Studies of Mecteinism of sex determination and sex diferentiation in fish.

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Our studies indicate that endogenous estrogen biosynthesis occurs in undifferentiated XX gonads but not XY gonads before the appearance of any morphological sexual dimorphism, and that endogenous estrogens are required for ovarian differentiation. To identify the down-stream gene products during ovarian and testicular differentiation, we performed subtractive hybridization using mRNA derived from normal and estrogen treated XY gonads. We identified ten regulated gene products, seven of which related to ovarian differentiation and three to testicular differentiation. Two out of the ten gene products were expressed in germ cells, whereas the others were expressed in somatic cells.Sex reversal was induced in genetically sex-controlled female tilapia by a 30 days treatment with methyltestosterone(MT) or aromatase inhibitor(AI). Gene expression profiles were compared with a control group by modified differential display at Day 12 (initiation period of sex differentiation) and Day 30(just af … More ter completion of sex differentiation). At 12,16 up-regulated and 21 down-regulated genes were identified, where at Day 30,14 up-regulated and 19 down-regulated genes were identified. These genes were cloned and sequenced, followed by homology searches and gene expression analysis.In this study, we examined the mechanism of sex change in fish using a protogynous species. AI induced compete a sex change from female to male. In contrast, AI and estradiol-17b(E2) in combination did not bring about the sex change. These results strongly suggest that endogenous E2 has critical role in sex change.Using in vitro tissue culture, we succeeded in inducing restructuring complete ovarian tissue to mature testicular tissue with sperm in 3-4 weeks. To the best of our knowledge, this is the first demonstration of "in vitro sex change" from ovary tissue to a complete testis in vertebrates. This ability to experimentally induce this change has important implication for future research on sex determination and sex differentiation in vertebrates. Less