Stress granule assembly can facilitate but is not required for TDP‐43 cytoplasmic aggregation

Stress granules (SGs) are hypothesized to facilitate TAR DNA‐binding protein 43 (TDP‐ 43) cytoplasmic mislocalization and aggregation, which may underly amyotrophic lateral sclerosis pathology. However, much data for this hypothesis is indirect. Additionally, whether P‐bodies (PBs; related mRNA‐protein granules) affect TDP‐43 phenotypes is unclear. Here, we determine that induction of TDP‐43 expression in yeast results in the accumulation of SG‐like foci that in >90% of cases become the sites where TDP‐43 cytoplasmic foci first appear. Later, TDP‐43 foci associate less with SGs and more with PBs, though independent TDP‐43 foci also accumulate. However, depleting or over‐expressing yeast SG and PB proteins reveals no consistent trend between SG or PB assembly and TDP‐43 foci formation, toxicity or protein abundance. In human cells, immunostaining endogenous TDP‐43 with different TDP‐43 antibodies reveals distinct localization and aggregation behaviors. Following acute arsenite stress, all phospho‐TDP‐43 foci colocalize with SGs. Interestingly, in SG assembly mutant cells (G3BP1/2ΔΔ), TDP‐43 is enriched in nucleoli. Finally, formation of TDP‐43 cytoplasmic foci following low‐dose chronic arsenite stress is impaired, but not completely blocked, in G3BP1/2ΔΔ cells. Collectively, our data suggest that SG and PB assembly may facilitate TDP‐43 cytoplasmic localization and aggregation but are likely not essential for these events.