VAMP4 KO mice show a normal pancreatic morphology but increased insulin levels. (A) Representative H&E staining of the pancreas from WT and KO mice at 14 wk of age. Scale bars, 500 μm. (B) Representative confocal images of costaining for insulin (red) and glucagon (green) in islets isolated from WT and KO mice. The nuclei of cells were stained with DAPI (blue). Scale bars, 10 μm. (C and D) Islet-to-pancreas area percentage (D) and islet density in the pancreas (C) from WT and KO mice quantified by H&E staining of the pancreas shown in A. (E–H) The percentage of β cells among total cells (E), ratio of β cells to α cells (F), and density of β cells (G) and α cells (H) in islets from WT and KO mice were quantified by immunofluorescence staining, as shown in B. (I and J) Quantification of the mean fluorescence intensity of insulin (I) and glucagon (J) in islets from WT and KO mice based on the immunofluorescence staining results shown in B. The data used for the analysis in C–J were based on 20 islets counted per pancreas. n = 3, 1 female and 2 male mice at 14 wk of age. Immunofluorescence images were captured by confocal microscopy with a 40× (NA = 1.30) oil objective at room temperature. The data are presented as the mean ± SEM. ****, P < 0.0001. The statistical analyses were performed with two-tailed unpaired Student’s t test (C–J).