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Title: Zebrafish C9orf72 loss-of-function models of Amyotrophic Lateral Sclerosis and Frontotemporal Dementia
Author: Rounding, Natalie
ISNI:       0000 0004 7230 912X
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2018
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Background: A noncoding (G4C2)n hexanucleotide repeat expansion in chromosome 9 open reading frame 72 (C9orf72) is a major cause of both amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), together referred to as C9-ALS/FTD. It is unknown how the repeat expansion causes C9-ALS/FTD, however there is evidence that C9orf72 mRNA levels are reduced in patients, suggesting C9orf72 loss-of-function (LOF) via haploinsufficiency may contribute to C9-ALS/FTD. Understanding how haploinsufficiency may lead to the development of C9-ALS/FTD is dependent on a better understanding of C9orf72 protein function. Recent work from our laboratory and others in cell lines have shown that C9orf72 regulates autophagy, but the in vivo relevance of autophagy-deficits remains unclear. Objectives: To investigate if C9orf72 LOF via haploinsufficiency results in C9-ALS/FTD due to defective autophagy using a stable zebrafish C9orf72 LOF model. Methods: Genome editing techniques were used to target sequences within exon 1 and exon 7 of the zebrafish orthologue of C9orf72 (C13H9orf72; zgc10846). To investigate the effects of C13H9orf72 LOF, we characterised survival, motor function and anxiety-like behaviour. Immunohistochemical analysis of neuromuscular junctions (NMJs) was also performed. To investigate the role of C9orf72 in autophagy in vivo, autophagic flux was measured. Additionally, we looked for symptoms of splenomegaly, due to recent evidence that full ablation of C9orf72 in mice resulted in immune system-related pathology. Results: Three independent lines of zebrafish carrying different frameshift mutations in exon 1 (SH470) and exon 7 (SH448 and SH451) were characterised. Survival monitoring suggests that mutations in C13H9orf72 do not lead to loss of viability. A subtle reduction in motor function is observed in adult C13H9orf72 LOF zebrafish, but no corresponding NMJ pathology, and there is no evidence of anxiety-like behaviour in adults. Zebrafish C13H9orf72 was found to interact with a member of the autophagy initiation complex, but further work is needed to determine whether it plays a regulatory role in autophagy in zebrafish. Additionally, no signs of significant splenomegaly were observed in these zebrafish. Conclusions: Results obtained do not support the hypothesis that C9orf72 LOF is sufficient to cause C9-ALS/FTD alone, which complements published findings in C9orf72 LOF mouse models.
Supervisor: Grierson, A. J. ; De Vos, K. J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available