Effects of RA on shh/vhh-1 expression and pectoral fin bud development. Embryos were treated with 1 x 10^-6M RA (B, D, E, G, and H) in 0.5% DMSO for a period of 2 hr at 24 hr postfertilization. Controls (A, C, and F) were incubated in 0.5% DMSO for the same period of time. RA-treated and control embryos and larvae were fixed at 48 hr (A and B), 56 hr (C and D), and 72 hr (E, F, G, and H). The normal pattern of shh/vhh-1 expression in the posterior part of the pectoral fin bud is indicated by an arrow. Ectopic shh/vhh-1 expression is indicated by an arrowhead. The rotation of the pectoral fin bud that normally occurs during the third day of development (compare A and C) does not occur in RA-treated embryos (B, D, and E). RA-treated embryos show a swelling of the pharyngeal arch region (open triangles in B, D, and E). (A-D) Dorsal views; (E) lateral view with anterior to the left. (F-H) Dissected pectoral fin buds. (H) Caudal view of a fin comparable to that shown in (G) and which shows the thickening of the fin at the base (dotted line). Scale bars (A-E), 100 μm; (F-H), 50 μm.

Effects of RA on shh/vhh-1 expression in caudal floor plate cells and notochord. Embryos were treated with RA as in Fig. 1 and were fixed at 56 hr. (A) Residual expression of shh/vhh-1 in floor plate cells at the caudal end of control larvae at 56 hr. At this stage, there is no longer expression of shh/vhh-1 in the notochord. (B and C) Representative examples of shh/vhh-1 expression in RA-treated fish. The caudal-most floor plate cells (arrow) express comparatively higher levels of shh/vhh-1 compared to the same cells in controls. Patches of cells positive for shh/vhh-1 are located in what appears to be an extension of the notochord and/or cells in contact with the extension of the notochord (arrowheads). The caudal neural keel in RA-treated fish is thicker than that in controls. n, notochord; nk, neural keel. Scale bars, 50 μm.