FIG. 5.

β-Cell mass failed to expand in response to exendin-4 treatment in Bmi1^−/− mice. A: Protein levels of Bmi1 and p16 in isolated islets from 6-week-old wild-type and Bmi1^−/− mice. Data were representative of pooled islets from three experiments with 3–5 mice per group. B: Protein levels of Bmi1 and p16 in Min6 cells transfected with Bmi1 fused with an NH₂-terminal myc tag. C: Schematic representation of the Ink4a/Arf locus, with blue regions, marked 1–4, indicating the amplified regions in the ChIP studies (top panel) and ChIP analysis for the indicated antibodies at the Ink4a/Arf locus in islets isolated from wild-type (WT) and Bmi1^−/− mice (4 weeks old) (bottom panel). On the x-axis, “5” indicates binding for the negative control corresponding to exon 2 in the Hox C13 locus. P values were determined by unpaired Student's t test. D and E: Analysis of β-cell mass (D) and β-cell proliferation (E) of wild-type and Bmi1^−/− mice after seven constitutive days' injection of exendin-4. Values are representative of 5–6 slides spanning the whole pancreas of each mouse and three mice per group. Error bars indicate ± SE. *P < 0.05; **P < 0.005. Tub, β-tubulin.