Gene Regulatory Mechanisms of Mll4 in Tooth Enamel Development

Project Summary/Abstract In the U.S., more than 10% of infants are born with dental anomalies, including amelogenesis imperfecta (AI), a group of inherited enamel disorders caused by disruptions in gene expression. The study of enamel development, or amelogenesis, is critical for understanding these congenital disorders and developing novel therapies, which could have significant implications for oral health. However, the transcriptional and epigenetic mechanisms that regulate amelogenesis remain poorly understood. Kabuki syndrome, a rare genetic disorder caused by mutations in the MLL4 (KMT2D) gene, often presents with dental anomalies such as enamel defects, highlighting the importance of understanding the molecular mechanisms underlying enamel development. The long-term goal is to identify and characterize epigenetic regulators that control enamel development and contribute to dental anomalies like AI. The objective of this proposal is to define the role of MLL4, an epigenetic coactivator, in amelogenesis and explore why mutations in MLL4, as seen in Kabuki syndrome, lead to enamel defects. MLL4 is a histone H3-lysine 4 methyltransferase that promotes transcriptionally active chromatin, facilitating gene expression, but its role in regulating enamel formation is still unclear. To address this, a conditional knockout (Mll4-cKO) mouse model was generated, enabling robust deletion of Mll4 in dental epithelial cells responsible for amelogenesis. Based on preliminary studies, the hypothesis is that MLL4 coordinates multiple stages of amelogenesis by regulating gene expression necessary for cell differentiation and enamel formation. Using a combination of histological, radiographic, cellular, biochemical, genetic, and genome-wide approaches, along with an established Mll4-cKO mouse model that exhibits AI, two key questions will be investigated. Aim 1 will define the stages of amelogenesis that require Mll4 activity using the mouse incisor model. Aim 2 will delineate the molecular mechanisms by which Mll4 governs gene expression at different amelogenesis stages. Collectively, these experiments will provide crucial insights into the regulatory mechanisms driving enamel formation and could offer novel therapeutic targets for AI and other dental disorders.