Abstract
Filamentous influenza A (IAV) virions can resist inactivation at the level of cell entry. Filaments therefore predominate over spherical particles in clinical infections and may enable viruses to persist and evolve in the face of immune pressure. Despite this, the mechanism of virion shape regulation is not well understood. Shape distribution is currently viewed as a defined feature of a viral genome. However, unpublished data in our lab show that shape can be tuned phenotypically in response to external pressures, without a genetic change. Our goal is to investigate non-genetic determinants of shape in order to begin piecing together the overall mechanism of shape regulation. I performed single-cycle infections with influenza A virus in the presence of inhibitors targeting defined steps in the virus life cycle. I measured the resulting dynamic shape effects using our novel flow virometry approach. Unlike traditional electron microscopy, this technique enables us to measure the shape of many individual fluorescently-labeled virus particles in a high-throughput manner. My results reveal that shape changes actively in response to treatment within a single cycle of infection, in which genetic change is unlikely. Overall, reduced viral yields correlate with increased amounts of filaments. Additionally, I show that inhibiting viral production after endocytosis leads to greater amounts of filaments for greater input particles. This is consistent with host cell membrane surface tension playing a role in phenotypic tuning of shape. I further demonstrate that membrane surface tension can also explain how certain published genetic changes affect shape. Based on our results, we propose shifting the field’s current perspective on virion shape regulation to include both genetics and external environment. Our insight can also be used to inform antiviral strategies, in order to avoid inhibitors which drive formation of filamentous particles.