Talk abstracts
Talk on Saturday 09:15-09:30am submitted by Anton Blatnik
A novel SMN mutant implicates correction of UsnRNP biogenesis and pre-mRNA splicing as critically associated with suppression of SMA
Anton J Blatnik III (Genetics & Genome Sciences, Case Western Reserve University School of Medicine), Vicki L McGovern, Summer Baxley, Kaitlyn M Kray (Biologcial Chemistry & Pharmacology, The Ohio State University Wexner Medical Center), Mitchell Drumm (Genetics & Genome Sciences, Case Western Reserve University School of Medicine), W David Arnold (Physical Medicine & Rehabilitation, Neurology & Medical Pharmacology and Physiology, University of Missouri School of Medicine), Xueyong Wang, Mark Rich (Neuroscience Cell Biology & Physiology, Wright State University), Arthur H M Burghes (Biologcial Chemistry & Pharmacology, The Ohio State University Wexner Medical Center)
Abstract:
The Survival Motor Neuron (SMN) protein forms a complex responsible for building the uridine-rich small nuclear ribonucleoproteins (UsnRNP) that constitute the targeting and catalytic subunits of the spliceosome. Insufficient production of SMN protein is causal of the motor neuron disease, Spinal Muscular Atrophy (SMA). It is not understood why low levels of an essential, ubiquitously expressed protein would result in the selective SMA phenotype. SMNs role in assembly of spliceosomal UsnRNPs supports the hypothesis that mis-splicing of motor neuron-ciritical transcripts is responsible, but evidence is lacking. We have identified a novel SMN mutant (SMN2B) that suppresses the development of SMA in mice when expressed at SMA-causing levels. Our experiments show that SMN2B UsnRNP assembly activity is not different from wild-type and that despite low SMN2B abundance, UsnRNA expression is corrected to wild-type, correcting compensatory UsnRNA overexpression in SMA mice. We sequenced cytoplasmic and nuclear RNA from wild-type, SMA, and SMN2B mouse spinal cords to assess the extent of transcript mis-splicing. Nuclear RNA sequencing identifies many alternatively spliced events in SMA, in which intron retention is the largest category. As previously reported, introns spliced by the minor spliceosome are preferentially retained. Furthermore, minor introns that are also sterically short (<200nt) are the most affected. Analysis of the cytoplasmic RNA sequencing indicates that transcripts in which intron-retention was identified in nuclear RNA sequencing are globally reduced in abundance in SMA. This is the first description that increased intron retention in SMA may explain broad changes to the levels of mature RNAs in the cytoplasm. Nearly all alternatively spliced events detected in SMA are rescued to wild-type in SMN2B. This study provides a granular view of the effects of mis-splicing in SMA and that its correction is critically associated with SMA suppression.
Keywords: splicing, UsnRNP, SMN