferred to M2 media. The ovarian follicles were punctured with a 30-gauge needle, and the cumulus cells were gently removed from the cumulus-oocyte complexes using a narrow-bore glass pipette. The oocytes were then transferred into α-MEM (Life technologies, 12571-063) supplemented with 5% Fetal Bovine Serum (FBS) (Sigma-Aldrich, F0926), 10 ng/ml Epidermal Growth Factor (Sigma-Aldrich, E4127), and 0.2 mM 3-isobutyl-1-methylxanthine (IBMX; Sigma-Aldrich). One hour after collection, GV oocytes exhibiting visible perivitelline spaces, which have the surrounding-nucleolus (SN)-type chromatin, were culled. They were then incubated in M2 media containing 10 μg/ml cytochalasin B, 0.1 μg/ml colcemid (Sigma-Aldrich), and 0.2 mM IBMX for 15 min. Then, GV nuclei were isolated by using a Piezo-driven micromanipulator. After washing with 0.2% BSA/PBS, the GV nuclei were transferred into an Eppendorf LoBind 1.5 ml tube. For each experiment, 115-150 GV nuclei were collected for liDNase-seq.
To obtain C57BL6(B6)/PWK hybrid embryos, a natural mating scheme was used. To obtain PWK/B6 hybrid embryos, in vitro fertilization of PWK oocytes with B6 sperm was used, and the 2-cell embryos were transferred into surrogate ICR strain mothers. Dissection of E6.5 embryos into EPI, EXE, and VE was performed. To collect E9.5 placental cells, the B6GFP mice from Jackson laboratory were purchased [C57BL/6-Tg(CAG-EGFP)131sb/LeySopJ, Stock number 006567]. MII oocytes and sperms were collected from superovulated 8-week old B6GFP or PWK mice. After in vitro fertilization, the 2-cell embryos were transferred into surrogate ICR strain mothers. At E9.5, placentae were harvested, cut into ˜0.5 mm pieces, transferred into 50 ml tubes, and treated with 2 ml of 0.25% Trypsin-EDTA (Thermo Fisher Scientific, 25200) at 30° C. for 15 min in a shaker at 200 rpm to dissociate placental cells. Trypsin treatment was stopped by the addition of 2 ml DMEM containing 10% FBS. After pipetting, the tubes were centrifuged and the pelleted cells were washed with 0.2% BSA/PBS three times. DAPI was added at the final concentration of 1 μM in the final cell suspension. The GFP-positive cells were sorted using a BD FACSaria machine (BD Biosciences) with DAPI positive cells excluded as dead cells. Approximately 10,000-20,000 GFP-positive cells were collected from each placenta, which corresponded to 40-60% of total placental cells.
Plasmid Construction and mRNA Preparation
To generate the Kdm6bWT construct, the cDNA encoding the carboxyl-terminal part containing the catalytic domain (amino acid 1025-End) was amplified. The PCR amplicon was cloned between a Flag tag and poly(A) of the pcDNA3.1-Flag-poly(A)83 plasmid. The H1390A Kdm6bMUT construct were generated by using PrimeSTAR mutagenesis (TAKARA). Primers used for the mutagenesis are 5′-CCAGGCgctCAAGAGAATAACAATTTCTGCTCAGTCAACATCAAC-3′ and 5′-CTCTTGagcGCCTGGCGTTCGGCTGCCAGGGACCTTCATG-3′. All constructs were verified by DNA sequencing. The plasmids for wild-type and H189A mutant Kdm4d were previously described.
After linearization by a restriction enzyme, the construct was purified with phenol-chloroform extraction. mRNA was synthesized by in vitro transcription using a mMESSAGE mMACHINE T7 Ultra Kit (Life technologies) according to manufacturer's instructions. The synthesized mRNA was purified by lithium chloride precipitation and diluted with nuclease-free water. mRNA aliquots were stored in −80° C. until use.
mRNA Injection
MII oocytes were collected from superovulated 8 week-old BDF1 females and inseminated with BDF1 sperm. At 2.5 hpf, fertilized oocytes were transferred into M2 media and mRNA was injected using a Piezo impact-driven micromanipulator. mRNA injection was completed by 4 hpf. The mRNA concentrations of Kdm6bWT and Kdm6bMUT were 1.8 μg/μl, and those of Kdm4dWT and Kdm4dMUT were 1.5 μg/μl. When preparing Kdm6b-injected PG embryos, MII oocytes were chemically activated by treating with 3 mM SrCl2 in Ca2+-free KSOM containing 5 μg/ml cytochalasin B. At 4 hrs post-activation (hpa), the embryos were washed with KSOM. At 5 hpa, they were injected with mRNA.
