Fig. 1.

Cic acts downstream of Cact to repress the zen VRE enhancer. (A) Toll- and Dorsal-dependent transcriptional control in the ventral region of the embryo. Toll activation leads to the nuclear translocation of Dl, which then activates zygotic genes such as twi and snail (sna), while repressing others such as zen and tld. These differential outcomes depend on the presence of additional transcription factor binding sites in target enhancers, which are recognized by basic helix–loop–helix (bHLH) activator factors and at least one unidentified repressor (question mark). D, dorsal; V, ventral. (B–E, Left) Early stage 5 embryos of the indicated maternal genotypes stained for Dorsal protein. (B–E, Right) Boxed areas are shown in higher magnification. Note the presence of Dorsal in dorsal nuclei of cact⁻ and cact⁻ cic⁵ mutant embryos. (F–I) Patterns of VRE-lacZ reporter expression in the indicated maternal genotypes. In I, the reporter is derepressed in cic⁵ mutant embryos, even when Dorsal is constitutively nuclear. Photographs in B–I were taken at 200× magnification.