αOGTKOmice show significant deficiency in islet glucagon content, single cell glucagon content, and in vitro glucagon secretion.In vitro glucose inhibited glucagon secretion in male mice (A), (n = 3 per group), islet glucagon content normalized by islet DNA content (B), and single α-cell glucagon content (C), (n = 4 per group). qPCR assessments of Arx (D), Nkx2.2 (E), FOXA2 (F), and Gcg (G) transcripts and western blot assessments (H, note that 4H and 5H are from the same western blot membrane, and thus, 4H actin is reused here) of FOXA2 (I), CPE (J), proglucagon (K) proteins from OSMI-treated αTC-1 cells treated with OSMI-1 inhibitor or DMSO (control) in 3 or 25 mM glucose for 24 h (n = 3). Immunoprecipitation of FOXA2, followed by immunoblot against O-GlcNAc (RL2) (L) and immunoprecipitation of O-GlcNAcylated proteins (via RL2 antibody), followed by immunoblot against FOXA2 (M) (n = 2 each).