Fig. 2. Expression of N-cadherin protein during development of the pioneer myoblasts. (A,E,G,I) N-cadherin; (B-D,F,H) overlay of desmin and N-cadherin. (A) A newly-formed somite in a 22ss embryo showing homogeneous expression of N-cadherin, including the medial region that generates pioneer myoblasts (P). Note enhanced immunoreactivity in the apical adherens junctions. (B) Somite 26 in a 28ss embryo showing the initial bending of desmin-positive pioneers (green) under the forming DM. Desmin-positive pioneers still in the epithelium (arrowhead), and the bending cells, no longer express N-cadherin. (C-E) Somite 23 in two 28ss embryos. Arrowheads indicate mesenchymal pioneers in the dissociated somite that are desmin⁺/N-cadherin^- during migration (D,E). N-cadherin is enriched at the apical pole of DM cells (E, arrow). (F,G) Frontal section as in C-E, revealing desmin⁺/N-cadherin^- pioneers (delimited by a thin white line) underneath the DM. Pioneers are predominantly located in the rostral domain of the segment. (H,I) Somite 22 in a 30ss embryo. Upon differentiation into myofibers, pioneers reexpress N-cadherin (arrowheads). DM, dermomyotome; EC, ectoderm; NT, neural tube; SC, somitocoele; Scl, sclerotome. Scale bar: 40 µm in A-C,H-I; 20 µm in D-G.