The meiotic division in oocytes is arrested in the G2 phase of the cell cyc
le. Resumption of meiosis, also known as oocyte maturation, entails a G2 to
M transition. At the G2-M boundary, maturation promoting factor (MPF) acti
vation is usually induced via several ways, including tyrosine dephosphoryl
ation of p34(cdc2) and synthesis of cyclin B according to cell type and spe
cies. Previous studies in our laboratory demonstrated that glucocorticoids
directly inhibit the meiotic maturation of pig oocytes in vitro. The aim of
this study was therefore to investigate the influence of glucocorticoids o
n the expression of p34(cdc2) and cyclin B1 in resumption of meiosis of pig
oocytes. We detected the relative levels and association of p34(cdc2) and
cyclin B1, Isolated cumulus-enclosed oocytes were cultured in Waymouth MB75
2/1 medium supplemented with sodium pyruvate (50 mu g/ml), LH (0.5 mu g/ml)
, FSH (0.5 mu g/ml), and estradiol-17 beta (1 mu g/ml) in the presence or a
bsence of dexamethasone (DEX) for 24 hr; they then were cultured without ho
rmonal supplements in the presence or absence of DEX for an additional 24 h
r. We found that cyclin B1, as well as p34(cdc2), was already present in fu
lly grown G2-arrested pig oocytes when removed from the follicle, In these
oocytes, cyclin B1 and p34(cdc2) were already associated in complex. Treat
ment with DEX at concentrations of 1 mu g/ml or above decreased the level o
f cyclin B1, but had no effect on the level of p34(cdc2), Th, exposure of o
ocytes to DEX also decreased the amount of complexed p34(cdc2)-cyclin B1, T
hese findings suggest that the inhibitory action of DEX on meiotic maturati
on could be due, at least in part, to the reduced amount of p34(cdc2)-cycli
n B1 complex, (C) 2000 Wiley-Liss, Inc.