CDK4 and diabetes mellitus: Because p16 and cyclin D/Cdk4 complexes are known to regulate proliferation of pancreatic islet cell progenitors (Tsutsui et al., 1999; Krishnamurthy et al., 2006) and p16 was strongly expressed in islets of CAG-rtTA3 mice (Fig. S14, Supporting information), we tested CAG-rtTA3:TetOp-16 mice treated with Dox d20-40 for diabetes.