POSITIVE FEEDBACK BETWEEN MAP KINASE AND MOS DURING XENOPUS OOCYTE MATURATION

Mos is a serine-threonine protein kinase and a key regulator of meiosi s. One function of Xenopus Mos is to activate mitogen-activated protei n kinase (MAPK) through direct phosphorylation and activation of MAPK kinase (MAPKK). All three members of this signal cascade can individua lly induce hormone-independent reentry of oocytes into meiosis I. Howe ver, their inducing efficiency is reduced in the absence of protein sy nthesis. Here we show that de novo Mos synthesis is required for induc tion of meiosis I by active MAPKK or Mos-MAPK coinjection. In addition , MAPK efficiently phosphorylates Mos at Ser-3 in vitro. These results suggest that a positive feedback loop exists between MAPK and Mos dur ing oocyte maturation. De novo synthesis of Mos, and other proteins, i s required for progression from meiosis I to the metaphase arrest at m eiosis II; therefore, one function of MAPK during normal Xenopus oocyt e maturation might be to stimulate the synthesis or accumulation of Mo s that is required for the completion of meiosis. (C) 1996 Academic Pr ess, Inc.