DNA PROBE SEQUENCE FOR GENETIC SEX IDENTIFICATION OF LITOPENAEUS VANNAMEI AND ACQUISITION METHOD

Abstract

The present invention relates to a DNA sequence showing difference between the female and male individuals of Litopenaeus vannamei and its corresponding acquired method. The method comprises: respectively conducting high-through put sequencing on the mixing pools of female individuals and male individuals in by high-through put sequencing platform; conducting bioinformatic analysis on the sequencing results to screen out sequences showing significant difference between the mixing pools of female and male individuals; verifying the obtained sex difference sequence in individuals from different sources; and finally, obtaining a probe sequence for female and male identification of L. vannamei, so that the genetic sexe of this species can be accurately identified using the sequences. The method of the present invention has the characteristics of high efficiency, accuracy and reliability, and possess broad application potential in the early sex identification and sex control research of prawns.

Description

TECHNICAL FIELD

The present invention relates to the prawn sex identification and sex control technology in the aquaculture biotechnology, andparticularlyto a DNA sequence for genetic sex identification of Litopenaeusvannamei and its acquired method.

BACKGROUND

L. vannamei is the species which has been farmed most productively among all penaeidae shrimp in China or even in the world. At present, the world average annual output is more than 3,000 thousand tonnes. Like other prawn species, L. vannamei has significant difference between female and male individuals in size. The growth rate of female individuals at the middle and later stage is far higher than that of male individuals. Thus, the monosex control of L. vannamei is usefulin order toculturea monosex population, thereby having important significance to increase the output and benefit of the prawn culture industry.

Identification of the genetic sex of an individual is the basis for realizing the culture of a monosex population of L. vannamei. Though the sexes of female and male shrimpcan be identified through the morphological externalsex characters when shrimpsgrown to a certain stage.In scientific research and actual production, if early identification of sexes can be realized by a molecular method at the juvenilestage, experiments and culture can be undertaken specifically to individuals of a certain sex, so that the efficiency of the scientific research and actual production can be greatly improved.

In the research of sex markers for prawns, there were already some reports of sex marker screening, for example, Staelens et al. (Staelens, J., Rombaut D., Vercauteren I., Argue B., Benzie J. and Vuylsteke M. High-density linkage maps and sex-linked markers for the black tiger shrimp (Penaeusmonodon). Genetics, 2008, 179(2): 917-925.) constructeda high-density genetic linkage map for P. monodon, and found two sex difference markersin the genetic linkage map. It was validated that the markers could be used as markers for sex identification in a population of P. monodon from other genetic sources. Moreover, the team also applied for a relevant patent (Chinese invention patent No. 200780015173.9, entitled “Sex-Specific Markers for Shrimps and Prawns”). However, the markers could not be used for the sex identification of L. vannamei clue to the difference between prawn species. In the study of L. vannamei, Zhang et al. (Zhang, L.,Yang C., Zhang Y., LiL., Zhang X., Zhang Q., Xiang J. A genetic linkage map of Pacific white shrimp (Litopenaeus vannamei): sex-linked microsatellite markers and high recombination rates. Genetica, 2006, 131(1): 37-49) screened a sex-specific microsatellite site of L. vannamei by means of a QTL mappingmethod. However, it was validated that the microsatellite marker was family specific and could not be used asa marker forsex identification in other sourced population. Similarly,Alcivar-Warren et al. (Alcivar-Warren, A., Meehan-Meola D., Park S. W., Xu Z., Delaney M., Zuniga G. ShrimpMap: A low-density, microsatellite-based linkage map of the pacific whiteleg shrimp, L. vannamei: Identification of sex-linked markers in linkage group 4. Journal of Shellfish Research, 2007, 26(4): 1259-1277.) also found sex-specific microsatellite markers of L. vannamei, but the markers were onlyrestrictedto the researched population. In the research of Fenneropenaeus chinensis, thoughmore linkage maps were constructed, no corresponding sex identification markers were reported (Li, Z. X., Li J., Wang Q., He Y., Liu P. AFLP-based genetic linkage map of marine shrimp Penaeus (Fenneropenaeus) chinensis. Aquaculture, 2006, 261(2): 463-472; Sun, Z. N., Liu P., Li J., Meng X., Zhang X. Construction of a genetic linkage map in F. chinensis (Osbeck) using RAPD and SSRmarkers. Hydrobiologia, 2008,596: 133-141;Liu, B., Wang Q, Li J., Liu P., He Y. A genetic linkage map of marine shrimp Penaeus (Fenneropenaeus) chinensis based on AFLP, SSR, and RAPD markers. Chinese Journal of Oceanology and Limnology, 2010, 28(4): 815-825.). By means of gene differential expression analysis, one gene showed differential expression between female and male of F. chinensis was screened out (Li, S., Li F., Xie Y., Wang B., Wen R., Zhang C., Yu K., Xiang J. Screening of Genes Specifically Expressed in Males of F. chinensis and Their Potential as Sex Markers. Journal of Marine Biology, 2013, 1-9.), and the marker was developed as a marker for female and male sex identification (Chinese invention patent, No. 101709332A). However, so far, no markers for sex identification of L. vannamei have been reported.

