Gfm200

Wild type (E14), RAD21-mAID-eGFP^{29 (link)}, and CTCF-AID-eGFP^{27 (link)} mouse embryonic stem (mES) cells were cultured on plates pre-coated with 0.1% gelatin (Sigma-Aldrich, G1393) in Glasgow Modified Essential Medium (Gibco, 11710035) supplemented with 10% fetal bovine serum (Gibco, 10270106), 0.01 mM 2-Mercaptoethanol (Gibco, 31350010), 2.4 mM L-glutamine (Gibco, 25030024), 1× non-essential amino acids (Gibco, 11140050), 1× sodium pyruvate (Gibco, 11360070) and 20 ng/ml recombinant mouse leukemia-inhibitory factor (Cell Guidance Systems, GFM200). Cells were grown at 37 °C and 5% CO₂. Half of the media was exchanged daily and cells were passaged every 2 days by trypsinization (Gibco, 25300054).

H1 human embryonic stem cells and E14 mouse embryonic stem cells were obtained from the 4D Nucleome Consortium and cultured according to 4D Nucleome Consortium-approved protocols (https://www.4dnucleome.org/). In brief, H1 cells were grown at 37 °C under 5% CO₂ on Matrigel (Corning, 354277)-coated dishes. Cells were maintained in complete mTeSR medium prepared from basal medium (Corning, 85851) with 5× supplement (Corning, 85852). Medium was replaced daily. Cell passage numbers were kept below P10. E14 cells were cultured on plates coated with 0.1% gelatin (EMD, SF008) in serum-free 2i/LIF medium; this medium was made from base medium (1:1 mixture of NeuroBasal medium (Gibco, 21103-049) and DMEM/F12 medium (Gibco, 11320-033) supplemented with 0.5× N2 supplement (Gibco, 17502-048), 0.5× B27 supplement (Gibco, 17504-044) and 0.05% bovine serum albumin (BSA) fraction V (Gibco, 15260-037)), supplemented with 1 µM PD0325901 (Reprocel, 04-0006-02C), 3 µM CHIR99021 (Reprocell, 04-0004-02C), 0.15 mM monothioglycerol (Sigma, M6145-25ML) and 1,000 U ml⁻¹ LIF (Cell Guidance Systems, GFM200). Medium was replaced daily, and cell passage number was kept below P10.