M. Osada, T. Takamura, H. Sato, K. Mori
Abstract:
In bivalve molluscs, the possibilities of both heterosynthetic and autosynthetic pathway of yolk synthesis are proposed. However, no direct evidence for the vitellogenesis was provided and the hormonal control is unclear. In this paper the formation of a major yolk protein during oogenesis in the scallop and the potential regulatory system were demonstrated.
The cytoplasm of oocytes were only immunoreactive to rabbit anti- scallop yolk protein serum (anti-YP). Yolk protein content in the ovary determined by enzym-liked immunosorbent assay (ELISA) showed the same profile as a watersoluble protein and RNA contents in the ovary during oogenesis, and accounted for over 80% of water-soluble protein at spawning stage in March. These results lead us to a firm believe in the synthesis of a major yolk protein inside the ovary. An in vivo consecutive administration of estradiol-17Beta (E2) in the ovary at the growing stage increased in yolk protein content, and the increase in yolk protein in ovarian pieces culture with E2 in vitro indicated a dose-dependent manner. This finding strongly supported the production of yolk protein inside the ovary and suggested the vitellogenesis controlled by estrogen. In addition a factor in the cerebral-pedal ganglion extract significantly enhanced the in vitro production of yolk protein, which was heat stable, trypsin-chymotrypsin resistant, and estimated to be molecular weight of less than 10,000. Droloxifen which is a non-steroidal estrogen antagonist/agonist also caused a marked increase in the in vitro production of yolk protein and estrogen receptor-like immunoreactivity was observed only in the growing oocyte. Vitellogenesis in the scallop and the involvement in the central nervous system will be discussed.
(Education and Research Center of Marine Bio-resources, Tohoku Univ. Konorihama-mukai 15, Onagawa-cho, Oshika-gun, Miyagi 986-2242, Japan)