Effects of Cdk4- or Cdk2-deficiency on proliferation of endocrine cells in Men1+/− and Men1+/+ pancreatic islets. (A) Immunohistochemistry for the proliferation marker Ki67 with pancreatic islets and tumors from 15-month-old mice with the indicated genotypes. (B) Percentages of Ki67+ cells in the following tissue groups: group 1, wild-type islets; group 2, Men1+/− islets with normal morphology; group 3, Men1+/− dysplastic/hyperplastic islets; group 4, Men1+/− islet adenomas; group 5, Men1+/−; Cdk4−/− islets; group 6, Men1+/−; Cdk2−/− islets with normal morphology; group 7, Men1+/−; Cdk2−/− dysplastic/hyperplastic islets; group 8, Men1+/−; Cdk2−/− islet adenomas; group 9, Cdk4−/− islets; group 10, Cdk2−/− islets. At least 1,000 cells were counted within each category. (C) The expression of CDK4 protein in pancreatic islets and tumors from 15-month-old mice with the indicated genotypes.