The characteristics and expression profile of follicle-stimulating hormone and luteinizing hormone during gonadal development in silver pomfret

The hypothalamic-pituitary-gonadal (HPG) axis, particularly follicle-stimulating hormone (Fsh) and luteinizing hormone (Lh), is essential for the regulation of teleost reproduction. However, their expression dynamics and receptor distribution during gonadal development in silver pomfret remain poorly understood. This study aimed to characterize the expression profiles and cellular localization of Fshβ, Lhβ and their receptors (Fshr and Lhr) in the pituitary and gonads and to evaluate their potential roles in reproductive regulation. The different staining method and transmission electron microscopy (TEM) were used to analyse the structural changes of the pituitary gland during the reproductive season. Quantitative PCR (qPCR) and immunohistochemical (IHC) were used to detect the expression pattern of Fshβ and Lhβ. The results showed that the number of endocrine granules significantly increased before the reproductive season, and their electron density intensified. During the spawning season, the secretory granules gradually depleted, leading to the appearance of vacuolization. In the pituitary gland, the expression of fshβ in Stage IV was significantly higher in the female pituitary, but significantly higher in Stage V in the male. Fshβ and Lhβ signals were mainly located in the proximal pars distalis (PPD) and pars intermedia (PI) regions of the pituitary. In the gonad, Fshr signals were observed in the spermatogonia type A cells and Sertoli cells in testes, whereas Lhr signals were observed in spermatogonia and secondary spermatocytes in the testes. Fshr and Lhr signals were both observed in the follicle cells surrounding the oogonia and vitellogenic oocytes in the ovary of silver pomfret. The expression patterns of fshβ and fshr were essentially similar after different hormone treatments in the gonad and methyltestosterone (MT) could influence the expression of fshβ, lhβ and fshr in the testis. Taken together, our data suggest that Fshβ and Lhβ promote the development and maturation in the gonad, and Fshr and Lhr may be involved in ovary maturation and spawning.