GSM3690689: CN_02_ATAC_Seq; Homo sapiens; ATAC-seq
For ATAC-seq, we harvested 50,000 cells by centrifugation at 500 g x 5 min at 4C. We washed cells once with PBS buffer and resuspended the cell pellets in 50 uL of cold lysis buffer (10 mM Tris-HCl, pH7.4, 10 mM NaCl, 3 mM MgCl2, 0.1% IGEPAL CA- 630). We collected cell pellets, discarded the supernatants, and immediately continued to transposition reaction in 50 uL transposition reaction mix. We incubated the transposition reaction at 37C for 30 min, immediately followed by purification through a QIAGEN MinElute Kit. We stored the purified DNAs at  20 C until generating sequencing library. The library was generated and sequenced at University of Minnesota Genomic Center.We have followed the protocol as previously described (Buenrostro et al., 2013) with minor modifications. Specifically, we thawed the transposed and purified DNAs and carried out PCR in 50 uL of reaction with NEBNext High Fidelity 2X Master mix and 5 ul of 25 mM Forward/Reverse ATAC-seq index, i.e., standard barcoded primers of Nextera kit (FC-121-1030), for each sample. After reaction, we purified samples with SPRI beads and eluted the PCR products in 12 uL elution buffer. We checked the DNA library by picogreen quantification and the size of the fragments with an Agilent High Sensitivity DNA chip. Libraries were diluted to 2 nM and pooled for downstream sequencing. The library was generated and sequenced at University of Minnesota Genomic Center.We have followed the protocol as previously described (Buenrostro et al., 2013) with minor modifications: (1) using the standard Nextera primer set for PCR amplification of the transposed DNA fragments, (2) monitoring qPCR reaction to determine the number of additional cycles for full PCR amplification, and (3) using Agilent High Sensitivity DNA chip for library size validation. Specifically, we thawed the transposed and purified DNAs and carried out an initial 5-cycle PCR (1 cycle: 72 C for 5 min; 1 cycle: 98 C for 30 s; then 5 cycles: 98 C for 10 s, 63 C for 30 s, 72 C for 1 min) in a 50 mL of reaction including NEBNext High Fidelity 2X Master mix and 5 mL of 25 mMForward/Reverse ATAC-seq index, i.e., standard barcoded primers of Nextera kit (FC-121-1030), for each sample.We then used qPCR to determine the number of additional cycles of PCR amplification that were required, by using the cycle number that corresponds to 1/3 of the maximum fluorescent intensity (typically +5, +6, +7) shown on real-time PCR plots on ABI7900 (Applied Biosystems). After the reactions were subjected to additional PCR cycles, we purified each sample with SPRI beads and eluted the PCR products in 12 mL elution buffer. We checked the DNA library by picogreen quantification and the size of the fragments with an Agilent High Sensitivity DNA chip (the library should be sized between 200-700 bp). Libraries were diluted to 2 nM and pooled for downstream sequencing. For the initial OCR profiling, we pooled all the 6 libraries (2 for iPSC, 1 for N-d27, 1 for N-d33, and 2 for N-d41) and sequenced on a HiSeq 2500 using a PE 2x50 bp flow cell in a single sequencing lane. For the additional ATAC-seq on the unedited and edited iNs, we followed the same procedures as described above. We achieved > 120 million passing-filter reads for the lane and the average quality scores for all libraries are all above Q30 for both R1 and R2.