SHH and hydrops fetalis: Both HF morphogenesis and regeneration are enabled by well-orchestrated epithelial–mesenchymal interactions (EMIs) via biological signaling pathways, such as WNT, BMP, Sonic hedgehog (SHH), and Ectodysplasin A (EDA) pathways (St-Jacques et al., 1998; Millar, 2002; Zhang et al., 2009; Mikkola, 2011; Sennett and Rendl, 2012; Ohyama, 2019).