Effects of Brca1 knock-down on Ezh2 targeting

The Polycomb repressive complex 2 (PRC2) is important for the maintenance of stem cell pluripotency and suppression of cell differentiation by promoting histone H3 lysine 27 trimethylation (H3K27me3) and silencing expression of genes regulating differentiation. Here we show decreased expression of BRCA1 promotes EZH2 re-targeting genome wide and enhances H3K27me3 levels at PRC2 target loci in mouse ES cells. R1 mouse ES cells were transfected with control siRNA and Brca1 specific siRNA. At 48h after transfection, cells were harvested and subjected to ChIP assay with Ezh2 antibody. Brca1 wild-type (AB2.2) and Brca1 deficient (PL2F8) mouse ES cells were harvested and subjected to ChIP assay with Ezh2 antibody. Fragmented DNA obtained from ChIP assay was repaired by DNA Terminator End Repair Kit (Lucigen Corporation, Middleton, WI) and purified by QIAquick PCR purification kit. Then two unidirectional linkers JW102 and JW103 were annealed and ligated to the blunt ends DNA at 16°C overnight. The purified products were amplified to 2 μg by LM-PCR. NimbleGen Mouse ChIP 3x720K RefSeq Promoter Array (Roche) were used for the hybridization. Relative enrichments were calculated by dividing the normalized level of ChIP DNA to that of input DNA at corresponding locus. Labeling, hybridization and washing were carried out according to manufacturer’s instructions. Experiments in AB2.2 and PL2F8 cells were performed in duplicate.