Figure 3.

YY1 regulates glucose homeostasis in adult β-cells. (A) Schematic diagram showing the experimental strategy using adult Pdx1^CreERT/+;Yy1^fl/fl mice. Tam was administered within 2 weeks and analyses were performed at 2 weeks after Tam treatment; this was the washout period. (B) Western blotting showing a significant reduction in islet YY1 expression in Pdx1^CreERT/+;Yy1^fl/fl compared with Yy1^fl/fl (control) mice at 2 weeks after Tam administration. Data are presented as mean ± SEM; **P < 0.01; n = 9 mice per group; islets of three pancreata were pooled for each band. (C) Immunostaining of frozen pancreatic sections for GCG (green), INS (green), or SST (green) and YY1 (red) with nuclear Hoechst counterstain (blue) at 2 weeks after Tam treatment showing specific knockout of YY1 in INS⁺ β-cells. Scale bars: 100 μm. (D) Quantification of (C) showing at least 90% of INS⁺ β-cells were YY1 deficient. Data are presented as mean ± SEM; ***P < 0.001; n = 9 mice per group. (E–H) The physiological change in mice was recorded in terms of (E) body weight, (F) fed blood glucose levels, (G) fasting blood glucose levels, and (H) glucose tolerance test at 2–12 weeks after Tam treatment, showing the onset of hyperglycemia and impaired glucose tolerance after β-cell loss of YY1. Data are presented as mean ± SEM; *P < 0.05, **P < 0.01, ***P < 0.001 compared with the control group; ##P < 0.01, ###P < 0.001 compared with other time points; n = 7 mice in the control group and n = 7–13 mice in the cKO group. (I) Immunostaining of frozen pancreatic sections for INS (green) with nuclear Hoechst counterstain (blue) at 2 and 6 weeks after Tam administration, respectively. Scale bars: 2,000 μm. (J) Quantification of (I) showing significantly reduced β-cell mass at 2 and 12 weeks after Tam administration, respectively. Data are presented as mean ± SEM; *P < 0.05, **P < 0.01; n = 3–4 mice per group.