Fig. 3. Quantitative effects of ectopic Notch activation on endocrine and exocrine differentiation in explant cultures of E10.5 dorsal pancreatic buds. The frequency of endocrine and exocrine differentiation was determined by direct counting of GFP-positive epithelial cells in epithelial buds infected with lentiviral vectors encoding either GFP alone, GFP and Hes1, or GFP and Notch1-IC. Top, graphical representation depicting frequency of amylase, insulin, glucagon, nestin and Ptf1-P48 expression in cells infected with indicated vector. Y-axis indicates fraction of GFP-positive, E-cadherin-positive epithelial cells expressing given marker. Bottom, numerical data generated by direct cell counts. Values indicate mean (%)±s.e.m. (bold), as well as corresponding absolute cell counts. Both acinar and beta cell differentiation are prevented by Notch pathway activation, reflected by significant reductions in the frequency of cells expressing either amylase or insulin following infection with either GFP;Hes1 or GFP;Notch1-IC compared with GFP alone. In contrast, the frequency of cells expressing glucagon, nestin or Ptf1-P48 are affected to lesser degrees. Asterisks indicate P<0.05 compared with GFP alone, as determined by two-sample Z-test.