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    scNMT-seq v2

    Liyun Zhao, Thomas Lefevre, Thierry Voet, Bernard Thienpont

    Published: 2022-09-14 DOI: 10.17504/protocols.io.q26g7yrz3gwz/v1
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    Abstract

    scNMT-seq (single cell Nucleosome, Methylome, and Transcriptome sequencing) allows the parallel study of a single cell chromatin status, methylation profile, and transcriptome.

    Here, we are developing and testing modifications of the scNMT-seq pipeline. The protocol is carried out in 96w plates and typically takes 4-5 days to complete.

    The number of pre-amplification cycles is adjusted to tackle the problem of poor recovery after BS conversion.Primers are optimized for first-strand and second-strand synthesis to solve the problem of unmapped reads and poor amplification. Both are testified as compatible with theoriginal the original scNMTseq.

    Steps

    Cell isolation and GpC methylation

    1.

    Prepare plates containing 2.5µl GpC methylase reaction mixture in each well:

    ABCD
    Component (initial)Component(final)Volume (µl)Mastermix (110 samples)
    M.CviPI reaction buffer (10x)1x0.2527.5
    M.CviPI (4U/µl)2U0.555
    SAM (320µM)160µM1.25137.5
    IGEPAL (10%)0.1%0.0252.75
    RNasein (20U/µl)1U/µl0.12513.75
    Nuclease-free water0.3538.5
    2.

    Isolate cells manually or using FACS in 2.5µLof GpC methylase reaction buffer

    3.

    After cell isolation, spin down plates at ≥1000g for ≥ 10s 4°C

    4.

    Incubate the samples at 37°C for 0h 15m 0s

    5.

    Stop reaction by adding 5µL RLT plus buffer

    6.

    Stoe the plates at-80°C until processed

    Oligo-dT30VN bead preparation

    7.

    Add55µLDynabeads into a new Eppendorf tube. Place the tube on a magnet for 0h 2m 0s and discard supernatant

    8.

    Resuspend beads in 200µL Dynabead solution A ( NaOH, NaCl) 0.1Molarity (M) NaOH, 0.05Molarity (M) NaCl). Place the tube on a magnet for 0h 2m 0s and discard supernatant

    9.

    Repeat step 8 once

    10.

    Resuspend beads in 200µL Dynabead solution B ( NaCl) 0.1Molarity (M) NaCl). Place on a magnet for 0h 2m 0s and discard supernatant

    11.

    Resuspend the beads in55µLof 2x B&W ( NaCl, Tris-HCl, EDTA) 2Molarity (M) NaCl, 10millimolar (mM) Tris-HCl, 1millimolar (mM) EDTA) and 55µL Biotinylated Oligo-dT30VN (100micromolar (µM)).

    Incubate 0h 20m 0s on a thermomixer while shaking at 2000rpm at Room temperature

    In the meantime, prepare the bead resuspension buffer bead resuspension buffer

    AB
    Superscript FS buffer (5x)220µl
    Nuclease-free Water825µl
    RNase inhibitor (20U/µl)55µl

    After adding RNase inhibitor, use beads within 30min

    In the meantime, prepare 1x B&W buffer by mixing Nuclease-free water with 2x B&W buffer 1x B&W buffer by mixing 440µL Nuclease-free water with 440µL 2x B&W buffer

    12.

    Place beads on a magnet for0h 2m 0s and discard supernatant

    13.

    Resuspend the beads in 200µL 1x B&W buffer. Place beads on a magnet for 0h 2m 0s and discard supernatant

    14.

    Repeat step 13 three more times

    15.

    Resuspend the beads in the bead resuspension buffer

    Physical separation of mRNA and gDNA

    16.

    Thaw the 96-well plate containing the single cell lysates on ice

    17.

    Add ERCC spike-ins 1µL ERCC spike-ins at 1:1Million - 1:128Million dilution to each sample using a multi-dispensing pipette. Run the pulse centrifugation program to spin ERCCs down to the bottom

    18.

