ABSTRACT Prader-Willi syndrome (PWS) is a neurogenetic disorder caused by the loss of paternally inherited genes on chromosome 15q11-q13. Atypical deletions that cause PWS have narrowed the genetic region critical for the disorder to a 91kb locus including SNORD116. SNORD116 is cluster of 30 highly similar C/D box small nucleolar RNAs (snoRNAs). Canonical C/D box snoRNAs anneal to and mediate 2'O-methylation (2'-OMe) of ribosomal RNAs, however, the SNORD116 copies lack complementarity to rRNAs. Instead they are hypothesized to modify mRNAs or lncRNAs, but direct targets for SNORD116 have not been identified. Thus, their function in neurons is not known. Fortunately, every individual with PWS has an intact, but epigenetically repressed copy of the PWS critical region, including SNORD116, on their maternal allele. We have recently shown that the maternal copy of SNORD116 can be activated in PWS neurons by depleting ZNF274, a KRAB domain zinc finger protein. Not only does this suggest an intriguing therapeutic approach to PWS, but also provides a critical tool to help understand how SNORD116 is regulated in neurons. The overall goal of this proposal is to better understand the molecular underpinnings of PWS. We will determine the chromatin states and long-range chromatin interactions of active and inactive 15q11-q13 alleles in iPSCs and neuronal derivatives. We will investigate how activation of SNORD116 via ZNF274 depletion and histone methyltransferase inhibition impact the chromatin state and long-range interactions. Finally, we will identify the direct 2'-O-methylation targets of SNORD116 and determine how they influence PWS-related differentially expressed genes.

NARRATIVE The overall goal of this proposal is to better understand the molecular underpinnings of Prader-Willi syndrome (PWS), which results from loss of the SNORD116 region of the paternal chromosome 15q11-q13. We will carry out a comprehensive set of experiments to learn 1) how maternal SNORD116 is repressed, particularly by ZNF274 and histone methyltransferases 2) how long-range chromatin interactions of active and inactive 15q11-q13 alleles in iPSCs and neuronal derivatives contribute to regulation and 3) the molecular targets of RNA modification (2'-O methylation) directed by the SNORD116 snoRNAs and how these modifications influence PWS-related differentially expressed genes.