Extended Data Figure 6. Cellular resolution of redundant Gli3 enhancer activities at the onset of digit formation.

(a, b) Individual Gli3 enhancer activities as detected by immunofluorescence (mm1179: green, hs1586: red) in forelimbs of transgenic reporter embryos. Sox9 (gray) marks chondrogenic progenitors of the mesenchymal condensations forming digit primordia (digits 1–5, from anterior to posterior). (c, d) Co-localization of mm1179 and hs1586 enhancer activities in hand plates of double enhancer transgenic embryos. Close-ups (right panels) show that the anterior mesenchyme (Fig. 2c) harbors many cells with dual enhancer activities (yellow). A fraction of double enhancer positive cells carries the signature of Sox9 digit progenitors (white, bottom). n=3 independent embryos per genotype were analyzed, with similar results. Nuclei, detected via Hoechst, are colored blue. Scale bars, 100 μm (a, b) and 50 μm (c–f).