Figure 2

Vertebrate ar-C homolog enhancers function in the midline of zebrafish. (a) Vista plot comparison (AVID global sequence alignment algorithm) of shha intron 2 from zebrafish (base line), mouse, chick, Latimeria, and tench (bottom to top). The peaks showing more than 70% identity in a 50 base pair window are highlighted in orange. The scheme of the zebrafish shha intron 2 on the bottom marks the position of the zebrafish ar-C (blue rectangle), and the second and third exons (black rectangles). The remaining panels show a transgenic analysis of shh intron 2 fragments from vertebrates. Microinjected embryos are shown at 24 high-power fields with lateral view onto the trunk at the level of the midline. (b) Zebrafish embryo injected with control gfp-reporter construct, containing a minimal 0.8 kilobase zebrafish shha promoter. Also shown are embryos injected with gfp-reporter construct containing shh(a) intron 2 sequences from (c) zebrafish, (d) tench, (e) Latimeria, and (f) chick. The lines on the left side of each image mark the level of the notochord and the floor plate. The arrows point to floor plate cells and the arrowheads to notochord cells. The stacked-column graphs on the right side represent the quantification of the transient gfp expression. The columns show the percentage of the embryos with more than 15 green fluorescent protein (GFP)-positive cells per embryo (dark green), embryos with fewer than 15 cells (light-green), and nonexpressing embryos (white). Numbers of injected embryos are given in Table 1. ar, activation region; c, chick; E, exon; ect, ectopic; fp, floor plate; I, intron; k, kilobase; l, Latimeria; m, mouse; nt, notochord; pr, promoter; t, tench; z, zebrafish.