Vitellogenin Synthesis in the Ovary of Scallop, Patinopecten yessoensis: Control by Estradiol-17b and the Central Nervous System MAKOTO OSADA 1n , TERUKI TAKAMURA 2 , HARUKO SATO 2 , and KATSUYOSHI MORI 2 1 Laboratory of Integrative Aquatic Biology, Field Science Center Graduate School of Agricultural Science, Tohoku University, Oshika, Japan 2 Laboratory of Aquacultural Biology, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan ABSTRACT Elucidation of a profile of scallop vitellin formation associated with oogenesis and its endocrine control, and identification of a vitellogenin synthesizing site were immunologically undertaken by using anti-scallop Vn serum. Vn content increased during ovarian growth and accounted for more than 80% of the watersoluble protein of the ovary at the mature stage. In vivo injection of estradiol–17b (E 2 ) resulted in an increase in Vn content in the ovary. In vitro accumulation of Vn in the ovarian tissue was promoted with E2 and a vitellogenesis promoting factor (VPF) from cerebral plus pedal ganglion which was heat stable, less than MW 10,000 and trypsin/ chymotrypsin resistant. Estrogen receptor (ER)-like immunoreactivity was found in the growing oocyte and the auxiliary cell in close contact with growing oocytes, in which Vn immunoreactivity was also found. It is suggested that the vitellogenin synthesis occurred inside the ovary, especially in the auxiliary cell, and is controled by E2 and VPF via ER. J. Exp. Zool. 299A:172–179, 2003. r 2003 Wiley-Liss, Inc. INTRODUCTION The egg yolk proteins of oviparous animals are generally synthesized outside the oocytes as precursors or vitellogenins (Vtgs), e.g. in the liver of vertebrates, intestine of nematodes and fat body of insects (Wahli, ’88). In molluscs endogenous proteinaceous yolk formation was proposed to account for the main type of vitellogenesis (De Jong-Brink et al., ’83), while it is still unclear whether the synthesis of major yolk protein occurs through an autosynthetic or heterosynthetic pathway (Pipe, ’87; Eckelbarger and Davis, ’96). However, Barre et al. (’91) and Bride et al. (’92) demonstrated in an immunological and molecular biological study that a site of Vtg synthesis in the garden snail was the digestive gland. Vitellins (Vns), accumulated in the oocytes for embryonic and larval development (Li et al., ’98a), in the Pacific oyster Crassostrea gigas and the scallop Patinopecten yessoensis have been isolated and characterized (Suzuki et al., ’92; Osada et al., ’92). Synthesis of Vtg is postulated to be within the ovary because the immunolocalization of Vn has been observed only in the vitellogenic oocyte (Suzuki et al., ’92; Osada et al., ’92), but little information is available concerning the Vtg synth- esis and endocrine control of vitellogenesis in bivalve molluscs. We have reported an estrogen profile during the reproductive cycle, described the distribution of estrogen producing cells, and suggested that estrogen may contribute to the development of gametes in the scallop and Pacific oyster (Matsu- moto et al., ’97). In vivo and In vitro administra- tion of estradiol-17b (E 2 ) promoted the increase in Vn content in the ovary of Pacific oyster, suggest- ing that Vtg may be synthesized inside the ovary and that E 2 may be a major factor controling Grant sponsor: Japanese Ministry of Education, Culture, Sports, Science and Technology; Grant number: 1066071. n Correspondence to: Dr. Makoto Osada, Laboratory of Integrative Aquatic Biology, Field Science Center Graduate School of Agricultural Science, Tohoku University, Onagawa, Oshika 986-2242, Japan. E-mail: mosada@bios.tohoku.ac.jp Received 19 June 2002; Accepted 10 February 2003 Published online in Wiley InterScience (www.interscience.wiley. com). DOI: 10.1002/jez.a.10276 r 2003 WILEY-LISS, INC. JOURNAL OF EXPERIMENTAL ZOOLOGY 299A:172–179 (2003)