Fig. 3. The primary myotome derived from the medial somite extends throughout the whole segment and pioneer fibers localize superficially. (A) Microinjection of CM-DiI to the center of the DMQ of an epithelial flank-level somite. (B) Formation of dye-labeled fibers that span the entire rostrocaudal and mediolateral extents of a segment. (C) Transverse section counterstained for desmin reveals the dorsoventral distribution of pioneer fibers (arrows pointing to red cells), which localize from the DML to the VLL and occupy a superficial position (towards the DM epithelium) within the desmin-positive myotome (green). C, caudal; L, lateral; M, medial; R, rostral; DM, dermomyotome; DRG, dorsal root ganglion; EC, ectoderm; Myo, myotome; NT, neural tube; Scl, sclerotome. Scale bar: 10 µm.