    Take 4 tubes(1069µLper tube ) of G&T wash buffer( Tris–HCl ,  KCl, MgCl2, 0.5% Tween 20 Solution) 50millimolar (mM) Tris–HCl8.3, 75millimolar (mM) KCl, 3millimolar (mM) MgCl2, 0.5% Tween 20 Solution) and add to each tube137.5µL DTT and RNaseIn 25µL RNaseIn

    19.

    Add G&T-Seqwash buffer 50µL G&T-Seqwash buffer per well to the“G&T-Seq wash plate”

    20.

    Add Oligo-dT beads 10µL Oligo-dT beads per well to the“bead plate”

    21.

    Add an empty non-skirted 96 well plate labeled “gDNA collection”

    22.

    Spin all plates and run the adapted G&T-separation program robotically or manually.

    While the separation program is running, prepare the RT master mix RT master mix

    ABCD
    Component (C_initial)C_finalVolume(µl)Mastermix (110 samples)
    dNTP (10mM)1mM0.555
    TSO (100µM)1µM0.055.5
    MgCl2 (1M)6mM0.033.3
    Betain (5M)1M1110
    S II First strand buffer (5x)1x1110
    DTT (100mM)5mM0.2527.5
    Nuclease-free water1.8198
    RNase inh (20U/µl)0.5U/µl0.12513.75
    Superscript reverse transcriptase II (200U/µl)10U/µl0.2527.5

    Adding enzyme within less than 30 min before running the Reverse Transcription program

    Note
    Separation is performed robotically on the Hamilton platform in this protocol. If performed manually, steps should be as follows

    22.1.

    Manually pipette 10µL of prepared oligo-dT beads to each well of the sample plate using a multichannel pipette

    22.2.

    Mix at maximum speed for 0h 20m 0s

    22.3.

    Place on magnet for 0h 5m 0s. Aspirate 17.5µL and transfer to the empty low-bind plate for gDNA collection

    22.4.

    Add 15µL of G&T-seq wash buffer off magnet.

    22.5.

    Mix at maximum speed for 0h 10m 0s

    22.6.

    Place on magnet for 0h 2m 0s. Aspirate 15µL and transfer to the empty low-bind plate for gDNA collection

    22.7.

    Repeat steps 22.3-22.6 twice more

    Note
    Lysate (17.5ul) combined with 3 washes (15ul each) should now have been collected into the gDNA plate

    Reverse transcription

    23.

    Collect the polyA(+) mRNA plate and using the multi-dispenser dispense RT master mix 5µLRT master mix into each well of the bead-containing 96-well plate

    24.

    Seal the mRNA and gDNA plates and spin.

    Store gDNA at -80°C until processed

    25.

    Incubate the polyA(+) mRNA 96-well plate on a thermomixer C using the program below (approx. duration 1h 45m 0s)

    ABCD
    CycleTemp (°C)TimeMixing (rpm)
    1422 min2000
    24260 min1500
    35030 min1500
    46010 min1500
    26.

    In the meantime prepare PCR mastermix PCR mastermix

    ABC
    ComponentVolume(µl)Mastermix (110 samples)
    KAPA HiFi HotStart ReadyMix (2x)6.25687.5
    IS PCR primer (10µM)0.12413.64
    Nuclease-free water1.13124.3

    PCR amplification of cDNA

    27.

    Add PCR reaction mastermix 7.5µLPCR reaction mastermix, seal the plate and centrifuge

    28.

    Resuspend the beads for0h 0m 30s at 2000rpm using the Thermomixer

    29.

    Perform cDNA amplification as follows

    ABC
    CyclesTemperature(°C)Time
    1983 min
    18-259820 s
    6715 s
    726 min
    1725 min
    14Hold

    Amplification cycles differ

    PCR cleanup of amplified cDNA

    30.

    Add Agencourt AMPure beads 12.5µL Agencourt AMPure beads (1:1 ratio), mix thoroughly by pipetting up and down

    31.

    Incubate0h 5m 0s at Room temperature

    32.

