CBP may coordinate dorsal-ventral axis specification in <i>Drosophila</i> embryos.

<p>A) The <i>Drosophila</i> embryo is divided into segments along its anterior-posterior axis, whereas different germlayers arise along the dorsal-ventral axis. CBP occupancy genome-wide is over-represented at targets for the two key morphogens in dorsal-ventral patterning, Toll/Dorsal and Dpp/Medea. By contrast, anterior-posterior activators such as Bicoid and Caudal overlap the genomic distribution of CBP to a much smaller extent. B) Summary of histone modifications, Dorsal, and CBP occupancy at Dorsal-target genes in different tissues. An average of the four histone acetylations tested is colored green and H3K27 tri-methylation blue, CBP is colored red and Dorsal (dl) light blue. The size of the spheres represents protein/histone modification abundance and is drawn to scale. Dorsal represses <i>tld</i> and <i>zen</i> together with Groucho (Gro), whereas Zelda and possibly other factors (?) activate these genes. Although CBP binding is associated with gene expression and Dorsal binding genome-wide, CBP can also associate with silent genes. One reason that silent CBP-bound genes are not activated could be that H3K27me3-repressed chromatin restricts histone acetylation.