CELL-CYCLE CALCIUM TRANSIENTS DRIVEN BY CYCLIC CHANGES IN INOSITOL TRISPHOSPHATE LEVELS

TRANSIENT changes in intracellular calcium ([Ca2+](i)) have been shown to punctuate the cell cycle in various types of cells in culture(1-5) and in early embryos(6-12). The [Ca2+](i) transients are correlated w ith cell-cycle events: pronuclear migration, nuclear envelope breakdow n, the metaphase-anaphase transition of mitosis, and cytokinesis. Mito tic events fan be induced by injecting calcium and prevented by inject ing calcium chelators into the sea urchin embryo(10,13). Cell-cycle ca lcium transients differ from the transients linked to membrane signal transduction pathways: they are generated by an endogenous mechanism, not by plasma membrane receptor complexes, and their trigger is unknow n. We reporthere that the phosphoinositide messenger system oscillates during the early embryonic cell cycle in the sea urchin, leading to c yclic increases in inositoltrisphosphate that trigger cell-cycle [Ca2](i) transients and mitosis by calcium release from intracellular stor es.