REQUIREMENT FOR MAPK ACTIVATION FOR NORMAL MITOTIC PROGRESSION IN XENOPUS EGG EXTRACTS

The p42 mitogen-activated protein kinase (MAPK) is required for progre ssion through meiotic M phase in Xenopus oocytes. This report examines whether it also plays a role in normal mitotic progression. MAPK was transiently activated during mitosis in cycling Xenopus egg extracts a fter activation of the cyclin-dependent kinase Cdc2-cyclin B. Interfer ence with MAPK activation by immunodepletion of its activator MEK, or by addition of the MEK inhibitor PD98059, caused precocious terminatio n of mitosis and interfered with production of normal mitotic microtub ules. Sustained activation of MAPK arrested extracts in mitosis in the absence of active Cdc2-cyclin B. These findings identify a role for M EK and MAPK in maintaining the mitotic state.