Fixed ex vivo tissue samples were snap frozen and homogenised using a metal mortar. The homogenised tissue was resuspended in nuclear lysis buffer (50 mM Tris-HCl pH 8.1, 10 mM EDTA pH 8.0, 1% SDS) supplemented with protease inhibitors (Roche) and incubated on ice for a minimum of 5 minutes. The DNA SMART ChIP-seq kit (Clontech, 634865) was used to generate Illumina-compatible sequencing libraries from 100pg to 2ng of DNA from two independent H3K9me2 ChIP experiments and associated input.