SMAD6 and hydrops fetalis: Expression of TGF-beta/BMP-related genes was also increased during the late stages of HF and skin morphogenesis, including BMP2, BMP4 and BMP8A. We also found that some BMP inhibitors were up-regulated in E120 skin, such as SMAD6 and SMAD7, which are important for antagonising TGF-beta/BMP activity and balance BMP inhibition [56] (Table 4, S6 Fig).