Spatial regulation of engrailed expression in the Drosophila embryo.

Novel patterns of engrailed RNA were observed in early Drosophila embryos injected with cycloheximide, an inhibitor of protein synthesis. From these patterns, we infer that there are several superimposed systems of spatial regulation which in combination localize engrailed expression in the embryo. Activation of engrailed transcription progresses with an anterior-to-posterior polarity. Superimposed are systems of negative regulation that repress expression in the anterior 30% of the embryo and in the interbands between stripes. We suggest that products of known segmentation genes are the repressors that suppress engrailed expression in interbands.