GSM8722886: mESC WT, CBX7, Replicate 2; Mus musculus; ChIP-Seq
Cells were grown to 80% confluence on 150cm plates and fixed with 11% solution containing formaldehyde (Thermo Fisher #28908), 50mM HEPES-KOH(pH 7.5), 100mM Nacl, 0.5M EDTA, 0.5M EGTA for 10 min. 1/20 of the plates volume equivalent of freshly prepared Glycine 2.5M(stock) was added to quench the reaction for 5min . The supernatant was aspirated, and the cells were washed twice with 5 ml PBS and harvested on ice using cell scrapers . Cells were pelleted at 2950 x g for 10 min at 4°C, washed 1x with 10 ml cold PBS, and pelleted once more. Cell pellets were flash freeze in liquid nitrogen and store at -80°C until processing day. Cell pellet collected from 6 plates of cells was resuspended in 5 ml of Lysis Buffer 1 (50 mM HEPES-KOH, pH 7.5; 140 mM NaCl, 1mM EDTA, 10% glycerol, 0.5% NP-40, 0.25% Triton X-100), allowed to rotate for 10 min at 4°C, and pelleted at 2950 x g for 10 min at 4°C. Cells were then resuspended in 5 ml of Lysis Buffer 2 (10 mM Tris-HCL pH 8.0, 200 mM NaCl, 1 mM EDTA, 0.5 mM EGTA), allowed to rotate for 10 min at room temperature, and pelleted at 2950 x g for 10 min at 4°C. Cells were then resuspended in 3 ml of Lysis Buffer 3 (10 mM Tris-HCl pH 8, 100 mM NaCl, 1 mM EDTA, 0.5 mM EGTA, 0.1% Na-Deoxycholate, 0.5% N-lauroylsarcosine) and then transfer to 15ml sonication tubes (Diagenode cat# C01020031). Cells were sonicated on a Bioruptor Pico at 4°C for 20min of 30'' ON-OFF cycles with 1.2 g of sonication beads. After sonication, samples were transferred to 2 separate 1.5 ml microtube and centrifuged at 20,000 x g for 15 minutes at 4°C. The supernatant was transferred to new 15 ml tubes. To check sonication efficiency, 50µl of sonicated samples was transferred to a new microtube with 50µl PBS and incubated at 65°C for 3hr on an Eppendorf Thermomixer shaking at 1000rpm to decrosslink. DNA was purified with the QIAquick PCR Purification Kit (Qiagen cat# 28106) and eluted in 50µl of H20. 1 ug of decrosslinked chromatin from each sample were run in a 1% agarose gel at 100V for 45min and imaged on a Bio-rad ChemiDoc XRS+. DNA concentration in the sonicated decrosslinked samples were measured via qubit, and this concentration was then used to estimate the concentration of chromatin in the un-decrosslinked samples. 2ug of Antibody (see Key Resources table for list of antibodies) was bound to 50 ul of Dynabeads Protein G (Thermo Fisher 10004D), previously washed with 1 ml of 0.5% BSA in 1x PBS three times, and rotated end-to-end overnight at 4°C (Eppendorf cat# 0030108051). After binding of the antibodies, beads were washed with 1 ml of 0.5% BSA in 1x PBS three times. 10ug of chromatin was added to 1.5ml LoBind tube (Eppendorf cat# 0030108051) containing pre-bound antibodies beads and brought up to 500µl final volume with Lysis Buffer and rotated end-to-end overnight at 4°C. 5 µl was removed as input material (1%) and placed in a separate microtube at 4°C completing the volume to 50uL with Lysis Buffer 3. Beads were washed 6 times with 1 ml Wash Buffer (50 mM Hepes-KOH, pH 7.6; 500 mM LiCl, 1 mM EDTA, 1% NP-40; 0.5% Na-Deoxycholate) and once with 1 ml TE containing 50 mM NaCl. Beads were dried after the last wash by removing as much TE as possible. 210 ul of Elution Buffer (50 mM Tris-HCl, pH 8; 10 mM EDTA, 1% SDS) was added to each sample and 150 ul elution buffer were added to each input sample that was previously set aside. To elute immunocomplexes from beads, samples were incubated at 65°C for 15 minutes on an Eppendorf Thermomixer shaking at 1000rpm. Tubes were centrifuged for 3min at 960xg at RT and 200µl of supernatant was transferred to a new tube and reverse crosslinked overnight at 65°C. Next day, 200 ul of TE was added to each decrosslinked sample and input, and the samples were treated sequentially with 0.2 mg/ml RNAse A (Sigma R5503) at 37°C and 0.2 ug/ml Proteinase K (NEB P8107S) at 55°C for two hours each. DNA purification was performed with the QIAquick PCR Purification Kit (Qiagen cat# 28106) and eluted in 50µl of H2O and quantified by Qubit Immunoprecipitated DNA was used to generate libraries using the NEBNext Ultra DNA Library Prep Kit for Illumina (New England Biolabs cat# 7370L. Lot: 10193454) following the manufacturer's instructions.