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Fig. 7 Expression of shh in median fins was assessed in shh:gfp (green fluorescent protein) transgenic zebrafish (Shkumatava et al.,[2004]) by means of confocal microscopy. Black patches are melanophores. Anterior is to the left and dorsal to the top. A: After prescreening for presence or absence of gfp, gfp-negative embryos were used to provide baseline levels of autofluorescence. B: Expression of shh as evidenced by gfp in the ventral diencephalon and the floor plate of the neural tube (not shown) were as expected (Ekker et al.,[1995]). C: Expression in the floor plate of the neural tube (not shown in C, but see F) is maintained for an extensive period of time as a new domain of expression is observed in the caudal fin. Both mesenchyme in the fin and fin rays themselves show strong expression. D: This is observed more clearly in the anal fin. Ray expression is distinct, and anal fin mesenchyme shows high levels of shh. E: Although it appears that the cartilage cells of the radials (arrowheads) express shh, this is an artifact caused by bleed-over of the high levels of mesenchyme fluorescence. F: Absence of shh in the hypurals is apparent, while expression in the distal caudal mesenchyme, caudal fin rays (arrows), and floor plate of the neural tube (or perhaps dorsal notochord, n, see Ekker et al.,[1995]) is maintained. G: The pattern of expression in the anal fin after segmentation is complete shows expression in the mesenchyme in the shape of an H, with the hollow portions of the H consisting of the distal (bottom row of arrowheads) and proximal (top row of arrowheads) radials. The alternating angled light and dark lines in G and H are an artifact of the confocal microscope. H: Although interradial shh expression is maintained after radial segmentation (radials not in plane of section here, but see G), the highest levels of shh expression are observed in the distal and still developing fin rays (arrows), which are not in the plane of section in G.