Tegument Assembly, Secondary Envelopment and Exocytosis

Hogue, Ian B.

doi:10.21775/cimb.042.551

Cited by 5 publications

(9 citation statements)

References 205 publications

(252 reference statements)

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“…This mechanism is in contrast to studies which have been performed in alphaherpesviruses, where single PRV virus particles have been shown to travel to the plasmamembrane and be released by fusion (Hogue et al, 2014). Our data however, does not exclude the existence of a separate egress pathway analogue to the mechanisms shown for alphaherpesviruses (reviewed in (Hogue, 2022)). Compared to previous studies, our new correlative 3D-CLEM workflow provides a major technological advancement as it permits us to observe whole cells in a defined infection state with less effort compared to precise but tedious serial sectioning (Schauflinger et al, 2013).…”

Section: Discussioncontrasting

confidence: 96%

Intermittent Bulk Release of Human Cytomegalovirus

Flomm

Soh

Schneider

et al. 2021

Preprint

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Human Cytomegalovirus (HCMV) is a highly prevalent herpesvirus that establishes lifelong latent infection in humans. It is the leading cause of congenital disabilities and a significant cause of disease in immunocompromised patients (1). HCMV significantly remodels host cell processes and membranes for the effective production of virus progeny (2). Their final morphogenesis process occurs in the cytoplasm, where capsids acquire the proteinaceous tegument layer and enveloping membrane. This involves budding into host membranes and subsequent exocytosis of assembled virions by fusion with the plasma membrane (3). Envelopment and exocytosis are thought to be mediated by small vesicles, leading to the continuous release of individually wrapped virions. However, groups of enveloped virus particles are also found inside multivesicular bodies (MVBs) (4, 5). Whether enveloped particles in MVBs reflect a productive envelopment and egress pathway or are targeted for lysosomal degradation has remained unknown.Using a novel correlative light and electron microscopy (CLEM) workflow that enables imaging of virus morphogenesis in whole cells, we present evidence that HCMV envelopment does occur at MVBs, generating large intracellular accumulations of enveloped virions in HFF cells. Virus-filled MVBs carried exosomal markers and were found to traverse the cytoplasm to the plasma membrane by volumetric, live-cell lattice light-sheet microscopy. Using a pH-sensitive biosensor, we show that virus particles were released in bulk by fusion of MVBs with the plasma membrane leading to ‘patches’ of particles on the plasma membrane.This hitherto undescribed envelopment and exocytosis pathway of HCMV, leading to the recurrent bulk release of virus particles, possibly involves the late-endosome/exosome pathway.Significance StatementHCMV is able to cause disease affecting various organs. Understanding how HCMV can infect a wide variety of cells is essential for developing antiviral strategies. Recent work suggests that HCMV particles with varying glycoprotein repertoires facilitate entry into different target cells. How this glycoprotein diversity at the single-particle-level is generated is unclear. Different envelopment and egress pathways might play a role.Here, using HFF cells, we present direct functional evidence that HCMV uses multivesicular bodies for the bulk release of virus particles into membrane-associated accumulations as a novel, alternative HCMV egress pathway. Future work will aim to illuminate how different egress pathways might lead to varying virion compositions.

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Section: Discussioncontrasting

confidence: 96%

Intermittent Bulk Release of Human Cytomegalovirus

Flomm

Soh

Schneider

et al. 2021

Preprint

View full text Add to dashboard Cite

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“…This mechanism is in contrast to studies that have been performed in alphaherpesviruses, where single PRV virus particles have been shown to travel to the plasma membrane and be released by fusion [49]. Our data, however, does not exclude the existence of a separate egress pathway, in analogy to the mechanisms shown for alphaherpesviruses (reviewed in [77]). Compared to previous studies, our new correlative 3D-CLEM workflow provides a major technological advancement permitting us to observe whole cells in a defined infection state without the need for serial sectioning [47].…”

