Fig. 2. Wnt signaling from the neural tube downregulates Wnt6 expression in the ectoderm overlying the somites. (A) Separation of the somite from the axial organs by insertion of an aluminium foil barrier induces an upregulation of Wnt6 expression in the ectoderm covering the somites (between arrowheads), the Wnt6 expression domain now extending medially to the barrier. (B) Removal of the right half of the neural tube induces Wnt6 expression in the somites on the right (between arrowheads). (C) Implantation of Wnt3a-producing cells into the epithelial somites of HH stage 14 embryos leads to the inhibition of Wnt6 expression in the ectoderm overlying the somites (between arrowheads). (D) Transverse section through the operated region in A showing the upregulation of Wnt6 expression due to the absence of signals from the axial organs. Wnt6 expression is extended lateromedially (arrowhead). The location of the somite is indicated by an asterisk. (E) Transverse section of the embryo shown in B. Wnt6 expression is extended lateromedially (arrowhead). The asterisk marks the region where the neural tube has been removed. (F) Transverse section at the region of operation in C showing the loss of Wnt6 expression in the ectoderm overlying the somite (arrowhead), position of cells is indicated by broken lines.