Molecular cloning of the cDNAs encoding pituitary glycoprotein hormone alpha- and gonadotropin II beta-subunits of the Japanese eel, Anguilla japonica, and increase in their mRNAs during ovarian development induced by injection of chum salmon pituitary homogenate.

cDNAs encoding the glycoprotein hormone alpha- and gonadotropin (GTH) II beta-subunits of Japanese eel (Anguilla japonica) pituitary were cloned using the polymerase chain reaction. The nucleotide sequence of the glycoprotein hormone alpha-subunit cDNA was 364 base pairs (bp) long, encoding 117 amino acids, and that of the GTH II beta-subunit cDNA was 433 bp long, encoding 140 amino acids. The deduced amino acid sequence of each mature subunit showed high homology with those of other teleosts, indicating that the structure of GTH subunits has been conserved during the evolution of teleosts. Changes in the expression of these subunit genes during ovarian development induced artificially by the injection of chum salmon pituitary homogenate were examined using Northern blot analysis. Glycoprotein hormone alpha-subunit mRNA increased almost linearly during ovarian development, whereas GTH II beta-subunit mRNA was detected only at the late vitellogenic and migratory nucleus stages. These data indicate that eel GTH II is synthesized mainly at the late vitellogenic and migratory nucleus stages, and suggest that GTH II plays an important role in final oocyte maturation of Japanese eel. Changes in the expression of glycoprotein hormone alpha- and GTH II beta-subunits mRNA correlate with the serum estradiol-17 beta (E(2)) and testosterone profile during ovarian development. The increase in mRNA of both subunits is probably due to positive feedback of E(2) and testosterone produced by ovarian follicles in response to the GTH contained in chum salmon pituitary homogenate.