Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 1998 May;72(5):4022-31.
doi: 10.1128/JVI.72.5.4022-4031.1998.

Two types of virus-related particles are found during transmissible gastroenteritis virus morphogenesis

C Risco  1 , M Muntión, L Enjuanes, J L Carrascosa
Affiliations

Two types of virus-related particles are found during transmissible gastroenteritis virus morphogenesis

C Risco et al. J Virol. 1998 May.

Abstract

The intracellular assembly of the transmissible gastroenteritis coronavirus (TGEV) was studied in infected swine testis (ST) cells at different postinfection times by using ultrathin sections of conventionally embedded infected cells, freeze-substitution, and methods for detecting viral proteins and RNA at the electron microscopy level. This ultrastructural analysis was focused on the identification of the different viral components that assemble in infected cells, in particular the spherical, potentially icosahedral internal core, a new structural element of the extracellular infectious coronavirus recently characterized by our group. Typical budding profiles and two types of virion-related particles were detected in TGEV-infected cells. While large virions with an electron-dense internal periphery and a clear central area are abundant at perinuclear regions, smaller viral particles, with the characteristic morphology of extracellular virions (exhibiting compact internal cores with polygonal contours) accumulate inside secretory vesicles that reach the plasma membrane. The two types of virions coexist in the Golgi complex of infected ST cells. In nocodazole-treated infected cells, the two types of virions coexist in altered Golgi stacks, while the large secretory vesicles filled with virions found in normal infections are not detected in this case. Treatment of infected cells with the Golgi complex-disrupting agent brefeldin A induced the accumulation of large virions in the cisternae that form by fusion of different membranous compartments. These data, together with the distribution of both types of virions in different cellular compartments, strongly suggest that the large virions are the precursors of the small viral particles and that their transport through a functional Golgi complex is necessary for viral maturation.

PubMed Disclaimer

Figures

FIG. 1
FIG. 1
TGEV virions in different regions of infected ST cells. Sections of freeze-substituted cells (A to C) and a conventionally embedded cell (D) are shown. (A) Certain areas of the infected cell, mainly close to the nucleus, accumulate characteristic budding profiles (arrows) and large virions with an internal electron-dense periphery and clear center (arrowheads). (B) Closer to the plasma membrane, virions exhibit a smaller size and a homogeneously dense internal core (arrows). Some of these viral cores clearly exhibit polygonal contours (arrowheads). (C and D) Most of the extracellular virions are small particles with dense cores (arrows), although a few large viral particles are also seen in the extracellular environment (arrowhead in panel D). Abbreviations: sv, secretory vesicle; ci, cilium; pm, plasma membrane; mv, microvilli. Bar, 200 nm.
FIG. 2
FIG. 2
Collection of images corresponding to the different TGEV-related assemblies detected in infected ST cells. Sections of conventionally embedded cells (A, C, D, and I) and fixed, freeze-substituted cells (B, E, F, G, H, and J) are shown. (A to D) Different stages of the budding profiles. All stages present a dense cytoplasmic structure (arrows) interacting with smooth-walled membranes (arrowheads) and a variable curvature, from flat (A) to almost spherical (D). In panel C, part of the dense material is apparently not interacting with the membrane and looks like a cytoplasmic tail (arrow). Budding profiles originate large spherical viral particles with an electron-dense internal periphery and a clear center (E and F). Smaller virions have an internal dense core that frequently exhibit polygonal contours (arrows in panels G and H). Budding profiles (arrow in panel I) and both large and small viral particles (I and J) react with polyclonal anti-TGEV antibodies, as shown by immunogold labeling. Bar, 100 nm.
FIG. 3
FIG. 3
Binding of an RNase-gold complex to sections of infected ST cells. (A) The signal concentrates on RNA-containing cellular structures, such as, for example, the rough endoplasmic reticulum (RER)-associated ribosomes and free ribosomes. Binding to individual ribosomes is distinguished (arrows). Some signal on mitochondria (mi) is also detected. (B) This RNase-gold complex also reacts with both small (arrows) and large (arrowheads) virions. The RNA-gold probe binds to the dense periphery of large virions. Pretreatment of the sections with nonconjugated RNase (20 μg/ml) abolished the subsequent binding of the RNase-gold complex to both RNA-containing cellular structures (C) and to TGEV particles (labeled v in panel D). r, ribosome; SV, secretory vesicle. Bar, 200 nm.
FIG. 4
FIG. 4
Size distribution of TGEV cores in viral particles from ultrathin sections of TGEV-infected cells. Only intracellular virions from freeze-substituted samples were included in the quantification. The percentage of viral cores with a defined diameter is represented. Core size (diameter [in nanometers]) classes were established as follows: 1, <36; 2, >36 to 38; 3, >38 to 41; 4, >41 to 44; 5, >44 to 47; 6, >47 to 50; 7, >50 to 53; 8, >53 to 56; 9, >56 to 59; 10, >59 to 62; 11, >62 to 65; 12, >65 to 68; 13, >68 to 71; 14, >71 to 74; 15, >74 to 77; 16, >77 to 80; 17, >80 to 83; 18, >83 to 86; 19, >86 to 89; 20, >89. Virions belonging to the two extremes of the core size distribution are shown in the two micrographs: the small virion on the left corresponds to class 8, while the large virion on the right corresponds to class 19. A total of 505 virions were included in the measurements.
FIG. 5
FIG. 5
Effect of BFA and nocodazole treatment on TGEV assembly. (A) Large virions (arrowheads) and small dense viral particles (arrows) coexist within the Golgi complex (G) of normal infected cells. (B) BFA causes the disappearance of the Golgi complex as a distinguishable structure, together with the formation of large cisternae (asterisks), some of them apparently derived from the rough endoplasmic reticulum (RER), since they have ribosomes (r) attached. TGEV virions assemble in association with these cisternae (arrowheads point to budding profiles). Large viral particles with an electron-dense internal periphery and clear center (arrows) accumulate in these conditions. Some ERGIC-like tubular membranes are visible in these cells (pairs of arrows). (C) Abnormal Golgi stack (G) from a nocodazole-treated infected ST cell. Both budding profiles (arrowheads) and small dense virions (arrows) are seen within the altered membranes of the stack. mi, mitochondria; pm, plasma membrane. Bar, 200 nm.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Arnheiter H, Dubois-Dalcq M, Lazzarini R A. Direct visualization of protein transport and processing in the living cell by microinjection of specific antibodies. Cell. 1984;39:99–109. - PubMed
    1. Becker W B, McIntosh K, Dees J H, Chanock R M. Morphogenesis of avian infectious bronchitis virus and a related human virus (strain 229E) J Virol. 1967;1:1019–1027. - PMC - PubMed
    1. Bendayan M. Ultrastructural localization of nucleic acids by the use of enzyme-gold complexes. J Histochem Cytochem. 1981;29:531–541. - PubMed
    1. Bendayan M. The enzyme-gold cytochemical approach: a review. In: Hayat M A, editor. Colloidal gold: principles, methods, and applications. Vol. 2. San Diego, Calif: Academic Press, Inc.; 1989. pp. 117–147.
    1. Booy F P. Cryoelectron microscopy. In: Bentz J, editor. Viral fusion mechanisms. Boca Raton, Fla: CRC Press, Inc.; 1993. pp. 21–54.

Publication types

LinkOut - more resources