The Role of GSK-3beta in Palate Development and Fusion

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DESCRIPTION (provided by applicant): Craniofacial birth defects represent devastating psychosocial complications as well as a significant socioeconomic burden. Among them, cleft palate posed an annual "national bill" exceeding $100 million in 2004 in direct hospital costs alone and is highly prevalent as the incidence is roughly 0.1% (one in 1000 children), making it the second most common birth defect. Previous studies indicate that the pathogenesis of cleft palate is multifactorial and likely has both genetic and environmental factors. Much of our knowledge of craniofacial clefting arises from case studies of patients and although limited, selected animal models. A number of genes have been identified to be associated with the cleft palate phenotype, but the etiology of the majority of cases remains elusive. Affected children require multiple operations to address not only palate closure, but also associated problems with speech, feeding, dentition, and other craniofacial growth deficiencies. The function of GSK-32 has previously been shown to be intimately related to and necessary for normal craniofacial development. The central hypothesis of this application is that signal transduction pathways dependent on GSK-32 control the development of the secondary palate. This proposal will use genetic analysis and novel protein regulation techniques to study the roles of GSK-32 in palate formation. Two Specific Aims are proposed to explore the roles of GSK-32 in palatogenesis and fusion. The first aim will address the mechanistic requirements of GSK-32 signaling in palatogenesis while the second aim brings a new technique to control levels of GSK-32 protein to the study of palate development. In the first aim, the mechanism(s) underlying the cleft of the secondary palate in GSK-32 mutant mice will be explored. Palatal shelves in this mutant have previously been shown to develop seemingly appropriately during embryogenesis, but fail to fuse. This deficiency may be the result of defective palatal shelf growth, cell apoptosis and/or transdifferentiation, and the first part of this aim will look in vivo to investigate markers of these processes during palatogenesis in mutant compared to the wild-type palates. In the second part, in vitro organ culture will be used to determine if the mutant palateal shelves are capable of fusion when placed in apposition in organ culture. In the second aim, the study of palatogenesis using a drug-dependent GSK-32 allele during distinct stages will be undertaken. Because GSK-32 is required at different times in different regions, complete early loss of its activity may preclude study of its action at a downstream time and location for example, growth and fusion events in the palate after defective maxillogenesis. This system is novel and requires further investigation and adaptation to in vitro protocols. Taken together, these two aims will pinpoint the spatial and temporal requirements of GSK-32 signaling and greatly advance our knowledge of the mechanistic causes of human orofacial clefting. Furthermore, the new protein regulation techniques that we develop will serve as a template for future developmental studies. PUBLIC HEALTH RELEVANCE: Children and families affected by cleft palate must not only endure multiple, physiologically challenging surgeries to address palate closure, but also associated problems with speech, feeding, dentition, and other facial growth deficiencies. In addition, cleft palate brings with it devastating psychosocial implications for many children as well as significant socioeconomic burden exceeding $100 million in direct hospital costs alone. These facts are significant and while certain genes and environmental factors have been associated with the development of cleft palate, the cause in the majority of cases remains unknown and further study is extremely important.