Molecular mechanism of inductive and inhibitory regulation in the spawning of marine bivalves : Analysis of a novel inhibitor from the central nervous system

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15580155
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: General fisheries
• Research Institution: Tohoku University
• Principal Investigator: OSADA Makoto Tohoku University, Graduate School of Agricultural Science, Associate Professor, 大学院・農学研究科, 助教授 (30177208)
• Co-Investigator(Kenkyū-buntansha): INABA Kazuo University of Tsukuba, Shimoda Marine Research Center, Professor, 下田臨海実験センター, 教授 (80221779) ; KYOZUKA Kei-ichiro Tohoku University, Graduate School of Science, Associate Professor, 大学院・理学研究科, 助教授 (40124573)
• Project Period (FY): 2003 – 2004
• Keywords: Serotonin / Oocyte Maturation / Spawning / Oocyte Maturation Arresting Factor / Prostaglandin F2α / Serotonin Receptor / Bivalve

Research Abstract

a)Molecules related to the regulation of oocyte maturation and spawning in marine bivalves
The serotonin (5-HT)-induced egg release has been strongly inhibited by a novel factor from the cerebral and pedal ganglion (CPG) and prostaglandin F2α (PG F2α). PG F2α strongly inhibited 5-HT-induced egg release, but not oocyte maturation, thus suggesting that PGF2α may suppress 5-HT-induced ciliary movement in the gonoduct. We found a novel factor from CPG of the scallop to inhibit 5-HT-induced oocyte maturation and thereby result in the suppression of egg release. We named the novel inhibitor Oocyte Maturation Arresting Factor (OMAF). It was demonstrated that the proteinaceous OMAF is received by a receptive mechanism of oocyte and OMAF appears to be a universal substance to inhibit 5-HT-induced oocyte maturation in bivalve species.
b)Signaling pathway of OMAF
OMAF is transported to egg surface through blood flow and inhibits oocyte maturation induced by 5-HT, which is mediated through 5-HT recep tor in the oocyte membrane, via a receptive mechanism of its own. 5-HT induced oocyte maturation and subsequent egg release through the gonoduct in the presence of extracellular Ca^<2+>. OMAF reduced an increase in intracellular Ca^<2+> induced by 5-HT, suggesting that the OMAF inhibits an extracellular Ca^<2+> influx into oocyte via Ca^<2+> channels.
c)Scallop 5-HT cDNA (5-Htpy) cloning and the structure and predicted function
RT-PCR and subsequent Nested PCR were carried out using degenerate primers designed from the conservative region of 3rd, 6th and 7th transmembrane domains and 3', 5' RACE was followed. We obtained 5-HTpy cDNA of ca 2.0 kbp containing ORF encoding 454 amino acid residues. The 5-HTpy was clustered into 5-HT1 subtype receptor group coupled with Gi, in which the intracellular transduction of 5-HT via 5-HTpy coupled with Gi inhibits cAMP production and induces extracellular Ca^<2+> influx into oocyte.
The spawning of bivalves triggered by 5-HT is regulated by PGF2α and OMAF at the gonoduct and oocyte, respectively, and full-grown oocyte is arrested at the dictyate stage of meiotic prophase until spawning.