Isolation of epidermal progenitors from control, Eed cKO, Ring1a/b 2KO, and Eed; Ring1a/b 3KO mice was done as previously described (Cohen et al. 2019 (link)). P0 back skins were collected and incubated for 4–6 h in 1.26 U/mL dispase (Invitrogen) at 4°C. The epidermis was gently peeled from the underlying dermis, followed by 0.25% trypsin treatment for 15 min at 37°C. The cell suspension was washed twice with 1× PBS; stained with 1:200 Sca1-PerCP-Cy5.5 (Biolegend), 1:100 α6-integrin-FITC (eBiosciences), and 1:200 EpCAM-APC (Biolegend) for 30 min on ice; and washed twice with 1× HBSS before cell sorting. Interfollicular epidermis, enriched for epidermal progenitors, was sorted as EpCAM(+), Sca1(+), and α6-integrin(high). For ChIP and ChIP-seq analyses, cell suspensions were stained for cell viability and cross-linked before staining and FACS sorting as described above. All cell isolations were performed on a FACS Influx instrument (BD) in the Flow Cytometry Core Facility at Icahn School of Medicine at Mount Sinai.