Fig. 5. Injection of sog mRNA locally inhibits the transcription of a dorsal-specific gene, but activates its transcription at a distance from the site of injection. Lateral views of snake (snk) mutant embryos hybridized with Race (blue) and sog (brown) riboprobes. Late cellularization (A,C) and post gastrulation (stage 7 by developmental time; B,D). (A,B) Race expression in uninjected embryos is restricted to the anterior domain, and no endogenous sog transcription is present. (C,D) Embryos injected in a dorsal anterior position (marked by arrow) with a small bolus of sog mRNA (brown). Race expression is inhibited by sog at the site of injection, and is activated at a distance from the source of sog, both more posteriorly (bracket) and at a ventral-anterior position. Note that the white ‘halo’ is more pronounced in the older embryo, corresponding to inhibition of endogenous Race expression outside the domain of detectable sog mRNA.