Analysis of the transport modes of nuclear herpesvirus capsids
Final Report Abstract
Herpes virus es are large DNA viruses that utilize the host nucleus for genome replication as well as capsid assembly. After maturation, these 125 nm large capsid assemblies must cross the nucleoplasm to engage the nuclear envelope and bud int o the cytoplasm through a process called nuclear egress. Early studies suggested that herpes virus infection induces nuclear F-actin and that capsids are transported on t hese filaments via a motor-dependent mechanism. However direct evidence, visualizing capsids transporting on F-actin filaments was missing. In this project, we reevaluated this model and found that herpes virus infection does not induce nuclear F-actin nor that F -actin depolymerizing drugs have an effect on nuclear motility. By developing a custom light-sheet microscopy methodology as well as a custom-tailored single particle tracking software we instead found that the enlargement of nuclear corral size during infection allows capsids to diffuse almost unobstructed. Moreover, capsids can hop between corrals through active diffusion in which another energy -dependent process kicks the passively diffusing capsid. We show trough simple geomet rical estimates that 50-70% of nuclear capsids can reach the nuclear membrane through Brownian motion in these enlarged corrals. We therefore provide a revised model in which the virally induced restructuring of the nuclear architecture allows capsids to reach sites of nuclear egress through Brownian motion. In addition, we recently solved the in situ structure of the nuclear egress complex in cooperation with the Grünewald lab, Ox ford, UK. We found that the nuclear egress complex consists of two honey-comb-like layers. As the inner layer has slightly smaller spacing, membrane bending into a sphere is induced that packs capsids very tightly. Taken together these results point to a new view on nuclear capsid egress in which stochastic motion and self-organization facilitate all necessary steps. In addition theses results may provide a blueprint for a mechanism by which large cellular complexes can cross and exit the nucleus.
Publications
- Cellular Mechanisms of Alpha Herpes virus Egress: Live Cell Fluorescence Microscopy of Pseudorabies Virus Exocytosis. PLoS Pathogens, 2014
Hogue I.B., Bosse J. B., Hu J. R., Thiberge S.Y., Enquist L.W.
(See online at https://doi.org/10.1371/journal.ppat.1004535) - Nuclear herpesvirus capsid motility is not dependent on F-actin. mBio, 2014
Bosse J.B., Virding S., Thiberge S.Y., Scherer J., Wodrich H., Ruzsics Z., Koszinowski U.H. & Enquist L.W.
(See online at https://doi.org/10.1128/mBio.01909-14) - Remodeling nuclear architecture allows efficient transport of herpes virus capsids by diffusion. Proc Natl Acad Sci USA, 2015
Bosse J.B., Hogue I.B., Feric M., Thiberge S.Y., Sodeik B., Brangwynne C.P., Enquist L.W.
(See online at https://doi.org/10.1073/pnas.1513876112) - Structural Basis of Vesicle Formation at the Inner Nuclear Membrane. Cell, 2015
Hagen C. (…) Bosse J. B. (…) Enquist L.W. (…) Mettenleiter T.C., Grünewald K.
(See online at https://doi.org/10.1016/j.cell.2015.11.029) - The diffusive way out: Herpes viruses remodel the host nucleus, enabling capsids to access the inner nuclear membrane. Nucleus, 2016
Bosse J.B., Enquist L.W.
(See online at https://doi.org/10.1080/19491034.2016.1149665)
