Fig. 2. Modified forms of Smad2 are valid markers of concentration-dependent activin transduction. (A) Schematic representation of the Myc-Smad2, GST-Smad2 and GFP-Smad2 fusion constructs. (B) Myc-Smad2, GST-Smad2 and GFP-Smad2 are almost equally efficient at inducing Eomes and Xbra. Each embryo was injected with the indicated amount of Myc-Smad2, GST-Smad2 or GFP-Smad2 mRNA. Animal caps were dissected at stage 8.5, cultured until stage 10.5 and gene expression was assayed by RNase protection. WE, whole embryo. (C) Induction of Xbra by injection of untagged Smad2 mRNA. Reproduced, with permission, from Shimizu and Gurdon (Shimizu and Gurdon, 1999). (D) GFP-Smad2 accumulates in the nucleus in response to activin signalling. Dissociated animal cap cells from GFP-Smad2-injected embryos were treated with activin for 15 minutes, and loaded onto a fibronectin substrate. When control embryos reached stage 10-10.5, the cells were observed by confocal microscopy.