Fig. 6

Reporter expression begins in ectodermal cells prior to mesenchymal cells in the pectoral fin folds. (A-L) double transgenic reporter line Tg(2Pand1:eGFP; 2PΔepi:mCherry) at 2 d.p.f., allowing visualization of the ectodermal- and mesenchymal-expressing cells simultaneously. Despite the presence of mesenchymal expression within Tg(2Pand1:eGFP), this line was used to assess ectodermal reporter expression to ensure all potential cis-regulatory elements are included. Tg(2Pand1:eGFP) reporter expression in ectodermal cells and mesenchymal cells are presented in green (B, F, J), Tg(2Pepi:mCherry) reporter expression in mesenchymal cells are presented in red (C, G, K). Ectodermal and mesenchymal images are merged (D, H, L) to visualize ectodermal eGFP and mesenchymal mCherry expression simultaneously. Reporter expression in ectodermal (J, L) and mesenchymal (K, L) cells is present in the median fin fold at 2 d.p.f. In contrast, the pectoral fin fold displays reporter expression in the epithelium only at 2 d.p.f. (indicated by the white arrowheads) (F-H). Note again, the absence of reporter expression in the early pectoral fin fold (indicated by the yellow arrowheads) (F, H). Tip of the yolk sac extension displays autofluorescence (B-D). A, Anterior; P, Posterior; D, Dorsal; V, Ventral. Scale bars: 300 µm in A-D; 30 µm in E-H; 50 µm in I-L.