Biology subjects

Gall-Duncan, T.

Publications and source records attributed to Gall-Duncan, T..

4 recordsLinked to original sources

bioRxiv2025

Striatal pathology in Spinocerebellar Ataxia Type 1 mice: A comparative study with Huntingtons disease

Spinocerebellar ataxia type 1 (SCA1) and Huntingtons disease (HD), are motor diseases caused by CAG expansions in ATXN1 and HTT, where SCA1 shows prominent cerebellar neurodegeneration and HD shows prominent striatal neurodegeneration, particularly in the Medium Spiny Neurons (MSNs). Since human and mouse studies demonstrate progressive striatal vulnerability in SCA1, we examined age-dependent molecular, cellular and functional striatal attributes in SCA1 (f-ATXN1146Q/2Q) knockin mice, by assessing RNA-sequencing, immunohistochemistry and electrophysiology. Striatal mRNAs are downregulated in SCA1 mice, many in common with HD mice, and specificity in MSNs is supported by the rescue of transcriptomic dysregulation with deletion of mutant Ataxin1 from MSNs. Immunohistochemistry assessed dopamine receptor 1 (D1R) and 2 (D2R) expression in indirect and direct MSNs. In HD mice (HttQ175/Q7), expression of both D1R and D2R proteins in MSNs decreased with age in parallel with their RNA levels. In the SCA1 mouse striatum, D1R protein expression decreased with age as seen in murine HD striatum. In contrast, while D2R protein level was decreased similar to D1R protein at 5-weeks of age, by 40-weeks expression of D2R protein recovered to levels recorded in WT mice. Electrophysiological assessment showed a reduction of excitatory synaptic transmission in SCA1 mouse MSNs, indicating functional deficits early in disease. In contrast to cerebellar and many other aspects of SCA1 pathology known to depend on proper nuclear localization of ATXN1 with an expanded polyglutamine, mutating ATXN1s nuclear localization failed to correct striatal MSN RNA and protein downregulations, indicating a difference in how ATXN1 exerts its pathological effects between the cerebellum and the striatum. Together, these data provide a molecular and cellular basis of striatal pathology in SCA1.

neuroscience↗

bioRxiv2025

Interventionally targeting somatic CAG expansions can be a rapid disease-modifying therapeutic avenue: Preclinical evidence.

Huntington disease (HD) is caused by inherited CAG expansions, which continue expanding somatically in affected brain regions to hasten disease onset and progression. Therapeutically diminishing somatic expansions is expected to be clinically beneficial. However, it is not known if interventionally modifying somatic CAG expansions will actually modify in vivo clinically-relevant phenotypes, what the therapeutic window is, or which phenotypes will be altered. Here we show that acute (6-week) delivery of the contraction-inducing slipped-CAG DNA ligand naphthyridine-azaquinolone to young (4-week-old) (CAG)120 HD mice, induces contractions throughout brain regions, improves motor function (locomotion, balance, coordination, muscle strength), molecular disease landmarks (mHTT aggregates, nuclear envelope morphology, nucleocytoplasmic mRNA transport, transcriptomic dysregulation, neuroinflammation), and neurodegeneration. Beneficial effects of modifying somatic expansions were also evident in muscle and blood, where blood CAG instability correlated with brain instability and blood serum had diminished levels of neurofilament light (a biomarker for neurodegeneration) -- offering blood as having elements of target engagement and efficacy. These data support that targeting somatic repeat expansions can be a rapid disease-modifying therapeutic avenue for HD and possibly other repeat expansion diseases. Our findings support an etiologic pathway interconnected to somatic CAG expansions that will inform the design of clinical trials expecting clinical benefit by modulating somatic expansions.

genetics↗

bioRxiv2024

Huntingtin is an RNA-binding protein and participates in NEAT1-mediated paraspeckles

AbstractHuntingtin protein, mutated in Huntington disease, is implicated in nucleic acid- mediated processes, yet evidence for direct huntingtin-nucleic acid interaction is limited. Here we show wildtype and mutant huntingtin co-purify with nucleic acids, primarily RNA, and interact directly with G-rich RNAs in in vitro assays. Huntingtin RNA immunoprecipitation sequencing from patient-derived fibroblasts and neuronal progenitor cells expressing wildtype and mutant huntingtin revealed NEAT1 as a significantly enriched transcript. Altered NEAT1 levels were evident in Huntingtons disease cells and postmortem brain tissues, and huntingtin knockdown decreased NEAT1 levels. Huntingtin co-localized with NEAT1 in paraspeckles, and we identified a high-affinity RNA motif preferred by huntingtin. This study highlights NEAT1 as a novel huntingtin interactor, demonstrating huntingtins involvement in RNA-mediated functions and paraspeckle regulation. One-Sentence SummaryHTT is an RNA-binding protein that interacts with G-rich sequences, including those in the paraspeckle lncRNA NEAT1.

cell biology↗

bioRxiv2022

Antagonistic roles of canonical and alternative RPA in tandem CAG repeat diseases

Tandem CAG repeat expansion mutations cause >15 neurodegenerative diseases, where ongoing expansions in patients brains are thought to drive disease onset and progression. Repeat length mutations will involve single-stranded DNAs prone to form mutagenic DNA structures. However, the involvement of single-stranded DNA binding proteins (SSBs) in the prevention or formation of repeat instability is poorly understood. Here, we assessed the role of two SSBs, canonical RPA (RPA1-RPA2-RPA3) and the related Alternative-RPA (Alt-RPA, RPA1-RPA4-RPA3), where the primate-specific RPA4 replaces RPA2. RPA is essential for all forms of DNA metabolism, while Alt-RPA has undefined functions. RPA and Alt-RPA are upregulated 2- and 10-fold, respectively, in brains of Huntington disease (HD) and spinocerebellar ataxia type 1 (SCA1) patients. Correct repair of slipped-CAG DNA structures, intermediates of expansion mutations, is enhanced by RPA, but blocked by Alt-RPA. Slipped-DNAs are bound and melted more efficiently by RPA than by Alt-RPA. Removal of excess slipped-DNAs by FAN1 nuclease is enhanced by RPA, but blocked by Alt-RPA. Protein-protein interactomes (BioID) reveal unique and shared partners of RPA and Alt-RPA, including proteins involved in CAG instability and known modifiers of HD and SCA1 disease. RPA overexpression inhibits rampant CAG expansions in SCA1 mouse brains, coinciding with improved neuron morphology and rescued motor phenotypes. Thus, SSBs are involved in repeat length mutations, where Alt-RPA antagonistically blocks RPA from suppressing CAG expansions and hence pathogenesis. The processing of repeat length mutations is one example by which an Alt-RPA{leftrightarrow}RPA antagonistic interaction can affect outcomes, illuminating questions as to which of the many processes mediated by canonical RPA may also be modulated by Alt-RPA.

genetics↗