SUMMARYOF THE INVENTION

Sequences have significant difference of sequencing depth in a mixing pool of male individuals.

A total of 16 sequences showing significant difference between the mixing pools of female and male individuals are found by bioinformatic analysis, and the above-mentioned 16 sequences are amplified using primers designed by Primer 3 Plus on-line design software (http://primer3plus.com/cgi-bin/dcv/primer3plus.cgi).

A total of 16 female and 16 male shrimp from differet sources are selected, the above-mentioned 16 sequences are amplified using the designed PCR primers. The amplified sequence of each individual are analyzed. As a result, one DNA sequence showing significant difference between the acquired female and male individuals, where the sequence in the female individuals is SEQLvSDF, and the sequence in the male individuals is SEQLvSDM, the different site of the two sequences locates at120bp position, the female individual is G/C heterozygote, and the male individual is C homozygote. The primer for amplifying this sequence is:

LvSDPF:
CCAGACAGAAATGATCTCCTTTGA,
LvSDPR:
AGAAAAGAAAAGAGGAAAGCAGGA.

The further analysis is conducted to verify whether theabove-mentionedsex marker could be applicable in other sourced populations. A total of 80 female shrimps and 80 male shrimps are analyzed using the above-mentioned primer. It includs 20 female and 20 male individuals purchased from a market randomly, 20 female and 20 male individuals from different families bred incenter of Hainan Guangtai Marine Breeding Corporation, 20 female and 20 male individuals from Kona BayMarine Resources imported in 2012, 20 female and 20 male individuals from Shrimp Improvement System imported in 2014. The amplified sequence is sequenced by a Sanger sequencing method. The result verifies that the sequence indeedly shown difference between female and male, wherein the female individual, the sequence is:

(1) Sequence features:

Genome Sequence: base pair; type: nucleotide; chain type: double chain; topology: linear

(2) Molecular type: DNA

(3) Assumed: No

(4) Antisense: No

SEQLvSDF:
CCAGACAGAAATGATCTCCTTTGACAGAACCGGTGACATATTGTACTTGA
GATAAACCACATATAAATCAGTAAACCCCGAGGGCAAGTACAAATTTAGT
TTAAGACAATGATTTTGAA[G/C]TGTGAAAATGCAAACGAAACCGCGGG
ATTCGTCTAATTCGCCAATTACGGCTCAGCTAACGAGGTAGCGCTAAAGC
GCACTATAACAATCTACAGACCTTTCGACTCCAGCACTTTCAGATGTATT
TCGAATCGTGTACACATTACCGGAAGGCGAATGGAAATGAGGTTATTATT
TTTGTTACATCATTTTCAAGATGGCTGGCTTTGTTGAACATCGGCAAGAA
TATTGTGAGGTCTCCGACTCCACTCCCCCGGGGGCCCTCCTCCATCCTGC
ACCACGCCCCTTGCCTTCTCCCTCCCTTATTCTCCTCCTTACCCTTGTTT
CTCTTAGGCTTCCCCCACGGTTTCTTTCGTTAACTCTTATCTATCCTGCT
TTCCTCTTTTCTTTTCT

and in the female individual, the sequence is:

