TheCspg2Gene, Disrupted in thehdfMutant, Is Required for Right Cardiac Chamber and Endocardial Cushion Formation

Autor: Mjaatvedt, C.H., Yamamura, H., Capehart, A.A., Turner, D., Markwald, R.R.
Zdroj: Developmental Biology; October 1998, Vol. 202 Issue: 1 p56-66, 11p
Abstrakt: The heart defect (hdf) mouse is a recessive lethal that arose from a transgene insertional mutation on chromosome 13. Embryos homozygous for the transgene diein uteroby embryonic day 10.5 postcoitus and exhibit specific defects along the anterior–posterior cardiac axis. The future right ventricle and conus/truncus of the single heart tube fail to form and the endocardial cushions in the atrioventricular and conus/truncus regions are absent. Because thehdfmouse mutation provided the opportunity to identify a gene required for endocardial cushion formation and for specification or maintenance of the anterior most segments of the heart, we initiated studies to further characterize the phenotype, clone the insertion site, and identify the gene disrupted. Chromosome mapping studies first identified the gene,Cspg2(versican), as a candidatehdfgene. In addition, an antibody recognizing a glycosaminoglycan epitope on versican was found to be positive by immunohistochemistry in the extracellular matrix of normal wild-type embryonic hearts, but absent in homozygous hearts. Expression analysis of theCspg2gene showed that the 6/8, 6/9, and 7/9Cspg2exon boundaries were present in mRNA of normal wild-type embryonic hearts but absent in the homozygous mutant embryos. DNA sequence flanking the transgene was used to isolate from a normal mouse library overlapping genomic DNA segments that span the transgene insertion site. The contiguous genomic DNA segment was found to contain exon 7 of theCspg2in a position 3′ to the transgene insertion site. These four separate lines of evidence support the hypothesis thatCspg2is the gene disrupted by the transgene insertion in thehdfmouse line. The findings of this study and our previous studies of thehdfinsertional mutant mouse have shown that normal expression of theCspg2gene is required for the successful development of the endocardial cushion swellings and the embryonic heart segments that give rise to the right ventricle and conus/truncus in the outlet of the looped heart.
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