Cells were washed once with cold PBS, lysed in cold lysis buffer, and immediately centrifuged to collect nuclei. The nuclei pellet was resuspended in a transposition reaction mix (Illumina) and incubated at 37°C for 30 minutes. Following transposition, DNA was purified using the MinElute Kit (Qiagen) and amplified with NEBNext PCR Master Mix (New England Biolabs).