Zygotes were fixed in 3.7% paraformaldehyde (PFA) in PBS containing 0.2% Triton for 20 min. After 4× washes with PBS containing 10 mg/ml BSA (PBS/BSA), zygotes were treated with primary antibodies at 4° C. overnight. The primary antibodies used in this study were mouse-anti-H3K27me3 (1/500, Active Motif, 61017), rabbit anti-H3K9me3 (1/500, Millipore, 07-442), and rabbit anti-FLAG (1/2000, Sigma-Aldrich, F7524). After 3× washes with PBS/BSA, samples were incubated with a 1:250 dilution of fluorescein isothiocyanate-conjugated anti-mouse IgG (Jackson Immuno-Research) or Alexa Flour 568 donkey anti-rabbit IgG (Life technologies) for 1 h. The zygotes were then mounted on a glass slide in Vectashield anti-bleaching solution with 4′,6-diamidino-2-phenylindole (DAPI) (Vector Laboratories, Burlingame, Calif.). Fluorescence was detected under a laser-scanning confocal microscope with a spinning disk (CSU-10, Yokogawa) and an EM-CCD camera (ImagEM, Hamamatsu) or Zeiss LSM800.
All images were acquired and analyzed using the Axiovision software (Carl Zeiss). The fluorescent signal intensity was quantified with the Axiovision software. Briefly, the signal intensity within the maternal pronuclei was determined, and the cytoplasmic signal was subtracted as background. Then, the averaged signal intensity of the no-injection control zygotes was set as 1.0.
Low-input DNase-seq libraries were prepared as previously described with minor modifications. Embryos or nuclei collected in 1.5 ml tubes were resuspended in 36 μl lysis buffer (10 mM Tris-HCl, pH 7.5, 10 mM NaCl, 3 mM MgCl2, 0.1% Triton X-100) and incubated on ice for 5 min. DNase I (10 U/μl, Roche) was added to the final concentration of 80 U/ml (for the GV nucleus sample) or 40 U/ml (for all the other samples) and incubated at 37° C. for exactly 5 min. The reaction was stopped by adding 80 μl Stop Buffer (10 mM Tris-HCl, pH 7.5, 10 mM NaCl, 0.15% SDS, 10 mM EDTA) containing 2 μl Proteinase K (20 mg/ml, Life technologies). Then 20 ng of a circular carrier DNA [a pure plasmid DNA without any mammalian genes purified with 0.5× Beckman SPRIselect beads (Beckman Coulter) to remove small DNA fragments] was added. The mixture was incubated at 50° C. for 1 hr, then DNA was purified by extraction with phenol-chloroform and precipitated by ethanol in the presence of linear acrylamide (Life technologies) overnight at −20° C. Precipitated DNA was resuspended in 50 μl TE (2.5 mM Tris, pH 7.6, 0.05 mM EDTA), and the entire volume was used for sequencing library construction.
Sequencing library was prepared using NEBNext Ultra II DNA Library Prep Kit for Illumina (New England Biolabs) according to the manufactures' instruction with the exception that the adaptor ligation was performed with 0.03 μM adaptor in the ligation reaction for 30 minutes at 20° C. and that PCR amplification was performed using Kapa Hifi hotstart readymix (Kapa Biosystems) for 8-cycles. The PCR products were purified with ×1.3 volume of SPRIselect beads (Beckman Coulter) and then size selected with ×0.65 volume followed by ×0.7 volume of SPRIselect beads. The sample was eluted in 24 μl TE. The number of cycles needed for the second PCR amplification was determined by qPCR using 1 μl of the 1:1,000 diluted samples. The remaining 23 μl of the samples was then amplified with Kapa Hifi hotstart readymix (we used 7 cycles for all samples in this study). The PCR product was purified with ×1.3 volume of SPRIselect beads and then size selected with ×0.65 volume followed by ×0.7 volume of SPRIselect beads. The DNA was eluted in 30 μl of TE and quantified by Qubit dsDNA HS assay kit (Thermo Fisher Scientific, Q32854) and Agilent high sensitivity assay kit (Agilent Technologies). The libraries were sequenced on a Hiseq2500 with single-end 100 bp reads (Illumina).
