RNA-binding proteins with prion-like domains in ALS and FTLD-U

Abstract

Amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease) is a debilitating, and universally fatal, neurodegenerative disease that devastates upper and lower motor neurons. The causes of ALS are poorly understood. A central role for RNA-binding proteins and RNA metabolism in ALS has recently emerged. The RNA-binding proteins, TDP-43 and FUS, are principal components of cytoplasmic inclusions found in motor neurons of ALS patients and mutations in TDP-43 and FUS are linked to familial and sporadic ALS. Pathology and genetics also connect TDP-43 and FUS with frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U). It was unknown whether mechanisms of FUS aggregation and toxicity were similar or different to those of TDP-43. To address this issue, we have employed yeast models and pure protein biochemistry to define mechanisms underlying TDP-43 and FUS aggregation and toxicity, and to identify genetic modifiers relevant for human disease. We have identified prion-like domains in FUS and TDP-43 and provide evidence that these domains are required for aggregation. Our studies have defined key similarities as well as important differences between the two proteins. Collectively, however, our findings lead us to suggest that FUS and TDP-43, though similar RNA-binding proteins, likely aggregate and confer disease phenotypes via distinct mechanisms.

Figure 1

Prion-like domains of ALS disease proteins TDP-43 and FUS contribute to aggregation. (A) Domain architecture of TDP-43 and FUS with the location of the prion-like domains indicated. Both proteins also contain RNA-recognition motifs (RRMs) and glycine-rich regions (Gly-rich). (B) FUS and TDP-43 form cytoplasmic aggregates when expressed in yeast cells. Shown is a representative example of a yeast cell expressing a FUS-YFP fusion protein. (C) TDP-43 and FUS spontaneously aggregate in vitro. Shown is an example of filamentous aggregates formed by FUS (1–422) in vitro.