High temperature increases the gsdf expression in masculinization of genetically female Japanese flounder (Paralichthys olivaceus)

In teleosts, sex is plastic and is influenced by environmental factors. Elevated temperatures have masculinizing effects on the phenotypic sex of certain sensitive species. In this study, we reared genetic XX Japanese flounder at a high temperature (27.5 +/- 0.5 degrees C) and obtained a population of sex-reversal XX males (male ratio, 95.24%). We comparatively analyzed the dynamic characteristics of germ cells and gsdf (gonadal soma-derived factor) expression during sexual differentiation for the experimental (27.5 +/- 0.5 degrees C) and control (18 +/- 0.5 degrees C) groups. The results revealed that the germ cell proliferation inhibited and gsdf expression up-regulated in the experimental group, and the gsdf mRNA and proteins expressed in somatic cells that had direct contact with germline stem cells (with Nanos 2 protein expression) including spermatogonia and oogonia by ISH (in situ hybridization) and IHC (immunohistochemistry). In addition, we also overexpressed the gsdf in XX flounders, and the germ cell number of XX flounders bearing gsdf gene significantly decreased and sometimes disappeared completely, which was consistent with the results from high-temperature induction. Therefore, based on all the results, we speculated that the high expression of gsdf might inhibit germ cell proliferation during sex differentiation, and eventually cause sex reversal in the high-temperature induced masculinization of XX Japanese flounder.