Fig. 1. Induction of hs-Tcf expression blocks zygotic Wnt signaling in vivo. (A) In control (non-transgenic) embryos at shield stage following 2 hours of heat shock at 37°C, gsc expression is normally limited to the axial mesoderm (animal pole view, dorsal to the right). (B) In transgenic Tcf-expressing sibling embryos the mesoderm is dorsalized, as indicated by radial gsc expression 2 hours after heat shock at 37°C. (C-F) TOPdGFP in-situ hybridization of heat shocked embryos expressing the Tcf transgene (D,F) compared with non-transgenic siblings (C,E). Embryos were fixed following 2 hour (C,D) and 6 hour (E,F) recovery periods. TOPdGFP is down regulated throughout the embryo, notably in the brain and spinal cord.