Insulin and IGF-1 signaling in oocyte maturation.

Xenopus laevis oocytes possess insulin and/or insulin-like growth factor-1 (IGF-1) receptors and respond to respective hormones by increasing glucose transport and progressing from the G2 to M phase of the cell cycle (maturation). While molecular transduction mechanisms involving mitogen-activating kinases and cyclin-dependent kinases begin to be elucidated, missing links remain between the initial receptor tyrosine phosphorylation events and downstream signaling. The discovery that phosphotyrosines produced by receptor autophosphorylation or during substrate 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.