Extended Data Figure 7: Validation of the laser-ablation strategy.

a–h, Morphological disruption after laser ablation of Kaede-positive cells in the AER of Tg(tbx6:gal4-vp16); Tg(UAS:Kaede) double-transgenic embryos. Arrows mark the ablated cell while the adjacent cell, indicated by arrowheads, is not affected. i–l, Membrane blebbing, as visualized by photoconverted Kaede (red), can be observed in the AER of Tg(tbx6:gal4-vp16); Tg(UAS:Kaede) double-transgenic embryos. Before ablation the cell is clearly labelled by non-photoconverted Kaede (green) (i), whereas after ablation, blebbing is observed at selected time points (arrows) (j–l). m–v, Proof-of-concept experiment in which each Kaede-positive cell in the AER is sequentially ablated from Tg(tbx6:gal4-vp16); Tg(UAS:Kaede) double-transgenic embryos. Arrows mark ablated cells. Ablation is cell-specific, and does not occur in non-targeted Kaede-positive cells in the AER or the underlying mesenchyme. w–zc, Random ablation of AER cells before AFIC invasion does not affect fin formation. Using Tg(h2a f/z:nlsKikGR1) transgenic embryos, in which all nuclei are labelled by the photoconvertible protein Kikume, it is possible to ablate cells at 32 hpf within the AER before AFIC invasion. Arrows indicate targeted cells within the AER at 2 s before ablation (w) and after ablation at 2 s (x), 12 s (y) and 22 s (z). za–zc, In each experimental condition, 6 cells were ablated per AER. No differences in actinotrichia formation or overall morphology can be detected when comparing contralateral control (za) with laser-ablated (zb) conditions. Detailed quantification of fin fold and mesenchyme length does not reveal any significant differences between contralateral control and laser-ablated conditions (zc). P values are by unpaired Student’s t-test. Scale bars, 10 μm (a–l), 50 μm (m–v), 10 μm (w–z) and 100 μm (za–zc). Error bars in zc represent s.e.m.