Poster abstracts
Poster number 42 submitted by Manu Sanjeev
Role of SR proteins in mRNP remodeling and Nonsense Mediated Decay
Manu Sanjeev (Department of Molecular Genetics, OSU), Guramrit Singh (Department of Molecular Genetics, OSU)
Abstract:
After their transcription, all mRNAs in cells are compacted into large rod-shaped ribonucleoprotein (RNP) complexes with sizes comparable to the small ribosome subunit[1][2][3]. This packaging is crucial for genomic stability, and presumably for mRNA export and translation. The exon junction complex (EJC), along with a variety of peripheral proteins including several Serine Arginine rich (SR) proteins, forms the core of the packaged mRNPs[4]. Recent work from our lab has shown that EJCs and mRNPs are dynamic and undergo remodeling in the cytoplasm into smaller complexes that contain the EJC core but lack SR proteins[5]. The removal of SR proteins also reduces the Nonsense Mediated Decay (NMD) efficiency of target mRNAs. My overarching goal is to understand how different SR-rich proteins assemble on the periphery of the EJC core to form the mRNP in the nucleus, to identify the mechanism by which SR proteins are evicted from mRNPs in the cytoplasm to cause its remodeling, and to determine the effect of mRNP packaging on EJC dependent processes like mRNA export and NMD. Here, I show that the overexpression of SR protein kinase SRPK1, but not its kinase-dead mutant version, drastically slows down the NMD of a reporter RNA. This suggests that SRPK1 potentially plays a role in this remodeling presumably by phosphorylating SR proteins on mRNPs in the cytoplasm. Further, to understand if increased recruitment of peripheral EJC proteins (e.g. SRSF1 and RNPS1) confers increased NMD efficiency on mRNPs, I have developed reporter mRNAs containing enhanced EJC and SR protein recruitment signals. These reporters undergo NMD with increased efficiency as compared to a normal NMD reporter RNA[6]. I am currently testing if knockdown of SR proteins slows down the NMD of this reporter. Overall, this study provides insights into two important aspects of gene regulation: (i) how mRNP remodeling occurs in cells, and (ii) how changes in mRNP composition affects NMD efficiency.
References:
1. G. Singh et. Al, “The Clothes Make the mRNA: Past and Present Trends in mRNP Fashion,” Annu. Rev. Biochem., vol. 84, 2015.
2. M. Metkar et al., “Higher-Order Organization Principles of Pre-translational mRNPs.,” Mol. Cell, vol. 72, 2018.
3. S. Adivarahan et al., “Spatial Organization of Single mRNPs at Different Stages of the Gene Expression Pathway.,” Mol. Cell, vol. 72, 2018.
4. G. Singh et al., “The cellular EJC interactome reveals higher-order mRNP structure and an EJC-SR protein nexus,” Cell, vol. 151, 2012.
5. Mabin JW, Woodward LA, Patton RD et. Al, “The Exon Junction Complex Undergoes a Compositional Switch that Alters mRNP Structure and Nonsense-Mediated mRNA Decay Activity,” Cell Rep., vol. 25, 2018.
6. J. P. Gudikote et al, “RNA splicing promotes translation and RNA surveillance,” Nat. Struct. Mol. Biol., vol. 12, 2005.
Keywords: mRNP remodeling, EJC, SRPK1