Two Sox9 messenger RNA isoforms: Isolation of cDNAs and their expression during gonadal development in the frog Rana rugosa

Sox is a family of SRY-related testis-determining genes. We have isolated two different mRNA isoforms of the frog Sox9 gene from adult frog testis cDNAs. One form (Sox9 α) encodes a 482 amino acid protein containing the HMG box, whereas the other form (Sox9 β), which completely lacks the HMG box, is a truncated 265 amino acid protein of Sox9 α. Sox9 α is 82% similar to mouse, 86% to chicken, and 77% to trout Sox9 at the amino acid level. Sox9 expression was up-regulated in embryos after stage 16, and was seen in both developing testes and ovaries. The size of Sox9 transcripts was determined to be 7.8 knt by Northern blot analysis. In addition, Sox9 α expression was found prominently in the testis and brain among various tissues of adult frogs examined, and was considerably higher than Sox9 β. The fact that Sox9 is expressed in both sexes suggests that this gene is involved in gonadal development of male and female frogs. This is dissimilar to the pattern in birds and mammals, in which Sox9 expression is male-specific. (C) 2000 Federation of European Biochemical Societies.