SUMMARY Imprinted expression of UBE3A is neuron-specific and occurs because the paternally-inherited allele is silenced. A long non-coding antisense transcript, UBE3A-ATS, is expressed in a neuron-specific manner and mediates UBE3A imprinting by an unknown mechanism. The overall goal of this proposal is to understand the processes underlying the regulation of neuron-specific expression of UBE3A-ATS and repression of paternal UBE3A in human neurons. We propose to investigate three different aspects regulating UBE3A imprinted expression: 1) the regulation of coding versus non-coding SNRPN RNAs in human neurons; 2) the tissue-specific regulation of UBE3A-ATS, the distal portion of the SNRPN ncRNA; and 3) the mechanism by which UBE3A-ATS leads to the repression of paternal UBE3A. We will use patient-specific induced pluripotent stem cells (iPSCs) derived from Angelman syndrome (AS) patients and their neuronal derivatives for these studies. We will dissect the functional elements of the cis-acting boundary element restricting UBE3A-ATS expression to neurons and determine the developmental timing of their removal. We will determine how SNRPN coding versus non-coding RNA is produced and manipulate expression levels of UBE3A-ATS and UBE3A to determine their effect on UBE3A imprinting. Finally, we will test the hypothesis that UBE3A-ATS silences paternal UBE3A via a transcriptional interference mechanism. A thorough understanding of the mechanisms underlying UBE3A imprinted expression may reveal novel gene regulatory mechanisms applicable elsewhere in the genome, and may identify novel therapeutic targets for treating AS.