Maturation process of Japanese encephalitis virus in cultured mosquito cells in vitro and mouse brain cells in vivo

Abstract

The maturation process of Japanese encephalitis (JE) virus in C6/36 cells in vitro and in mouse brain cells in vivo was studied by electron microscopy. In the C6/36 cell infection, 500 to 2250 virions per cell were released into the medium during the period of study; yet, no virus budding process was observed at the host cell membranes. JE virions at various maturation stages appeared within the cisternae of rough endoplasmic reticulum (RER) of infected cells at 24 hours p.i.; and, although C6/36 cells did not show a well-developed Golgi apparatus, the virions appeared to be carried to the cell surface within host-cell secretory vesicles for extracellular release as early as 24 hours p.i. The occurrence of a secretory-type intracellular transport of maturing JE virus particles was well recognizable in brain cells of infected mice, in which JE virus particles were found almost exclusively in the cisternae of RER, in the Golgi apparatus, and in various vesicles, including coated vesicles, in the vicinity of the Golgi apparatus. Our previous study of dengue-2 virus morphogenesis and our present study of JE virus morphogenesis differed substantially at various stages of maturation. Possible mechanisms which explain these differences were discussed.

Comparison of replication rates and pathogenicities between the SA 14 parent and SA 14-14-2 vaccine strains of Japanese encephalitis virus in mouse brain neurons

“…Thus, the results of both the virus titration and morphological observation indicated that, following intracerebral inoculation into mice, the SA 14 parent strain of JE virus replicated vigorously and spread rapidly to a majority of neurons in the mouse brain, while the SA 14-14-2 strain replicated poorly and infected only a small number of neurons in scattered small foci before disappearing. Since JE virus replicates by trans-type maturation [6,9], it is believed that the viral growth in host cells occurs in the following sequence: (a) viral entry and uncoating at the cell surface, (b) viral replication at smooth endoplasmic reticulum (SER) and viral translation on RER, (c) viral assembly and maturation in the host-cell secretory channel, and (d) viral release into the extracellular space by secretory-type exocytosis. Therefore, it seems reasonable to believe that poor viral replication results from either partial impairment or complete blockage of one or more of the above processes.…”

“…JE virus genome released into the cytoplasm replicates genomic RNA and translates viral proteins on the endoplasmic reticulum membranes and discharges the viral products into the rough endoplasmic reticulum (RER) cisternae for viral assembly [9]. The progeny virions assembled in the cisternae are released extracellularly through the host-cell secretory channel via the Golgi apparatus by secretory-type exocytosis [6,10,17]. Likewise, in the infection of mouse brain neurons, JE virus has been shown to replicate selectively in the neuronal secretory system including RER and the Golgi apparatus, causing characteristic ultrastructural changes of these cytoplasmic organelles [10,11].…”

Isolation of Capsid Protein Dimers from the Tick-Borne Encephalitis Flavivirus and In Vitro Assembly of Capsid-Like Particles

“…Translation of the single long open reading frame gives rise to the structural and nonstructural (NS) viral proteins, with the structural proteins encoded in the 5Ј-terminal third of the genome in the order C-prM/M-E. The intracellular assembly of flaviviruses is not precisely understood but is believed to take place at the endoplasmic reticulum, because in infected cells, viral particles first become visible in this compartment by electron microscopy (EM) (5,10,15,30,35,36). The primary assembly products are immature particles that contain the prM protein and are noninfectious (6,9,13,32,41).…”

trans -Packaged West Nile Virus-Like Particles: Infectious Properties In Vitro and in Infected Mosquito Vectors

“…The WNV structural proteins prM and E are cotranslationally inserted into the endoplasmic reticulum (ER) membrane and processed by signal peptidases, producing proteins that encapsidate C together with the viral RNA, by budding into the ER lumen (18,32). At a later step in viral maturation, prM on these particles is cleaved into mature M protein by a cellular furin protease prior to release from the cell (43).…”