Chromatin immunoprecipitation was performed according to the Diagenode AutoiDeal ChIP-qPCR kit (Diagenode) standard protocol. Samples of 6 x 106 cells were sonicated using the Diagenode Bioruptor Pico (Diagenode), with 10 cycles of 30 sec “on” and 30 sec “off”. Correct DNA fragmentation was verified by agarose gel electrophoresis. Immunoprecipitation was performed with 4 x 10^6 cells using a CTCF antibody (Diagenode). CTCF ChIP-seq libraries were prepared in triplicate using the Illumina TruSeq ChIP Sample Preparation kit. We performed 1 x 50 bp single-end sequencing with Illumina Hiseq 4000.