Ki67, histone H3, and BrdU labeling of β cells. Adjacent 4-μm-thick pancreatic section from mice at E18.5, P10, P30, and P120 were costained with anti-insulin Ab’s (to identify β cells) and anti-Ki67, or anti-histone H3 or anti-BrdU Ab’s (to provide an index of proliferation). Positive cells were visually scored, and the number of Ki67-positive cells was plotted as a function of the number of histone H3–positive (upper panel) or BrdU-positive cells (lower panel). Regression analysis was performed using the Statsview software. r2 = 0.9 for the H3/Ki67 and 0.9 for the BrdU/Ki67 correlation (P < 0.0001).