RAC1 and hydrops fetalis: Of the 26 HF morphogenesis candidates, Rac1 was in essence already validated, as prior genetic studies reported that Rac1 was essential for HF integrity but not epidermal maintenance (Behrendt et al., 2012; Chrostek et al., 2006) (our morphogenetic screen would not have captured Rac1’s postnatal roles for example in wound-repair, stem cell function and tumorigenesis).