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A ROLE FOR AMP-ACTIVATED PROTEIN KINASE IN MEIOTIC INDUCTION IN MOUSE OOCYTES.
Downs, Stephen1, 1
ABSTRACT- In mammalian oocytes, a decrease in cAMP, brought about by the action of cAMP phosphodiesterase (PDE), is thought to initiate germinal vesicle breakdown (GVB) by the inactivation of cAMP-dependent protein kinase. However, the product of PDE activity, 5'-AMP, is a potent trigger of an important regulatory enzyme, AMP-activated protein kinase (AMPK). The aim of this study was to evaluate a possible role for AMPK in meiotic induction, using oocytes obtained from eCG-primed, immature mice. When 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR), an activator of AMPK, was tested on 17-18-h cultures of denuded oocytes (DO) and cumulus cell-enclosed oocytes (CEO) maintained in meiotic arrest by dbcAMP or hypoxanthine, GVB was dose-dependently induced. Meiotic induction by AICAR in dbcAMP-supplemented medium was initiated within 3 h in DO and 4 h in CEO. Four-hour cultures revealed that AICAR stimulated GVB in DO when meiotic arrest was maintained with dbcAMP, hypoxanthine, 8-AHA-cAMP, guanosine or milrinone, but was ineffective in olomoucine- or roscovitine-arrested oocytes, indicating that it acts upstream of maturation-promoting factor. Adenosine monophosphate also dose-dependently stimulated GVB in DO when meiotic arrest was maintained with dbcAMP or hypoxanthine. This effect was not mimicked by other monophosphate or adenosine nucleotides and was not affected by inhibitors of ecto-phosphatases. An uptake experiment using 3H-AMP showed that DO accumulated radiolabel, but a large portion of this uptake may require extracellular conversion to adenosine. Adenosine promoted meiotic induction in CEO when adenosine deaminase was inhibited with deoxycoformycin. Finally, pulsing DO with forskolin for 3 h led to meiotic induction in DO arrested with dbcAMP but not milrinone. It is concluded that culture conditions promoting AMP accumulation activate AMPK and lead to meiotic induction.
KEY WORDS: oocytes, meiotic induction, AMP-activated kinase, AICAR
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