RNA-seq libraries were prepared as previously described. Briefly, reverse transcription and cDNA amplification were performed using whole embryo lysates with SMARTer Ultra Low Input RNA cDNA preparation kit (Clontech, 634890). When processing 2-cell AG, GG and a-amanitin-treated IVF embryo samples, 1 μl of 1:40,000 diluted ERCC (External RNA Controls Consortium) standard RNA (Life technologies) was added to each of the tubes at the step of cell lysis. cDNAs were then fragmented using the Covaris M220 sonicator (Covaris) with microTUBE-50 (Covaris) into average 150-160 bp fragments. The fragmented cDNAs were end-repaired, adaptor ligated and amplified using NEBNext Ultra DNA Library Prep Kit for Illumina according to the manufacturer's instruction (New England Biolabs). Single end 100 bp sequencing was performed on a HiSeq2500 sequencer (Illumina).
liDNase-Seq Data Analysis
Reads of liDNase-seq data were firstly trimmed of low quality and adapter with trim_galore, and then mapped to the mouse genome (mm9) using Bowtie v0.12.9. ‘−m 1’ parameter to keep unique mapping hits. The reads with mapping quality (MAPA)≤10 or redundant reads that mapped to the same location with the same orientation were removed with SAMtools. The DHS peaks in liDNase-seq data were identified by Hotspot program with FDR<=0.01. The DHS peaks from all 33 libraries were merged using ‘bedtools merge’ from bedtools. The number of reads in each DHS for each library was calculated using ‘multiBamSummary’ from deepTools and normalized to the total number of mapped reads and to the length of DHS (possibility of a tag located on a position per 1 kb per million mapped reads). Reads of sex chromosomes were removed because the number of sex chromosomes is different between the parental pronuclei and between androgenetic and gynogenetic embryos. The Pearson correlation coefficient (r) of tag densities at genome-wide DHSs was calculated to measure the correlation between replicates. For identification of parental allele-specific DHSs in zygotes and morula embryos, a stringent cutoff was used (RPKM mean>2, RPKM>1 in all replicates in a biased allele, and mean value fold change larger than 4 between the two alleles). The 431 most reliable Ps-DHSs were identified by applying an additional criterion ‘RPKM>1 in all replicates of paternal PNs of microinjected zygotes’ to Ps-DHSs. The RefSeq gene assembly (mm9) from the UCSC Genome Browser database and CGIs previously defined were used as genomic feature distribution analysis in
A custom reference sequence combining mouse genome (mm9) with the ERCC control was constructed. Reads of RNA-seq were mapped to the reference genome with TopHat v2.0.6 or STAR (github.com/alexdobin/STAR). All programs were run with default parameters unless otherwise specified. Uniquely mapped reads were subsequently assembled into transcripts guided by the reference annotation (UCSC gene models) with featureCounts from subread-v1.5.1. For all 2-cell RNA-seq libraries, library size factors were estimated with ‘estimateSizeFactors’ function form R package DESeq only using ERCC read counts. After the library size was normalized, the expression level of each gene was quantified with normalized FPKM (fragments per kilobase of exon per million mapped fragments). The Pearson correlation coefficient (r) of gene expression level was calculated to indicate the correlation between duplicates. For identification of newly synthesized transcripts at the 2-cell stage, statistically non-significant genes were filtered out between AG or GG and a-amanitin treated 2-cell embryo. To this end, adjusted P value was calculated with ‘nbinomTest’ function form R pakage DESeq using a negative binomial model, and only genes with FDR<0.05 were selected. Additional cutoffs [Mean FPKM (AG or GG)>2 and fold-change (FC) (AG/Ama or GG/Ama)>2] were then applied. As a result, 4,381 and 3,916 genes were identified as newly synthesized genes in AG and GG 2-cell embryos, respectively. For identifying AG- and GG-specific DEGs in 2-cell embryos, the gene expression level (FPKM) of each gene in a-amanitin 2-cell embryos was subtracted from that of AG and GG embryos. Genes showing FC (AG/GG or GG/AG)>10 were identified as DEGs.
