BMP4 and hydrops fetalis: Our previous study also shows that other classical pathway marker genes like Wnt5a, CTNNB1, DKK4, and BMP4 reported in mouse (Saxena et al., 2019) and human HF (Koch et al., 2020) were also being expressed in hair placode formation during the induction and organogenesis stages in pig (Jiang et al., 2019).