Misregulation of the pre-mRNA splicing process has been associated with disease, particularly neurodegenerative disorders. However, the mechanisms underlying disease are largely unknown, partially because of the absence of an ideal disease model that can directly link splicing abnormalities and neurodegeneration. Recently, we demonstrated that a mutation in one of the mouse multicopy U2 snRNA (small nuclear RNA) genes causes pre-mRNA splicing abnormalities and cerebellar neuron degeneration in a dosage-dependent manner. Degeneration of motor, cortical, and hippocampal neurons also occurs in this mutant mouse. U2 snRNAs are basal components of the major spliceosome, which is responsible for the majority (99%) of human pre-mRNA splicing. Our transcriptome analysis revealed that only a subset of alternative splicing events, including splicing of small introns, is disrupted in the mutant cerebellum. Therefore, this mutant strain not only provides the definitive evidence to directly link the dysfunction of splicing to degeneration f neurons in different regions in the central nervous system (CNS), but it also presents an experimental paradigm with which to better understand the disease mechanisms. My long-term career goal is to study the disease mechanisms underlying neurodegeneration caused by the splicing abnormalities by using this novel mutant mouse strain and its disease-associated allele. In this application, I will generate transgenic lines for the expression of the mutant U2 snRNAs in a tissue-specific and dosage-controllable manner. By crossing to tissue-specific Cre lines, I will determine the cell autonomous and/or non-cell autonomous effects of the mutant U2 snRNAs on neurodegeneration, and the cell type sensitivities to the splicing abnormalities induced by the expression of the mutant U2 snRNAs. In addition, I will identify the RNA targets disrupted by expression of the mutant U2 snRNAs in motor neurons, which are primarily affected in several motor neuron diseases potentially caused by misregulation of splicing. The comparison between the altered RNA targets in motor neurons and those we identified in the mutant cerebellum will help to elucidate the common mis-spliced transcripts that might be the most vulnerable targets to the splicing abnormalities and the disruption of these targets might drive the pathogenesis of neurodegeneration. Lastly, I will determine the intronic regulatory elements essential for the retention of small introns, which are heavily retained in the mutant cerebellum, and examine whether the RNA transcripts containing intronic regulatory elements are toxic to neurons. The data generated from these proposed experiments will not only deepen our understanding of the molecular and cellular pathways important for the pathogenesis of neurodegeneration caused by misregulation of splicing, but will also provide a basis for the future therapeutic development.
The misregulation of pre-mRNA splicing has been associated with neurodegenerative disorders, including spinal muscular atrophy (SMA) and amyotrophic lateral sclerosis (ALS), but the underlying disease mechanisms are largely unknown. Based on a unique mutant mouse strain and its disease-associated allele that directly link splicing abnormalities with neurodegeneration, I propose a series of experiments to address several outstanding, but unsolved, questions in the field. The potential outcome from the experiments outlined in this proposal will not only help us better understand the disease mechanisms of these diseases but will also provide a basis for the development of rational therapeutic strategies.