Non-syndromic cleft lip and cleft palate, one of the major groups of congenital birth defects in human beings. Despite the frequent occurrence, relatively little is known about the developmental and genetic basis that leads to a cleft lip and/or cleft palate formation. Mammalian palatogenesis is a complex and multiple step process, largely depending on the sequential and reciprocal tissue interactions. Members of several families of growth factors have been demonstrated to play a role in mediating such tissue interaction during palatogenesis, including BMP, FGF, TGF?, and Shh. Recent studies have begun to implicate a role of Wnt signaling in the palate development. The cleft palate phenotype has been linked to mutations in WNT3 and WNT5A in humans. We have found that Wnt5a-deficiency leads to a complete cleft of the secondary palate, which exhibits distinct phenotypic alterations at histology, cellular and molecular levels in the anterior and posterior palate. We further demonstrated that Ror2, a orphan tyrosine kinase receptor for Wnt5a noncanonical signaling, genetically interacts with Wnt5a and mediates Wnt5a noncanonical signaling in regulating directional cell migration and cell proliferation in the developing palate. However, Wnt5a mutants exhibit much severer palatal defects histologically as compared to that in Ror2-/- palate or Wnt5a+/-;Ror2+/- palate, indicating an involvement of another receptor(s). Based on these observations and the fact that mice deficient in Ryk exhibit a cleft palate phenotype and the absence of the canonical Wnt signaling activity in the developing palate, we hypothesized that Wnt5a signals through Ror2- and Ryk- mediated noncanonical pathway to regulate palatogenesis.
Three aims are proposed to test this hypothesis: 1) to establish that Wnt5a does not signal through the canonical pathway to regulate palatogenesis;2) to determine that Wnt5a signals through Ror2-mediated noncanonical pathway to regulate epithelial-mesenchymal interaction during palatogenesis;and 3) to define the role of Ryk in mediating Wnt5a signaling in palate development. A combination of genetic crosses, histological, cellular and molecular assays, as well as in vitro organ culture and cell migration assays will be utilized to accomplish these goals. The results obtained will provide an insight for a better understanding of the mechanisms of cleft palate formation in humans.
Cleft palate represents one of the most frequent human birth defects. This complex birth defect is caused by both multigenic and environmental contributions. Despite the frequent occurrence, relatively little is known about the developmental and genetic basis that leads to a cleft palate formation. The growth factor plays vital roles in embryogenesis. Mutations in several WNT growth factors have been associated with human cleft palate defect. This proposal studies the role of Wnt signaling in the regulation of the palate development and attempts to establish molecular and cellular mechanisms underlying Wnt5a and its receptors during palatogenesis. The results obtained from this study will provide fundamental information for our understanding of cleft palate formation in humans, and provide an insight for the genetic prevention and therapy of the human cleft palate.
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