Transcriptomic approach reveals splicing dysregulation in spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is caused by a polyglutamine expansion in the ATXN1 gene leading to an expanded polyglutamine tract in the ATAXIN-1 protein. Ataxin-1 is broadly expressed throughout the brain and is known to be involved in regulating gene expression; however, it is not yet determined if mutant ataxin-1 regulates alternative splicing events. Utilizing SCA1 mouse models, we performed bulk RNA sequencing and looked for misregulated alternative splicing (mAS) events in SCA1 mouse cerebella. We found that mutant ataxin-1 causes mAS events to occur in the SCA1 mouse cerebella. Furthermore, we showed that abnormal splicing events predominantly occur in cell types that express mutant ataxin-1. Less than 25% of the mAS events were also differentially expressed genes (DEGs) and therefore their transcriptional dysregulation was previously unknown in the context of SCA1. We show through gene ontology analysis that mAS events reveal new biological pathways: mAS events showed changes in structural morphogenesis whereas DEGs showed changes in ion channel and transmembrane transport. We also report that mutant ataxin-1 causes dysregulation of expression of other ataxia-causing genes, providing evidence for molecular basis of clinical similarity among otherwise heterogeneous inherited cerebellar ataxias. We also identified the potential mechanism by which mutant ATXN1 causes mAS through its interaction with RBFOX1. Overall design: Comparative transcriptomic analysis of RNA-seq data for mouse cerebella extracted from WT FVB/NJ and Atxn1-82Q transgenic FVB/NJ mice. Samples were collected from 5-, 12-, 20-, and 52-week old mice with four biological replicates collected from 5-week old and three biological replicates collected from 12-, 20-, and 52-week old mice.