Expression of cyclin D1 and D3 in WT and cyclin D2^–/– mice during postnatal development. (A and B) Sections from pancreata of 4-day-old WT and cyclin D2^–/– mice were stained with anti_cyclin D3 and anti_insulin Ab’s. (A) In P4 WT mice, cyclin D3 expression is observed in exocrine and ductal tissue but is not observed in the endocrine pancreas. Arrow indicates islet lacking cyclin D3 expression. (B) In cyclin D2^–/– littermates, cyclin D3 expression is observed in exocrine and ductal tissue (arrowhead) but not observed in the β cells. (C) Sections from pancreata of 4-day-old cyclin D2^–/– mice were stained with anti_cyclin D1 and anti_insulin Ab’s. Cyclin D1 expression is not observed in the β cells in cyclin D2^–/– mice. (D_F) Sections from pancreata of 14-day-old WT and cyclin D2^–/– mice are stained with anti_cyclin D1, anti_glucagon (D and E), and anti_insulin (F) Ab’s. (D) Cyclin D1 is not expressed in the pancreas from WT P14 mice. (E) Cyclin D1 expression is observed within islets in pancreata from cyclin D2^–/– littermates. Arrow indicates cyclin D1 expression within an islet of P14 cyclin D2^–/– pancreas. (F) Cyclin D1 expression is observed in the nuclei of insulin-positive cells. Arrow indicates cyclin D1 expression in a β cell of P14 cyclin D2^–/– pancreas.