Genome-wide characterization of allelic chromatin in human fibroblast and lymphoblastoid cell lines by high-density allele-specific analyses

Cis-regulatory variants are predicted to mediate the majority of the common genetic risk associated to complex disease, yet the specific causal variants have thus far been poorly characterized. Allele-specific (AS) assessment of chromatin modifications has the potential to elucidate specific cis-regulatory mechanisms. However, development of chromatin landscapes at allelic resolution has been challenging since sites of variable signal strength require substantial read depth not commonly applied in next-generation sequencing based approaches. In this study, we addressed this by directly assessing AS chromatin states through parallel analyses of input DNA and chromatin immunoprecipitates (ChIP) on high-density Illumina genotyping arrays. Allele-specificity for the histone modifications H3K4me1, H3K4me3, H3K27ac, H3K27me3 and H3K36me3 was assessed using ChIP samples generated from 14 lymphoblast and 6 fibroblast cell lines. Allele-specificity of chromatin was assessed in 14 lymphoblast and 6 fibroblast cell lines by assaying PolII & histone ChIP samples (H3K4me1, H3K4me3, H3K27ac, H3K27me3, H3K36me3) in parallel with gDNA and cDNA on high-density Illumina genotyping arrays.