Effects of 1-methyladenine on nuclear Ca2+ transients and meiosis resumption in starfish oocytes are mimicked by the nuclear injection of inositol 1,4,5-trisphosphate and cADP-ribose.

The treatment of prophase-arrested starfish oocytes with the hormone 1-methyladenine (1-MA) induces the elevation of Ca2+ in both the cytoplasm and the germinal vesicle (nucleus), and is followed by the resumption of meiosis. The injection of the modulators of the intracellular Ca2+ channels inositol 1,4,5-trisphosphate (InsP3) or cyclic adenosine diphosphate ribose (cADPr) into the germinal vesicle promoted meiosis resumption in the absence of 1-MA in about 50% of the oocytes. Caged InsP3 or caged cADPr were injected into the nuclei of oocytes together with the Ca2+ indicator calcium green dextran; their photoreleasing elicited nuclear calcium spikes which, in the case of cADPr, had repetitive behaviour. The spikes were abolished by the nuclear injection of antagonists or antibodies to the InsP3 or cADPr-sensitive Ca2+ channels. cADPr-modulated channels were localized on the membranes of the nuclear envelope using specific antibodies conjugated with IgG-gold complexes.