In situ characterization of late Chikungunya virus replication organelle

Chikungunya virus (CHIKV) is a mosquito-borne pathogen responsible for an acute musculo-skeletal disease in humans. The viral RNA genome replication occurs in membrane spherules named replication organelles (ROs). In this work, we investigate the native structural organization of CHIKV ROs in their cellular context using in situ cryogenic-electron microscopy approaches at late replication stage. We observed previously unreported diameter heterogeneity of ROs at the plasma membrane of infected human cells. CHIKV ROs were only marginally detected in cytopathic vacuoles where they are homogeneous in size, suggesting a finely regulated internalization process. Our data show that ROs maintained at the plasma membrane beyond the first viral cycle are dynamically active both in viral RNA replication, in its export to the cell cytosol, but also in the production of viral proteins. We suggest that late CHIKV ROs have an amplifying role or represent an alternative pathway in the production of infectious viral particles. All these observations bring new insight into the CHIKV life cycle in human cells.