Fig. 9. Cyclopamine treatment disrupts formation of circumferential muscles in proboscis. Fluorescence micrographs of control embryos at early stage 11 (180 hours AZD; top row) and siblings treated with cyclopamine at 5 µM (middle row) or 10 µM (bottom row). In each embryo, micromere dm' had been injected with FDA (green) at stage 4 (10 hours AZD) and an N or OPQ cell with RDA (red) at stage 6a (20 hours AZD). The left column (A,D,G) shows intact embryos; in each row, the center and right columns are higher magnification views of the anterior (B,E,H) and posterior (C,F,I) of the same embryo, after dissecting the germinal plate from the yolk. In the control embryo, the segmentally iterated pattern of neurons arising from the O, P and Q lineages is visible along the ventral nerve cord (arrowheads in A); dm'-derived circumferential muscles are present throughout the inverted proboscis (bracket in A and B) and a network of dm'-derived fibers (arrows in C) is present in the caudal sucker. In the embryo treated with 5 µM cyclopamine, the segmental pattern of N-derived neurons (arrowheads in D) is not affected; circumferential fibers have formed in the proboscis, though it has failed to invert (bracket D and E) and the posterior fibers (arrows in F) appear as in controls. In the embryo treated with 10 µM cyclopamine, the N-derived neurons (arrowheads in G) and dm'-derived posterior fibers (arrows in I) are still comparable to those in controls, but the dm'-derived circumferential muscles are absent (G,H) and the proboscis is reduced in length. Scale bar: (A,D,G) 100 µm; (B,C,E,F,H,I) 40 µm.

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