(1) Sequence features:

Genome sequence: base pair; type: nucleotide; chain type: double chain; topology: linear

(2) Molecular Type: DNA

(3) Assumed: No

(4) Antisense: No

SEQLvSDM:
CCAGACAGAAATGATCTCCTTTGACAGAACCGGTGACATATTGTACTTGA
GATAAACCACATATAAATCAGTAAACCCCGAGGGCAAGTACAAATTTAGT
TTAAGACAATGATTTTGAACTGTGAAAATGCAAACGAAACCGCGGGATTC
GTCTAATTCGCCAATTACGGCTCAGCTAACGAGGTAGCGCTAAAGCGCAC
TATAACAATCTACAGACCTTTCGACTCCAGCACTTTCAGATGTATTTCGA
ATCGTGTACACATTACCGGAAGGCGAATGGAAATGAGGTTATTATTTTTG
TTACATCATTTTCAAGATGGCTGGCTTTGTTGAACATCGGCAAGAATATT
GTGAGGTCTCCGACTCCACTCCCCCGGGGGCCCTCCTCCATCCTGCACCA
CGCCCCTTGCCTTCTCCCTCCCTTATTCTCCTCCTTACCCTTGTTTCTCT
TAGGCTTCCCCCACGGTTTCTTTCGTTAACTCTTATCTATCCTGCTTTCC
TCTTTTCTTTTCT

The genetic sex of L. vannamei could be identified according to the sequence information obtained by sequencing.

The present invention has the following advantages:

• • 1 A DNA sequence for sex identification of L. vannamei is obtained so that the genetic sex identification of Litopenaeus vannamei can be realized.The method is not limited by the development stage, individual size and other factors of L. vannamei, and is a method for conducting genetic sex identification accurately.
  • 2 The sex identification is conducted by a sequencing method, thereby accuracy is very high.
  • 3 By means of the molecular marker, identification of sexes can be realized using only a little of tissue, and can be realized even for frozen and alcohol-soaked tissue.
  • 4 The acquired method for a DNA sequence for sex identification can be applied to other prawn species.

DETAILED DESCRIPTION

Embodiment 1

Acquisition Method of DNA Sequence for Genetic Sex Identification of L. vannamei

• • 1Muscular tissue were taken respectively from the male parent, female parent, 50 female progeny individuals and 50 male progeny individuals from the same family,the muscular tissue were fixed into liquid nitrogen immediately and then storedin a refrigerator of −80° C. for preservation.
  • 2 The DNA of the above-mentioned sample was extracted using TIANGEN plant Genomic DNA extraction kit(TIANGEN, Beijing), referring to description for operation methods.And the extracted DNAconcentration was measuredusing Nanodrop1000(Thermo, USA).
  • 3 The extracted DNA was diluted to 100 ng/μl respectively and four different libraries were constructed in accordance with a reduced-representation genome library construction method as follows: a male parent library and a female parent library were constructed respectively, and then a female progeny library by mixing the DNA of 50 female individuals, and a male progeny library by mixing the DNA of 50 male individuals were constructed respectively. High-through put sequencing on the above-mentioned four libraries were conducted using Hiseq2500 plat form to obtain original sequencing data of the four libraries.
  • 4 The sequencing data obtained were analyzed by bioinformatics method as follows: Denovo as sembling was conducted using the original data of male parent and female parent to obtain reduced-representation genome reference sequences. Then the sequencing data of the four libraries were mapped to the reference sequences, and the mapped read number of each reference sequence in the the female parent,the pools of female progeny, the male parent and pools of male progeny were calculated. The sequences showing much higher read depth in the female parent and female progeny pool than that in the male parent and male progeny pool were considered as a female-specific candidate sequence, and the sequences showing much higher read depth in male parent and male progeny pool than that of female parent and female progeny pool were considered as a male-specific candidate sequence.
  • 5 A total of 16 sequences showing significant difference between female and male were obtained by bioinformatic analysis. The above-mentioned 16 sequences were amplified using a designed primers designed by of Primer 3 Plus on-line design software (http://primer3plus.com/cgi-bin/dcv/primer3plus.cgi)..

