Ectopic Hedgehog Signaling Causes Cleft Palate and Defective Osteogenesis.

Cleft palate is a common birth defect that frequently occurs in human congenital malformations caused by mutations in components of the Sonic Hedgehog (S HH) signaling cascade. Shh is expressed in dynamic, spatiotemporal domains within epithelial rugae and plays a key role in driving epithelial-mesenchymal interactions that are central to development of the secondary palate. However, the gene regulatory networks downstream of Hedgehog (Hh) signaling are incompletely characterized. Here, we show that ectopic Hh signaling in the palatal mesenchyme disrupts oral-nasal patterning of the neural crest cell-derived ectomesenchyme of the palatal shelves, leading to defective palatine bone formation and fully penetrant cleft palate. We show that a series of Fox transcription factors, including the novel direct target Foxl1, function downstream of Hh signaling in the secondary palate. Furthermore, we demonstrate that Wnt/bone morphogenetic protein (BMP) antagonists, in particular Sostdc1, are positively regulated by Hh signaling, concomitant with downregulation of key regulators of osteogenesis and BMP signaling effectors. Our data demonstrate that ectopic Hh-Smo signaling downregulates Wnt/BMP pathways, at least in part by upregulating Sostdc1, resulting in cleft palate and defective osteogenesis.