    Pellet the beads on a Low-elution magnet for 0h 5m 0s

    33.

    Remove the supernatant without disturbing the beads

    34.

    Wash the beads twice with 150µL of freshly prepared 80% ethanol for 0h 0m 10s

    35.

    Allow the beads to dry for approximately 0h 5m 0s . Resuspend in25µL nuclease-free water. Incubate for 0h 2m 0s Room temperature

    36.

    Return the 96-well plate to the magnet and allow the Agencourt AMPure beads to settle for 0h 5m 0s

    37.

    Carefully transfer the supernatant to a new 96-well plate

    Note
    Quality control: QUBIT+BIOANALYZERexpected cDNA concentration: >= 1ng/µl expected cDNA length: 500-2000bp, peaking at 1-1.5kb

    Library preparation of cDNA (Nextera XT)

    38.

    Dilute the cDNA of each sample to 0.2ng/μl with nuclease-free water

    39.

    Add 2.5µL Tagment DNA(TD) buffer to a new Hard-Shell skirted 96-well plate

    40.

    Add diluted cDNA 1.25µL diluted cDNA and amplicon tagment mix 1.25µL amplicon tagment mix (ATM) to TD buffer and mix

    41.

    Centrifuge the plate at 280x g,20°C

    42.

    Incubate on a thermal cycler

    ABC
    SegmentTemp(°C)Duration(min)
    15510
    210Hold
    43.

    Add 1.25µLNeutralize Tagment Buffer (NT)

    44.

    Vortex & spin down at 800x g,20°C

    45.

    Incubate at Room temperature 0h 5m 0s

    46.

    Add Index (i7) adapter 1.25µL Index (i7) adapter to each column and Index 2 (i5) adapter 1.25µL Index 2 (i5) adapter to each row

    47.

    Add3.75µL Nextera PCR mastermix and mix

    48.

    Centrifuge the samples at 280x g,20°C and amplify as follows:

    ABC
    CycleTemp (°C)Duration
    1723min
    29530s
    3-149510s
    5530s
    7230s
    15725min
    164Hold
    49.

    Centrifuge the plate at 280x g,20°C

    50.

    Purify libraries at a 0.66:1 ratio and elute in EB buffer 12.5µL EB buffer

    Note
    Libraries can be stored for at least a year at -20°C

    51.

    Pool libraries and quantify using qPCR

    Note
    expected pool concentration: 4nM expected pool size: 250-1500bp

    scBS-seq library preparation (gDNA)

    52.

    Bisulfite conversion

    53.

    Prepare the CT conversion reagent by mixing M-Solubilisation buffer 7.9mL M-Solubilisation buffer and M-Dilution buffer 3mLM-Dilution buffer and 0h 15m 0s vortexing at Room temperature

    Finally,add1.6mL M-Reaction buffer and vortex0h 4m 0s at Room temperature

    54.

    Add AMPure XP beads 32.5µL AMPure XP beads to the gDNA plate (0.65:1 ratio)

    55.

    Incubate0h 20m 0s Room temperature

    56.

    Place the plate on the magnet for 0h 20m 0s and discard the supernatant

    57.

    Wash the beads twice with 200µL80% ethanol

    58.

    Resuspend the beads in10µL elution buffer, optionally containing 60fg unmethylated lambda DNA

    Note
    Do not transfer the samples from the beadsDo not dry the beads after the second wash, a dry step when purifying gDNA lowers recovery

    59.

    Add 65µL CT conversion reagent without mixing

    Note
    Watch out for bubbles, centrifuge shortly if necessary

    60.

    Incubate the mixture as follows:

    ABC
    SegmentTemperature(ºC)Duration(min)
    1988
    265180
    34Hold

    Note
    BS converted DNA is stable for 3 days at -20°C or 20h at 4°C

    Purification of the bisulfite converted DNA

    61.

    Mix 300µL M-binding buffer and 5µL MagBinding beads

    Note
    Tip: to minimize loss of sample due to pipetting use a thermomixer to mix instead of pipetting Use a deep-well plate

    62.

