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Journal of Virology, April 2001, p. 3675-3684, Vol. 75, No. 8
Institutes of
Infectology1 and Molecular
Biology,2 Friedrich-Loeffler-Institutes, Federal
Research Centre for Virus Diseases of Animals, D-17498 Insel Riems,
Germany
Received 27 November 2000/Accepted 23 January 2001
Egress of four important alphaherpesviruses, equine herpesvirus 1 (EHV-1), herpes simplex virus type 1 (HSV-1), infectious laryngotracheitis virus (ILTV), and pseudorabies virus (PrV), was
investigated by electron microscopy of infected cell lines of different
origins. In all virus-cell systems analyzed, similar observations were
made concerning the different stages of virion morphogenesis. After
intranuclear assembly, nucleocapsids bud at the inner leaflet of the
nuclear membrane, resulting in enveloped particles in the perinuclear
space that contain a sharply bordered rim of tegument and a smooth
envelope surface. Egress from the perinuclear cisterna primarily occurs
by fusion of the primary envelope with the outer leaflet of the nuclear
membrane, which has been visualized for HSV-1 and EHV-1 for the first
time. The resulting intracytoplasmic naked nucleocapsids are enveloped
at membranes of the trans-Golgi network (TGN), as shown
by immunogold labeling with a TGN-specific antiserum. Virions
containing their final envelope differ in morphology from particles
within the perinuclear cisterna by visible surface projections and a
diffuse tegument. Particularly striking was the addition of a large
amount of tegument material to ILTV capsids in the cytoplasm.
Extracellular virions were morphologically identical to virions within
Golgi-derived vesicles, but distinct from virions in the perinuclear
space. Studies with gB- and gH-deleted PrV mutants indicated that these two glycoproteins, which are essential for virus entry and direct cell-to-cell spread, are dispensable for egress. Taken together, our
studies indicate that the deenvelopment-reenvelopment process of
herpesvirus maturation also occurs in EHV-1, HSV-1, and ILTV and that
membrane fusion processes occurring during egress are substantially
different from those during entry and direct viral cell-to-cell spread.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.8.3675-3684.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Egress of Alphaherpesviruses: Comparative
Ultrastructural Study
*
Corresponding author. Mailing address: Institute of
Infectology, Friedrich-Loeffler-Institutes, Federal Research Centre for Virus Diseases of Animals, Boddenblick 5A, D-17498 Insel Riems, Germany. Phone: 49-38351-7206. Fax: 49-38351-7151. E-mail:
Harald.Granzow{at}rie.bfav.de.
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