The ectopic expression of Pax4 in δ cells results in islet hypertrophy and islet neogenesis. (A–D) Representative photographs of immunofluorescence analyses on pancreas sections of 2- (B), 5- (C), and 8-mo-old (D) transgenic and control pancreata (A) showing a dramatic increase in islet number and size. (E–J) Quantitative analyses of four animals from each group revealed an ∼1.5× increase in islet size (F) and an ∼2× increase in islet number (E) in 2-mo-old transgenic pancreata. Quantitative analyses of insulin⁺ area in 2-mo-old mice outlined an ∼4× increase, consistent with the observed increase in islet number and counts (G). At 5 and 8 mo of age (n = 7 and n = 5, respectively), a mean of 3×, 2×, and 8× increase in islet counts (E), size (F), and insulin⁺ area (G), respectively, was quantified in Sst-Cre::Pax4-OE pancreata as compared with age-matched controls. Quantification of insulin⁺ cell proportions within hypertrophic islets demonstrated an increase in 2- and 5-mo-old transgenic animals (n = 6) compared with controls (n = 7; H). Quantification of islet glucagon⁺ cell content in 2- and 5-mo-old mutant islets did not reveal any differences compared with controls (n = 7; I). A significant decrease in somatostatin⁺ proportions was observed in 2- and 5-mo-old mutant islets compared with controls (n = 7; J). All values are depicted as mean ± SEM. Statistics were performed with the Mann–Whitney test or unpaired t test with Welch’s correction. ***, P < 0.001; **, P < 0.01; *, P < 0.05. Bars, 500 µm. INS/Ins, insulin.