Abstract
Androgen administration has been widely used for masculinization in fish. The mechanism of the sex change in sexual fate regulation is not clear. Oral administration or pellet implantation was applied. We orally applied an aromatase inhibitor (AI, to decrease estrogen levels) and 17α-methyltestosterone (MT, to increase androgen levels) to induce masculinization to clarify the mechanism of the sex change in the protogynous orange-spotted grouper. After 3 mo of AI/MT administration, male characteristics were observed in the female-to-male sex change fish. These male characteristics included increased plasma 11-ketotestosterone (11-KT), decreased estradiol (E2) levels, increased male-related gene (dmrt1, sox9, and cyp11b2) expression, and decreased female-related gene (figla, foxl2, and cyp19a1a) expression. However, the reduced male characteristics and male-to-female sex change occurred after AI/MT-termination in the AI- and MT-induced maleness. Furthermore, the MT-induced oocyte-depleted follicle cells (from MT-implantation) had increased proliferating activity, and the sexual fate in a portion of female gonadal soma cells was altered to male function during the female-to-male sex change. In contrast, the gonadal soma cells were not proliferative during the early process of the male-to-female sex change. Additionally, the male gonadal soma cells did not alter to female function during the male-to-female sex change in the AI/MT-terminated fish. After MT termination in the male-to-female sex-changed fish, the differentiated male germ cells showed increased proliferating activities together with dormancy and did not show characteristics of both sexes in the early germ cells. In conclusion, these findings indicate for the first time in a single species that the mechanism involved in the replacement of soma cells is different between the female-to-male and male-to-female sex change processes in grouper. These results also demonstrate that sexual fate determination (secondary sex determination) is regulated by endogenous sex steroid levels.
Highlights
Many fish species are responsive to sex steroid induction of sexual determination and development
Sex steroids are important in the regulation of sexual fate in protogynous grouper In the present study, we demonstrate that AI-/MT-stimulated androgen elevation resulted in masculinization with high 11-KT levels in juvenile grouper
In the female-to-male sex change, oocytedepleted follicle cells alter their function from a female to male (Sertoli cells) sexual fate during the AI/MT-induced female-to-male sex change
Summary
Many fish species are responsive to sex steroid induction of sexual determination and development. Oocyte-depleted follicle cells alter the sexual fate from female to male during the female-to-male sex change [14]. Taken together, these data suggest that the mechanism for reprogramming the surrounding cells of the oocytes is varied among species. These data suggest that the mechanism for reprogramming the surrounding cells of the oocytes is varied among species These data indicate that in addition to a unidirectional signal, a reciprocal cross-talk occurs between germ and somatic cells, and this cross-talk plays an important role during sexual fate alternation. The mechanism of sexual fate alternation in the sex change is not clear
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