Section: Plos Pathogenscontrasting

confidence: 96%

Intermittent bulk release of human cytomegalovirus

et al. 2022

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Human Cytomegalovirus (HCMV) can infect a variety of cell types by using virions of varying glycoprotein compositions. It is still unclear how this diversity is generated, but spatio-temporally separated envelopment and egress pathways might play a role. So far, one egress pathway has been described in which HCMV particles are individually enveloped into small vesicles and are subsequently exocytosed continuously. However, some studies have also found enveloped virus particles inside multivesicular structures but could not link them to productive egress or degradation pathways. We used a novel 3D-CLEM workflow allowing us to investigate these structures in HCMV morphogenesis and egress at high spatio-temporal resolution. We found that multiple envelopment events occurred at individual vesicles leading to multiviral bodies (MViBs), which subsequently traversed the cytoplasm to release virions as intermittent bulk pulses at the plasma membrane to form extracellular virus accumulations (EVAs). Our data support the existence of a novel bona fide HCMV egress pathway, which opens the gate to evaluate divergent egress pathways in generating virion diversity.

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“…We hypothesized that differences in capsid composition between incoming and egressing capsids may prevent egressing capsids from interacting with NPCs. During entry, the majority of the tegument dissociates from the capsid [3][4][5][6][7]; however, during egress, tegument proteins are loaded onto capsids [30]. It may be that capsid-associated pUL16 and pUL21 on egressing nucleocapsids mask capsid proteins, such as pUL25 and pUL36, that function in capsid recruitment to NPCs.…”

Section: Plos Pathogensmentioning

confidence: 99%

“…The binding of ectopically expressed pUL16 and pUL21 to incoming capsids is unlikely for at least two reasons. First, the tegument is thought to form through a series of interactions between inner and outer tegument proteins [30] with pUL21 associating with capsids in the nucleus and pUL16 associating with capsids in the cytoplasm after nuclear egress [58,[62][63][64]. This suggests that the molecular interactions that mediate pUL16 and pUL21 capsid association are distinct, and that pUL16 and pUL21 are not loaded onto capsids as a pUL16/pUL21 complex.…”

Section: Plos Pathogensmentioning

confidence: 99%

“…Once in the cytoplasm, the nucleocapsids are transported along microtubules towards membranes derived from the trans-Golgi network, or late endosomes, where the nucleocapsids acquire their final envelope in a process called secondary envelopment [ 28 , 29 ]. After secondary envelopment, the now mature virions are transported within vesicles to the plasma membrane, where vesicle membranes fuse with the plasma membrane releasing the virions into the extracellular space [ 30 ].…”

Section: Introductionmentioning

confidence: 99%

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The Herpes Simplex Virus pUL16 and pUL21 Proteins Prevent Capsids from Docking at Nuclear Pore Complexes

Thomas,

Finnen,

Mewburn

et al. 2023

PLoS Pathog

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After entry into cells, herpes simplex virus (HSV) nucleocapsids dock at nuclear pore complexes (NPCs) through which viral genomes are released into the nucleoplasm where viral gene expression, genome replication, and early steps in virion assembly take place. After their assembly, nucleocapsids are translocated to the cytoplasm for final virion maturation. Nascent cytoplasmic nucleocapsids are prevented from binding to NPCs and delivering their genomes to the nucleus from which they emerged, but how this is accomplished is not understood. Here we report that HSV pUL16 and pUL21 deletion mutants accumulate empty capsids at the cytoplasmic face of NPCs late in infection. Additionally, prior expression of pUL16 and pUL21 prevented incoming nucleocapsids from docking at NPCs, delivering their genomes to the nucleus and initiating viral gene expression. Both pUL16 and pUL21 localized to the nuclear envelope, placing them in an appropriate location to interfere with nucleocapsid/NPC interactions.

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Tegument Assembly, Secondary Envelopment and Exocytosis

Cited by 5 publications

References 205 publications

Intermittent Bulk Release of Human Cytomegalovirus

Intermittent Bulk Release of Human Cytomegalovirus

Intermittent bulk release of human cytomegalovirus

The Herpes Simplex Virus pUL16 and pUL21 Proteins Prevent Capsids from Docking at Nuclear Pore Complexes

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