INHIBITION OF GERMINAL VESICLE BREAKDOWN AND POLAR BODY FORMATION BY NICOTINAMIDE IN STARFISH AND SURF CLAM OOCYTES*

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Abstract
Nicotinamide inhibited both germinal vesicle breakdown (GVBD) and polar body formation (PBF) in surf clam [Spisula solidissima] and starfish [Asterina pectinifera and Asterias amurensis] oocytes. In the surf clam nicotinamide at 0.3 mM completely blocked PBF in the fertilized oocytes. For blockage of GVBD higher concentration was required. In the starfish, nicotinamide (30 mM) prevented PBF but not GVBD, when added 7 min after the commencement of 1-methyladenine (1-MeAde) administration. PBF may be blocked by nicotinamide independent of its effect on GVBD. In the case of starfish, NAD+ was more effective than nicotinamide in inhibiting oocyte maturation. Nicotinamide also blocked GVBD induced by microinjection of the cytoplasm containing maturation-promoting factor (MPF) obtained from 1-MeAde-treated oocytes. Nicotinamide may prevent the action of MPF rather than inhibiting the interaction of 1-MeAde with cell membrane or the induction of MPF.