The expression profiles of cyp19a1, sf-1, esrs and gths in the brain-pituitary during gonadal sex differentiation in juvenile Japanese eels

Eels are gonochoristic species whose gonadal differentiation initiates at the yellow eel stage and is influenced by environmental factors. We revealed some sex-related genes were sex dimorphically expressed in gonads during gonadal sex differentiation of Japanese eel (Anguilla japonica); however, the expression of sex-related genes in the brain-pituitary during gonadal sex differentiation in eels is still unclear. This study aimed to investigate the sex-related gene expressions in the brain-pituitary and tried to clarify their roles in the brain and gonads during gonadal sex differentiation. Based on our previous histological study, the control eels developed as males, and estradiol-17β (E2) was used for feminization. Our results showed that during testicular differentiation, the brain cyp19a1 transcripts and aromatase proteins were increased significantly; moreover, the cyp19a1, sf-1, foxl2s, and esrs (except gperb) transcripts in the midbrain/pituitary also were increased significantly. Forebrain gnrh1 transcripts increased slightly during gonadal differentiation of both sexes, but the gnrhr1b and gnrhr2 transcripts in the midbrain/pituitary were stable during gonadal differentiation. The expression levels of gths and gh in the midbrain/pituitary were significantly increased during testicular differentiation and were much higher in males than in E2-feminized females. These results implied that endogenous estrogens might play essential roles in the brain/pituitary during testicular differentiation, sf-1, foxl2s, and esrs may have roles in cyp19a1 regulation in the midbrain/pituitary of Japanese eels. For the GnRH-GTH axis, gths, especially fshb, may be regulated by esrs and involved in regulating testicular differentiation and development in Japanese eels.