Extended Data Figure 8: Ablation of somite-derived cells from the AER results in increased proliferation of the underlying mesenchyme.

a–d, Ablation of somite-derived cells in the AER in embryos transgenic for Tg(tbx6:gal4-vp16) and Tg(UAS:Kaede) results in an increased mitotic index of the underlying mesenchyme as measured by EdU pulse labelling. All samples were analysed at 48 hpf. The endoskeletal disk is undergoing condensation in controls (arrowheads) (a, b), while this is not evident in MTZ-treated animals (arrow) (c). d, Quantification of EdU staining observed in the mesenchyme of pectoral fins after MTZ-induced ablation of somite-derived cells from the AER. e, Inhibition of Fgf signalling reduced the mitotic index in pectoral fins that have undergone MTZ-mediated ablation of somite-derived cells in the AER. The mitotic index of control fins is significantly lower compared to MTZ-treated pectoral fins. However, after treatment with the Fgf inhibitor SU5402, both MTZ-treated and untreated pectoral fins are reduced to a similar mitotic index. Scale bars, 40 μm. P values are by ANOVA with Tukey’s post-hoc analysis. Error bars in d and e represent s.e.m.