Analysis of Nsdhl-deficient embryos reveals a role for Hedgehog signaling in early placental development.

The X-linked Nsdhl gene encodes a sterol dehydrogenase involved in cholesterol biosynthesis. Mutations in this gene cause the male lethal phenotypes in human CHILD syndrome and bare patches (Bpa) mice. Affected male embryos for several mutant Nsdhl alleles die in mid-gestation with a thin and poorly vascularized placental labyrinth. The timing and specific abnormalities noted suggest a defect in one or more developmental signaling pathways as a possible mechanism. Here, we examined the possible involvement of the hedgehog signaling pathway in the placental pathology of Nsdhl mutants using a transgenic mouse line (Ptch1(tm1Mps)) that contains a lacZ reporter under the control of the promoter for Ptch1, the gene that encodes the major hedgehog receptor. We demonstrate expression of Ptch1 in allantoic mesoderm of the placenta from wild-type mid-gestation embryos. The evidence suggests that the signaling is induced by Indian hedgehog that is produced by distal (ectoplacental) visceral endoderm cells that migrate into the allantoic mesoderm before embryonic day 10.0. Using a ubiquitously expressed, X-linked lacZ transgene that undergoes normal X-inactivation, we demonstrate that the placental defects in Nsdhl/+ female embryos are non-cell autonomous. Further, affected placentas from mutant Nsdhl(Bpa-8H) male embryos demonstrate markedly decreased or no Ptch1-lacZ staining and no migration of Ihh expressing cells into the developing placenta. These data strongly implicate the hedgehog signaling pathway in the pathogenesis of the placental defects in NSDHL deficiency and provide evidence for a role for the hedgehog pathway in the development of a functional mammalian placenta.