Meeting Abstract

S5-2.1  Saturday, Jan. 5  Genetic and hormonal regulation of gonadal development and sexual plasticity in fish NAGAHAMA, Y.; Ehime Univ. nagahama.yoshitaka.mh@ehime-u.ac.jp

Among the vertebrates, teleost fishes display the greatest diversity of sexual phenotypes, thus providing an excellent model to study molecular mechanisms of sex determination, sexual differentiation and sexual plasticity. We identified dmy as the sex-determining gene of the medaka (Oryzias latipes). Recently, we developed a gene-specific transgenic RNA interference (RNAi) technology for the analysis of loss-of-function phenotypes that develop over long periods of time, and used it to knock down the dmy gene in genetically male (XY) fish. Knockdown of dmy strongly downregulated the expression of only other male-associated genes, and upregulated the expression of female-associated genes in XY gonads during the early stages of sexual differentiation. We previously showed that a sharp decrease in estrogen production triggers female to male sex reversal in an adult sex-changing fish, the saddle-back wrasse (Thalassoma duperrey). Therefore, in this study, we used aromatase inhibitors (AIs) to block the conversion of androgens to estrogens and examined whether lack of estrogen can reverse the gonadal morphology in two adult, sexually-mature gonochoristic species, medaka and Nile tilapia (Oreochromis niloticus). Interestingly, we found that AIs were effective in blocking estrogen production and induced a complete sex reversal from females to males in both medaka and tilapia. Further, AIs were sufficient to induce not only the testicular structure, but also the phenotypic transformation including sexual behavior. Our data, for the first time in any vertebrates, has shown that sexual plasticity is preserved even in adulthood.