Loss of glucagon receptor function stimulates beta cell proliferation in a species-specific manner. (A) Beta cells stained for EdU to assess their proliferation in 5 dpf (days post-fertilization) wild-type (gcgr+/+, black bar) and gcgra/b−/− (abbreviated gcgr−/−, green bar) zebrafish (n = 8 per group, unpaired t test, ∗∗p < 0.01 versus gcgr+/+). (B) Beta cell number in 5 dpf gcgr+/+ (black bar) and gcgr−/− (green bar) zebrafish (n = 24–30 per group, unpaired t test, ∗∗∗∗p < 0.0001 versus gcgr+/+). (C) Beta cell number after knockdown of slc7a2 (+/+, black bar; −/−, green bar) in 5 dpf gcgr−/− zebrafish (n = 8–15 per group, unpaired t test, ∗∗∗∗p < 0.0001 versus slc7a2+/+). (D) Beta cell number in 6 dpf gcgr+/+ (black bar) and gcgr−/− (green bar) zebrafish after 3 days of treatment with PBS or RAPA (n = 6–7 per group, one-way ANOVA with Fisher's LSD, ∗∗∗∗p < 0.0001 versus PBS/gcgr+/+, ∗p < 0.05 versus PBS/gcgr−/−). (E) Representative images of pancreatic islet beta cell proliferation in 8 week treated IgG/GCGR-Ab-treated C57BL6 mice. Insulin (green), Ki67 (red), and DAPI (blue) are shown. White arrow indicates a Ki67+ insulin + cell. (F) Quantification of pancreatic islet beta cell proliferation in control IgG (black bar) and GCGR-Ab-treated (blue bar) mice (all males, unpaired t test, ∗∗p < 0.01 versus IgG). (G) Quantification of pancreatic islet beta cell proliferation in Slc7a2+/+ (black bars) and Slc7a2−/− (blue bars) IgG or GCGR-Ab-treated mice (n = 2–5 females and 3–6 males per group, one way ANOVA with Tukey's multiple comparisons test, ∗∗p < 0.0001 versus Slc7a2+/+ IgG, ∗∗∗p < 0.001 versus Slc7a2+/+ GCGR-Ab). (H) Schematic of approach for human islet subcapsular renal transplantation in NSG recipient mice followed by PBS or GCGR-Ab treatment. Created with BioRender.com (I) Representative images of beta cell proliferation in human islet grafts after 4 weeks of PBS or GCGR-Ab-treatment. Grafts were immunostained for insulin (green), Ki67 (red), and DAPI (blue). Dashed yellow lines indicate kidney-graft boundary. (J) Quantification of beta cell proliferation in transplanted human islets in PBS (black circles) or GCGR-Ab-treated (orange circles) mice (n = 2 female and 5 male donors [see Supplemental Table 1], unpaired t test, ∗p < 0.05 versus PBS).