Research Project
7127747
[unreadable] DESCRIPTION (provided by applicant): PROJECT SUMMARY: Ts65Dn mice represent the best-characterized animal model for Down syndrome (DS). These mice carry the T65Dn marker chromosome, producing trisomy for a region of mouse chromosome 16 (MMU16) that includes orthologs of about 50% of the genes on human chromosome 21 (HSA21). Forty percent of DS individuals display congenital heart defects (CHD), and we hypothesize that the Ts65Dn mice will display phenotypes related to defective cardiac development. We have demonstrated that the transmission rate of segmental trisomy in Ts65Dn is near the expected 50% at birth, but declines to 34% of offspring by weaning, with selective loss of Ts65Dn neonates within 48 hours of birth. Gross anatomical and histological examination of cadavers indicates aortic arch and AV cushion related septal defects in Ts65Dn neonates. These observations support the hypothesis that one or more candidate genes for DS CHD occur within the trisomic region of Ts65Dn. We will examine genes contained in distal MMU16 and proteins normally expressed in the endocardial cushions to determine if the pathways of cell signaling and differentiation critical to normal cardiac septation are modulated by overexpression of the Ts65Dn genes. We plan to investigate the cardiac development of Ts65Dn mice through the following Specific Aims: 1. Determine the range of cardiac anomalies present in Ts65Dn embryos. Gross plus histological examination using light and scanning electron microscopy will be performed on embryonic hearts of the eupoid (wild type, wt) and trisomic siblings at critical stages of cardiac morphogenesis to determine the incidence and phenotypic range of cardiac defects in Ts65Dn offspring. 2. Analyze the process of epithelial to mesenchymal transformation (EMT), critical to AV endocardial cushion formation, in Ts65Dn transgenic hearts using an in vitro EMT/ migration assay. 3. Investigate the biochemical and molecular differences between Ts65Dn and wt cardiac tissues with emphasis on genes within the Ts65Dn region. Cardiac developmental gene markers and candidate DS CHD genes will be analyzed using in situ hybridization and immunohistology to determine the temporal- spatial patterns of gene and protein expression in endocardial cushions and derivative structures. RATIONALE: Mouse models are commonly used to analyze underlying genetic causes of human disease, as well as to identify the genes that are critical for normal mammalian development. Defining the dosage sensitive genes and the mechanisms by which their misexpression contributes to congenital heart defects in DS will provide insights into the roles of diploid genes during normal cardiac development and may suggest ameliorative strategies for congenital heart defects in DS or euploid individuals. [unreadable] [unreadable] [unreadable]
