RNA Kinetics in Membraneless Organelles

Membraneless organelles (or biomolecular condensates) emerge as a new paradigm underlying subcellular organization that is driven by liquid-liquid phase separation of RNAs and RNA-binding proteins from their surrounding cellular milieu. Mutations in several RNA-binding proteins cause amyotrophic lateral sclerosis (ALS), a neurodegenerative disease of the human motor neuron system. These RNA-binding proteins are normally found in membraneless organelles, such as stress granules. Accordingly, mutations that cause ALS, alter RNA binding protein functions and stress granule dynamics. Furthermore, stress granule resident proteins have been found in pathological insoluble aggregates (inclusions) of ALS brains or spinal cords. Therefore, ALS is a compelling focus disease for investigating stress granules connections to human health. Apex proximity proteomics has proven an extremely useful technology to uncover new facets of stress granule biology. By utilizing Apex labeling with three independent stress granules baits, mass spectrometry and follow up molecular studies, we identified dozen of new SG proteins. We further investigated stress granules under basal conditions, with cellular stress and when a proline-arginine repeat model of C9orf72 subtype of ALS was introduced. These efforts revealed pathways and posttranslational modifications that are active in regulating stress granule dynamics and go awry in a C9orf72 subtype of ALS, shedding light on new molecular patho-mechanisms and suggesting new therapeutic targets for neurodegeneration.