CBP Occupancy in Drosophila Embryos Figure 6. Histone acetylation by CBP at genes repressed by Dorsal is restricted by H3K27me3 in the neuroectoderm. A and F) In situ hybridization with digoxigenin-labeled tolloid (tld) and zerknu¨llt (zen) RNA probes in 2–4 hour old wild-type (wt) and mutant embryos that alter the Dorsal protein gradient. Embryos are oriented with anterior to the left and dorsal up. The Dorsal protein is converted to a repressor of tld and zen expression since the Dorsal-binding sites are flanked by AT-rich elements that bind co-factors and recruit the Groucho co-repressor. B and G) ChIP-seq peaks for CBP in wild-type (wt) and gd7 mutant embryos (raw data without cut-off), as well as Dorsal ChIP-chip peaks in wild-type are shown for the tld and zen loci. Occupancy is plotted as log2-fold enrichment over input. C–E and H–J) ChIP-qPCR of CBP, Dorsal, H3K9ac, H3K18ac, H3K27ac, and H4ac, as well as H3K27me3 and H3K9me3 occupancy at tld and zen in wild-type (wt) and mutant embryos. Occupancy is plotted as in Figure 5. Error bars indicate standard deviation, see Results for T-tests. In Tollrm9/rm10 mutant embryos, there is minimal histone acetylation at the tld and zen promoters although CBP binds to a significant extent. The high levels of H3K27 tri-methylation in these embryos may restrict histone acetylation by CBP and other HATs. doi:10.1371/journal.pgen.1002769.g006 PLoS Genetics | www.plosgenetics.org 10 June 2012 | Volume 8 | Issue 6 | e1002769