Expression of uncx4.1 during somite patterning and formation. Whole-mount in situ hybridization of uncx4.1 at (A) 12.5 hours post fertilization (hpf), (B) 19 hpf, (C) 12 hpf, (D, E) 15.5 hpf, (F) 13 hpf, (G, H) 18.5 hpf, (I) 14 hpf, and (L) 22 hpf. (A, B, F, G, L) Lateral view, and (C–F, H, I) dorsal view. (A–D, F–L) Anterior to left, and (E) to top. (A, B) Expression in presomitic mesoderm as shown by double in situ labeling with her1 and mespaa riboprobes. PSM = presomitic mesoderm. Dotted lines show boundary between presomitic mesoderm (PSM) and last formed somite. (C–E) Expression is absent in adaxial cells and colocalizes with myoD1 expression in muscle progenitor cells as shown by double in situ labeling with myoD1 riboprobe at (C) 12 hpf, and (D, E) 15.5 hpf. (F–H) Expression during muscle fibre differentiation as shown by double in situ labeling with the MF20 antibody at (F) 13 hpf, and (G, H) 18.5 hpf. (I, L) Expression throughout somitic mesoderm in fused somite mutant embryos at (I) 14 hpf, and (L) 22 hpf.