Profiles of PGH-alpha, GTH I-beta, and GTH II-beta mRNA transcript levels at different ovarian stages in the wild female Japanese eel Anguilla japonica.

The complete complementary DNA (cDNA) encoding pituitary gonadotropin II-beta subunit (GTH II-beta) of Japanese eel Anguilla japonica was cloned and sequenced, and the profiles of pituitary glycoprotein hormone alpha subunit (PGH-alpha), GTH I-beta, and GTH II-beta mRNA transcript levels at different stages of ovarian development before vitellogenesis in the wild females were investigated. The maturity of female eels was divided into four stages: juvenile, sub-adult, pre-silver, and silver stages based on ovarian development and skin color. The GTH II-beta cDNA was cloned by reverse transcription and polymerase chain reaction (RT-PCR) amplification from total pituitary RNA. The full length GTH II-beta cDNA was obtained using 5(')- and 3(')-rapid amplification of cDNA ends. The cloned eel GTH II-beta cDNA consists of 646 bp nucleotides, including 53 bp nucleotides of 5(')-untranslated region (UTR), 423 bp of open reading frame, and 170 bp nucleotides of 3(')-UTR followed by a poly(A) tail. It encodes a 140-amino acid precursor molecule of GTH II-beta subunit with a putative signal peptide of 24 amino acids and a mature peptide of 116 amino acids. RT-PCR analysis showed that the pituitary transcript levels of alpha subunit steadily increased during eel silvering. The expression of GTH I-beta and II-beta mRNA levels, however, varied in different ovarian developmental stages. The mRNA expression of both GTH I-beta and GTH II-beta were detectable in juvenile stage. The expression levels of GTH II-beta mRNA, but not GTH I-beta, were significantly increased in sub-adult stage. The transcript levels of GTH I-beta and II-beta subunits further increased in pre-silver and silver stages. We demonstrated for the first time that the differential transcription patterns of pituitary PGH-alpha, GTH I-beta, and GTH II-beta mRNAs occur during silvering of the wild female Japanese eels.