Fig. 7. TOPGal expression patterns maintained in Tcf3^-/- embryos. TOPGal transgenic, wild-type (WT) or Tcf3^-/- (KO) embryos of the indicated stages of development were stained with X-gal to identify the location of activation of Lef/Tcf-ß-catenin target genes. (A) Lateral view of a wild-type late streak embryo is weakly positive for TOPGal activity in the primitive streak region. (B,C) Tcf3^-/- embryos display TOPGal positive staining in the primitive streak region. The intensity of staining is indistinguishable from wild type. (D,D') Headfold staged Tcf3^-/- embryos display a TOPGal expression pattern indistinguishable from wild-type embryos (see Fig. 1C,D) and include positive TOPGal expression in the node. (E) Tail of a wild-type E8.5 embryo. TOPGal is present in the posterior node and the mesenchymal cells near the node. (F) Tcf3^-/- E8.5 embryo. TOPGal expression is found in the tail of the embryo. (F') Dorsal view shows a duplication of the node in this embryo. TOPGal is maintained in the same pattern as wild type in the node and the surrounding mesenchyme, despite the duplication.