External Seminar Petr CHLANDA "Influenza A Virus Morphology-Dependent Spread and Assembly revealed by in situ cryo-electron tomography"
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Petr CHLANDA, Center for Quantitative Analysis of Molecular and Cellular System- BioQuant, Heidelberg University, Germany - Department of Infectious Diseases – Virology, Heidelberg University Hospital, Germany
Title : "Influenza A Virus Morphology-Dependent Spread and Assembly revealed by in situ cryo-electron tomography"
Abstract :
Influenza A viruses (IAV) form pleomorphic virions, ranging from spherical to filamentous shapes. These morphologies influence viral entry, spread, and immune evasion. Laboratory-adapted strains are mostly spherical, but the determinants of morphology in physiological conditions remain unclear. To investigate this, we generated fluorescent reporter viruses with identical glycoproteins but distinct morphologies and applied correlative light and scanning electron microscopy. Filamentous IAV spread more slowly across cell lines, consistent with delayed entry observed by in situ cryo-electron tomography (cryo-ET), explaining the predominance of spherical forms in labs. Spread was not affected by cellular junction integrity, neuraminidase (NA) activity, or mucin, but filamentous virions had an advantage under hemagglutinin (HA)-targeted neutralizing antibodies.
IAV is a segmented negative-sense RNA virus, with eight genomic segments assembled into helical viral ribonucleoprotein complexes (vRNPs) in the nucleus. vRNPs traffic via Rab11 to the plasma membrane, where assembly is orchestrated by matrix protein 1 (M1), HA, and NA. Using in situ cryo-ET, we found that HA-containing membranes cluster vRNPs in Rab11a dependent manner. Our data show that in the absence of HA, vRNPs cluster on NA-containing membranes and virus assembly remains intact, indicating that vRNP clustering and trafficking are membrane-assisted but HA independent. Surprisingly, M1 forms multilayered helical complexes in the nucleus and cytosol, distinct from budding virions, and M1 layer formation precedes membrane attachment and vRNP bundle formation. We further revealed that the canonical 7+1 vRNP arrangement is established only during virus budding on the plasma membrane concomitantly with M1 layer formation.
Contact: Emmanuelle Quemin (emmanuelle.quemin@i2bc.paris-saclay.fr)