First,16 female and 16 male shrimp from different sources were selected, the above-mentioned 16 sequences were amplified using the designed PCR primers. The amplified sequence was analyzed in female and male individuals. As a result, one DNA sequence showing significant difference between all the female and male individuals was obtained. The obtained sequence was further verified in another 60 male individuals and 60 female individuals originated from different sources,and it was proved that the sequence was a female and male difference sequence. The primer for amplifying the sequence was :LvSDPF:CCAGACAGAAATGATCTCCTTTGA,LvSDPR:AGAAAAGAAAAGAG GAAAGCAGGA.

The amplified sequence in the female individual was SEQLvSDF:

CCAGACAGAAATGATCTCCTTTGACAGAACCGGTGACATATTGTACTTGA
GATAAACCACATATAAATCAGTAAACCCCGAGGGCAAGTACAAATTTAGT
TTAAGACAATGATTTTGAA[G/C]TGTGAAAATGCAAACGAAACCGCGGG
ATTCGTCTAATTCGCCAATTACGGCTCAGCTAACGAGGTAGCGCTAAAGC
GCACTATAACAATCTACAGACCTTTCGACTCCAGCACTTTCAGATGTATT
TCGAATCGTGTACACATTACCGGAAGGCGAATGGAAATGAGGTTATTATT
TTTGTTACATCATTTTCAAGATGGCTGGCTTTGTTGAACATCGGCAAGAA
TATTGTGAGGTCTCCGACTCCACTCCCCCGGGGGCCCTCCTCCATCCTGC
ACCACGCCCCTTGCCTTCTCCCTCCCTTATTCTCCTCCTTACCCTTGTTT
CTCTTAGGCTTCCCCCACGGTTTCTTTCGTTAACTCTTATCTATCCTGCT
TTCCTCTTTTCTTTTCT

and the amplified sequence in the male individual was SEQLvSDM:

CCAGACAGAAATGATCTCCTTTGACAGAACCGGTGACATATTGTACTTGA
GATAAACCACATATAAATCAGTAAACCCCGAGGGCAAGTACAAATTTAGT
TTAAGACAATGATTTTGAACTGTGAAAATGCAAACGAAACCGCGGGATTC
GTCTAATTCGCCAATTACGGCTCAGCTAACGAGGTAGCGCTAAAGCGCAC
TATAACAATCTACAGACCTTTCGACTCCAGCACTTTCAGATGTATTTCGA
ATCGTGTACACATTACCGGAAGGCGAATGGAAATGAGGTTATTATTTTTG
TTACATCATTTTCAAGATGGCTGGCTTTGTTGAACATCGGCAAGAATATT
GTGAGGTCTCCGACTCCACTCCCCCGGGGGCCCTCCTCCATCCTGCACCA
CGCCCCTTGCCTTCTCCCTCCCTTATTCTCCTCCTTACCCTTGTTTCTCT
TAGGCTTCCCCCACGGTTTCTTTCGTTAACTCTTATCTATCCTGCTTTCC
TCTTTTCTTTTCT.

Embodiment 2

Molecular Method for Genetic Sexual Identification of L. vannamei

In September 2013, a total of 60 L. vannamei were randomly selected from aquatic market in Qingdao, and then were delivered to the aquarium building in Institute of Oceanology, Chinese Academy of Sciences fortemporary rearing. The muscular tissue were taken out and stored in a refrigerator of −80° C. for frozen preservation.

