Actin-dependent regulation of RSV F-mediated cell–cell fusion revealed by visualizing its spatiotemporal dynamics

Respiratory syncytial virus (RSV) induces pathogenic syncytia via its fusion (F) protein, yet how it orchestrates fusion within the crowded plasma membrane remains unclear. By integrating live-cell and dSTORM imaging, we visualized the spatiotemporal dynamics of RSV F from secretion to membrane assembly. We show that RSV F efficiently traffics to the plasma membrane and triggers F-actin-enriched protrusions that facilitate fusion, depending on branched actin remodeling. Super-resolution imaging further reveals that RSV F reorganizes from nanoscale clusters into near-continuous ribbon-like nanodomains at cell-cell contacts, forming a stable fusion platform. This work directly visualizes the actin-driven nanoscale assembly of a viral fusogen, defining a key mechanism in RSV pathogenesis and revealing a nanoscale target for antiviral intervention, thereby underscoring the power of advanced nanoscopy to unravel complex host-pathogen interactions at the molecular level.