Islet morphology and electron microscopy. (a) Sections of pancreas were stained for non–β cells using a cocktail antibody as described in Methods. Representative sections of pancreas from WT and IRS-1^–/– mice show an approximately 2-fold increase in islet size in the latter. (b) Representative section of pancreas from an IRS-1^–/– mouse stained for insulin as described in Methods shows insulin staining of β cells in the islets. Spotty insulin staining can be observed throughout the exocrine pancreas, indicating the presence of insulin-containing cells. (c) Electron microscopic examination of β cells in islets from IRS-1^–/– mice was performed as described. A scant electron dense granulation pattern was observed in IRS-1^–/– β cells compared with WT cells. An increased number of autophagic vacuoles (arrows) were observed in individual IRS-1^–/– β cells. A representative photograph is shown. ×9,690.