Research on spinocerebellar ataxia type 8 (SCA8) supported by this application has led to two discoveries that fundamentally change our understanding of how a broad category of microsatellite expansion mutations are expressed. First, we demonstrated that the SCA8 CTG?CAG expansion is bidirectionally transcribed1. This was the first demonstration that a single expansion mutation could lead to the expression and accumulation of toxic CUG and CAG expansion RNAs and a CAG-encoded polyGln expansion protein1. Second, we discovered that the canonical rules of translation do not apply for CTG?CAG repeats and that CAG and CUG expansion transcripts can express homopolymeric expansion proteins in all three frames without an AUG start codon2. We showed this repeat associated non-ATG (RAN) translation is hairpin-dependent, occurs without frameshifting or RNA editing and is observed in cell culture and SCA8 patient tissues2. RAN translation also occurs in myotonic dystrophy type 1 (DM1)2, C9ORF72 amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD9)3-5, and fragile X tremor ataxia syndrome (FXTAS)6. The discoveries of bidirectional transcription and RAN translation change our understanding of how genes are expressed and highlight the need for therapies that target both sense and antisense transcripts as well as RAN proteins. Our central hypothesis is that both RNA and RAN gain of function (GOF) contribute to SCA8 and can be mitigated by therapies based on MBNL1 overexpression or RNA knockdown.
Our specific aims will test the following hypotheses: 1) RNA gain of function and RAN translation contribute to SCA8; 2) RAN translation can be modulated by MBNL proteins and stress pathways; 3) antisense oligo (ASO) knockdown of ATXN8 and ATXN8OS will block RNA and RAN effects and reverse disease in an SCA8 mouse model.

Public Health Relevance

We have discovered a new translational mechanism that directs expression of an unexpected category of proteins lacking the normal regulatory signals. The project goals are to understand how RNA and these novel proteins contribute to SCA8 and to develop therapeutic strategies.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Method to Extend Research in Time (MERIT) Award (R37)
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Special Emphasis Panel (ZRG1)
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Gwinn, Katrina
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University of Florida
Schools of Medicine
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Sznajder, ?ukasz J; Thomas, James D; Carrell, Ellie M et al. (2018) Intron retention induced by microsatellite expansions as a disease biomarker. Proc Natl Acad Sci U S A 115:4234-4239
Chen, Gang; Carter, Russell E; Cleary, John D et al. (2018) Altered levels of the splicing factor muscleblind modifies cerebral cortical function in mouse models of myotonic dystrophy. Neurobiol Dis 112:35-48
Cleary, John Douglas; Pattamatta, Amrutha; Ranum, Laura P W (2018) Repeat-associated non-ATG (RAN) translation. J Biol Chem 293:16127-16141
Ayhan, Fatma; Perez, Barbara A; Shorrock, Hannah K et al. (2018) SCA8 RAN polySer protein preferentially accumulates in white matter regions and is regulated by eIF3F. EMBO J 37:
Pattamatta, Amrutha; Cleary, John D; Ranum, Laura P W (2018) All in the Family: Repeats and ALS/FTD. Trends Neurosci 41:247-250
Grima, Jonathan C; Daigle, J Gavin; Arbez, Nicolas et al. (2017) Mutant Huntingtin Disrupts the Nuclear Pore Complex. Neuron 94:93-107.e6
Zu, Tao; Cleary, John D; Liu, Yuanjing et al. (2017) RAN Translation Regulated by Muscleblind Proteins in Myotonic Dystrophy Type 2. Neuron 95:1292-1305.e5
Khare, Swati; Nick, Jerelyn A; Zhang, Yalan et al. (2017) A KCNC3 mutation causes a neurodevelopmental, non-progressive SCA13 subtype associated with dominant negative effects and aberrant EGFR trafficking. PLoS One 12:e0173565
Cleary, John Douglas; Ranum, Laura Pw (2017) New developments in RAN translation: insights from multiple diseases. Curr Opin Genet Dev 44:125-134
Kumar, Ashok (2015) NMDA Receptor Function During Senescence: Implication on Cognitive Performance. Front Neurosci 9:473

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