library_construction_protocol: After 24 hours, cells were treated with 1% formaldehyde (Cat. F8775, Sigma-Aldrich) for 10 min at room temperature (RT). Ten, the reaction was quenched by adding glycine 0.125 M. After spinning and washing with PBS solution, the cross-linked tissue samples were stored at -80 °C. During ChIP experiments, lysis bufer 1 (50 mM Hepes–KOH, 140 mM NaCl, 1 mM EDTA, 10% glycerol, 0.5% NP-40, 0.25% Triton X-100, ddH2O), supplemented with protease inhibitors (Roche) was added to previously fixed-samples; they were homogenized using an ultra-turrax (VWR). After, samples were washed in lysis buffer 2 (10 mM Tris–HCl, 200 mM NaCl, mM EDTA, 0.5 mM EGTA, ddH2O) and lysis buffer 3 (10 mM Tris– HCl, 100 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 0.1% Na-deoxycholate, 0.5% N-Lauroylsarcosine, ddH2O), both supplemented with protease inhibitors (Roche). Obtained chromatin was sheared on Bioruptor sonicator (Diagenode) set at high potency for 30 pulses, each one comprised of 60 s ON and 30 s OFF. After checking the chromatin smear, 1% of the sample volume was collected and stored at -20 °C to be next used as input sample, while 2 µg of H3K9Me3 antibody (Cat 13969, Cell Signaling Technology), previously incubated all day at 4° C in a rotation wheel with Dynabeads (Thermo Fisher Scientific), was added to the remaining sample volume. After overnight incubation in a rotation wheel at 4° C, immunoprecipitated samples (IPs) were washed with RIPA wash buffer (50 mM Hepes–KOH, 500 mM LiCl, 1 mM EDTA, 1% NP-40, 0.7% Na-deoxycholate, ddH2O) for 6 times; after spinning, dynabeads were removed in a magnetic stand, samples were eluted in Elution Buffer (TE 1X and 2% SDS) and incubated overnight at 65° C to remove crosslinks. The recovered material was purified using QIAquick PCR purification kit (Qiagen) and DNA was quantified using Qubit® dsDNA High Sensitivity Assay Kit (Thermo Fisher Scientific). As negative control of the ChIP protocol, an IP reaction against rabbit IgG (Cat. 2729S; Cell Signaling) was performed. ChIP-Seq libraries were created adapting the TruSeq ChIP protocol (Illumina): around 50 ng of IPs and input were used for library preparation. Libraries were run on a NextSeq 500 sequencer (Illumina) using a 1×75 bp high-output kit (Illumina) with 8 IPs (50 M reads per sample) or 4 input samples (100 M read per sample) for run.