Figure 5.

Transmission electron microscopy of islet cells from a 4-week-old male Ins2-proinsulin-R(B22)E homozygote (Hom), highlighting heterogeneity in the abundance of insulin secretory granules. A: Lower power view, with β-cells identified. The cell at the bottom and the two cells in the upper left corner exhibit glucagon secretory granules; random blood glucose (BG) was taken at the time of euthanasia. B: The yellow boxed area from A shown at higher power. Vesiculotubular clusters (VTCs) are a pre-Golgi compartment. A more detailed electron microscopy survey is presented in Supplementary Fig. 3. C: For each indicated genotype and diet, total β-cell granule numbers were counted per unit area (25-µm² boxed areas). Those with a classic electron-dense granule core were considered to be mature (green), and those lacking the classic electron-dense core were considered to be underfilled (red). Quantification compared HFD-fed (H) WT and heterozygous (Het) conditions and normal chow (N) diet–fed Het and Hom conditions. Data are mean ± SD. **P < 0.01, ****P < 0.0001. Mito, mitochondrion.