• • 1. The DNAof the above-mentioned sample were extracted using a Tiangenplant Genomic DNA extraction kitreferring to the description of operation methods. The extracted DNAconcentration was measured using Nanodrop1000(Thermo, USA).
  • 2. PCR amplification was conducted on the extracted DNA using the following amplification primer:

LvSDPF:
CCAGACAGAAATGATCTCCTTTGA,
LvSDPR:AGAAAAGAAAAGAGGAAAGCAGGA.

The amplification systemwere as follows:

Template (connection product) 2 μl
LvSDPF (10 pmol/μl)           0.5 μl
LvSDPR (10 pmol/μl)           0.5 μl
ExTaqDNABuffer (MgCl2+)       2.5 μl
dNTP (10 mmol/L)              0.5 μl
Ex Taq DNA polymerase         0.25 μl
Sterile water                 18.75 μl
Total volume                  25 μl

The PCR reaction program comprises: conducting predegeneration for 3 min at 94° C., and then following 35 circles of 30s at 94° C., 30s at 53° C., and 30s at 72° C., then with a final extension for 10min at 72° C.

• • 3. PCR products were electrophoresed by agarose and then DNA was extracted using a TIANGENgel extraction kit. The amplified sequence was sequenced by ABIPRISMTM3700 Genetic Analyzer using an LvSDF primer.
  • 4. Read the peak diagram document of the sequencing result using Bioeditsoftware to look for the nucleotide at 120 bp positon of LvSDF and LvSDM sequence. The individual was judged as female if the position is G/C heterozygote, and the individual was judged as male if the position is C homozygote.

Result: Among the 60 shrimp individuals, the nucleotide at 120 bp position of LvSDF and LvSDMwasG/C heterozygote in 34 individuals, and the corresponding individuals were identified as female. The nucleotide at 120 bp position of LvSDF and LvSDM was C homozygous in 26 individuals and the corresponding individuals were identified as male.

The method of the present invention has the characteristics of high efficiency, accuracy and reliability, and possesses broad application potential in the early sex identification and sex control research of prawns.

Claims

1. A method for genetic sex identification of Litopenaeusvannamei, characterized in that:extracting the DNA of shrimp individuals whose genetic sex identification is to be conducted; using a pair of primer LvSDPF:CCAGACAGAAATGATCTCCTTTGA and LvSDPR:AGAAAAGAAAAGAGGAAAGCAGGA to amplify the target sequence,and then Sanger sequencing is conducted on the obtained amplified sequence, the nucleotide at the 120 bp position of the above-mentioned sequence is read using Bioedit software in the peak diagram document, if the nucleotide at this positionisG/C heterozygote,the corresponding individualis judged as female individual, and if the nucleotide at this position is C homozygote,it is judged as a male individual.

2. A DNA probe for genetic sex identification of L. vannamei, characterized in that the amplified sequences in claim 1 are SEQLvSDF and SEQLvSDM sequence, female individual DNA contains the characteristic SEQLvSDF sequence, as listed in SEQIDNO:1; and male individual contains the characteristic SEQLvSDM sequence, as listed in SEQIDNO:2; The SEQLvSDF sequence in the female individual is:

3. An acquisition method for a DNA probe used in genetic sex identification of L. vannamei of claim 2, comprising the following steps: a couple of sexually mature male and female individuals are taken for mating, the progeny individuals are cultured to be sexually mature, then 50 female progeny individuals and 50 male progeny individuals are randomly selected and DNA are extracted from the parents and the selected progeny individuals; the DNA is used to construct the reduced-representation genome library for high-through put sequencing ;the sequencing data of male parent,female parent and progeny individuals are analyzed using bioinformatics method; the sequences with significant difference of read depth between the pool of female parent and female progeny and the pool of male parent and male progeny are identified as candidate sex different sequences; these sequences are further verified in the populations from other sources, and finally one DNA sequence for genetic sex identification of L vannameiwas obtained.