Paraspeckles and stress granules via RNA-binding protein FUS

Movie. High magnification Z-stack of a live hiPS cell colony expressing mEGFP-tagged RNA-binding protein FUS in control cells (left panel) and in the presence of 500 µM sodium arsenite for 15 min (right panel). Cells were imaged in 3D on a spinning-disk confocal microscope. Movie starts at the bottom of the cells and ends at the top. Scale bar, 5µm.

Movie. High magnification Time-lapse movie of a live hiPS cell colony expressing mEGFP-tagged RNA-binding protein FUS. Six minutes after the introduction of 500 µM sodium arsenite, cells were imaged every 5 sec in 3D on a spinning-disk confocal microscope. A single mid-level plane is shown. The inset is a 2.5x enlargement of the boxed region to show detail of aggregate formation. Frames were histogram matched to adjust for photobleaching. Movie plays at 25x real time. Scale bar, 5 µm.

Observations

• RNA-binding protein FUS (Fused In Sarcoma) is a DNA/RNA binding protein involved in transcription, mRNA splicing and transport, and DNA repair. 
• FUS forms various condensed-phase compartments in cells. In the absence of a stressor, FUS compartments form in the nucleus, including at sites of active genes, DNA damage, and paraspeckles (RNA-protein bodies in the interchromatin space). Stressful conditions (e.g. generation of reactive oxygen species (ROS)) lead to a redistribution of FUS from the nucleus to the cytoplasm, where it localizes to stress granules.
• In unstressed hiPS cells imaged with spinning-disk light microscopy, mEGFP-tagged FUS has a granular appearance within the nucleoplasm including some relatively bright spots which may be paraspeckles. In the absence of a stressor, there is no mEGFP-tagged FUS in the cytoplasm. 

After the application of the stressor sodium arsenite to hIPS cells, mEGFP-tagged FUS appears as puncta in the cytoplasm that join together, reflecting stress granule nucleation and coalescence. Concurrently, the intensity of FUS decreases in the nucleoplasm.​