Dissecting the molecular composition and function of contact between membrane-bound and membrane-less organelles - PROJECT SUMMARY Membrane-bound organelles interpret the cellular environment and metabolic status to regulate cellular homeostasis. Lysosomes, once viewed as static membrane-bound organelles responsible for the disposal and recycling of cellular waste, have been increasingly appreciated as signaling hubs that can sense cellular status and regulate cellular metabolism. RNA granules, such as stress granules and transport granules, are membrane- less organelles that assemble through multivalent interactions between RNA and proteins. RNA granules have been hypothesized to act as hubs for RNA metabolism since they concentrate factors involved in various RNA processing pathways. Despite increasing evidence showing membrane-less organelles are essential parts of cellular compartmentalization, how they coordinate with membrane-bound organelles to organize cytosolic space and regulate cell homeostasis remains poorly understood. I have recently discovered a novel contact between lysosomes and RNA granules, which has opened up new areas of research on interactions between membrane-bound and membrane-less organelles. The overarching goal of this proposal is to understand how membrane-bound and membrane-less organelles interact to maintain RNA homeostasis. We will use the lysosome-RNA granule contact as a model, and employ multi-disciplinary approaches such as advanced light and EM microscopy and proximity labeling-based omics, to investigate how the coordinated actions of membrane-bound and membrane-less organelles ensure spatiotemporal control of RNA metabolism. In the first project, we will use live cell imaging and volume EM to elucidate how lysosome-associated signaling, metabolites, and lipid composition regulate RNA granule assembly and disassembly. In the second project, we will use proximity labeling tools to dissect the RNA and protein composition of lysosome-RNA granules contact. In the third project, we will use single-molecule tracking to explore the role of lysosomes in regulating mRNA localization, translation, and degradation. The fundamental knowledge to be gained by this study will unveil the molecular composition and function of contact between lysosome and RNA granule, and provide a framework for understanding how membrane-bound organelle communicates with membrane-less organelle to maintain cellular homeostasis.
