663B Poster - 10. Cell biology: Cytoskeleton, organelles and trafficking
Friday April 08, 2:00 PM - 4:00 PM

Authors:
shravan girada; jen Nguyen; Tzu-Han Lin; Amy Kiger

Affiliation: Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego

Keywords:
d. membrane dynamics; l. lipids in signaling

Muscles are complex cells with specialized structures for contraction. While arrays of sarcomeres perform contraction, it is the network of plasma membrane invaginations, called Transversal (T)-tubules, that coordinate sarcomere contractions. We study T-tubule requirements in body wall muscles of Drosophila at different growth stages, which allows live imaging of the membrane network. We uncovered an endogenous requirement for shibire, a Dynamin large GTPase, in the initiation of T-tubule disassembly within a wildtype developmental muscle remodeling program. Consistent with its role in disassembly, overexpression of shibire led to inappropriate T-tubule fragmentation and defective muscle function for larval mobility. These results indicate the importance for regulation of a normal dynamin function in T-tubule disassembly that may also hint at how dominant mutations in a conserved human DNM2 lead to centronuclear myopathy (CNM).
Previously, we implicated Class II PI3-kinase, Pi3K68D (or PI3KC2), in abdominal muscle remodeling defects associated with loss of Mtm PI3-phosphatase, a homolog of human MTM1 linked to a recessive (X-linked) form of CNM. We now identify a requirement for Pi3K68D in T-tubule disassembly at initiation of regulated muscle remodeling. Remarkably, disruption of Pi3K68D function also prevented the ectopic T-tubule fragmentation induced by shibire overexpression. Interestingly, mammalian PI3KC2A activity has been shown to recruit DNM2 for its role in endocytic vesicle formation, raising the question whether a shared pathway is also involved in T-tubule fragmentation. Our current studies unveil Pi3K68D phosphoinositide dependence, sites of Pi3K68D and Shibire function and the contributions of other endocytic pathway members in T-tubule disassembly. Altogether, our results suggest shared elements between the mechanism for dynamin-mediated endocytosis and T-tubule membrane disassembly and elevate the prospects of human PI3KC2A-targeted therapies for both dominant DNM2- and recessive MTM1-related myopathies.