The Potential Role of Protein Kinase B in Meiotic Induction of Mouse Oocytes

Britney Burger
Marquette University
Mentor: Dr. Stephen Downs

Mouse oocytes are arrested in Prophase I of Meiosis I due to high levels of Cyclic AMP (cAMP) until experiencing a hormonal surge by Gonadotropins which trigger the release of the oocytes from the ovaries and induce meiotic resumption.  Much work has been done to investigate the elements involved in regulating this meiotic induction in mouse oocytes, in hopes to establish a biochemical pathway by which these elements act to induce meiotic maturation.  Although the regulation of meiotic induction in mouse oocytes is still not fully understood, it has been established in our lab that a stress-related enzyme, AMP-activated protein kinase (AMPK), is present in mouse oocytes and that it plays a crucial role in the regulation of meiotic resumption.  Activation of AMPK by 5’AMP (a product of cAMP degradation), follicle stimulating hormone (FSH), a EGF-like protein Amphiregulin, heat stress, or the adenosine analog AICA riboside (AICAR), has been shown to induce resumption of meiosis in mouse oocytes.  Previous studies from other labs have suggested a potential role for Protein Kinase B in meiotic resumption.  They have implied that PKB is involved in CDK1 activation in mammalian oocytes.  It is still unclear, however, where PKB is situated in the pathway to meiotic induction.   This led us to our present study in which we examine the possible role of PKB in the meiosis-inducing action of AMPK.  LY294002 is an established specific inhibitor of the P13K pathway in which PKB is involved.  LY294002 was used in the following experiments to inhibit the action of PKB.  It was used to test whether it could (1) inhibit FSH-induced maturation in mouse oocytes; (2) Block heat stimulation of meiotic induction; (3) Inhibit the stimulation of meiotic resumption by Amphiregulin; (4) Block AICAR-induced maturation; and (5) Inhibit meiotic maturation by blocking C75 activation of Fatty Acid Oxidation, which is shown to activate meiotic induction somewhere downstream of AMPK. If by inhibiting the action of PKB in cultures supplemented with stimulators of AMPK, we could also inhibit maturation of oocytes, it could be suggested that PKB lies downstream of AMPK in the pathway to meiotic induction in mouse oocytes.  LY294002 was successfully able to block the meiotic induction of oocytes by inhibiting FSH, heat, Amphiregulin, and AICAR induced maturation.  The PKB inhibitor could not block meiotic induction by the Fatty Acid Oxidation activator, C75.  These results strongly implicate the involvement of Protein Kinase B in the meiosis-inducing action of AMPK and suggest that it is activated downstream of AMPK and upstream of Fatty Acid Oxidation.
 

<Summer Research Program Home