Fig. 7. A model for the sequential action of Wnts on somite epithelialisation and compartimentalisation. (A) The Wnt6 signal, secreted by the ectoderm, binds to Fz7 receptor expressed by the cells of the segmental plate. (B) This interaction activates the canonical, ß-catenin pathway that controls the expression of paraxis and maintains the epithelial structure of the dorsal part of the somite, while the ventral region disaggregates to form the sclerotome. (C) Cells in the medial-most region of the dermomyotome receive a Wnt1 signal from the dorsal neural tube, which activates Fz2 receptor and induces Wnt11 expression in this region, thus defining the dorsomedial compartment of the dermomyotome.