The DNA methylation level at DHSs was calculated using methpipe v3.4.2. When calculating the DNA methylation level at each DHS, to get enough coverage of WGBS reads, each DHS was extended to both up and downstream 2 kb to include more nearby CpG sites. The oocyte-methylated gDMR was defined by >80% methylation in oocytes and <20% in sperm. For
Statistical analyses were implemented with R (www.r-project.org/). Pearson's r coefficient was calculated using the ‘cor’ function with default parameters.
Known imprinting information was downloaded from www.geneimprint.com/site/genes-by-species.Mus+musculus.
A customized pipeline was used to split the hybrid RNA-seq data to their parental origin based on SNP information. The code can be found at github.com/lanjiangboston/UniversalSNPsplit.
All the liDNase-seq and RNA-seq datasets generated in this study were deposited at GEO database under accession number GSE92605. Sperm liDNase-seq datasets were from a previously publication (GSE76642). WGBS datasets for sperm and GV oocytes were downloaded from www.nodai-genome.org/mouse.html?lang=en. H3K27me3 ChIP-seq datasets of sperm, MII oocytes, and SNP-tracked maternal and paternal alleles of 1-cell embryos were downloaded from a previous publication (GSE76687).
All animal studies were performed in accordance with guidelines of the Institutional Animal Care and Use Committee at Harvard Medical School. MII-stage oocytes were collected from 8 week-old B6D2F1/J (BDF1) females superovulated by injecting 7.5 I.U. of PMSG (Millipore) and hCG (Millipore). For in vitro fertilization (IVF), MII oocytes were inseminated with activated spermatozoa obtained from the caudal epididymis of adult BDF1 or PWK (Jackson Laboratory, 003715) males in HTF medium supplemented with 10 mg/ml bovine serum albumin (BSA; Sigma-Aldrich). Spermatozoa capacitation was attained by 1 h incubation in the HTF medium. Zygotes were transferred to KSOM and cultured in a humidified atmosphere with 5% CO2/95% air at 37.8° C.
mRNA Injection
At 4 hrs post-fertilization (hpf), zygotes were transferred into M2 media and mRNA was injected using a Piezo impact-driven micromanipulator (Prime Tech Ltd., Ibaraki, Japan). The construction and preparation of mRNA were described above. The concentrations of injected mRNA of Kdm6bWT and Kdm6bMUT were 1.8 μg/μl, and those of Kdm4dWT and Kdm4dMUT were 1.5 μg/μl.
A probe for Xist RNA was prepared by using Nick translation reagent kit (Abbott Molecular, 07J00-001) with Cy3-dCTP (GE healthcare, PA53021), according to the manufacturer's instruction. The template DNA used for the probe preparation was a plasmid coding the full-length mouse Xist gene, a gift from Rudolf Jaenisch (pCMV-Xist-PA, 26760) (Wutz and Jaenisch, 2000). A probe for DNA FISH was prepared using the same kit with Green-dUTP (Abbott Molecular, 02N32-050). The template DNA was a BAC clone containing the Rnf12 locus (RP23-36C20). The fluorescent probes were ethanol precipitated with 5 μg Cot-1 DNA (Life technologies), 5 μg herring sperm DNA (Thermo Fisher Scientific), and 2.5 μg yeast tRNA (Thermo Fisher Scientific, AM7119), and then dissolved with 20 μl formamide (Thermo Fisher Scientific, 17899). The probes were stored at 4° C. Before being used, the probes (0.75 μl each) were mixed with 0.75 μl Cot-1 DNA, which had been ethanol precipitated and dissolved in formamide, and 2.25 μl of 4×SSC/20% Dextran (Millipore S4030). The probe mixtures were heated at 80° C. for 30 min and then transferred to a 37° C. incubator (‘pre-annealed probes’).
