CALCIUM-INDEPENDENT, MEIOTIC SPINDLE-DEPENDENT METAPHASE-TO-INTERPHASE TRANSITION IN PHORBOL ESTER-TREATED MOUSE EGGS

Mouse eggs, arrested at metaphase II of meiosis, form pronuclei as a r esult of fertilization or exposure to parthenogenetic agents, such as the phorbol es ter phorbol myristate acetate (PMA). Exposure of eggs t o the microtubule inhibitor colcemid caused the disappearance of the m eiotic spindle and prevented the PMA-induced release from metaphase. H owever, colcemid- and PMA-treated eggs which lacked spindles formed nu clei when treated in addition with the protein synthesis inhibitor cyc loheximide or the protein kinase inhibitor 6-dimethlyaminopurine. To p revent an increase in intracellular calcium concentration ([Ca2+](i)), eggs were exposed to the cell permeant acetoxymethyl ester (AIM) form of the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N'N'-tetraa cetic acid (BAPTA). Nuclei formed in 45% of eggs treated with BAPTA AM and PMA and in 90% of eggs treated with BAPTA AM, PMA, and cyclohexim ide, suggesting that an increase in [Ca2+](i) is not necessary for the PMA-induced release from metaphase. The [Ca2+](i) did not change in e ggs which formed nuclei in response to PMA, providing additional evide nce that PMA activates eggs without elevating the [Ca2+](i). (C) 1995 Academic Press, Inc.