INSULIN AND IGF-I SIGNALING IN OOCYTE MATURATION

Xenopus laevis oocytes possess insulin and/or insulin-like growth fact or-1 (IGF-1) receptors and respond to respective hormones by increasin g glucose transport and progressing from the G(2) to M phase of the ce ll cycle (maturation). While molecular transduction mechanisms involvi ng mitogen-activating kinases and cyclin-dependent kinases begin to be elucidated, missing links remain between the initial receptor tyrosin e phosphorylation events and downstream signaling. The discovery that phosphotyrosines produced by receptor autophosphorylation or during su bstrate phosphorylation serve as an anchor for src homology 2 domains of several signaling proteins had a major impact on understanding how cytoplasmic enzymes are recruited at the level of the plasma membrane for subsequent activation.