Kisspeptins, gonadotropins, and their receptors in the brain-pituitary-gonadal axis of Epinephelus akaara: Their relationship with oogonial proliferation and primary oocyte development

Previous studies have shown the regulation of follicle-stimulating hormone (Fshl3) and luteinizing hormone (Lhl3) during early ovarian differentiation and development from 30 to 160 days post-hatching (dph) in the red-spotted grouper. This study investigates the immunohistochemical identification of Fshl3 and Lhl3 in the pituitary and gene expression of kiss1, kiss2, gpr54, gnrh1, fsh beta, lh beta, fshr, and lhr in the brain, pituitary, and ovary from 160 to 420 dph in this species. Fshl3 and Lhl3 immunohistochemical signals were primarily detected in the proximal pars distalis area at each stage, with few Fshl3 or Lhl3 signals detected in the pars intermedia area at 160, 200, 270, 300, 330, 360, and 390 dph. The expression levels of fsh beta at 160 dph and fshr at 200 dph were significantly elevated, suggesting that increased fshr expression may reflect increased fsh beta levels. Therefore, Fshl3 may be more active than Lhl3 during oogonial proliferation and new oocyte generation. While expression levels of kiss1 and kiss2 at 270 and 390 dph, gpr54 at 360 dph, gnrh1 at 270 dph, and lh beta at 300 dph were significantly elevated, they were not significantly altered in most stages between 240 and 420 dph. However, a comparison of Fshl3 and Lhl3 signal intensity indicated that Fshl3 signals from 270 to 420 dph and Lhl3 signals from 240 to 420 dph were consistently higher than in earlier stages. These results suggest that Fshl3/Lhl3 may be active during primary oocyte development in the red-spotted grouper.