Spatially heterogeneous dynamics of droplets formed by arginine-rich dipeptides and poly-A RNA during liquid-liquid phase separation

Arginine-rich dipeptides (proline-arginine (PR)) are highly toxic products encoded by aberrant repeat expansion in the C9ORF72 gene, which is the most common cause of familial amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). These dipeptides have the capability to undergo liquid-liquid phase separation (LLPS) with components inside the membrane-less organelles (MLO) that could have a detrimental effect on fundamental cellular processes, potentially leading to injury or death in motor neurons. In this study, Raman spectroscopy was used to investigate the spatial variation within these liquid droplets in vitro, revealing concentration gradients of RNA in droplets. The findings were compared with fluorescence recovery after photobleaching (FRAP), offering insights into the spatially heterogeneous dynamics within the droplets. Understanding the mechanism is essential for unraveling the pathogenesis of neuronal diseases and may provide future therapeutic strategies.