Molecular cloning of genes for sex reversal in amphibians

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cDNA clones encoding the frog, Rana rugosa calnexin (2.2 kb) and calreticulin (2.4 kb) were isolated and sequenced. The CLX gene was weakly expressed only in the liver, while the CLT gene was expressed in all the tissues examined of adult frogs. Young frogs at stage XXV produced an extremely strong signal of the CLT gene expression in the ovary, but not in the testis. When the masculinization was induced by testosterone propionate (TP) , the CLT gene expression was significantly inhibited in gonads of tadpoles. In immunohistological studies, CLT was not appreciably detected in oocytes in ggonads of tadpoles at stage 18-19, but detected in the whole cytoplasm of growing oocytes of frogs after metamorphosis. This protein then was squeezed toward the nucleus as yolk granules were accumulated. Our results suggest that the CLT,but not CLX gene is expressed in oocytes during maturation in the frog, R.rugosa. The masculinization of this frog is at least partly associated with the suppression of the CLT gene expression in differentiating gonads. In addition, A 2.2-kb cDNA of Ad4BP,which is known to be a key gene for differentiation of gonad and adrenal in mammalians, was also isolated and sequenced. The Ad4BP gene expression during development of frogs and a sex hormonal regulation of its gene expression are now under investigations.