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J. Virol., Apr 1997, 2636-2646, Vol 71, No. 4
J Dubuisson, S Lustig, N Ruggli, Y Akov and CM Rice
After peripheral inoculation of mice, Sindbis virus replicates in a variety
of tissues, leading to viremia. In some cases, the virus can enter the
central nervous system (CNS) and cause lethal encephalitis. The outcome of
infection is age and virus strain dependent. Recently, two pairs of Sindbis
virus variants differing in neurovirulence and neuroinvasiveness were
derived by limited serial passaging in mouse brain. Two early passage
isolates (SVA and SVB) were neurotropic but did not cause lethal
encephalitis. SVB, but not SVA, was neuroinvasive. A second independent
pair of isolates (SVN and SVNI), which had undergone more extensive mouse
brain passaging, were highly neurotropic and caused lethal encephalitis.
Only SVNI could reach the brain after peripheral inoculation. From these
isolates, virion RNAs were obtained and used to construct full-length cDNA
clones from which infectious RNA transcripts could be recovered. The
strains recovered from these clones were shown to retain the appropriate
phenotypes in weanling mice. Construction and analysis of recombinant
viruses were used to define the genetic loci determining neuroinvasion. For
SVB, neuroinvasiveness was determined by a single residue in the E2
glycoprotein (Gln-55). For SVNI, neuroinvasive loci were identified in both
the 5' noncoding region (position 8) and the E2 glycoprotein (Met-190).
Either of these changes on the SVN background was sufficient to confer a
neuroinvasive phenotype, although these recombinants were less virulent. To
completely mimic the SVNI phenotype, three SVNI-specific substitutions on
the SVN background were required: G at position 8, E2 Met-190, and Lys-260,
which by itself had no effect on neuroinvasion. These genetically defined
strains should be useful for dissecting the molecular mechanisms leading to
Sindbis virus invasion of the CNS.
Copyright © 1997, American Society for Microbiology
Genetic determinants of Sindbis virus neuroinvasiveness
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093, USA.
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