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Abstract

Sex steroids play a crucial role in gonadal sex differentiation in many nonmammalian vertebrates, including hermaphroditic teleosts. The current study investigates the mRNA expression levels of gonadal cyp19a1a, dmrt1, sf-1, dax-1 and 11β-hsd in the protogynous orange-spotted grouper, Epinephelus coioides, at certain stages during sex differentiation and sex change. Among the genes whose mRNA levels were determined through quantitative RT-PCR analysis, cyp19a1a was predominantly expressed in the ovary, and its expression was much lower in the testis. The level of cyp19a1a expressed at 150 dah was significantly high enough to trigger the pre-gyno female development of protogynous (subadult) orange-spotted grouper. The continuous increase in testicle dmrt1 expression during sex differentiation peaked at the completion of sex change, suggesting a vital role before and after sex change. A remarkable increase in sf-1 expression occurred at the end of both sex differentiation and sex change. dax-1 expression exhibited little difference among the various stages during sex differentiation until successful sex change had occurred, when it presented a marked increase. Continuously increasing 11β-hsd expression levels were synchronized in accordance with the cumulative duration of sex differentiation and sex change durations. It was concluded that gyno sex differentiation of the orange-spotted grouper is initiated at the gonadal cyp19a1a expression level at approximately 150 dah, and the sequential involvement of gonadal cyp19a1a, dmrt1, sf-1, dax-1 and 11β-hsd expression dynamically regulates sex differentiation and sex change, which is transiently completed at an average age of 7 years. Epigenetic regulation of cyp19a1a plays a critical role in natural sex reversal, and our data suggest that dmrt1 plays a key role in initial testis differentiation and in the subsequent maintenance of male development. These findings further highlight the important roles of endogenous steroids in fish sex differentiation/maintenance.

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