A positive regulatory role for PIP3 in egg activation signal ing has been suggested by the finding that bp, a potent inhibitor U0126 cost for PTEN phosphoinositide phosphatase, pro motes tyrosine phosphorylation of Src and cortical con traction of Xenopus eggs. The results indicate that the elevation of PIP3 levels in eggs is sufficient for promoting Src dependent signal transduction for egg acti vation. We demonstrated that, in fertilized eggs, Akt was Inhibitors,Modulators,Libraries phos phorylated at Thr308. However, we did not detect the phosphorylation of another well known site, Ser473. This could be because the phosphoSer473 specific antibody employed in this study was not suitable for analysis of the Xenopus Akt protein.

However, immunoblotting has dem onstrated that the phosphoSer473 specific antibody well recognizes Akt protein in immature Xenopus oocytes and that the phosphoSer473 signals become decreased in pro gesterone treated, fully matured oocytes. Therefore, we suggest that fertilization Inhibitors,Modulators,Libraries promotes the phosphorylation of Akt selectively Inhibitors,Modulators,Libraries at threonine 308. In mammals, phosphorylation of Akt Thr308 and Ser473 is catalyzed by phosphoinositide dependent protein kinase Inhibitors,Modulators,Libraries PDK1 and mammalian target of rapamycin mTOR, respectively. So, we assume that the signaling pathway involving PDK1, not mTOR, operates to promote the phosphorylation and activation of Akt in fertilized eggs. Several cellular Inhibitors,Modulators,Libraries functions involve the activation of Akt. Of particular interest is the anti apoptotic func tion of Akt. Our preliminary experiments have shown that a caspase like protease is activated in eggs left unfertilized for several hours.

The results sug gest that fertilization is responsible for suppression of the caspases activation. Therefore, our future efforts will be directed at examining whether an anti apoptotic mecha nism is really operating in fertilized eggs and, if so, to clar ify how and where Akt is involved in this cellular function. Several studies have focused on the roles selleck chemicals llc of sperm associ ated PI 3 kinase in mammalian species. In human sperm, LY294002 blocks the acrosome reaction and enhances motility, but does not affect egg sperm interaction. More recently, Jungnickel et al. dem onstrated that in the mouse, the zona pellucida glycopro tein 3 induced acrosome reaction involves the PIP3 dependent activation of Akt. These results suggest that PI 3 kinase is required for Ca2 signaling in fertilizing sperm. In Xenopus, however, no information has yet been availa ble for the role of PI 3 kinase and/or Akt in the acrosome reaction or other fertilization related functions of sperm.