macroH2A histone variants act as a barrier upon reprogramming towards pluripotency

Here we report that the histone variant macroH2A acts as a barrier to induced pluripotency. Using fibroblasts isolated from macroH2A double knockout mice, we observed enhanced reprogramming efficiency compared to fibroblasts from wild type animals. We further show that macroH2A isoforms act synergistically in this process. Genomic analysis in wild type fibroblasts reveals that macroH2A1 and H3K27me3 domains co-localize and occupy pluripotency genes. While the absence of macroH2A does not affect H3K27me3 in fibroblasts, macroH2A1 is highly enriched at a set of Utx target genes that are reactivated early during iPS reprogramming. Mononucleosomes from Dermal Fibroblasts (from wt and macroH2A1 and macroH2A2 double knockout mice) were isolated and ChIP'd with mH2A1, H3K27me3 and H3K27ac antibodies. DNA from Input and ChIP samples was purified and sequenced on Illumina's Hiseq.