Fig. 4

Ablation and recovery of pancreatic β-cells in zebrafish larvae. A,B: Confocal projections of 96 hours postfertilization (hpf) Tg(ins:CFP-NTR)^s892 principle islets from larvae treated for 12 hr with dimethyl sulfoxide (DMSO) control (A) or Metronidazole (Mtz; B) and immunostained for CFP (cyan) and activated Caspase-3 (red). A: Caspase-3 staining is not observed in Cyan Fluorescent Protein-Nitroreductase-positive (CFP-NTR⁺) β-cells in DMSO-treated larvae. B: Strong staining for activated Caspase-3 and rounded β-cell morphology are seen in β-cells of Mtz-treated larvae (for clarity, A′ and B′ show only the Caspase-3 red channel fluorescence). C-H: Isolated pairs of Tg(ins:CFP-NTR)^s892 larvae monitored during the course of DMSO control (C,E,G) or Mtz prodrug treatment (D,F,H) by combined brightfield/ fluorescence microscopy (scale bars = 250 μm). Inset images are confocal projections of the pancreatic islet of similarly treated sibling larvae, which have been immunostained for Insulin (green) and Glucagon (red; scale bars = 50 μm). C,D: Untreated 84 hpf Tg(ins:CFP-NTR)^s892 larvae show strong CFP-NTR expression in the pancreatic islet (arrows). E,F: 110 hpf Tg(ins:CFP-NTR)^s892 larvae, 26 hr after addition of 0.1% DMSO vehicle or 5 mM Mtz in 0.1% DMSO. E: Islet development appears unaffected after exposure to DMSO (arrows); a centralized "core" of Insulin⁺ β-cells is enveloped by a shell of Glucagon⁺ α-cells (inset). F: After exposure to Mtz, the majority of β-cells have been ablated (asterisks). The surrounding α-cells appear to collapse into the resulting void, forming a more condensed mass; remaining β-cells are clustered nearest the extrapancreatic duct (inset, arrowhead). G,H: 145 hpf Tg(ins:CFP-NTR)^s892 larvae, 35 hr after washout of DMSO or Mtz. G: Pancreatic islet size and structure appears unaffected in DMSO (26 hr) /wash (35 hr) larvae (arrows and inset). H: Significant recovery of β-cell mass is evident in Mtz (26 hr) per wash (35 hr) larvae. Insulin⁺ β-cells repopulating the islet surround a centralized mass of Glucagon⁺ α-cells: an architecture inverse to the original one.