Decoding the mechanisms of cell-cell fusion - Renewal - 1

Ut Southwestern Medical Center, Dallas TX

Investigators

Linked publications, trials & patents

Abstract

PROJECT SUMMARY/ABSTRACT Cell-cell fusion is critical to the conception, development, and physiology of multicellular organisms, and is involved in a variety of biological processes, such as fertilization, placenta development, bone remodeling, immune response, and skeletal muscle development and regeneration. Failure in cell fusion leads to defects such as infertility, osteopetrosis, immune deficiency, pre-eclampsia, and congenital myopathy and muscular dystrophy. Compared with our understanding of intracellular vesicle fusion and virus-cell fusion, much less is known about the underlying mechanisms of cell fusion. A mechanistic understanding of cell fusion is not only important for fundamental biology but may also provide basis for its manipulation in therapeutic settings. My laboratory uses a multifaceted approach including genetics, molecular biology, biochemistry, biophysics, live imaging, super-resolution microscopy and electron microscopy to study the mechanisms underlying cell-cell fusion. Using Drosophila myoblast fusion as a model initially, we discovered the asymmetric fusogenic synapse, where one cell invades its fusion partner using F-actin-propelled invasive membrane protrusions to promote plasma membrane juxtaposition and fusion pore formation. Building on the insights that we learned about myoblast fusion in vivo, we have reconstituted high-efficiency cell-cell fusion in an otherwise non-fusogenic, non- muscle cell line and uncovered a novel function for invasive membrane protrusions in fusogen engagement across the apposing plasma membranes. Furthermore, we have discovered dynamic mechanosensory responses in the receiving fusion partner and demonstrated that mechanical tension is a driving force for cell- cell fusion. In the last grant period, we have extrapolated the mechanism that we discovered in Drosophila to vertebrate models and demonstrated that myoblast fusion in zebrafish and mouse is also mediated by invasive protrusions at the asymmetric fusogenic synapses. Moreover, we have elucidated the mechanism by which the large GTPase dynamin bundles actin at the fusogenic synapse, uncovered how inter-organ steroid hormone signaling promotes myoblast fusion via direct transcriptional regulation of a single key effector gene, and discovered a novel function for the ABC G1/G4 transporters and free/accessible cholesterol in promote protrusion formation and cell-cell fusion. In the next five years, we will expand our research into three new directions. First, we will perform mechanistic studies to understand the function of the unconventional fusogen, Myomaker, by dissecting the interaction between Myomaker and the actin cytoskeleton and investigating whether Myomaker affects the local lipid composition on plasma membrane. Second, we will investigate how the Hippo-YAP/TAZ-TEAD signaling pathway regulates the cell fusion machinery, by characterizing the actin cytoskeleton phenotypes in TEAD2DN cells, identifying TEAD target genes involved in cell fusion, and pinpointing the TEAD-binding sites in target genes. Third, we will explore whether altered mechanical tension causes myofiber splitting in Duchenne muscular dystrophy, by vvisualizing satellite cell-induced myofiber splitting on micropatterns at the single-fiber level and modulating myofiber stiffness to alleviate fiber splitting. Our research will not only provide novel insights into the fundamental principles of cell-cell fusion, but also have far-reaching impact on a broad range of fields, including membrane biology, cell biology, and development and disease.