UCSF

Very little is known about the role of Ras signaling in tooth development although upstream receptor tyrosine (RTK) signaling that activates Ras and regulators of Ras signaling, like proteins encoded by the Sprouty genes, are known to be important in tooth development. The RASopathies, including Costello syndrome (CS) and Cardio-facio-cutaneous syndrome (CFC), are syndromes caused by gain-of-function mutations in the Ras pathway and are characterized by a wide range of cardiac, musculoskeletal, dermatological, and developmental abnormalities. These syndromes provide an excellent model to study the role of Ras signaling in tooth development, and thus, we analyzed the craniofacial and dental phenotypes of CS and CFC at family conferences in 2009 and 2011. CS and CFC have in common craniofacial characteristics including macrocephaly, bitemporal narrowing, and convex facial profile. Additionally, individuals with CFC have hypoplastic supraorbital ridges, and CS individuals have characteristic micrognathia, full cheeks, large appearing mouth, and thick appearing lips. There were some overlapping dental characteristics between CS and CFC, including malocclusion, but overall, CS had more dysmorphic dental characteristics compared to CFC. CS individuals had class III molar relationship, delayed tooth development and eruption, gingival hyperplasia, thickening of the alveolar ridge, and high-arched palate more often compared to CFC. Moreover, CS individuals had a hypoplastic enamel defect that was not present in CFC. To further understand the role Ras in enamel formation, we obtained a CS mouse model and found that the CS mouse model had a similar hypoplastic enamel phenotype. Further analysis revealed that the progenitor cells were hyperproliferative, and the enamel producing ameloblasts lacked cell polarity and had delayed enamel protein expression, resulting in the enamel defect. Next, I utilized MEK1/2 (PD0325901) and PI3'K (GDC-0941) inhibitors to dissect the roles of the Ras effector pathways in amelogenesis. MEK inhibition rescued the ameloblast loss of polarity and delayed differentiation while MEK or PI3'K inhibition rescued the hyperproliferation phenotype. Thus, this dissertation work reveals a role for Ras signaling in amelogenesis, and knowledge gained about Ras signaling in the tooth may be applied to efforts to bioengineer teeth and further understand Ras in development and cancer.