Investigations on influenza A virus morphology

Goldfarb, Daniel Max (2022) Investigations on influenza A virus morphology. PhD thesis, University of Glasgow.

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Clinical isolates of influenza A virus (IAV) typically form a pleomorphic population of virions that present as a continuum of morphologies broadly classified as filaments, bacilli, and spheres. Laboratory strains of IAV, however present mainly as spherical and bacilliform particles, suggesting a role for filaments in vivo. How these filaments form is not fully understood, but it has previously been shown that mutations in the viral matrix protein (M1) can be determinants of filament formation. In this work we show that filament formation also depends on multiple other genetic factors. To this end, we compared two IAV strains A/equine/Ohio/03 (O/2003) and A/equine/South Africa/4/03 (SA/2003) and found that SA/2003 could form filaments while O/2003 could not, despite no differences in their M1 sequences. To map the genetic basis of this difference, we generated reassortant viruses between O/2003 and SA/2003 and identified segments 1 (encoding polymerase basic protein 2, PB2), 4 (haemagglutinin, HA) and 6 (neuraminidase, NA) as determinants of morphology. We established that single mutations in segments 4 and 6, which alter the HA and NA proteins, alter virion morphology. To our surprise, we also identified three synonymous mutations in segment 1 of the virus that were determinants of filament formation despite not altering any known protein. We then extended this work to unravel the associated mechanisms of this change and found despite some differences in the activity of NA, contribution of HA to filament production, and differences in segment 1 RNA structure, there was no clear underlying mechanism. Given, that we were unable to identify the mechanisms associated with the change in morphology, we further extended this work to identify the factors involved in morphogenesis. To characterize IAV filament morphogenesis we employed cryogenic electron tomography (Cryo-ET) of vitrified equine fibroblasts (E. Derm). Although we were unable to identify any additional factors associated with IAV budding, we were able to generate a robust pipeline for studying filament formation. These results show that M1 is not the only determinant of IAV morphology, and that the ability to form filaments, a poorly studied but natural characteristic of IAV infection, is in fact modulated by multiple proteins and RNA determinants.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QR Microbiology > QR355 Virology
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Infection & Immunity > Centre for Virus Research
Funder's Name: Medical Research Council (MRC)
Supervisor's Name: Murcia, Professor Pablo R., Bhella, Professor David and Hutchinson, Dr. Edward
Date of Award: 2022
Depositing User: Theses Team
Unique ID: glathesis:2022-82872
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 May 2022 10:25
Last Modified: 01 Aug 2022 08:43
Thesis DOI: 10.5525/gla.thesis.82872
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