CHANGES IN TRANSCRIPTION OF PITUITARY GLYCOPROTEIN-HORMONE-ALPHA AND GONADOTROPIN-II-BETA SUBUNITS DURING OVARIAN DEVELOPMENT INDUCED BY REPEATED INJECTIONS OF SALMON PITUITARY HOMOGENATE IN THE JAPANESE EEL, ANGUILLA-JAPONICA

To investigate transcription of pituitary glycoprotein hormone alpha a nd gonadotropin II beta (GTH II beta) subunits in female Japanese eel, gene quantitation systems using reverse transcription-polymerase chai n reaction (RT-PCR) were developed, using beta-actin as an internal co ntrol gene. These systems were not only sensitive, but also precise, w ith low coefficients of variation within and between assays (below 20 and 30 %, respectively). Using these quantitation systems, we investig ated how transcription of both subunits changed in Japanese eel during ovarian development induced by repeated injections of salmon pituitar y homogenate (SPH). Transcriptional level of pituitary glycoprotein ho rmone alpha was similar to that of beta-actin before SPH injection, an d increased slowly during ovarian development, reaching a maximum (3-f old increase over initial levels) at the migratory nucleus stage. In c ontrast, the level of GTH II beta mRNA was very low (about one-tenth t hat of beta-actin) before SPH injection, but expression increased mark edly during ovarian development with an approximate 120-fold increase over initial levels (12 times that of beta-actin) at the migratory nuc leus stage. These results suggest that GTH II synthesis in female eel was activated during ovarian development induced by repeated SPH injec tions. The increase in mRNA levels of both subunits mRNA is probably d ue to sex steroids produced in eel ovarian follicles. Unexpectedly, tr anscriptional level of GTH II beta was abnormally high compared to tha t of pituitary glycoprotein hormone alpha at the migratory nucleus sta ge. These results suggest that repeated SPH injections induced aberran t endocrine conditions in female Japanese eels.