RELEASE OF MOUSE EGGS FROM METAPHASE ARREST BY PROTEIN-SYNTHESIS INHIBITION IN THE ABSENCE OF A CALCIUM SIGNAL OR MICROTUBULE ASSEMBLY

Mouse egg activation, which includes release from meiotic metaphase II arrest, results from fertilization-induced increase in intracellular calcium concentration ([Ca2+](i)). However, during egg activation caus ed by exposure to the protein synthesis inhibitor, cycloheximide, [Ca2 +](i) did not change. Although eggs fertilized in the presence of micr otubule inhibitors remain arrested at metaphase, eggs treated for 32 h r with cycloheximide and the microtubule inhibitor, colcemid, formed n uclei. In untreated eggs aged in culture for 24 hr, the microtubule sp indles became deformed. These eggs formed nuclei after exposure to cyc loheximide, but not the calcium ionophore A23187. Our results indicate that eggs in which protein synthesis is inhibited are released from m etaphase without an increase in [Ca2+](i), and despite disruption of t he spindle. (C) 1995 Wiley-Liss, Inc.