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

Abstract

Previous studies have shown the regulation of follicle-stimulating hormone (Fshβ) and luteinizing hormone (Lhβ) 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 Fshβ and Lhβ in the pituitary and gene expression of kiss1, kiss2, gpr54, gnrh1, fshβ, lhβ, fshr, and lhr in the brain, pituitary, and ovary from 160 to 420 dph in this species. Fshβ and Lhβ immunohistochemical signals were primarily detected in the proximal pars distalis area at each stage, with few Fshβ or Lhβ signals detected in the pars intermedia area at 160, 200, 270, 300, 330, 360, and 390 dph. The expression levels of fshβ at 160 dph and fshr at 200 dph were significantly elevated, suggesting that increased fshr expression may reflect increased fshβ levels. Therefore, Fshβ may be more active than Lhβ 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 lhβ at 300 dph were significantly elevated, they were not significantly altered in most stages between 240 and 420 dph. However, a comparison of Fshβ and Lhβ signal intensity indicated that Fshβ signals from 270 to 420 dph and Lhβ signals from 240 to 420 dph were consistently higher than in earlier stages. These results suggest that Fshβ/Lhβ may be active during primary oocyte development in the red-spotted grouper.

Keywords

• Brain-pituitary-gonadal axis
• Kisspeptins
• Gonadotropins
• Gonadotropin receptors
• Teleost