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    Gene Expression Dual Index Library Construction

    Melanie Königshoff, Melanie Königshoff, Nayra Cardenes, Robert Lafyatis, Heidi Monroe

    Published: 2024-06-18 DOI: 10.17504/protocols.io.n92ld8r7xv5b/v1
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    Abstract

    The Chromium Single Cell Gene Expression Solution upgrades short read sequencers to deliver a scalable microfluidic platform for 3’ digital gene expression by profiling 500-10,000 individual cells per sample.

    Once cDNA is amplified, enzymatic fragmentation and size selection are used to optimize the cDNA amplicon size. P5, P7, i7 and i5 sample indexes, and TruSeq Read 2 (read 2 primer sequence) are added via End Repair, A-tailing, Adaptor Ligation, and PCR. The final libraries contain the P5 and P7 primers used in Illumina amplification.

    This protocol details the gene expression dual index library construction and sequencing.

    Before start

    Equilibrate to Room temperature (RT) – Fragmentation Buffer (2000091), Adaptor Oligos (2000094), Ligation Buffer (2000092) and Dual Index Plate TT Set A (3000431)* Place on ice– Fragmentation Enzyme (2000090/2000104), DNA Ligase (220110/220131) and Amp Mix (2000047/2000103)

    • Thaw at 65°C- Cleanup Buffer (2000088)

    Attachments

    snRNAseq_ProtocolsIO format_NCE202405.docx

    Steps

    Gene Expression Dual Index Library Construction

    1.

    Fragmentation, End Repair & A-tailing

    1.1.

    Prepare a thermal cycler with the following incubation protocol:

    ABC
    Lid TemperatureReaction VolumeRun Time
    65°C50 µl~35 min
    StepTemperatureTime
    Pre-cool block4°CHold
    Fragmentation32°C5 min
    End Repair & A-tailing65°C30 min
    Hold72°CHold

    Thermocycler protocol.

    1.2.

    Vortex fragmentation buffer. Verify there is no precipitate.

    1.3.

    Prepare fragmentation mix On ice. Pipette mix and centrifuge briefly.

    Fragmentation Mix

    ABCD
    Reagents1X (μl)4X+10% (μl)8X+10% (μl)
    Fragmentation Buffer52244
    Fragmentation Enzyme104488
    Total1566132

    Calculation for the Fragmentation Mix preparation.

    1.4.

    Transfer ONLY 10µLpurified cDNA sample from pellet cleanup to a tube strip. The remaining 30µL(75%) cDNA sample can be stored at 4°C for up to 72h 0m 0s or at -20°C for up to 4 weeks for generating additional 3ʹ Gene Expression libraries.

    1.5.

    Add 25µL buffer EB to each sample.

    1.6.

    Add 15µL fragmentation mix to each sample.

    1.7.

    Pipette mix 15× (pipette set to 35 µl)On ice. Centrifuge briefly.

    1.8.

    Transfer into the pre-cooled thermal cycler (4°C) and press “SKIP” to initiate the protocol.

    2.

    Post Fragmentation,End Repair & A-tailing Double Sided Size Selection – SPRIselect:

    2.1.

    Vortex to resuspend SPRIselect reagent. Add 30µL SPRIselect (0.6X) reagent to each sample. Pipette mix 15× (pipette set to 75 µl).

    2.10.

    Remove the ethanol.

    2.11.

    Repeat sub-steps 2.9 and 2.10 for a total of 2 washes.

    2.12.

    Centrifuge briefly. Place on the magnet. Low until the solution clears. Remove remaining ethanol.

    2.13.

    Remove from the magnet. Add 50.5µL buffer EB to each sample. Pipette mix 15× (pipette set to 45 µl).

    2.14.

    Incubate 0h 2m 0s at Room temperature.

    2.15.

    Place on the magnet. High until the solution clears.

    2.16.

    Transfer50µL sample to a new tube strip.

    2.2.

    Incubate 0h 5m 0s at Room temperature.

    2.3.

    Place on the magnet. High until the solution clears. DO NOT discard supernatant.

    2.4.

    Transfer75µLsupernatant to a new tube strip.

    2.5.

    Vortex to resuspend SPRIselect reagent. Add 10µLSPRIselect reagent (0.8X) to each transferred supernatant. Pipette mix 15× (pipette set to 80 µl).

    2.6.

    Incubate 0h 5m 0s at Room temperature.

    2.7.

    Place on the magnet. High until the solution clears.

    2.8.

    Remove 80µL supernatant. DO NOT discard any beads.

    2.9.

    Add 125µL 80% ethanol to the pellet. Wait 0h 0m 30s.

    3.

    Adaptor Ligation

    3.1.

    Prepare adaptor ligation Mix. Pipette mix and centrifuge briefly.

    Adaptor Ligation Mix:

    ABCD
    Reagents1X (μl)4X+10% (μl)8X+10% (μl)
    Ligation Buffer2088176
    DNA Ligase104488
    Adaptor Oligos2088179
    Total50220440
    3.2.

    Add 50µL adaptor ligation mix to 50µL sample. Pipette mix 15× (pipette set to 90 µl). Centrifuge briefly.

    3.3.

