Poster abstracts

Poster number 93 submitted by Fuad Mohammad

Intronic GU-repeat region dictates alternative splicing of an ultra-conserved poison exon in BRD2

Fuad Mohammad (Center for Childhood Cancer and Blood Diseases at Nationwide Childrens Hospital), David A. Greenberg (Battelle Center for Mathematical Medicine at Nationwide Childrens Hospital), Dawn S. Chandler (Center for Childhood Cancer and Blood Diseases at Nationwide Childrens Hospital)

Abstract:
Juvenile myoclonic epilepsy (JME) is a common form of idiopathic generalized epilepsy, with a strong genetic pathophysiology. Genes associated with JME have only recently been discovered; yet the contribution of these genes to JME have not been elucidated outside of family-based linkage analysis. We focus on understanding how one gene identified through linkage analysis, BRD2, is regulated and altered in JME; specifically, how changes in the alternative splicing of BRD2 affect its expression. The importance of proper BRD2 expression is highlighted in mouse models, where Brd2 null mice lack proper CNS development and heterozygous Brd2+/- mice show hypersensitivity to induced seizures. We predict that a potential source of BRD2 mis-regulation in JME patients involves differential inclusion of the ultra-conserved poison exon 2a. Exon 2a inclusion in BRD2 pre-mRNA is thought to cause premature translation termination. Using cycloheximide and caffeine, both of which are known to inhibit nonsense mediated decay (NMD), we show that transcripts containing exon 2a are targets for NMD in tissue culture. To understand the effect of mutations on exon 2a inclusion, we focused on characterizing the splicing impact of polymorphic regions in BRD2 that show high association with JME in linkage studies. Using a BRD2 minigene system in tissue culture, we show increased exon 2a inclusion when shortening a GU repeat region in intron 2. Furthermore, overexpression or inhibition of a splicing regulator, CELF1 which binds GU-rich elements and is associated with epilepsy in mouse models, modulates endogenous BRD2 exon 2a inclusion. These initial studies suggest a role for BRD2 alternative splicing in the etiology of JME, and future studies will focus on how mutations found in patient samples affect exon 2a inclusion. We hope to use these findings to engineer targeted therapeutics using antisense oligonucleotide technology in order to one day modulate BRD2 splicing and expression in JME.

Keywords: BRD2, Ultraconserved Exons, NMD Gene regulation