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Fig. 4 Retinoic acid signaling from anterior somites rescues pectoral fin development in nls. Anterior is towards the left: lateral (A,B,D,E,G,H) and dorsal views (C,F). Transmitted light (A,C,D,F) and fluorescent (B,E,G,H) images taken at 48 hpf. (A-C) Wild-type donor cells (red fluorescence in B) occupying somites (s) 2-7 in a nls host are able to rescue pectoral fin (pec) development and tbx5 expression on the transplanted side (dark area in pectoral fin in A,B; arrow in C); chevron-shaped lines mark somite boundaries. The embryo in B was processed for in situ hybridization prior to photography, resulting in apparent enhancement of unspecific autofluorescence within the yolk. (D-F) Wild-type donor cells occupying most of somites 3-6 in a nls host rescue pectoral fin development (arrow in D) and tbx5 expression (arrow in F). (G,H) Donor cells transplanted to the dorsal aspect of somites 1-7 (G) or to somites posterior to somite 6 (H) are unable to rescue pectoral fin development (not shown). Scale bar: 100 µm.