P7 Cap2 and EC ATAC data

TAC-seq was performed using the Active Motif ATAC-seq Kit (Cat# 53150) according to the manufacturer’s instructions. Approximately 50,000 EC were processed per sample. Cells were washed with 100 µl of ice-cold PBS and centrifuged at 500 × g for 5 minutes at 4°C. The cell pellet was resuspended in 100 µl of pre-chilled ATAC lysis buffer and immediately centrifuged again at 500 × g for 10 minutes at 4°C. The resulting nuclei pellet was resuspended in the Tagmentation Master Mix and incubated at 37°C for 30 minutes in a thermomixer. Following tagmentation, DNA was purified according to the protocol. Library amplification was performed as recommended and purified using SPRI bead cleanup. Sequencing was conducted using paired-end 150 bp reads. Sequencing reads were mapped using the nfcore/atacseq pipeline of the mouse reference genome47 (mm39). Peak calling was performed using MACS2, and differential chromatin accessibility analysis was carried out using HOMER and DESeq2.