Fig. 2. Expression of Dermo-1 in trout embryo. (A) Stage 10B embryo (approximately 10 somites). Lateral view: labelling is observed in the dorsal domain of the somites (arrowheads) and in cephalic mesenchyme. (B) Stage 13 embryo (approximately 30 somites). Lateral view: Dermo-1 transcript appears in the ventral domain of rostral somites (arrowheads). (C) Stage 18 embryo (segmentation is nearly complete). Lateral view: labelling has progressed up to post-anal somites. (D,E) Stage 12 (20 somite) embryo. Transverse sections through posterior (D) and anterior (E) trunk: labelling is initially present in the dorsal domain of the somite and then appears in the ventral domain of the somite (E: arrow). (F) Stage 40 somite embryo. Transverse section through middle trunk: labelling narrows to the outermost domain of the somite and is observed in sclerotome cells. (G) Stage 20 (somitogenesis is complete). Transverse section through posterior trunk: Dermo-1 transcript is present in somitic external cells (arrow), sclerotome cells and cells intercalated between neural tube and myotome. (H–K) Dual-colour in situ hybridisation for Dermo-1 (dark blue) and myogenin (red). (H–J) Serial transverse sections through posterior (H), middle (I) and anterior trunk (J) of a stage 12 embryo (approximately 20 somites). Dermo-1 and myogenin expression progressively intermingle in the maturing somite. (K) Transverse section through posterior trunk of an eyed-stage embryo. Dermo-1 labelling is external to the myogenin-expressing primary myotome. n, notochord; nt, neural tube; s, somite. Scale bar, 200 µm in A and B, 250 µm in C, 40 µm in D, 30 µm in E, 35 µm in F, 45 µm in G and 35 µm in H–K.