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PKB/AKT is involved in resumption of meiosis in mouse oocytes
Author(s) -
Kalous Jaroslav,
Solc Petr,
Baran Vladimir,
Kubelka Michal,
Schultz Richard M.,
Motlik Jan
Publication year - 2006
Publication title -
biology of the cell
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.543
H-Index - 85
eISSN - 1768-322X
pISSN - 0248-4900
DOI - 10.1042/bc20050020
Subject(s) - germinal vesicle , protein kinase b , biology , cyclin dependent kinase 1 , microbiology and biotechnology , phosphorylation , centrosome , kinase , maturation promoting factor , oocyte activation , oocyte , biochemistry , cell cycle , apoptosis , embryo
Background information . In fully grown mouse oocytes, a decrease in cAMP concentration precedes and is linked to CDK1 (cyclin‐dependent kinase 1) activation. The molecular mechanism for this coupling, however, is not defined. PKB (protein kinase B, also called AKT) is implicated in CDK1 activation in lower species. During resumption of meiosis in starfish oocytes, MYT1, a negative regulator of CDK1, is phosphorylated by PKB in an inhibitory manner. It can imply that PKB is also involved in CDK1 activation in mammalian oocytes. Results . We monitored activation of PKB and CDK1 during maturation of mouse oocytes. PKB phosphorylation and activation preceded GVBD (germinal vesicle breakdown) in oocytes maturing either in vitro or in vivo . Activation was transient and PKB activity was markedly reduced when virtually all of the oocytes had undergone GVBD. PKB activation was independent of CDK1 activity, because although butyrolactone I prevented CDK1 activation and GVBD, PKB was nevertheless transiently phosphorylated and activated. LY‐294002, an inhibitor of phosphoinositide 3‐kinase—PKB signalling, suppressed activation of PKB and CDK1 as well as resumption of meiosis. OA (okadaic acid)‐sensitive phosphatases are involved in PKB‐activity regulation, because OA induced PKB hyperphosphorylation. During resumption of meiosis, PKB phosphorylated on Ser 473 is associated with nuclear membrane and centrosome, whereas PKB phosphorylated on Thr 308 is localized on centrosome only. Conclusions . The results of the present paper indicate that PKB is involved in CDK1 activation and resumption of meiosis in mouse oocytes. The presence of phosphorylated PKB on centrosome at the time of GVBD suggests its important role for an initial CDK1 activation.