Morula embryos were fixed at 78 hpf in 2% paraformaldehyde (PFA) in PBS containing 0.5% Triton X-100 for 20 min at room temperature. After 3× washes with PBS containing 1 mg/ml BSA (PBS/BSA), embryos were treated with 0.1 N HCl containing 0.02% Triton X-100 for 15 min at 4° C. After 3× washes with 2×SSC containing 0.1% BSA, embryos were incubated in 15 μl of 10% formamide/2×SSC in a glass dish (Electron Microscopy Science, 705430-30). All embryos were sunk and attached to the bottom of the glass dish by gentle pipetting. After 5 min, 15 μl of 30% formamide/2×SSC was added. After 5 min, 90 μl of 60% formamide/2×SSC was added to make the final formamide concentration 50%, and embryos were incubated for additional 30 min at room temperature. The formamide solution containing embryos were covered with mineral oil. The samples were heated at 80° C. for 30 min, and then transferred to a 37° C. incubator for at least 30 min. The embryos were picked in a glass pipette, transferred into 4.5 μl of ‘pre-annealed probes’ covered with mineral oil on another glass dish, and incubated in 37° C. for at least 24 hrs. Embryos were washed with pre-warmed (42° C.) 2×SSC containing 0.1% BSA and left in the last drop for 30 min. After 3× wash with 1% BSA/PBS, they were mounted on a glass slide in Vectashield anti-bleaching solution with 4′,6-diamidino-2-phenylindole (DAPI) (Vector Laboratories, Burlingame, Calif.). Fluorescence was detected under a laser-scanning confocal microscope Zeiss LSM800.
The procedure of immunostanining and quantification was described above.
The bed files including RPKM values in 100 bp bins for H3K27me3 ChIP-seq in inner cell mass (ICM) were downloaded from GEO under the number GSE76687. Bed files labeled maternal or paternal containing RPKM values for two parental alleles and allelic reads were normalized to total reads number. ‘bedtools makewindows’ was used to generate 1000 bp bins for mm9 genome, then RPKM value for each bin was calculated by ‘bedtools map’. All the bins are classified to three categories of no signal, biallelic, maternal bias using a signal cutoff of 1 and a fold change cutoff of 4. A sliding window approach was used to identify windows containing maternal biased H3K27me3 bins with criteria of the window size of 20 kb, the minimum bin number of 3 and the percentage of maternal biased H3K27me3 bins larger than 50%. Overlapped windows were merged with “bedtools merge”. A total of 5986 windows were identified in the genome.
RNA-seq libraries were prepared as described above with minor modifications.
Briefly, reverse transcription and cDNA amplification were performed using whole embryo lysates with SMARTer Ultra Low Input RNA cDNA preparation kit (Clontech, 634890). cDNAs were then fragmented using Tagmentation with Nextera XT DNA library prep kit (Illumina). The fragmented cDNAs were amplified using Nextera PCR master mix according to the manufacturer's instruction. Single end 100 bp sequencing was performed on a HiSeq2500 sequencer (Illumina).
Reads of RNA-seq were mapped to the reference genome with STAR (github.com/alexdobin/STAR). All programs were run with default parameters unless otherwise specified. Uniquely mapped reads were subsequently assembled into transcripts guided by the reference annotation (UCSC gene models) with featureCounts from subread-v1.5.1. After the library size was normalized, the expression level of each gene was quantified with normalized FPKM (fragments per kilobase of exon per million mapped fragments). The Pearson correlation coefficient (r) of gene expression level was calculated to indicate the correlation between duplicates.
Statistical analyses were implemented with R (www.r-project.org/). Pearson's r coefficient was calculated using the ‘cor’ function with default parameters
A customized pipeline was used to split the hybrid RNA-seq data to their parental origin based on SNP information. The code can be found at github.com/lanjiangboston/UniversalSNPsplit.
RNA-seq datasets generated in this study were deposited at GEO database under accession number GSEXXXXX. The WGBS dataset for GV oocytes was downloaded from www.nodai-genome.org/mouse.html?lang=en. WGBS reads from same 100 bp bins were pooled together to calculate the average methylation level and minimal coverage of 10 reads was required. H3K27me3 ChIP-seq datasets of sperm, MII oocytes, and SNP-tracked maternal and paternal alleles of 1-cell, 2-cell, and inner cell mass of blastocyst embryos were downloaded from a previous study (GSE76687). The oocyte DNaseI-seq datasets were from above (GSE92605).
