Fig. 4

Igfbp1a increases βcell regeneration by potentiating α to βcell transdifferentiation

A-E. Control and Tg(bactin:igfbp1a)overexpressing larvae were treated with MTZ from 3 to 4 dpf to ablate β cells and analyzed at 6 dpf, after 2 days of regeneration. Representative confocal images (A, B) of control and Tg(bactin:igfbp1a)overexpressing Tg(ins:dsRed);Tg(gcg:GFP);Tg(ins:FlagNTR) larvae. A bihormonal glucagon and insulinexpressing cell (gcg⁺;ins⁺) is indicated by an arrow. Representative confocal images (C, D) of control and Tg(bactin:igfbp1a)overexpressing Tg(gcg:GFP);Tg(ins:FlagNTR) larvae stained for Pdx1. Pdx1 and glucagonexpressing cells (pdx1⁺;gcg⁺) are indicated by arrows. Scale bars: 20 µm. (E) Quantification of gcg⁺;ins⁺ and pdx1⁺;gcg⁺ cells in the control and Tg(bactin:igfbp1a) group; ***P < 0.001, **P = 0.0012; n = 18 and 18 in the control groups, n = 15 and 10 in the Tg(bactin:igfbp1a) groups, for the gcg⁺;ins⁺ and pdx1⁺;gcg⁺ quantification, respectively.

F-I. Lineagetracing evidence supports α to βcell transdifferentiation. (F) Schema for temporal and spatial lineage tracing. loxPmediated excision of the STOP cassette permits heatinducible expression of the stable fusionprotein H2BGFP. Control and bactin:igfbp1aoverexpressing Tg(hsp:loxPmCherrySTOPloxPH2BGFP);Tg(gcg:CRE);Tg(ins:FlagNTR) larvae were first heatshocked at 3 dpf to label the glucagonexpressing cells with the stable fluorescent protein H2BGFP, thereafter treated with MTZ from 3 to 4 dpf to ablate the β cells, and analyzed at 6 dpf after 2 days of regeneration. Note that the temporal control of the lineage tracing is mediated by a heatshock. (G) Quantification of insulinexpressing cells that originate from α cells. Control larvae, n = 13; bactin:igfbp1a larvae, n = 16. **P = 0.0051. Representative confocal images (H, I) at 6 dpf (after 2 days of regeneration) of control and bactin:igfbp1aoverexpressing larvae stained for insulin, glucagon, topro, and H2BGFP. ins⁺;H2BGFP⁺ cells are indicated by the arrowheads, and H′ and I′ show staining against only insulin and H2BGFP. Moreover, most ins⁺;H2BGFP⁺ cells no longer express glucagon. Scale bars: 15 µm.