Visualizing Nudivirus Assembly and Egress

Abstract

Enveloped viruses hijack cellular membranes in order to provide the necessary material for virion assembly. In particular, viruses that replicate and assemble inside the nucleus have developed special approaches to modify the nuclear landscape for their advantage. We used electron microscopy to investigate cellular changes occurring during nudivirus infection and we characterized a unique mechanism for assembly, packaging, and transport of new virions across the nuclear membrane and through the cytoplasm. Our three-dimensional reconstructions describe the complex remodeling of the nuclear membrane necessary to release vesicle-associated viruses into the cytoplasm. This is the first report of nuclear morphological reconfigurations that occur during nudiviral infection. IMPORTANCE The dynamics of nuclear envelope has a critical role in multiple cellular processes. However, little is known regarding the structural changes occurring inside the nucleus or at the inner and outer nuclear membranes. For viruses assembling inside the nucleus, remodeling of the intranuclear membrane plays an important role in the process of virion assembly. Here, we monitored the changes associated with viral infection in the case of nudiviruses. Our data revealed dramatic membrane remodeling inside the nuclear compartment during infection with Oryctes rhinoceros nudivirus, an important biocontrol agent against coconut rhinoceros beetle, a devastating pest for coconut and oil palm trees. Based on these findings, we propose a model for nudivirus assembly in which nuclear packaging occurs in fully enveloped virions.

Endoparasitoid lifestyle promotes endogenization and domestication of dsDNA viruses

“…The major contribution of nudiviruses to endogenization may be explained by their wide host range in arthropods [45]. Their nuclear replication constitutes another plausible explanatory factor [46], since it may facilitate contact with host DNA. In addition, their tropism for gonads may favor the endogenization in germinal cells [47].…”

Processing hair follicles for transmission electron microscopy

“…Valuable tool in understanding hair biology. 130,135 Correlative light and electron microscopy (CLEM) Specific proteins localized at an ultrastructure level using nano gold markers.…”

“…The development of electron tomography and volume microscopy has aided in the 3D visualization of the precise geometry of complex macromolecular, subcellular or cellular structures including interaction of keratins and desmosomes. 25,[130][131][132] CLEM of high-pressure frozen and freezesubstituted samples, rather than a conventionally processed sample, can be ideal for simultaneously preserving the ultrastructural and antigenic epitopes; and dark-field scanning transmission electron microscopy (DF-STEM) then enables visualization of immunogold markers at high-resolution without the need for any post-staining or silver enhancement procedures. 71 While advancements in electron tomography have enabled the 3D visualization of macromolecular process, a limited sampling volume limits the investigation of features that span more than a few…”

“…For instance, while the association between desmosomes and keratins is well‐established, their network organization is largely unknown. The development of electron tomography and volume microscopy has aided in the 3D visualization of the precise geometry of complex macromolecular, subcellular or cellular structures including interaction of keratins and desmosomes 25,130‐132 . CLEM of high‐pressure frozen and freeze‐substituted samples, rather than a conventionally processed sample, can be ideal for simultaneously preserving the ultrastructural and antigenic epitopes; and dark‐field scanning transmission electron microscopy (DF‐STEM) then enables visualization of immunogold markers at high‐resolution without the need for any post‐staining or silver enhancement procedures 71 …”

Inhibition of PIKFYVE kinase interferes ESCRT pathway to suppress RNA virus replication

“…In the occurrence of release, the host cell membrane can be hijacked or fused with the viral membrane in the enveloped virus. 7,8 ESCRT pathway usually participates in RNA viruses' intracellular replication, such as human immunodeficiency virus (HIV), 9 and bluetongue virus (BTV), 10 and also in a certain kind of DNA virus' replications including herpes simplex virus (HSV), 11,12 hepatitis B virus (HBV), 13 and Epstein-Barr virus (EBV). 14 Emerging studies have revealed that multiply nonenveloped viruses may also hijack cell membranes, allowing them to lurk in the membrane to facilitate immune escape or avoid immune neutralization and clearance.…”