Fig. 3

RA-Responsive Genes Are Expressed in the Forelimb Field

(A–E) Expression of nkx2.5, gata4, retd, hoxb5b, and raldh2 relative to ntl, which marks the notochord; dorsal views of flatmounted embryos, anterior to the top, at the 8 somite stage. Brackets and numbers indicate the mean distance of the limit of gene expression relative to the tip of the notochord, measured in notochord cell diameters (ncds). (A and B) The posterior portions of nkx2.5 and gata4 expression overlap with the notochord. (C) retd expression is found posterior to nkx2.5 and gata4 expression. (D and E) hoxb5b is expressed closer to raldh2 expression in the somites, a major source of RA in the embryo.

(F) Schematic of the WT LPM fate map at the 8 somite stage, indicating locations of atrial (green, A), ventricular (red, V), and fin (blue, F) progenitors relative to the anterior-posterior axis of the notochord, measured in ncds. Numbers in the table represent the number of labeling experiments in which each progenitor type was detected at a certain ncd position; n indicates the total number of experiments at each position. Experiments were performed on both the left and right sides of the embryo; no asymmetries were observed.

(G–I) When RA signaling is reduced, FPs are absent and CPs frequently occupy FP territory.

(J) In hoxb5b morphants, FPs are present and CPs rarely occupy FP territory.