Histone H4 lysine 20 monomethylation is not a mark of transcriptional silencers

Silencers are cis-regulatory elements that down-regulate the expression of target genes. While thousands of silencers have been identified experimentally, a predictive chromatin signature has not been found. H4K20me1 was previously reported to be enriched in silencers, but through reanalysis we found that this enrichment is marginal and was primarily driven by the biased selection of elements used in the screen. We generated H4K20me1 ChIP-seq in Drosophila S2 cells and confirmed that H4K20me1 does not mark transcriptional silencers but instead is associated with active transcription. Transcriptional silencers remain a poorly annotated and difficult to predict class of cis-regulatory elements. Overall design: ChIP-seq of the histone modification H4K20me1 (with 3 different commercial antibodies) and of H3K27me3 in Drosophila S2 cells, with input chromatin provided as control, and ChIP-seq of H4K20me1 with 2 of those 3 commercial antibodies from human K562 cells, with input chromatin provided as control. ChIP-seq peaks are compared to published locations of elements shown to have silencer activity in these two cell types.