The cytoarchitecture of Zika

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A comparison of Zika virus infection in human neuroblastoma and mosquito cells

Text by Danielle Offerdahl

In keeping with the Rocky Mountain Laboratories tradition of tick-borne disease research, our research group has concentrated on the study of tick-borne flaviviruses.  However, with the recent explosion of Zika virus (ZIKV), we broadened our research to include this mosquito-borne flavivirus.  In the ongoing pandemic, ZIKV, a virus traditionally considered to cause a mild illness, has emerged as a significant neuropathogen.  We, therefore, elected to use both a mosquito and a human neuroblastoma cell line to illuminate the impacts of ZIKV infection on these two distinct cell lines via light and electron microscopy.  Initially, we tried using an Aedes aegypti cell line, as this is the primary mosquito vector in the ZIKV outbreak, but were surprised to find no virus production or evidence of infection within these cells.  Fortunately, an Aedes albopictus cell line, C6/36, was permissive for infection.

The ZIKV-infected cell lines showed all the hallmarks of flavivirus infection. However, during our transmission electron microscopy studies, we observed the presence of  20-30 nm circular structures within the 60-100 nm vesicle/spherules that characterize flavivirus replication compartments.  While electron dense material within these vesicles has been previously reported for other flaviviruses, no common shape had been described.  The application of dual-tilt 3D electron tomography (ET) allowed us to show that the circular structures were, in fact, smaller spherical structures that may reflect that actual replicative intermediates of RNA and proteins.  We performed virion and vesicle counts on the ET renderings and then calculated the numbers present in a single cell at 72 hours post-infection.  Interestingly, the calculated values for the human neuroblastoma cells were one log higher than the counts for the mosquito cells, mimicking the one log difference seen in viral titer between the cell lines at this time point.  The observations provided by this study create a relevant platform for future investigations the biology of ZIKV infection in both mammalian and arthropod cell lines.

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3D surface rendering of membrane within Zika virus Paraiba (2015) infected human neuroblastoma cells.  Round, hollow vesicles and smaller, solid virions are seen in abundance.

Introducing the authors

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Pictured from left to right: Marshall Bloom, Bryan Hansen, Dave Dorward, and Danielle Offerdahl.

About the research

Cytoarchitecture of Zika virus infection in human neuroblastoma and Aedes albopictus cell lines
Danielle K. Offerdahl, David W. Dorward, Bryan T. Hansen, Marshall E. Bloom
Virology, Volume 501, 15 January 2017, Pages 54–62, open access