We use in vivo models to study how insulin-secreting cells can duplicate themselves during normal growth and in response to increased metabolic demand for insulin. We are interested in understanding which cell cycle molecules promote and inhibit beta cell replication. We seek to manipulate the expression of these molecules to induce the expansion of beta cells in vivo and ex vivo. This knowledge could prove to be key in designing methods to induce beta cell replication in islets prior to transplantation.