Phosphorylation of MAP kinase and p90rsk and its regulation during in vitro maturation of cumulus-enclosed rabbit oocytes
Numerous studies have demonstrated that activation of the mitogen-activated protein (MAP) kinase is involved in the maturation of oocytes. In this study, the expression and phosphorylation of MAP kinase and p90rsk, one of the substrates of MAP kinase, during rabbit oocyte maturation were studied. The results showed that MAP kinase phosphorylation began to occur after germinal vesicle breakdown (GVBD) and the active form was maintained until metaphase II. p90rsk was also activated after GVBD following MAP kinase activation. Immunofluorescent analysis showed that p90rsk was enriched in the nuclear area after GVBD and was gradually localised to the spindle. When GVBD was inhibited by increased cAMP or decreased protein kinase C activity, the phosphorylation of both MAP kinase and p90rsk was blocked. Our data suggest that (1) MAP kinase/p90rsk activation is not necessary for GVBD, but plays an important role in the post-GVBD events including spindle assembly in rabbit oocytes; and (2) MAP kinase/p90rsk activation is down-regulated by cAMP and up-regulated by protein kinase C in cumulus-enclosed rabbit oocytes.(Received June 17 2002)
(Accepted July 27 2002)
Key Words: MAP kinase; Microtubule; Oocyte; p90rsk; Rabbit.
c1 All correspondence to: Qing-Yuan Sun, State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100080, P.R. China. Tel: +86 10 62563923. Fax: +86 10 62565689. e-mail: email@example.com or firstname.lastname@example.org