Y. Gotoh et al., INITIATION OF XENOPUS OOCYTE MATURATION BY ACTIVATION OF THE MITOGEN-ACTIVATED PROTEIN-KINASE CASCADE, The Journal of biological chemistry, 270(43), 1995, pp. 25898-25904
Mitogen-activated protein kinase (MAPK) and MAPK kinase (MAPKK) are ac
tivated during Xenopus oocyte maturation concomitant with the activati
on of maturation promoting factor (MPF). We reported previously that a
n anti-MAPKK neutralizing antibody inhibited progesterone- or Mos- ind
uced initiation of oocyte maturation. Here, we show that injection of
CL100 (also called MAPK phosphatase-1) into immature oocytes inhibited
progesterone-induced oocyte maturation as well as MAPK activation and
that injection of mRNA encoding a constitutively active MAPKK induced
activation of histone H1 kinase and germinal vesicle breakdown in the
absence of progesterone. Injection of recombinant STE11 protein (a ye
ast MAPKK kinase) also induced initiation of oocyte maturation. These
data support the idea that the MAPKK/MAPK cascade plays an important r
ole in oocyte maturation. Interestingly, injection of the active MAPKK
mRNA or the STE11 protein resulted in induction and accumulation of M
os protein. Furthermore, in the presence of cycloheximide, the STE11-i
nduced activation of MPF as well as the induction and accumulation of
Mos was blocked, and the activation of MAPK was greatly reduced. The i
ncrease in Mos protein and the activation of MAPK by injecting cyclin
A protein into immature oocytes were both blocked also by cycloheximid
e treatment. These results are consistent with an idea that there may
exist a positive feedback loop consisting of Mos, the MAPKK/MAPK casca
de, and MPF, which may be important for the initiation of oocyte matur
ation induced by progesterone.