| Summary: | Gonadal differentiation is tightly regulated by the initial sex determining gene and the downstream sex-related genes in vertebrates. However, sex change in fish can alter the sexual fate from one sex to the other. Chemical-induced maleness in the protogynous orange-spotted grouper is transient, and a reversible sex change occurs after the chemical treatment is withdrawn. We used these characteristics to study Amh signaling during bi-directional sex change in the grouper. We successfully induced the female-to-male sex change by chemical (aromatase inhibitor, AI, or methyltestosterone, MT) treatment. A dormant gonad (a low proliferation rate of early germ cells and no characteristics of both sexes) was found during the transient phase of reversible male-to-female sex change after the withdrawal of chemical administration. Our results showed that amh (anti-mullerian hormone) and its receptor amhr2 (anti-mullerian hormone receptor type 2) were significantly increased in the gonads during the process of female-to-male sex change. Amh is expressed in the Sertoli cells surrounding the type A spermatogonia in the female-to-male grouper. Male-related gene (dmrt1 and sox9) expression was immediately decreased in MT-terminated males during the reversible male-to-female sex change. However, Amh expression was found in the surrounding cells of type A spermatogonia-like cells during the transient phase of reversible male-to-female sex change. This phenomenon is correlated with the dormancy of type A spermatogonia-like cells. Thus, Amh signaling is suggested to play roles in regulating male differentiation during the female-to-male sex change and in inhibiting type-A spermatogonia-like cell proliferation/differentiation during the reversible male-to-female sex change. We suggest that Amh signaling might play dual roles during bi-directional sex change in grouper.
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