Fig. 3. S-FR4-Fc and S-FR1-Fc disrupt gastrulation in Xenopus embryos. At gastrula stage, the expression of the mesodermal marker Brachury (in blue), which is normally expressed as a ring around the blastopore (E), is downregulated in cells co-injected with ß-galactosidase and S-FR4-Fc (A) or S-FR1-Fc (C) RNA. ß-galactosidase expression is detected in red. Arrowheads in A,C indicate the region in which Brachyury is downregulated. Overexpression of S-FR4-Fc (B) or S-FR1-Fc (D) in the dorsal blastomeres of early Xenopus embryos produce gastrulation defects, which lead later in development (around stage 28) to grossly abnormal embryos, when compared with control embryos injected with ß-galactosidase RNA only (F). Note that high and low doses of injected RNA were comparable with those used by Amaya et al. (Amaya et al., 1991; Amaya et al., 1993).