| Budget Amount *help |
¥14,900,000 (Direct Cost: ¥14,900,000)
Fiscal Year 2005: ¥6,800,000 (Direct Cost: ¥6,800,000)
Fiscal Year 2004: ¥8,100,000 (Direct Cost: ¥8,100,000)
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| Research Abstract |
The gobiid fish, Trimma okinawae, possesses ovarian and testicular tissues simultaneously in its gonad and is able to change sex repeatedly in both directions depending on its social surroundings. As sex change in both directions can be socially manipulated, T.okinawae provides an excellent animal model to investigate molecular mechanisms of sex change. The involvement of gonadotropins in sex change was examined by determining the changes in gonadotropin (FSH and LH) receptor gene (GtHRs) expression in gonads during the onset of sex changes from female to male and male to female. The results were intriguing as the expression of the GtHRs was found to be confined to the active gonad of the corresponding sexual phase. When the sex change was occurring from female to male, initially the ovary had high levels of FSHR and LHR, which eventually went up in the testicular tissue once the fish had realized the fact that it was bigger than the other in the aquarium. Opposite of this scenario was
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observed if another fish bigger than the newly sex-changed male was introduced into this aquarium. Swapping of the gonads started with switching of the GtHR expression that was discernible within 12-24 hrs of the visual cue. Our findings show that the gonads of successive sex changing fish possess the intrinsic mechanism to respond to the social cue differentially. Additionally, this location switching of GtHR expression also could substantiate the importance of hypothalamo-pituitary-gonadotropic axis.
The wrasse, Pseudolabrus sieboldi, changes sex from female to male. In this study, to investigate the role of estradio1-17β (E2) and 11-ketotestosterone (11KT) in the conversion between oogenesis and spermatogenesis in the gonad, ovarian and testicular tissues were incubated with E2 or 11-KT respectively using in vitro organ culture system. In the culture of ovarian tissues with 11KT, the cysts of spermatozoa, spermatids, and spermatocytes appeared, while oocytes disappeared. On the contrary, E2 treatment could not organize the cysts of any testicular germ cells in ovarian tissues. In the culture of testicular tissues with 11KT, the cysts of spermatozoa, spermatids, and spermatocytes were observed, while with E2, there was a complete degeneration of testicular tissues. This newly developed organ culture system will provide an excellent in vitro system to study the molecular mechanisms of sex change in fish. Less
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