Samples were sequenced on the Illumina HiSeq system using 100 bp single-end reads according to the manufacturer’s specifications. ChIP-seq reads were sorted and aligned using the 4C-seq pipeline of the BBCF HTSstation (David et al. 2014, Plos ONE and available at http://htsstation.epfl.ch). Samples were mapped to the ENSEMBL Mouse assembly NCBIM37 (mm9). Libraries (single end reads) were prepared according to the manufacturers description Cells were isolated in PBS supplemented with 10% Fetal Calf Serum. Tissue sample were further made single cell by collagenase treatment and applying a cell-strainer cap (BD Biosciences). Chromatin was crosslinked in the presence of 2% formaldehyde. Nuclei were sonicated to generate fragments with average length around 300 bp. Immuno-precipitated DNA was prepared using the TruSeq ChIP Sample Preparation Kit (Illumina)