UC San Diego

T-tubules are specialized plasma membrane invaginations in muscle cells critical for contraction. However, despite the significance to muscle function, how T-tubule membranes form and remodel is poorly understood. Our laboratory identified a developmental myofiber remodeling program during Drosophila metamorphosis with distinct membrane trafficking requirements for regulated T-tubule disassembly and reassembly. Through a timecourse analysis by live cell microscopy imaging in intact myofibers, I narrowed the progression of T-tubule disassembly to a 12-hour “disassembly window,” during which I observed an upregulation in both endosomal and autophagy membrane flux. I performed colocalization and genetic experiments that suggest disassembled T-tubule membrane enters into a distinct and transient endosomal-lysosomal trafficking pathway critical for the remodeling process. Furthermore, I examined Rab2, Rab7, Rab35, and Sbf requirements in T-tubule disassembly, and discovered RNAi defects in both T-tubule and endosomal membrane flux during the disassembly window. In addition, I characterized a parallel upregulation and requirement for autophagy in the T-tubule disassembly process. I propose a model that integrates T-tubule disassembly with endolysosomal and autophagic pathways, with potential implications in muscle maintenance and function. This study underscores the value of myofiber remodeling to understand not only T-tubule dynamics, but also to serve as a sensitized system for illuminating fundamental membrane trafficking mechanisms.