OSCILLATION OF INOSITOL POLYPHOSPHATES IN THE EMBRYONIC CLEAVAGE CYCLE OF THE XENOPUS-LAEVIS

Evidence suggests that a transient increase in intracellular calcium ([Ca2+](i)) is an important modulator during the cell division cycle in early embryos. We have recently shown that inhibition of Ins(1,4,5)P-3-induced Ca2+ release in the cleaving Xenopus embryos greatly lengthens the cell cycle duration. In this report, we have directly measured the changes of Ins(1,4,5)P-3 content during the first two cleavage cycles in the Xenopus embryos. HPLC profiles of cell extracts from dividing embryos show oscillations of inositol polyphosphates throughout the cleavage cycle with a transient production of Ins(1,4,5)P-3 by the time of cleavage furrow completion. In addition, cyclic changes in inositol phospholipids, phosphatidylinositol 4,5-bisphosphate (PIP2) and phosphatidylinositol 4-phosphate (PIP) were detected during the cleavage cycle. These data strongly suggest the involvement of PIP2 turnover and periodic increase in Ins(1,4,5)P-3 triggers [Ca2+](i) transients during the early embryonic cell cycle in the Xenopus. (C) 1995 Academic Press, Inc.