REGULATION OF NUCLEAR-ENVELOPE ASSEMBLY DISASSEMBLY BY MAP KINASE

Mouse eggs arrested in metaphase II display high levels of cdc2/cyclin B1 and MAP protein kinase activities. Following fertilization there i s a time-dependent decrease in the activity of each of these protein k inases. The decline in cdc2/cyclin B1 protein kinase correlates with t he resumption of meiosis and the emission of the second polar body and precedes the decline in MAP kinase activity, which correlates tempora lly with the formation of the male and female pronuclear envelopes. Th ese results suggest that high levels of MAP kinase activity are incomp atible with the presence of a pronuclear envelope. To test this possib ility, we expressed in mouse eggs a constitutively active form of MAP kinase kinase (MEK) whose only known target is p42/p44 MAP kinase. We show that following fertilization cdc2/cyclin B1 kinase activity decli nes and a second polar body is emitted. The endogenous MAP kinase rema ins active, however, and no pronuclear envelopes form. Thus, high leve ls of MAP kinase activity by itself in mouse eggs appear incompatible with the presence of a pronuclear envelope. (C) 1996 Academic Press, I nc.