B6D2F1/J (BDF1) mice were used for the collection of recipient oocytes for SCNT. For mouse embryonic fibroblast (MEF) cell preparation, Xist KO female mice maintained in 129S1/SvImj background (Marahrens et al., 1997) were mated with CAST/EiJ males to generate Xist heterozygous KO embryos in 129/CAST F1 background. For cumulus and Sertoli cell preparation, Xist KO female mice in C57BL/6N background (Sado et al., 2005) were mated with DBA/2N males to generate Xist heterozygous KO embryos in BDF1 background. All animal experiments were approved by the Institutional Animal Care and Use Committees of Harvard Medical School and RIKEN Tsukuba Institute.
Primary MEF cells were derived from Xist KO male mouse embryos at 13.5 dpc. After removal of head and all organs, minced tissue from remaining corpus was dissociated in 500 μl of 0.25% Trypsin with 1 mM EDTA (Thermo Fisher Scientific #25200056) for 10 min at 37° C. Cell suspension was diluted with equal amount of DMEM (Thermo Fisher Scientific #11995-073) containing 10% FBS and Penicillin/Streptomycin (Thermo Fisher Scientific #15140-022) and pipetted up and down 20 times. The cell suspension was diluted with fresh medium and plated onto 100 mm dishes and cultured at 37° C. Two days later, MEF cells were harvested and frozen. Frozen stocks of MEF cells were thawed and used for experiments after one passage.
Cumulus cells were collected from wildtype (WT) and Xist heterozygous KO adult females (RIKEN BioResource Center, RBRC01260) through superovulation by injecting 7.5 IU of pregnant mare serum gonadotropin (PMSG; Millipore #367222) and 7.5 IU of human chorionic gonadotropin (hCG; Millipore #230734). Fifteen to seventeen hours after the hCG injection, cumulus-oocyte complexes (COCs) were collected from the oviducts and treated briefly with Hepes-buffered potassium simplex-optimized medium (KSOM) containing 300 U/ml bovine testicular hyaluronidase (Calbiochem #385931) to obtain dissociated cumulus cells.
Sertoli cells were collected from testes of 3-5 day-old WT or Xist KO male mice as described (Matoba et al., 2011). Testicular masses were incubated in PBS containing 0.1 mg/ml collagenase (Thermo Fisher Scientific #17104-019) for 30 min at 37° C. followed by 5 min treatment with 0.25% Trypsin with 1 mM EDTA at room temperature. After washing for four times with PBS containing 3 mg/ml bovine serum albumin, the dissociated cells were suspended in Hepes-KSOM medium.
Kdm4d mRNA Synthesis
Kdm4d mRNA was synthesized by in vitro transcription (IVT) as described previously (Matoba et al., 2014). Briefly, a pcDNA3.1 plasmid containing full length mouse Kdm4d followed by poly(A)83 (Addgene #61553) was linearized by XbaI. After purification, the linearized plasmid DNA was used as a template for IVT using mMESSAGE mMACHINE T7 Ultra Kit (Thermo Fisher Scientific #AM1345). The synthesized mRNA was dissolved in nuclease-free water and quantified by NanoDrop ND-1000 spectrophotometer (NanoDrop Technologies). After the mRNA is diluted to 1500 ng/μl, aliquots were stored at −80° C.
Mouse somatic cell nuclear transfer was carried out as described previously (Matoba et al., 2014; Ogura et al., 2000). Briefly, recipient MII oocytes were collected from adult BDF1 female mice through superovulation by injecting 7.5 IU of PMSG and 7.5 IU of hCG. Fifteen to seventeen hours after the hCG injection, cumulus-oocyte complexes (COCs) were collected from the oviducts and treated briefly with Hepes-KSOM containing 300 U/ml bovine testicular hyaluronidase to obtain MII oocytes. Isolated MII oocytes were enucleated in Hepes-buffered KSOM medium containing 7.5 μg/ml of cytochalasin B (Calbiochem #250233) by using Piezo-driven micromanipulator (Primetech #PMM-150FU). The nuclei of cumulus or Sertoli cells were injected into the enucleated oocytes. MEF cells were fused with enucleated oocytes by inactivated Sendai virus envelope (GenomOne CF; Ishihara Sangyo #CF001). After 1 h incubation in KSOM, reconstructed SCNT oocytes were activated by incubating in Ca-free KSOM containing 3 mM strontium chloride (SrCl2) and 5 μg/ml cytochalasin B for 1 h, and further cultured in KSOM with 5 μg/ml cytochalasin B for 4 h. Activated SCNT embryos were washed 5 h after the onset of SrCl2 treatment (hours post activation, hpa) and cultured in KSOM in a humidified atmosphere with 5% CO2 at 37.8° C. Some SCNT embryos were injected with ˜10 pl of 1500 ng/μl mouse Kdm4d mRNA at 5-6 hpa by using a Piezo-driven micromanipulator.
