β-cell Markers and Insulin Secretion in 6-month-old B-Cyb5r3 Mice. Immunostaining of pancreas sections from 6-month-old female B-Cyb5r3 vs. RIP-Cre+ control mice. (A) Insulin (red), Glucagon (green), Somatostatin with Pancreatic Polypeptide (SMS + PP) (blue), and DAPI (white). (B) Insulin (red), Glut2 (green), and DAPI (blue). (C) Insulin (red), MafA (green), and DAPI (blue). (D) Insulin (red), Cyb5r3 (green), Pdx1 (blue), and DAPI (white). (E) FoxO1 (green) and DAPI (blue) (n = 3 per group). (F) Glucose- and (G) secretagogue-stimulated insulin secretion in B-Cyb5r3 vs. RIP-Cre+ islets (n = 4 samples each containing five islets from three mice for GSIS). (G) Mitochondrial respiration in B-Cyb5r3 vs. RIP-Cre+ islets. Vertical lines indicate timing of addition of glucose (25 mM), Oligomycin (ATP synthase inhibitor), FCCP (uncoupler), and rotenone (complex I inhibitor). Islets from five mice were pooled in n = 9 wells per genotype, with each well containing 70 islets. All data are presented as means ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001 by Student t test.