OptoGranules reveal the evolution of stress granules to ALS-FTD pathology

Stress granulesare non-membranous assemblies of mRNA and protein that form in response to a variety of stressors. Genetic, pathologic, biophysical and cell biological studies have implicated disturbances in the dynamics of membrane-less organelles, such as stress granules, as a pathobiological component of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia(FTD). This confluence of evidence has inspired the hypothesis that these diseases reflect an underlying disturbance in the dynamics and material properties of stress granules; however, this concept has remained largely untestable in available models of stress granuleassembly, which require the confounding variable of exogenous stressors. Here we demonstrate the development and use of a light-inducible stress granulesystem, termed OptoGranules, which permits discrete, experimental control of the dynamics and material properties of stress granulesin living cells in the absence of exogenous stressors. The nucleator in this system is Opto-G3BP1, a light-sensitive chimeric protein assembled from the intrinsically disordered region (IDR) and RNA-binding domain of G3BP1 combined with the light-sensitive oligomerization domain of Arabidopsis thaliana cryptochrome2 (CRY2) photolyasehomology region (PHR). Upon stimulation with blue light, Opto-G3BP1 initiates the rapid assembly of dynamic, cytoplasmic, liquid granulesthat are composed of canonical stress granulecomponents, including G3BP1, PABP, TIA1, TIAR, eIF4G, eIF3η, ataxin2, GLE1, TDP-43 and polyadenylatedRNA. With this system, we demonstrate that persistent or repetitive assembly of stress granulesis cytotoxic and is accompanied by the evolution of stress granulesto neuronal cytoplasmic inclusionsthat recapitulate the pathology of ALS-FTD.