The cis-regulatory elements responsible for the olSix3.2 expression are contained in a 4.5 kb genomic region. (a) VISTA comparison of the 5' olSix3 genomic region plotted against those from Fugu rubripes, Tetraodon nigroviridis, and Danio rerio. The blocks of sequences (75% identity over 100 base pairs) conserved among the four species are indicated in pink. (b) Schematic structure of the 5' olSix3.2 genomic region/enhanced green fluorescent protein (EGFP) reporter construct (cI) containing ten highly conserved noncoding regions represented as light blue rectangles A to L. The red rectangle represents the 5'-untranslated region and the first nine nucleotides of the olSix3.2 coding sequence in frame with a nuclear EGFP reporter (green). (c to h) Bright field images; and (i to n) epi-fluorescence dorsal views of cI transgenic embryos at different stages of development (as indicated). Note that the cI construct drives EGFP reporter expression to the same olSix3.2 expression domain, recapitulating its entire pattern (compare with Figure 1). The arrowhead in panel k points to the olfactory pits. The inset in panel n shows a frontal section through the eye (dotted line), where EGFP is expressed in the amacrine cells. The section was counter-stained with propidium iodine (red). Hy, hypothalamus; Te, telencephalon; Th, thalamus.