Abstract
FUS mutations can occur in familial amyotrophic lateral sclerosis (fALS), a neurodegenerative disease with cytoplasmic FUS inclusion bodies in motor neurons. To investigate FUS pathology, we generated transgenic zebrafish expressing GFP-tagged wild-type or fALS (R521C) human FUS. Cell cultures were made from these zebrafish and the subcellular localization of human FUS and the generation of stress granule (SG) inclusions examined in different cell types, including differentiated motor neurons. We demonstrate that mutant FUS is mislocalized from the nucleus to the cytosol to a similar extent in motor neurons and all other cell types. Both wild-type and R521C FUS localized to SGs in zebrafish cells, demonstrating an intrinsic ability of human FUS to accumulate in SGs irrespective of the presence of disease-associated mutations or specific cell type. However, elevation in relative cytosolic to nuclear FUS by the R521C mutation led to a significant increase in SG assembly and persistence within a sub population of vulnerable cells, although these cells were not selectively motor neurons.
Highlights
Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons, leading to muscle weakness and atrophy and eventually fatal paralysis [1]
In comparison to FUS-WT-GFP, mutant FUS-R521C-GFP was mislocalized to the cytosol resulting in a diffuse appearance in whole mount transgenic larvae (Figure 1A)
The same was observed in dispersion primary cell cultures derived from these fish: FUS-WT-GFP was confined to the nucleus of all cells in culture, while FUS-R521C-GFP was universally mislocalized to the cytosol in all cells (Figure 1B)
Summary
Amyotrophic lateral sclerosis (ALS) is a debilitating neurodegenerative disease characterized by the progressive loss of upper and lower motor neurons, leading to muscle weakness and atrophy and eventually fatal paralysis [1]. Cell pathology in sporadic ALS (sALS) and fALS involves the presence of insoluble, ubiquitin-positive, cytosolic inclusions of TDP43, SOD1 or FUS accompanied by the selective death of motor neurons [3,5,6]. Linkage between SGs and pathological FUS inclusions in fALS is suggested in post-mortem tissue where inclusions in part label positive for SG markers [8,15,16,17]. These inclusions usually reside in specific neurons in afflicted parts of the motor or cognitive system, indicating vulnerability and sensitivity of certain cell populations, the basis for selective susceptibility is unclear given that FUS is ubiquitously expressed. Inclusions could represent a marker or response to injury or dysfunction
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