IGFBP1 Increases β-cell Regeneration by Promoting α- to β-cell Transdifferentiation (2016)
Figure 2

Figure 2. Igfbp1a’s effect on β-cell regeneration is specific and functionally relevant.

(A-C) Igfbp1a promotes β cell regeneration, rather than β cell survival. To trace β cells, we exposed Tg(ins:kaede) larvae to UV light (which causes the existing Kaede protein to switch from emitting green fluorescence to emitting red fluorescence) just before ablating the β cells by MTZ treatment from 3-4 dpf. After regeneration, the newly formed β cells are green, whereas the β cells that survived ablation are yellow (overlap of green and red). (A&B) Representative confocal images at 6 dpf of control and bactin:igfbp1a-overexpressing Tg(ins:kaede);Tg(ins:CFP-NTR) transgenic larvae; arrows indicate surviving (yellow) β cells. Scale bars: 10 μm. (C) Quantification of β cell regeneration (green bars) and β cell survival (yellow bars) per larva at 6 dpf. ***P<0.001: n=20 larvae in the control group; n=27 larvae in the bactin:igfbp1a-overexpressing group. (D-F) Igfbp1a does not promote δ-cell regeneration. We treated control and bactin:igfbp1a-overexpressing Tg(sst:flag-NTR);Tg(sst:dsRed) larvae with MTZ from 3-4 dpf to ablate δ cells, and then allowed them to regenerate until 6 dpf. (D&E) Representative confocal images at 6 dpf of control and bactin:igfbp1a-overexpressing larvae showing comparable number of δ cells after 2 days of regeneration. Scale bars: 15 μm. (F) Quantification of the total number of δ cells per δ-cell ablated larva at 6 dpf compared to the baseline number of δ cells in non-ablated control larvae. P=0.2325. n=13 in the control group, n=7 in the bactin:igfbp1a group. (G) Other Igfbps do not promote β-cell regeneration. We injected Tg(ins:kaede);Tg(ins:CFP-NTR) transgenics with either transposase mRNA (control; n=31) or transposase mRNA + one of six different igfbps, igfbp2a (n=25), igfbp2b (n=25), igfbp3 (n=26), igfbp5a (n=17), igfbp6b (n=34), and igfbp7 (n=17), treated them with MTZ from 3-4 dpf to ablate their β cells, and then quantified their β cells after 2 days of regeneration, at 6 dpf; ns=nonsignificant; (igfbp2a P=0.986, igfbp2b P=0.037, igfbp3 P=0.979, igfbp5a P=0.999, igfbp6b P=0.997, and igfbp7 P=0.999). (H) Tg(pcsk1:GFP) is expressed in regenerating β cells within the islet (arrowheads), but not outside the islet (arrow), at 6 dpf in larvae overexpressing igfbp1a. Scale bar: 15 μm. (I&J) Free-glucose levels during β-cell regeneration in control (bactin:mCherry) and bactin:igfbp1a-overexpressing Tg(ins:kaede);Tg(ins:CFP-NTR) larvae (I), as well as in Tg(ins:kaede);Tg(ins:CFP-NTR) larvae injected in the pericardial sac at 4 dpf with 1 ng of recombinant mouse Igfbp1 (J). We treated larvae with MTZ from 3-4 dpf to ablate their β cells, and monitored their free-glucose levels at 3-7 dpf. Free-glucose levels were significantly lower after genetic igfbp1a overexpression or Igfbp1-protein injection (red lines) than in controls (black lines) at 7 and 6 dpf, respectively. Baseline reference levels of free glucose throughout development are shown for a different set of larvae without β-cell ablation. n=24 larvae (four pools of six larvae) per data point.