    Transfer the samples to the M-binding buffer - MagBinding beads mix and incubate 0h 5m 0s Room temperature

    63.

    Pellet the beads on a magnet for 0h 3m 0sand discard the supernatant

    64.

    Resuspend the beads in200µL M-Wash buffer

    65.

    Pellet beads on the magnet and discard the supernatant. Resuspend the beads in 100µLM-Desulphonation buffer and incubate 0h 15m 0s``Room temperature

    Note
    The beads sink quite fast to the bottom, during these 15 mins you can slowly mix on regular basis with the thermomixer

    66.

    Pellet beads on the magnet and discard the supernatant. Wash the beads twice with 200µL M-Wash buffer

    67.

    Dry the beads on a heating element at 55°C for 0h 10m 0s

    In the meantime, prepare the pre-amplification mix as follows pre-amplification mix as follows

    ABCD
    ComponentAmount (µl)Final concentrationMastermix (110 samples)
    Blue buffer (10×)41x440
    dNTP mix (10mM)1.60.4mM176
    Preamp Oligo (10 µM)1.6O.4 µM176
    H2O32.83608
    Total volume404400

    Pre-amplification

    68.

    Resuspend the beads in a 40µL pre-amplification mix

    69.

    Incubate the mixture at 55°C for 0h 4m 0s and place it on the magnet

    70.

    After the beads are pelleted transfer 39µL to a new plate

    71.

    Incubate the samples 0h 3m 0s at65°C and immediately cool on a pre-cooled aluminum rack

    Centrifuge the plate at 500x g

    72.

    Add 1µL klenow exo- polymerase (50U/µl)

    Vortex the samples and amplify as follows:

    ABCD
    SegmentTemp (ºC)Duration (min)Ramp speed (ºC/min)
    145-
    24-378.254
    33730-
    44Hold
    73.

    In the meantime, prepare 6 tubes of pre-amplification mix pre-amplification mix

    Note
    Only add klenow exo to the mix before use

    ABCD
    ComponentAmount (µl)Final concentrationMastermix (    samples)
    Blue buffer (10×)0.251x
    dNTP mix (10mM)0.10.4mM
    Preamp Oligo (10 µM)14 µM
    Klenow exo- (50 U/µl)0.510 U/µl
    H2O0.65
    Total volume2.5
    74.

    Heat the plate to 95°Cfor 0h 0m 45sand transfer it to an aluminum rack pre-cooled on ice

    75.

    Centrifuge the plate at 500g for 0h 0m 10s at 15-25°C

    76.

    Add 2.5µL of the pre-amplification mix

    77.

    Repeat steps 72-76 five more times

    78.

    Incubate as follows:

    ABCD
    SegmentTemp (ºC)Duration (min)Ramp speed (ºC/min)
    145-
    24-378.254
    33790-
    44Hold

    Note
    The first-strand product can be stored ON at 4°C or for at least a month at -20°C

    Exonuclease I treatment

    79.

    Dilute the samples to a volume of98µLwith nuclease-free water

    80.

    Add exonuclease I 2µL exonuclease I (20U/µl) to the pre-amplified product and incubate 1h 0m 0s at 37°C with the heated lid set to 50°C

    Purification

    81.

    Add AMPure XP beads 75µL AMPure XP beads (0.75:1 ratio) and mix thoroughly by pipetting up and down

    Note
    Tip check the volume of some samples first and adjust volumes of beads to add accordingly

    82.

    Incubate 0h 10m 0s Room temperature

    In the meantime, prepare Adaptor 2 mix Adaptor 2 mix

    ABCD
    ComponentAmount (µl)Final concentrationMastermix (     samples)
    Blue buffer (10×)4.71x
    dNTP mix (10mM)1.90.4mM
    Adapter 2 Oligo (10 µM) 1.90.4µM
    H2O38
    Total volume46.5
    83.

    Place on the magnet for 0h 3m 0sand discard the supernatant

    84.

    Add 200µL of 80% (vol/vol) ethanol while keeping the plate on the magnet then discard ethanol after ±10sec

    85.

