CYCLOHEXIMIDE-INDUCED ACTIVATION OF MOUSE EGGS - EFFECTS ON CDC2 CYCLIN-B AND MAP KINASE-ACTIVITIES/

Fertilization of metaphase II-arrested mouse eggs results in resumptio n of meiosis and a decrease in both cdc2/cyclin B kinase and MAP kinas e activities; the decrease in cdc2/cyclin B kinase activity precedes t he decrease in MAP kinase activity. Cycloheximide treatment of metapha se II-arrested mouse eggs also results in resumption of meiosis but by passes the fertilization-induced Ca2+ transient. However, it is not kn own if cycloheximide treatment results in the same temporal changes in cdc2/cyclin B kinase and MAP kinase activities that are intimately as sociated with resumption of meiosis. We report that cycloheximide-trea ted mouse eggs manifest similar temporal changes in the decrease in bo th cdc2/cyclin B kinase and MAP kinase activities that occur following fertilization, although cortical granule exocytosis is not stimulated . The decrease in cdc2/cyclin B kinase activity, however, does not see m to be required for the decrease in MAP kinase activity, since the de crease in MAP kinase activity still occurs in cycloheximide-treated eg gs that are also incubated in the presence of nocodazole, which inhibi ts cyclin B degradation and hence the decrease in cdc2/cyclin B kinase . Following removal of these drugs, cdc2/cyclin B kinase activity rema ins high, MAP kinase activity increases to levels similar to that in t he metaphase II-arrested eggs, and a spindle(s) forms with the chromos omes aligned on a metaphase plate. Results of these experiments sugges t that some other protein with a relatively short half-life, e.g. c-no s, a known upstream activator of MAP kinase, may be responsible for ev ents leading to the decrease in MAP kinase activity.