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Multistep process of FUS aggregation in the cell cytoplasm involves RNA-dependent and RNA-independent mechanisms
Tatyana A Shelkovnikova1, Hannah K Robinson2, Joshua A Southcombe2
1School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, UK, Institute of Physiologically Active Compounds Russian Academy of Sciences, 1 Severniy proezd, Chernogolovka 142432, Moscow Region, Russian Federation and shelkovnikovat@cardiff.ac.uk buchmanvl@cf.ac.uk.
Abstract:
Fused in sarcoma (FUS) is an RNA-binding protein involved in pathogenesis of several neurodegenerative diseases. Aggregation of mislocalized FUS into non-amyloid inclusions is believed to be pivotal in the development of cell dysfunction, but the mechanism of their formation is unclear. Using transient expression of a panel of deletion and chimeric FUS variants in various cultured cells, we demonstrated that FUS accumulating in the cytoplasm nucleates a novel type of RNA granules, FUS granules (FGs), that are structurally similar but not identical to physiological RNA transport granules. Formation of FGs requires FUS N-terminal prion-like domain and the ability to bind specific RNAs. Clustering of FGs coupled with further recruitment of RNA and proteins produce larger structures, FUS aggregates (FAs), that resemble but are clearly distinct from stress granules. In conditions of attenuated transcription, FAs lose RNA and dissociate into RNA-free FUS complexes that become precursors of large aggresome-like structures. We propose a model of multistep FUS aggregation involving RNA-dependent and RNA-independent stages. This model can be extrapolated to formation of pathological inclusions in human FUSopathies.
Insights
Mislocalized FUS protein forms novel RNA granules and aggregates in cells, distinct from stress granules. This multistep aggregation process, involving RNA, may explain pathological inclusions in FUS-related neurodegenerative diseases.
Area of Science:
- Cellular Biology
- Neuroscience
- Biochemistry
Background:
- Fused in sarcoma (FUS) is an RNA-binding protein implicated in neurodegenerative diseases.
- The precise mechanism of FUS aggregation into pathological inclusions remains unclear.
- Mislocalized FUS in the cytoplasm is thought to be crucial for disease pathogenesis.
Purpose of the Study:
- To elucidate the mechanism of FUS aggregation and formation of cytoplasmic inclusions.
- To characterize novel RNA granules and aggregates formed by FUS.
- To propose a model for FUS aggregation relevant to FUSopathies.
Main Methods:
- Transient expression of FUS deletion and chimeric variants in cultured cells.
- Microscopy to observe the formation and structure of FUS granules and aggregates.
- Analysis of RNA and protein recruitment during FUS aggregation.
Main Results:
- FUS accumulates in the cytoplasm, nucleating FUS granules (FGs) dependent on its N-terminal domain and RNA-binding ability.
- FGs cluster to form larger FUS aggregates (FAs), distinct from stress granules.
- Under attenuated transcription, FAs lose RNA, dissociate, and form precursors for aggresome-like structures.
Conclusions:
- A multistep FUS aggregation model involving RNA-dependent and RNA-independent stages is proposed.
- This model provides insight into the formation of pathological inclusions in FUSopathies.
- FUS granules represent a novel type of RNA granule with implications for neurodegeneration.