Molecular cloning of the cDNAs encoding two gonadotropin beta subunits (GTH-I beta and -II beta) from the goldfish, Carassius auratus.

Two types of cDNAs (GTH-I beta and -II beta) that encode the beta subunit of goldfish gonadotropin were cloned from a goldfish pituitary cDNA library. The nucleotide sequence of GTH-I beta cDNA was 616 bp long, encoding 130 amino acids, and that of GTH-II beta was 552 bp long, encoding 140 amino acids. These two types of goldfish GTH beta subunits showed an identity of 52% in the nucleotide sequence and 38% in the amino acid sequence. When compared to mammalian GTH beta subunits, goldfish GTH-I beta showed higher homology to FSH-beta s than LH-beta s, and goldfish-II beta to LH-beta s. Genomic Southern blot analysis revealed that cyprinid species harbored genes which were homologous to goldfish GTH-I beta and -II beta, demonstrating the duality of GTH in cyprinid fish as has been shown in other teleost fish. Northern blot analysis of GTH-I beta and -II beta mRNAs in goldfish at differing stages of ovarian maturity (immature, maturing, mature, and regressed) showed that both GTH-I beta and -II beta mRNA levels increased with the progression of maturity and declined in regressed stage. These results suggested that gonadal development in the goldfish was regulated by the two GTHs.