Fig. 1. Race expression depends on high levels of dpp and zen activity. Dorsal views of stage 5/6 embryos with anterior towards the left. Embryos were hybridized with Race (A-E) or zen (F) probes. (A) Wild type. Race transcripts are present in a five- to six-cell wide dorsal stripe in the main body region and in two broader patches in the region that will form head structures. (B) Race is absent in dpp^hr4 homozygotes. (C) Race is expressed weakly in a broad domain in the main body region of sog^SY06 hemizygous embryos. The head domains are relatively strong and also broader. (D) Race expression is normal in dpp^hr4 heterozygotes. (E,F) Race transcripts are absent from the main body region, but appear normally in the head region of dpp^hr4/+; zen^w36/+ embryos (E), although zen expression is normal (F). The expression in the head domains appears to be less sensitive to a drop in dpp and zen activities.