A study of the induction of cell division in amphibian oocytes by insulin

Abstract

Ripe Xenopus oocytes, 1.4 mm in diameter, arrested in prophase of meiosis I undergo meiotic cell division in vitro upon exposure to insulin. The role of insulin binding in mediating the response of the oocyte has been investigated. Scatchard analysis of specific insulin binding to oocytes revealed curvilinear kinetics with a K D of 1.4 n M and 4 × 10 7 receptors per oocyte for the high-affinity component. However, the EC 50 for induction of cell division by insulin was 12 n M in the presence of 10 mg/ml bovine serum albumin. Oocytes treated with Pronase to remove all residual follicle cells still responded to sodium insulin, indicating induction occurred at the level of the oocyte. Using high levels of human anti-insulin receptor antibody, which was demonstrated to bind specifically to the oocyte, 50% of specific insulin binding was prevented. Under these conditions, neither the dose-response curve for induction of cell division by insulin nor the time course was changed by the presence of antireceptor antibody. Other studies demonstrate that pure insulin-like growth factor can induce cell division in oocytes. These results indicate that the induction of cell division in amphibian oocytes by insulin is not mediated by the high-affinity component of insulin binding and may involve interaction of insulin with insulin-like growth factor receptors.