Molecular characterization of rockfish (Sebastes schlegeli) gonadotropin subunits and their mRNA expression profiles during oogenesis

In an attempt to understand the reproductive regulation in viviparous teleosts, gonadotropin (GTH) subunit cDNAs were characterized and the expression levels of GTH subunit mRNAs in the pituitary glands of the rockfish, Sebastes schlegeli (Scorpaeniformes, Scorpaenidae), were examined by Northern blot analysis. The complete sequences of rockfish GTH subunits (GTHα, FSHβ, and LHβ) were determined by rapid amplification of cDNA ends (RACE) and nucleotide sequencing. Based on the RACE analysis, the cDNAs of GTHα, FSHβ, and LHβ consisted of 655, 540, and 529 nucleotides encoding peptides of 132, 130, and 143 amino acids, respectively. The mature peptides of rockfish FSHβ, LHβ, and common GTHα showed high sequence identities (FSHβ, 58-62%; LHβ, 86-94%; and GTHα, 87-88%) to those of other perciforme (e.g., orange spotted grouper, red seabream, stripped bass, and sea bass). In a sequence alignment of the mature peptides, rockfish FSHβ exhibited a unique feature, the lack of a conserved N-glycosylation site. This is in contrast to both LHβ and GTHα which contain one and two N-glycosylation sites, respectively, and is consistent with those of other teleosts. The mRNA levels of the GTHα subunit increased at the vitellogenic stage and remained steady from ovulation to post-parturition. FSHβ mRNA levels increased abruptly during the vitellogenic stages and then decreased during ovulation, embryonic development, and post-parturition. LHβ mRNA levels were observed to rapidly increase during the vitellogenic stage, reached its highest levels during ovulation and was then followed by a decrease at post-parturition. These results suggest that in the female rockfish FSH and LH syntheses are predominant during vitellogenesis and oocyte maturation, respectively.