Fig. 1

Regulatory function of the S4.2 enhancer in zebrafish embryos. (A) Schematic view of the zebrafish fgf8 gene. The five exons constituting zebrafish fgf8 (exons 1a, 1b, 1d, 2, and 3) and seven highly conserved sequences in the vicinity of fgf8 are indicated by blue and red boxes, respectively (Inoue et al., 2006). The transcriptional start site is marked with a bent arrow. The downstream gene, hagoromo (hag), is also called fbxw4. (B–D) Tg embryos showing stable expression of S4.2-EGFP or S4.2R-EGFP at 26 hpf (B, C) and 48 hpf (D). (E, G–I) Endogenous mRNA expression of fgf8 at the bud (E), 8-somite (G), 20-somite stages (H), and 34 hpf (I). (F, J–L) mRNA expression of S4.2-EGFP as determined using WMISH. (M, M′, N) Confocal microscopic views of embryos at the 16-somite stage (M, bright field; M′, epifluorescence), and a merged view at 24 hpf (N), showing GFP expression in the anteriormost hindbrain. (O, O′) Comparison of the mRNA expression of S4.2-EGFP with that of wnt1 using two-color WMISH (O, bright field; O′, epifluorescence view of the same embryo); egfp expression (purple) occurs caudal to the expression of wnt1 (red). (B–L, O, O′) Lateral views with anterior to the left and dorsal to the top (B–D, G–L, O, O′), or with anterior to the top and dorsal to the right (E, F). (M, M′, N) Dorsal views with anterior to the top. Arrowheads mark the MHB. dos, distal optic stalk; dd, dorsal diencephalon; dt, dorsal telencephalon; op, olfactory placode; os, optic stalk; ov, otic vesicle; r1/r2/r4, rhombomeres 1/2/4. Scale bars, 200 μm (B–L, J, O, O′) or 50 μm (M, M′, N).