Fig. 4: Decreased insulin signalling predisposes α-cells to insulin production in islets with an intact β-cell mass.

a, Transgenes for α-cell tracing and insulin receptor (IR) and IGF1 receptor (IGF1R) downregulation in adult α-cells. b, Experimental design. c,d, Immunofluorescence on islets (c) and RT-qPCR of purified YFP⁺ α-cells from αIR/IGF1R KO mice (d). Impaired insulin/IGF1 signalling does not lead to insulin protein production but induces insulin, Pdx1 and Nkx6.1 gene expression. Black bars indicate mice with intact insulin IGF1R signalling (cnt mice); red bars indicate mice in which insulin and IGF1R signalling are compromised. Data are shown as mean ± s.e.m.; n = 5 independent biological samples (that is, one mouse or pool of mice per sample); two-tailed Mann–Whitney test (IR, P = 0.0079; IGF1R, P = 0.0159; IRS2, P = 0.0317; INS1, P = 0.0317; PDX1, P = 0.0079 and NKX6.1, P = 0.0079). The experiment was performed once. e, Experimental design for α-cell tracing and insulin signalling blockade with S961 in mice with intact β-cell mass. Islets were analysed either immediately after stopping S961 (analysis 1) or one month later (analysis 2). f, Immunofluorescence of islets from S961-treated mice. YFP⁺ α-cells expressing insulin are present only in islets of mice analysed during S961 treatment (analysis 1). The experiment was performed once on 3–5 consecutive sections per animal with similar results. The mice were treated asynchronously according to their availability. g, Percentage of YFP⁺ α-cells expressing insulin after treatment with or without S961 treatment (analyses 1 and 2). Horizontal bars indicate the mean; n = 5, 6 and 4 animals for control (no treatment), S961 (1 month) and S961 (1 month) + STOP (1 month), respectively; two-tailed Mann–Whitney test (P = 0.0025) comparing S961 (1 month) versus controls. h, Experimental design for α-cell tracing and STZ-induced β-cell ablation followed by either blockade of residual insulin signalling with Wortmannin or S961, or insulin-signalling enhancement through insulin administration (subcutaneous pellets). i, Percentage of converted α-cells after β-cell loss and inhibition or enhancement of residual insulin signalling. Horizontal bars indicate the mean; n = 7 mice for STZ and STZ + WORT groups and n = 6 mice for STZ + S961 and STZ + INS groups; two-tailed Mann–Whitney test (P = 0.0070, P = 0.0350 and P = 0.0047 for comparisons of STZ + WORT, STZ + S961 and STZ + INS with STZ, respectively). *P < 0.5, **P < 0.01. Scale bars, 10 µm. See Supplementary Table 1e for the source data.