SMO and hydrops fetalis: To determine the specific role of Shh in the epithelium of the developing HF, we abrogated Shh responsiveness in skin keratinocytes by K14-Cre-mediated inactivation of a conditional Smo allele (floxed; [K14-Cre; Smo f/f]) or by Shh-dependent removal using a Shhgfp-Cre knockin allele.