Beckwith-Wiedeman Syndrome (BWS), and Prader-Willi/Angelman Syndromes (PWS/AS) are rare developmental disorders with parent-of-origin effects that occur in 1/15,000 live births in the US. The molecular basis for these diseases is deregulation of imprinted gene clusters on 11 p15 and 15q11 caused predominantly by either deletions within imprinting control centers (ICC) or by epigenetic DMA methylation changes in the ICC. Elevated risk for AS and BWS has been associated with assisted reproductive technologies, which are thought to induce epigenetic loss of imprinting during in vitro embryo culture. This proposal tests the overall hypothesis that epigenetic alterations alone can cause developmental pathologies that model these syndromes as a result of global loss of imprinting (LOI), and further tests a therapeutic approach for correcting LOI events. As a means to determine the cumulative developmental effects of global LOI, we have established a new mouse model for genome-wide epigenetic deregulation using sequential gene inactivation and reactivation for the essential DMA methyltransferase Dnmtl in embryonic stem cells. DMA methylation is the primary mechanism in mammals for stable propagation of epigenetic silencing at imprinted loci as well as across the entire genome. Using this LOI model we will: (1) identify all DMA methylation-dependent imprinted genes using transcriptional profiling and DNA methylation analyses, (2) determine developmental phenotypic effects of genome-wide loss of imprinting with particular emphasis on fetal growth and characteristic symptoms from BWS, PWS, and AS observed in critical organs including pancreas, kidney and heart, (3) selectively correct individual gene expression abnormalities to assess the contribution of single genes to the complex phenotype using a novel transgenic RNAi strategy. This project will define the set of genes responsive to changes in DNA methylation state during preimplantation development that cause subsequent developmental anomalies when epigenetically misregulated. This study will fill a current gap in knowledge by prospectively connecting epigenetic alterations to resultant developmental defects during organogenesis, and further establishing the subsequent pathologies that are observed in the adult.