FL cells from e14.5 Pcl2+/+ and Pcl2-/- mice were isolated and CD71+Ter119-/lo and CD71+Ter119high fractions were sorted using a MoFlo sorter For ChIP-seq, sorted cells were crosslinked with 1% formaldehyde for 10 minutes at room temperature. Samples were sheared using a Covaris sonicator until DNA reached a final size of 75-700bp. 10ug of antibody (anti-Pcl2, Genway; anti-H3K27me3, Millipore) was bound to pre-blocked Protein A magnetic beads (Millipore), combined with sonicated DNA and incubated overnight. After incubation, beads were collected and DNA-antibody complexes were eluted at 65oC. Crosslinks were reversed overnight at 65oC. Samples were treated with Proteinase K and RNase A and DNA was purified using phenol-chloroform. 500,000 cells per sample were used for both IP and control (IgG, SantaCruz).