cDNA cloning of two gonadotropin β subunits (GTH-Iβ and -IIβ) and their expression profiles during gametogenesis in the Japanese flounder (Paralichthys olivaceus)

To clarify the profiles of two distinct gonadotropin (GTH-I and -II) mRNA levels during gametogenesis in a multiple spawner, the Japanese flounder (Paralichthys olivaceus), the cDNAs encoding GTH-I beta and -II beta from the pituitary gland have been cloned and sequenced. The nucleotide sequence of GTH-I beta was 542 bp long, encoding 120 amino acids, and that of GTH-II beta was 554 bp long, encoding 145 amino acids. In females, Northern blot analysis has revealed that relative mRNA levels of GTH-I beta and -II beta were low in immature fish, showed a gradual increase with ovarian development, and reached the highest level at the maturation stage. Both GTH-I beta and -II beta mRNA levels were highly correlated with gonadosomatic index (GSI) values and with circulating estradiol-17 beta and testosterone (T) levels. In males, the mRNA levels of GTH-I beta increased with the increase in GSI values and in circulating 11-ketotestosterone and T levels, whereas the mRNA levels of GTH-II beta did not show any correlation with GSI values and with circulating steroid levels, suggesting a difference in regulatory mechanisms of GTH-I and -II synthesis in males. The similar changes in GTH-I beta and -II beta mRNA levels during oogenesis are considered to be characteristic of GTH synthesis in multiple spawners, differing from the differential changes reported in annual spawners such as salmonids. (C) 2001 Ademic Press.