Two-cell stage SCNT embryos were transferred to the oviducts of pseudopregnant (E0.5) ICR females. The pups were recovered by caesarian section on the day of delivery (E19.5) and nursed by lactating ICR females. Some females were sacrificed at E4.5 and E10.5 for examining embryonic development.
Placentae at E19.5 were fixed in 4% paraformaldehyde (PFA) 4° C. overnight and routinely embedded in paraffin. Serial sections (4 μm in thickness) were subjected to periodic acid Schiff (PAS) staining.
Blastocysts were fixed with 4% paraformaldehyde (PFA) for 20 min at room temperature. After washing with PBS containing 10 mg/ml BSA (PBS/BSA), the fixed embryos were permeabilized by 15 min incubation with 0.5% Triton-X 100. After blocking in PBS/BSA for 1 h at room temperature, they were incubated in a mixture of primary antibodies including rabbit anti-H3K27me3 antibody (1/500, Millipore, 07-449), goat anti-Oct4 antibody (1/500, SantaCruz, sc-8628) and mouse anti-Cdx2 antibody (1/100, BioGenex, AM392-5M) at 4° C. overnight. Following three washes with PBS/BSA, the embryos were incubated with a mixture of secondary antibodies including fluorescein isothiocyanate-conjugated anti-mouse IgG (1/400, Jackson Immuno-Research), Alexa Flour 546 donkey anti-rabbit IgG (1/400, Thermo Fisher Scientific) and Alexa Flour 647 donkey anti-goat IgG (1/400, Thermo Fisher Scientific) for 1 h at room temperature. Finally, they were mounted with Vectashield with 4′,6-diamidino-2-phenylindole (DAPI) (Vector Laboratories #H-1200). The fluorescent signals were observed using a laser-scanning confocal microscope (Zeiss LSM510) and an EM-CCD camera (Hamamatsu ImagEM).
IVF and SCNT embryos of the early blastocyst stage (96 hours after fertilization or activation) were directly subjected to bisulfite conversion using the EZ DNA Methylation-Direct Kit (Zymo Research, D5020). Thirty-nine and 36 embryos were used for preparing the IVF and SCNT samples, respectively. A small amount (0.01 ng) of unmethylated Lambda DNA (Promega, D152A) was added to each sample before bisulfite conversion to serve as spike-in controls for evaluating bisulfite conversion efficiency. Sequencing libraries were prepared using the EpiGnome Methyl-Seq kit (Epicenter, EGMK81312) following the manufacturer's instructions. Libraries were only amplified for 12 cycles, and were then purified using Agencourt AMPure XP beads (Beckman Coulter, A63880). Final libraries were subjected to single-read (100 bp) sequencing on a HiSeq 2500 sequencer (Illumina) with PhiX spike-in control.
Six IVF or SCNT embryos of the early blastocyst stage (96 hours after fertilization or activation) were directly lysed and used for cDNA synthesis using the SMARTer Ultra Low Input RNA cDNA preparation kit (Clontech, 634936). After amplification, the cDNA samples were fragmented using a Covaris M220 sonicator (Covaris). Sequencing libraries were made with the fragmented cDNA using NEBNext Ultra DNA Library Prep Kit for Illumina according to manufacturer's instructions (New England Biolabs, E7370). Single-read 50 bp sequencing was performed on a HiSeq 2500 sequencer (Illumina).
