Poster abstracts

Poster number 11 submitted by Caleb Embree

Investigating how spliceosome defects reduce nonsense mediated mRNA decay efficiency

Caleb Embree (Molecular Genetics), Manu Sanjeev (MCDB), Andreas Stephanou (Molecular Genetics)

Abstract:
Pre-mRNA splicing is an essential process in the gene expression pathway. Splicing is carried out by the spliceosome, a complex machine made up of five ribonucleoprotein complexes and over 200 other proteins. Mutations in spliceosome components occur in a number of diseases, including multiple types of cancer. Because pre-mRNA splicing occurs on most human protein-coding RNAs, spliceosome mutations have widespread effects in the cell. The effects of spliceosome mutations are commonly thought of as production of aberrant proteins as a result of mis-spliced mRNA. However, the spliceosome is tied to many essential downstream processes, including nonsense mediated mRNA decay (NMD), an essential RNA quality control and gene regulatory pathway. During pre-mRNA splicing, the spliceosome deposits a set of proteins on exon junctions called the exon junction complex (EJC), which is used to sense mRNAs targeted to NMD. We hypothesize that defects in spliceosome components create an overabundance of transcripts containing NMD-inducing features, which in turn overwhelms NMD. We have analyzed RNA-seq datasets from spliceosome component knockdown cells to examine the effect on NMD. Components of the activated spliceosome reduce the NMD efficiency as measured by effects on natural NMD targets. These data indicate that disruptions of the activated spliceosome cause a global reduction in NMD efficiency. We are further examining the relationship between pre-mRNA splicing and NMD by investigating pathogenic mutations in a specific spliceosomal protein, the U5 component EFTUD2. We have determined that autosomal dominant mutations in EFTUD2, which result in a rare cranio-facial disorder, compromise its interaction with BRR2, EFTUD2’s direct interactor within the spliceosome. We have also determined that some pathogenic mutations in EFTUD2 that result in C-terminal truncations which reduce its interaction with the EJC, possibly affecting EJC deposition. Together, we have shown that disruptions in the spliceosome have far-reaching effects on NMD efficiency, possibly as a result of overburdening the NMD pathway or by compromising EJC deposition.

Keywords: spliceosome, NMD, RNA regulation