Fig. 7. Regulation and localization of the thoracic dermal progenitors in chick embryo. At E3, activation by the dorsal neural tube of Wnt11 in the DML, then by the ectoderm of En1 in the intervening space of the medial dermomyotome. At E4, formation by migration of the dorsomedial and by delamination of the dorsolateral mesenchyme, which continue to express respectively Wnt11 and En1. It should be noted that a narrow third population that expresses Sim1 forms the border between the epaxial and hypaxial domains. ao, aorta; fo, forelimb; nc, notochord; nt, neural tube; Wd, Wolffian duct.