PDGFR-alpha signaling is critical for tooth cusp and palate morphogenesis.

Platelet-derived growth factor receptor alpha (PDGFR-alpha) and PDGF ligands are key regulators for embryonic development. Although Pdgfralpha is spatially expressed in the cranial neural crest (CNC)-derived odontogenic mesenchyme, mice deficient for Pdgfralpha are embryonic lethal, making it impossible to investigate the functional significance of PDGF signaling in regulating the fate of CNC cells during tooth morphogenesis. Taking advantage of the kidney capsule assay, we investigated the biological function of PDGF signaling in regulating tooth morphogenesis. Pdgfralpha and Pdgfa are specifically and consistently expressed in the CNC-derived odontogenic mesenchyme and the dental epithelium, respectively, throughout all stages of tooth development, suggesting a paracrine function of PDGF signaling in regulating tooth morphogenesis. Highly concentrated expression patterns of Pdgfralpha and Pdgfa are associated with the developing dental cusp, suggesting possible functional importance of PDGF signaling in regulating cusp formation. Loss of the Pdgfralpha gene does not affect proper odontoblasts proliferation and differentiation in the CNC-derived odontogenic mesenchyme but perturbs the formation of extracellular matrix and the organization of odontoblast cells at the forming cusp area, resulting in dental cusp growth defect. Pdgfralpha-/- mice have complete cleft palate. We show that the cleft palate in Pdgfralpha mutant mice results from an extracellular matrix defect within the CNC-derived palatal mesenchyme. The midline epithelium of the mutant palatal shelf remains functionally competent to mediate palatal fusion once the palatal shelves are placed in close contact in vitro. Collectively, our data suggests that PDGFRalpha and PDGFA are critical regulators for the continued epithelial-mesenchymal interaction during tooth and palate morphogenesis. Disruption of PDGFRalpha signaling disturbs the growth of dental cusp and interferes with the critical extension of palatal shelf during craniofacial development.