Loss of pdx1 in the β cell lineage results in increased proliferation of glucagon+ cells and decreased proliferation of insulin+ cells. Co-labelling of e17.5 and e18.5 pancreatic sections for either glucagon (green, A–C) or insulin (green, D–F) and phospho-histone H3 (red, A–F) reveals that in pdx1ΔE2β animals, the fraction of proliferating α cells is increased at e17.5 (compare arrowheads in A with B,C), while the proportion of insulin-expressing β cells actively proliferating is dramatically decreased at e18.5 (compare arrowheads in D with E,F). No difference was observed at e14.5 (not shown).