Figure 3.

Mimicking Viral Infection Promotes Formation of Cytoplasmic FAs

(A) Spontaneous FGs composed of endogenous protein (endoFGs) are present in the cytoplasm of two ΔNLS_het lines under basal conditions.

(B) SG markers G3BP1 and TIAR are absent from endoFGs.

(C) Non-overlapping localization of mutant FUS and SG proteins in endogenous mutant FUS (endoFUS) aggregates (endoFAs) formed in a FG-positive cell line (ΔNLS11_het) after poly(I:C) transfection. Images of FUS-positive SGs formed in a FG-negative line (ΔNLS10_het) are shown for comparison. Cells were analyzed 4 h post-transfection.

(D) Quantification of the number of cells containing endoFAs in ΔNLS_het lines (data for two lines combined) over a 24-h period post-transfection, where ≥500 cells were analyzed per line/time point. Data are represented as mean ± SEM.

(E) Formation of exoFAs in response to poly(I:C). WT cells were transfected with a FUS R522G GFP expression vector; 24 h later, cells were transfected with poly(I:C); and two cells with preformed exoFGs were followed up for 12 h using time-lapse confocal imaging. Two aggregates that eventually fuse to form one large aggregate are indicated with arrowheads. Also see Video S1.

In (A)–(C), representative confocal images (single optical section) are shown. Scale bars, 10 μm.