Clefts of the palate and/or lip are among the most common human craniofacial malformations and involve multiple genetic and environmental factors. Defects can only be corrected surgically and require complex life-long treatments. Our studies utilized the well-characterized mouse model with a consistent cleft palate phenotype to test small-molecule Wnt agonist therapies. We show that the absence of Pax9 alters the expression of Wnt pathway genes including and , proven antagonists of Wnt signaling. The functional interactions between Pax9 and Dkk1 are shown by the genetic rescue of secondary palate clefts in embryos. The controlled intravenous delivery of small-molecule Wnt agonists (Dkk inhibitors) into pregnant mice restored Wnt signaling and led to the growth and fusion of palatal shelves, as marked by an increase in cell proliferation and osteogenesis, while other organ defects were not corrected. This work underscores the importance of Pax9-dependent Wnt signaling in palatogenesis and suggests that this functional upstream molecular relationship can be exploited for the development of therapies for human cleft palates that arise from single-gene disorders.

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Clefts of the palate and/or lip arise in about 1/700 human live births and are caused by multiple genetic and environmental factors. Studies of mouse knockout models of cleft palate have improved our understanding of the molecular control of palatogenesis. While it is known that Pax9 regulates palatogenesis through Bmp, Fgf and Shh signaling, there is still much to learn about its precise relationship with other pathways. Here we show that alterations of Wnt expression and decreased Wnt activity in Pax9-/- palatal shelves are a result of Pax9’s ability to directly bind and repress the promoters of Dkk1 and Dkk2, proteins that antagonize Wnt signaling. The delivery of small-molecule Dkk inhibitors (Wnt agonists) into the tail-veins of pregnant Pax9+/- mice from E10.5 to E14.5 restored Wnt signaling, promoted cell proliferation, bone formation and restored the fusion of palatal shelves in Pax9-/- embryos. In contrast, other organ defects in Pax9 mutants were not corrected. These data uncover a unique molecular relationship between Pax9 and Wnt genes in palatogenesis and offer a new approach for treating cleft palates in humans.Summary StatementThese studies demonstrate that the Pax9/Wnt genes regulate murine palatogenesis. This unique molecular relationship is proven by the correction of cleft defects in Pax9-deficient mice through Wnt agonist therapies.