WGBS and reduced representation bisulfite sequencing (RRBS) reads were first trimmed using trim_galore to remove low-quality sequences and adapter sequences. Bismark (version 0.15.0) was used to align reads to a bisulfite converted reference genome (mm9). The coverage depth and methylation level of each cytosine were extracted from the aligned reads with bismark_methylation_extractor. When calculating methylation level for CpG sites, information from both strands was combined, and a coverage of at least five reads was required. DMRs were identified using methpipe (version 3.4.3) and were further filtered requiring at least 10 CpG sites and at least 10% methylation difference. Functional annotation of DMR associated genes (i.e., genes with a DMR located in the TSS±3kb region) was performed with clusterProfiler (version 2.4.3) in R. For allele specific methylation analysis of known ICRs, all detected CpGs within one ICR were pooled together, and a coverage of at least 5 detected CpGs in both alleles was required for further methylation comparison.
RNA-seq data were mapped to the mouse genome (mm9) with TopHat (version 2.0.14) with parameters “--no-coverage-search --no-novel-juncs --library-type=fr-unstranded”. Uniquely mapped reads were subsequently assembled into transcripts guided by the reference annotation (UCSC gene models) with Cufflinks (version 2.2.1). Expression levels of each gene was quantified with normalized FPKM (fragments per kilobase of exon per million mapped fragments). The Pearson correlation coefficient of gene expression level was calculated to indicate the correlation between duplicates.
After mapping the hybrid WGBS and RNA-seq data (129S1/Svj x CAST/EiJ) to the mouse genome (mm9), custom Perl scripts were used to split mapped reads to their parental origin on the basis of SNP information downloaded from the Mouse Genomes Project (ftp://ftp-mouse.sanger.ac.uk/REL-1211-SNPs_Indels/). The allelic reads were then processed individually.
Downloaded ChIP-seq and DIP-seq reads were mapped to the mouse genome (mm9) using Bowtie (version 2.1.0) with parameters “-D 20 -R 3 -N 1 -L 20 -i S,1,0.50” to obtain only those reads that are mapped uniquely with at most 3 mismatches. To visualize the signals in the genome browser, we generated wig track files for each data set with MACS2 (version 2.1.1) by extending the uniquely mapped reads (keeping at most two read at the same genomic position) to 200 bp toward the 3′ end and binning the read count to 50 bp intervals. Tag counts were further normalized in each bin to the total number of uniquely mapped reads (reads per million reads, RPM). The ‘computeMatrix’ program from deepTools was used to compute the ChIP-seq and DIP-seq signals over the DMRs or ICRs and their flanking regions.
Statistical analyses and plots were implemented with R (version 3.4.1, http://www.r-project.org). Pearson correlation coefficient was calculated using the ‘cor’ function with default parameters. Student's t-test (two-tailed, equal variance) was performed using the ‘t.test’ function with default parameters. ChIP-seq signals and DNA methylation levels were visualized as custom tracks in the Integrative Genomics Viewer genome browser.
The WGBS and RNA-seq datasets generated in this study have been deposited in Gene Expression Omnibus (GEO) under the accession number GSE109214.
Published Datasets Used in this Study
Maternal and paternal DNA methylation of the preimplantation embryos (2-cell, 4-cell, and ICM) was obtained from GSE56697 (Wang et al., 2014). RRBS data of different cells and somatic tissues were obtained from GSE11034 and GSE43719 (Soumillon et al., 2013). H3K27me3 ChIP-seq data were obtained from GSE49847 (Yue et al., 2014) and GSE76687 (Zheng et al., 2016). DIP-seq data of 5mC and 5hmC during PGC development were downloaded from SRP016940 (Hackett et al., 2013).
From the foregoing description, it will be apparent that variations and modifications may be made to the invention described herein to adopt it to various usages and conditions. Such embodiments are also within the scope of the following claims.
The recitation of a listing of elements in any definition of a variable herein includes definitions of that variable as any single element or combination (or subcombination) of listed elements. The recitation of an embodiment herein includes that embodiment as any single embodiment or in combination with any other embodiments or portions thereof.
All patents and publications mentioned in this specification are herein incorporated by reference to the same extent as if each independent patent and publication was specifically and individually indicated to be incorporated by reference.
This application claims the benefit of the following U.S. Provisional Application No. 62/654,199, filed Apr. 6, 2018, the entire contents of which are incorporated herein by reference.
This invention was made with government support under grant number HD092465 awarded by the National Institutes of Health. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/026074 | 4/5/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62654199 | Apr 2018 | US |
