Histone 3 抗体 (H3K27ac)

• Cell harvest and nuclear extraction
• • Dissect 3 Fore limbs (11.5 DAC) from mouse strain RjOrl:SWISS for each sample.
  • Dissociate the tissue into single cells in TrypLE for 15 min at 37 °C.
  • Centrifuge cell solution 5 min at 800 x g at RT.
  • Remove the liquid carefully.
  • Gently resuspend cells in 1 mL of Nuclear Extraction Buffer (20 mM HEPES-KOH pH 8.2, 20% Glycerol, 0.05% IGEPAL, 0.5 mM Spermidine, 10 mM KCl, Roche Complete Protease Inhibitor EDTA-free).
  • Move the solution to a 2 mL centrifuge tube.
  • Pellet the nuclei 800 x g for 5 min.
  • Repeat the NE wash twice for a total of three washes.
  • Resuspend the nuclei in 20 µL NE Buffer per sample.
• Concanavalin A beads preparation
• • Prepare one 2 mL microcentrifuge tube.
  • Gently resuspend the magnetic Concanavalin A Beads (antibodies-online, ABIN6952467).
  • Pipette 20 µL Con A Beads slurry for each sample into the 2 mL microcentrifuge tube.
  • Place the tube on a magnet stand until the fluid is clear. Remove the liquid carefully.
  • Remove the microcentrifuge tube from the magnetic stand.
  • Pipette 1 mL Binding Buffer (20 mM HEPES pH 7.5, 10 mM KCl, 1 mM CaCl₂, 1 mM MnCl₂) into the tube and resuspend ConA beads by gentle pipetting.
  • Spin down the liquid from the lid with a quick pulse in a table-top centrifuge.
  • Place the tubes on a magnet stand until the fluid is clear. Remove the liquid carefully.
  • Remove the microcentrifuge tube from the magnetic stand.
  • Repeat the wash twice for a total of three washes.
  • Gently resuspend the ConA Beads in a volume of Binding Buffer corresponding to the original volume of bead slurry, i.e. 20 µL per sample.
• Nuclei immobilization – binding to Concanavalin A beads
• • Carefully vortex the nuclei suspension and add 20 µL of the Con A beads in Binding Buffer to the cell suspension for each sample.
  • Close tube tightly incubates 10 min at 4 °C.
  • Put the 2 mL tube on the magnet stand and when the liquid is clear remove the supernatant.
  • Resuspend the beads in 1 mL of EDTA Wash buffer (20 mM HEPES pH 7.5, 150 mM NaCl, 0.5 mM Spermidine, Roche Complete Protease Inhibitor EDTA-free, 2mM EDTA).
  • Incubate 5 min at RT.
  • Place the tube on the magnet stand and when the liquid is clear remove the supernatant.
  • Resuspend the beads in 200 µl of Wash Buffer (20 mM HEPES pH 7.5, 150 mM NaCl, 0.5 mM Spermidine, Roche Complete Protease Inhibitor EDTA-free) per sample.
• Primary antibody binding
• • Divide nuclei suspension into separate 200 µL PCR tubes, one for each antibody (150,000 cells per sample).
  • Add 2 µL antibody (anti-H3K27ac antibody ABIN2667903, anti-H3K4me positive control antibody ABIN3023251, and guinea pig anti-rabbit IgG negative control antibody ABIN101961) to the respective tube, corresponding to a 1:100 dilution.
  • Incubate at 4 °C ON.
  • Place the tubes on a magnet stand until the fluid is clear. Remove the liquid carefully.
  • Remove the microcentrifuge tubes from the magnetic stand.
  • Wash with 200 µL of Wash Buffer using a multichannel pipette to accelerate the process.
  • Repeat the wash five times for a total of six washes.
• pAG-MNase Binding
• • Prepare a 1.5 mL microcentrifuge tube containing 100 µL of pAG mix per sample (100 µL of wash buffer + 58.5 µg pAG-MNase per sample).
  • Place the PCR tubes with the sample on a magnet stand until the fluid is clear. Remove the liquid carefully.
  • Remove tubes from the magnetic stand.
  • Resuspend the beads in 100 µL of pAG-MNase premix.
  • Incubate 30 min at 4 °C.
  • Place the tubes on a magnet stand until the fluid is clear. Remove the liquid carefully.
  • Remove the microcentrifuge tubes from the magnetic stand.
  • Wash with 200 µL of Wash Buffer using a multichannel pipette to accelerate the process.
  • Repeat the wash five times for a total of six washes.
  • Resuspend in 100 µL of Wash Buffer.
• MNase digestion and release of pAG-MNase-antibody-chromatin complexes
• • Place PCR tubes on ice and allow to chill.
  • Prepare a 1.5 mL microcentrifuge tube with 102 µl of 2 mM CaCl₂ mix per sample (100 µl Wash Buffer + 2 µL 100 mM CaCl₂) and let it chill on ice.
  • Always in ice, place the samples on the magnetic rack and when the liquid is clear remove the supernatant.
  • Resuspend the samples in 100 µl of the 2 mM CaCl₂ mix and incubate in ice for exactly 30 min.
  • Place the sample on the magnet stand and when the liquid is clear remove the supernatant.
  • Resuspend the sample in 50 µl of 1x Urea STOP Buffer (8.5 M Urea, 100 mM NaCl, 2 mM EGTA, 2 mM EDTA, 0.5% IGEPAL).
  • Incubate the samples 1h at 4°C.
  • Transfer the supernatant containing the pAG-MNase-bound digested chromatin fragments to fresh 200 µl PCR tubes.
• DNA Clean up
• • Take the Mag-Bind® TotalPure NGS beads (Omega Bio-Tek, M1378-01) from the storage and wait until they are at RT.
  • Add 2x volume of beads to each sample (e.g. 100 µL of beads for 50 µL of sample).
  • Incubate the beads and the sample for 15 min at RT.
  • During incubation prepare fresh EtOH 80%.
  • Place the PCR tubes on a magnet stand and when the liquid is clear remove the supernatant.
  • Add 200 µl of fresh 80% EtOH to the sample without disturbing the beads (Important!!! Do NOT resuspend the beads or remove the tubes from the magnet stand or the sample will be lost).
  • Incubate 30 sec at RT.
  • Remove the EtOH from the sample.
  • Repeat the wash with 80% EtOH.
  • Resuspend the beads in 25 µL of 10 mM Tris-HCl pH 8.2.
  • Incubate the sample for 2 min at RT.
  • Repeat the 2x beads clean up as described before (this time with 50 µL of beads for each sample).
  • Resuspend the beads + DNA in 20 µL of 10 mM Tris-HCl pH 8.2.
• Library preparation and sequencing
• • Prepare Libraries using KAPA HyperPrep Kit using KAPA Dual-Indexed adapters according to protocol.
  • Sequence samples on an Illumina NextSeq 500 sequencer, using a NextSeq 500/550 High Output Kit v2.5 (75 Cycles), 36 bp PE.
• Peak calling
• • Trim reads using using bbTools bbduk (BBMap - Bushnell B. - sourceforge.net/projects/bbmap/) to remove adapters, artifacts and repeat sequences.
  • Map aligned reads to the hg38 human genome using bowtie with options -m 1 -v 0 -I 0 -X 500.
  • Use SAMtools to convert SAM files to BAM files and remove duplicates.
  • Use BEDtools genomecov to produce Bedgraph files.
  • Call peaks using SEACR with a 0.001 threshold and the option norm stringent.

The protocol is published in PMID 36355069