Molecular Characterization of Gonadotropin Subunits (fshβ, Lhβ and Cgα) of Largemouth Bass ( Micropterus Salmoides ) and Their Expression in Response to Luteinizing Hormone‐releasing Hormone Analogue and Dopamine Antagonists

Gonadotropins (GtHs), including follicle-stimulating hormone (FSH) and luteinizing hormone (LH), are important hormones involved in gametogenesis, gonadal steroidogenesis, and maturation. In this study, GtH subunits (FSH beta, LH beta and CG alpha) of largemouth bass (Micropterus salmoides) were cloned and characterized, and their regulation by luteinizing hormone-releasing hormone analog (LHRHa2) and dopamine antagonist (DOM) treatment in vivo was investigated. The full-length cDNA sequences of FSH beta, LH beta, and CG alpha were 683, 576, and 685bp, encoding 120, 152, and 132 amino acids, respectively. The deduced amino acid sequence analysis revealed that GtH subunits contain conserved cysteine residues and potential N-linked glycosylation sites and showed high homology with the corresponding subunit sequences from other Perciformes by phylogenetic analysis. In the primary growth cortical alveoli stage of largemouth bass, the three GtH subunits were highly expressed in the pituitary, brain and ovary, but weakly in other tissues. After LHRHa2 and DOM injection, mRNA levels of FSH beta, LH beta, and CG alpha in the pituitary were significantly increased at 12 or 24 hr (p <.05), but significantly decreased at 48 hr; plasma FSH and LH levels showed a consistent trend. Histological analysis classified ovaries from LHRHa2- and DOM-treated fish into the early oocyte maturation stage and late vitellogenesis stage, while those from the control group fish were classified into the early vitellogenesis stage. These results suggested that both LHRHa2 and DOM stimulated GtH subunit expression, increased plasma FSH and LH and accelerated ovary development of largemouth bass, providing a framework for a better understanding of the mechanisms of hormone-mediated reproduction control in teleosts.