Accumulation of c-FOS protein in the nuclei of primary beta cells upon metabolic stimulations. A) Islets were isolated, trypsin digested, cultured and serum deprived at low glucose concentration (1 mM) for 20 hours. After 60 minutes of co-stimulation with 10 nM GLP-1 and 15 mM glucose or 0.2 mM cpt-cAMP and 15 mM glucose, islets (50–100 per condition) were fixed and analyzed by immunofluorescence staining of c-FOS (green) and of insulin (INS, red); nuclei were stained with the DNA reactive DAPI dye (violet). Fluorescence images shown separately for each dye or merged (c-FOS/DAPI; c-FOS/INS) are representative of three different experiments. Bar: 50 μm. B) Islets were isolated, maintained and serum deprived at low glucose concentration (1 mM) for 20 hours, prior to co-stimulation with 10 nM GLP-1 and 15 mM glucose or 0.2 mM cpt-cAMP and 15 mM glucose. After 90 minutes of stimulation, islets (~800 per condition) were trypsin digested, nuclear extracts were prepared and c-FOS expression analyzed by western blotting. TFIIB was used as loading control.