Molecular characterization of marbled eel (Anguilla marmorata) gonadotropin subunits and their mRNA expression profiles during artificially induced gonadal development

Three cDNA sequences encoding the gonadotropin subunits, common glycoprotein α subunit (GTHα), FSHβ and LHβ subunits were isolated from marbled eel. The cDNA of GTHα encodes 116 amino acids with a signal peptide of 24 amino acids and a mature peptide of 92 amino acids. The FSHβ subunit consists of 127 amino acids with a 22 amino acid signal peptide and a 105 amino acid mature peptide, while the LHβ subunit consists of 140 amino acids with a 24 amino acid signal peptide and a 116 amino acid mature peptide. Comparison of the deduced amino acid sequences of marbled eel GTHα, FSHβ, and LHβ with that of other fishes shows a high degree of conservation in the number of cysteine residues and potential N-linked glycosylation sites. The mRNA of GTHα, FSHβ and LHβ were not only detected in pituitary, but also in ovary and testes by RT-PCR. Quantitative realtime PCR analysis revealed that the GTHα and LHβ transcriptional levels in pituitaries of female and male eels gradually increased during the artificially inducing gonadal development, and peaked at late vitellogenic stage and spermiation stage, respectively. FSHβ mRNA in the pituitaries of female eels maintained a high level at previtellogenic stage, early vitellogenic stage as well as mid-vitellogenic stage but declined sharply at late vitellogenic stage and migratory nucleus stage. In male eels, the mRNA levels of FSHβ in the pituitaries were higher at early spermatogenesis stage than at both late spermatogenesis stage and spermiation stage. These results suggested that FSH would be in control of initiation and maintenance of gonadal growth and gametogenesis, whereas LH would be involved in the final gonadal maturation and spermiation/ovulation in the tropic eel Anguilla marmorata.