Quantitative analysis of cell‐surface hCD4 expression by FACS analysis confirmed efficient recombination of the floxed Mcl‐1 allele in HFSCs (Lin–/CD49f+/CD34+/SCA‐1–), IFE (Lin–/CD49f+/SCA‐1+) and the non‐defined HF keratinocyte population (Lin–/CD49f+/CD34–/SCA‐1–) (Figs. S2E, 2C) in K5‐Cre/Mcl‐1f/f and K5‐Cre/Mcl‐1f/+ mice. Here, CD34 is linked to hydrops fetalis.