2007 Fiscal Year Final Research Report Summary
Analysis of mechanisms controlling gonadal sex change in fish using an in vitro culture system
| Project/Area Number |
18580172
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
General fisheries
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| Research Institution | Hokkaido University |
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Principal Investigator |
TODO Takashi Hokkaido University, Faculty of Fisheries Sciences, Associate Professor (60303111)
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| Co-Investigator(Kenkyū-buntansha) |
NAKAMURA Masaru University of the Ryukyus, Tropical Biosphere Research Center, Professor (10101734)
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| Project Period (FY) |
2006 – 2007
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| Keywords | sex change / organ culture / sex steroid / ovary / testis / germ cell / wrasse |
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| Research Abstract |
Recently, we succeeded to induce in vitro spermatogenesis in a protogynous hermaphrodite fish, the three-spotted wrasse (Halichoeres trimaculatus) during organ culture of ovary with a serum-supplemented medium. This culture system appears to be a good model for further study of the mechanisms controlling gonadal sex change. In the present study, we re-examined this culture system for the three-spotted wrasse.
Ovarian tissue from sexually immature three-spotted wrasse was cultured in Leibovitz L-15 medium supplemented with 0.5% bovine serum albumin (BSA) or 10% fetal bovine serum (FBS) using a floating tissue culture method. Tissue was exposed to androgens for a few, weeks at 26℃. The effects of various concentrations of androgens and estrogen were also examined. Furthermore, the detection of apoptotic cells during the culture was performed using the TUNEL method.
In all experimental groups, including the control (no steroid), degeneration of oocytes and initiation of spermatogenesis was observed. Androgens enhanced the complete transition of ovarian tissue via spermatogonia to formation of spermatogenic crypts. There was no difference between supplementation with BSA and FBS. The effects of androgens on inducing spermatogenesis showed a dose dependent manner. Estrogen treatments reduced the degeneration of oocytes, and did not lead the occurrence of spermatogenesis. The TUNEL-positive oocytes were observed and increased during culture period.
These results show that the restructuring from ovary to testis in the wrasse could be induced in vitro with a serum-free medium. The results also suggest that the gonadal sex change can be triggered by basic in vitro culture due to a lack of endogenous factors (especially, estrogens) for female sexuality, and accelerated by androgens. Furthermore, oocyte apoptosis is might be an important mechanism of the gonadal sex change.
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