Valproic acid changes acetylation of some histone lysines at Hoxb promoter regions. (A) Levels of H3K9ac, H3K4me3, H3K27me3, H3K27ac and H4K8ac across Hoxb genes were assayed by chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) of chromatin from embryonic stem (ES) cells, either treated with 1 mM valproic acid (VPA) for 8 h (black bars) or untreated (white bars). Regions with bound (B)/unbound (UB) ratios >1.0 (dashed line) can be considered relatively enriched in that modification. Error bars represent the standard error of the mean of independent experiments (n = 3 for H3K27ac, n = 2 for the remainder): apparent absence of error bars occurs where the error is too low to be visible at this scale. (B) Positions of Hoxb primers (1.1, 1.2 et cetera.) are shown, along with the positions of the most upstream and downstream primer bases, relative to the TSS (-451, +450 etc.). (C) Levels of histone modifications across the retinoic acid response elements DR2 and DR5 assayed by ChIP-qPCR of chromatin from ES cells, either treated with 1 mM VPA for 8 h (black bars) or untreated (white bars).