Schexnaydre, E. | bioRxiv Science

bioRxiv2021

Whole-brain fluorescence-MRI coregistration for precise anatomical mapping of virus infection

Viral tropism within the brain and the role(s) of vertebrate immune response to neurotropic flaviviruses infection is largely understudied. We combined multimodal imaging (cm-nm scale) with single nuclei RNA- sequencing to study Langat virus in wildtype and interferon alpha/beta receptor knockout (Ifnar-/-) mice to visualize viral pathogenesis and define molecular mechanisms. Whole brain viral infection was imaged by Optical Projection Tomography coregistered to ex vivo MRI. Infection was limited to grey matter of sensory systems in wildtype mice, but extended into white matter, meninges and choroid plexus in Ifnar-/-mice. Cells in wildtype displayed strong type I and II IFN responses, likely due to Ifnb expressing astrocytes, infiltration of macrophages and Ifng-expressing CD8+NK cells, whereas in Ifnar-/-, the absence of this response contributed to a shift in cellular tropism towards non-activated resident microglia. Multimodal imaging-transcriptomics exemplifies a powerful way to characterize mechanisms of viral pathogenesis and tropism.

microbiology↗

bioRxiv2021

Clinically observed deletions in SARS-CoV-2 Nsp1 affect protein stability and its ability to inhibit translation

Nonstructural protein 1 (Nsp1) is a major pathogenicity factor of SARS-CoV-2. It inhibits host-cell translation, primarily through a direct interaction between its C-terminal domain and the mRNA entry channel of the 40S small ribosomal subunit, with an N-terminal {beta}-barrel domain fine-tuning the inhibition and promoting selective translation of viral mRNA. SARS-CoV-2 nsp1 is a target of recurring deletions, some of which are associated with altered COVID-19 disease progression. To provide the biochemical basis for this, it is essential to characterize the efficiency of translational inhibition by the said protein variants. Here, we use an in vitro translation system to investigate the translation inhibition capacity of a series of clinically observed Nsp1 deletion variants. We find that a frequently observed deletion of residues 79-89 destabilized the N-terminal domain (NTD) and severely reduced the capacity of Nsp1 to inhibit translation. Interestingly, shorter deletions in the same region have been reported to effect the type I interferon response but did not affect translation inhibition, indicating a possible translation-independent role of the Nsp1 NTD in interferon response modulation. Taken together, our data provide a mechanistic basis for understanding how deletions in Nsp1 influence SARS-CoV-2 induction of interferon response and COVID-19 progression.

microbiology↗