Cyclin D2 expression during pancreatic development. We carried out RT-PCR on RNA isolated from embryonic pancreata and stained pancreatic sections from various ages (as indicated) with anti_glucagon (green), anti_insulin (green), and anti_D-cyclin (red; as indicated) Ab’s. (A) Expression of cyclins D1, D2, and D3 in the developing pancreas by RT-PCR. RNA was isolated from E12.5 pancreata. (B) Cyclin D2 (cyc D2) expression in progenitor cells during early embryonic development. At E11.5, epithelial progenitor cells but not differentiated cells express cyclin D2. The dorsal pancreatic bud is outlined. At this stage, cyclin D2 expression is restricted to the epithelium and is not observed in the mesenchyme. (C) At P4, cyclin D1 (cyc D1) expression is not observed in the pancreas. (D) Cyclin D3 (cyc D3) is expressed in the exocrine and ductal (arrow) tissue but excluded from the endocrine pancreas. (E) Cyclin D2 is expressed throughout the pancreas at P4. Costaining with insulin Ab shows that cyclin D2 is expressed in the islets. At this stage, 34.5% ± 2.0% of islet cells express cyclin D2. (F) Higher magnification of an islet from E showing cyclin D2 expression is localized to the nucleus of β cells (arrows). (G) Cyclin D2 continues to be expressed in the endocrine pancreas at P7 (33.2% ± 4% of islet cells) and in the ductal tissue (arrow). (H) By P14, few cells in the endocrine pancreas express cyclin D2 (11.3% ± 1.4% of islet cells). Exocrine and ductal tissues do not show any expression of cyclin D2 at this stage.