Endocrine control of vitellogenesis in the Japanese scallop

The ELISA analysis with anti-scallop vitellin (Vn) serum demonstrated that an in vitro accumulation of Vn in the ovarian tissue was promoted with estradiol-17β and cerebral plus pedal ganglion (CPG) extract which was heat stable. Estrogen-like immunoreactivity was found in the growing oocyte and auxiliary cell. It was supposed that the vitellogenesis occurred inside the ovary and an oocyte growth appeared to be controled by estrogen and CPG via estrogen receptor (ER). Vitellogenin (Vtg) cDNA clone was isolated from the ovary by immunoscreening and the putative protein exhibited 20% of homology, compared with Vtgs of other oviparous animals. RNA blot-hybridization analysis revealed that over 10 kb of mRNA was detected only in the ovary and a high amount of Vtg mRNA during oocyte growth was retained until spawning stage. In situ hibrydization demonstrated Vtg mRNA expression in the auxiliary cells closely associated with growing oocytes. The content of mRNA in the ovarian tissue cultured in vitro with CPG showed no change although the CPG extract enhanced Vn accumulation. A transcription and translation of Vtg mRNA were supposed to be regulated by the different mechanisms, respectively.