Spleen cells were fixed with 1% formaldehyde and ChIP assays were performed as previously described (Wilson NK et al., 2010 Cell Stem Cell) using polyclonal antibodies against ERG-1/2/3 (clone C-17, Sc354X, Santa Cruz) and control nonspecific rabbit IgG (I5006, Sigma). Each sample was amplified and sequenced using the Illumina 2G Genome Analyzer, following manufacturer's instructions.