ALS-fellowship: Understanding the role of FUS in ALS through assessment and modulation of its phase separation behaviour in vivo.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease. Patients become paralyzed and die on average 3 years after onset of symptoms. There is no cure.
In inherited and sporadic forms of ALS, RNA binding proteins like TDP-43 and FUS become dysfunctional and start to aggregate in patient neurons. Thus, in order to design effective therapies, we need to know how these proteins become aggregative and toxic. 
Recently, it has been found that FUS undergoes a process known as liquid-liquid phase separation (LLPS), which allows it to concentrate together with similar proteins in subcellular locations. When LLPS is recapitulated in a test tube, FUS begins to aggregate in a way that is enhanced by ALS-associated mutations suggesting that LLPS is the starting point of aggregation and toxicity. 
In order to understand this process in vivo, I have created Drosophila which overexpress FUS in neurons. I have strategically altered the amino acid composition of FUS to change its ability to undergo LLPS, and aim to correlate this with toxicity. I will then use proteomics to determine which other proteins FUS interacts with while undergoing LLPS. I will perform an RNAi screen in flies to determine whether these proteins modify toxicity. Finally, I will translate these findings to humans by determining whether these modifiers can alter toxic phenotypes in iPSC-derived motor neurons from FUS patients, and determining whether they are dysregulated in patient tissue