Fig. 6. A model for the regulation of ectodermal Wnt6 expression and dermomyotome epithelialization. Arrows indicate positive inductions, while a line with bars represents inhibitory actions. (A) Epithelial somite: the expression of Wnt6 (red) is observed in the whole ectoderm covering the neural tube, paraxial mesoderm and the LPM. (B) Compartmentalized somite: Wnt6 expression (red) is restricted to the ectoderm covering the VLL and the LPM. BMP induces Wnt3a and Wnt1 expression in the neural tube, which in turn induces Wnt11 (green) expression in the DML. Wnt11 expression takes over the function of maintaining epithelialization in the DML and downregulates Wnt6 in the ectoderm overlying the central and medial region of the dermomyotome. Thus, epithelial morphology is restricted to the DML and VLL by dermomyotomal Wnt11 and ectodermal Wnt6, respectively.