    Incubate in a thermal cycler with the following protocol:

    ABC
    Lid TemperatureReaction VolumeRun Time
    30°C100 µl15 min
    StepTemperatureTime
    120°C15 min
    24°CHold
    4.

    Post Ligation Cleanup – SPRIselect:

    4.1.

    Vortex to resuspend SPRIselect reagent. Add 80µLSPRIselect (0.8X) reagent to each sample. Pipette mix 15× (pipette set to 75 µl).

    4.10.

    Remove from the magnet. Add 30.5µL buffer EB to each sample. Pipette mix 15x.

    4.11.

    Incubate 0h 2m 0satRoom temperature.

    4.12.

    Place on the magnet. Low until the solution clears.

    4.13.

    Transfer 30µL sample to a new tube strip.

    4.2.

    Incubate 0h 5m 0s at Room temperature.

    4.3.

    Place on the magnet. High until the solution clears.

    4.4.

    Remove the supernatant.

    4.5.

    Add 200µL 80% ethanol to the pellet. Wait 0h 0m 30s.

    4.6.

    Remove the ethanol.

    4.7.

    Repeat sub-steps 4.5 and 4.6 for a total of 2 washes.

    4.8.

    Centrifuge briefly. Place on the magnet. Low until the solution clears.

    4.9.

    Remove remaining ethanol. Air dry for 0h 2m 0s.

    5.

    Sample Index PCR

    5.1.

    Choose the appropriate sample index sets to ensure that no sample indices overlap in a multiplexed sequencing run. Record the 10× Sample Index name (PN-3000431 Dual Index Plate TT Set A well ID) used.

    5.2.

    Add 50µL Amp mix to 30µL sample.

    5.3.

    Add 20µL of an individual Dual Index TT Set A to each sample and record the well ID used. Pipette mix 5× (pipette set to 90 µl). Centrifuge briefly.

    5.4.

    Incubate in a thermal cycler with the following protocol:

    ABC
    Lid TemperatureReaction VolumeRun Time
    105°C100 µl~25-40 min
    StepTemperatureTime
    198°C45 sec
    298°C20 sec
    354°C30 sec
    472°C20 sec
    5Go to Step 2 – * # cycles calculated below
    672°C1 min
    74°CHold

    Note
    The total cycles should be optimized based on 25% carry forward cDNA yield/input calculated during cDNA QC & Quantification

    AB
    cDNA InputTotal cycles
    0.25-25 ng14-16
    25-150 ngDec-14
    150-500 ng10-Dec
    500-1,000 ng08-Oct
    1,000-1,500 ng06-Aug
    >1,500 ng5
    5.5.

    Store at 4°C for up to 72h 0m 0s or proceed to the next step.

    6.

    Post Sample Index PCR Double Sided Size Selection – SPRIselect

    6.1.

    Vortex to resuspend SPRIselect reagent. Add 60µL SPRIselect (0.6X) reagent to each sample. Pipette mix 15× (pipette set to 150 µl).

    6.10.

    Remove the ethanol.

    6.11.

    Repeat sub-steps 6.9 and 6.10 for a total of 2 washes.

    6.12.

    Centrifuge briefly. Place on the magnet. Low until the solution clears. Remove remaining ethanol.

    6.13.

    Remove from the magnet. Add 35.5µL buffer EB to each sample. Pipette mix 15× (pipette set to 35 µl).

    6.14.

    Incubate 0h 2m 0s at Room temperature.

    6.15.

    Place on the magnet. Low until the solution clears.

    6.16.

    Transfer 35µL sample to a new tube strip.

    6.17.

    Store at 4°C for up to 72h 0m 0s or at -20°C for long-term storage.

    6.2.

    Incubate 0h 5m 0s at Room temperature.

    6.3.

    Place on the magnet. High until the solution clears. DO NOT discard supernatant.

    6.4.

    Transfer 150µL supernatant to a new tube strip.

    6.5.

    Vortex to resuspend SPRIselect reagent. Add 20µL SPRIselect reagent (0.8X)to each transferred supernatant. Pipette mix 15× (pipette set to 150 µl).

    6.6.

    Incubate 0h 5m 0s at Room temperature.

    6.7.

    Place on the magnet. High until the solution clears.

    6.8.

    Remove 165µL supernatant. DO NOT discard any beads.

    6.9.

    Add 200µL 80% ethanol to the pellet. Wait 0h 0m 30s.

    7.

    Post Library Construction QC

    7.1.

    Run 1µL sample at 1:10 dilution on an Agilent Bioanalyzer High Sensitivity chip.

    7.2.

    Determine the average fragment size from the Bioanalyzer trace. This will be used as the insert size for library quantification.

    Sequencing

    8.

    3’ Gene Expression Library Sequencing Depth & Run Parameters:

    AB
    Sequencing DepthMinimum 20,000 read pairs per cell
    Sequencing TypePair-end, dual indexing
    Sequencing ReadRecommended Number of cycles
    Read 128 cycles
    i7 Index10 cycles
    i5 Index10 cycles
    Read 290 cycles
    9.

    Once quantified and normalized, the 3’ Gene Expression libraries should be denatured and diluted as recommended for Illumina sequencing platforms.

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