    Repeat 84 once. Dry the AMPure XP beads for 0h 5m 0s Room temperature

    Adapter 2 tagging

    86.

    Resuspend the beads in Adapter 2 mix 46.5µL Adapter 2 mix

    87.

    Incubate for 0h 10m 0s Room temperature

    88.

    Transfer samples to a new plate

    89.

    Heat mixture to 95°Cfor 0h 0m 45s then immediately cool on ice using an aluminum rack

    90.

    Spin down at 500g for 0h 0m 10s at 15–25°C

    91.

    Add Klenow exo- 1µL Klenow exo- (50 U/µl), vortex gently, and spin down at 500g for 0h 0m 10s at 15–25°C

    92.

    incubate as follows:

    ABCD
    SegmentTemp (ºC)Duration (min)Ramp speed (ºC/min)
    145-
    24-378.254
    33730-
    44Hold
    93.

    In the meantime, prepare 1 tube of Adapter 2 mix Adapter 2 mix

    ABCD
    ComponentAmount (µl)Final concentrationMastermix ( samples)
    Blue buffer (10×)0.251x
    dNTP mix (10mM)0.10.4mM
    Preamp Oligo (10 µM)14 µM
    Klenow exo- (50 U/µl)0.510 U/µl
    H2O0.65
    Total volume2.5
    94.

    Heat the plate to 95°C for 0h 0m 45s and transfer it to an aluminum rack pre-cooled on ice

    95.

    Centrifuge the plate at 500g for 0h 0m 10s at 15-25°C

    96.

    Add 2.5µL of the Adapter 2 mix

    97.

    Incubate as follows:

    ABCD
    SegmentTemp (ºC)Duration (min)Ramp speed (ºC/min)
    145-
    24-378.254
    33790-
    44Hold
    98.

    Add 37.5µL AMPure XP beads ( 0.75:1 ratio )

    99.

    Incubate 0h 10m 0s at room temperature

    In the meantime, prepare the library amplification mix library amplification mix

    ABCD
    ComponentAmount (µl)Final ConcentrationMastermix ( samples)
    KAPA HIFI HotStart ReadyMix (2x)251x
    PE1.0 (10µM)10.2µM
    Nuclease-free water23
    Total volume49
    100.

    Place on a magnet for 0h 3m 0s

    101.

    Place on a magnet for 0h 3m 0sand discard the supernatant

    102.

    Add 200µL ethanol (70%) without disturbing the beads. After 0h 0m 10s remove ethanol

    103.

    Repeat step 102 once then dry beads 0h 5m 0s at room temperature

    Library amplification

    104.

    Resuspend the beads in 49µL library amplification mix

    105.

    Incubate the mixture 0h 10m 0s Room temperature

    106.

    Place on a magnet and transfer supernatant to a new plate

    107.

    Add 1µL 10µM reverse iPCRTag primer (containing a sample-specific index)

    Amplify as follows:

    ABC
    CyclesTemperature (°C)Time
    1953 min
    17-209880 s
    6530 s
    7230 s
    1723 min
    14Hold

    Note
    The PCR product can be stored ON at 4°C or for at least a month at -20°C

    Purification of amplified libraries

    108.

    Add 37.5µl AMPure XP beads (0.75:1 ratio) and mix well

    109.

    Incubate 0h 10m 0s Room temperature

    110.

    Place on the magnet for 0h 3m 0s and discard supernatant

    111.

    Add 200µL ethanol (70%) without removing the plate from the magnet then discard the ethanol

    112.

    Repeat step 111 once then dry beads 0h 5m 0s

    113.

    Resuspend the beads in 15µL EB

    114.

    Incubate 0h 10m 0s Room temperature

    115.

    Place on a magnet then transfer supernatant to a new plate

    Note
    Library quantity and quality can be checked using Qubit HS Assay and Bioanalyzerexpected gDNA concentration: >= 1ng/µl expected fragment length: >200bp and on average 400-600bp Libraries can be stored for at least a year at -20°C

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