Characterization of gonadal glucocorticoid-induced leucine zipper (GILZ) protein expression during sex change in the protogynous orange-spotted grouper, Epinephelus coioides.

Steroid hormones have been proven as a key drive of sex change in sequentially hermaphroditic organisms. However, the upstream mechanism of sex steroid hormones regulation that affect sex change remain unknown. The main glucocorticoid in teleost fish is cortisol, which both regulates steroidogenesis and has antistress action. Thus, cortisol might be one of the prime factors in sex change. In this study, the glucocorticoid-induced leucine zipper (GILZ) gene, was proven to have a dramatic effect in orange-spotted groupers (Epinephelus coioides) during sex change at the early stage of gonadal transition. The specific action of the GILZ protein is at the pouch-shaped proliferative spermatogonia instead of the degenerative oocyte at the onset of sex change. Immunohistochemical (IHC) evidence revealed that GILZ performs intensively at undifferentiated spermatogonia in the early testis stage. These results imply that cortisol provokes a rise of GILZ through regulation caused by steroid hormones leading to sex change.