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Host alternation is necessary to maintain the genome stability of rift valley fever virus.

Moutailler S, Roche B, Thiberge JM, Caro V, Rougeon F, Failloux AB - PLoS Negl Trop Dis (2011)

Bottom Line: This genetic stability is assumed to result from a fitness trade-off imposed by host alternation, which constrains arbovirus genome evolution.The phosphoprotein NSs is not essential to viral replication allowing clones carrying deletions in NSs to predominate as they replicate slightly more rapidly.Our results strongly support the view that alternating replication is necessary to maintain the virulence factor carried by the NSs phosphoprotein.

View Article: PubMed Central - PubMed

Affiliation: Molecular Genetics of Bunyavirus, Department of Virology, Institut Pasteur, Paris, France.

ABSTRACT

Background: Most arthropod-borne viruses (arboviruses) are RNA viruses, which are maintained in nature by replication cycles that alternate between arthropod and vertebrate hosts. Arboviruses appear to experience lower rates of evolution than RNA viruses that replicate in a single host. This genetic stability is assumed to result from a fitness trade-off imposed by host alternation, which constrains arbovirus genome evolution. To test this hypothesis, we used Rift Valley fever virus (RVFV), an arbovirus that can be transmitted either directly (between vertebrates during the manipulation of infected tissues, and between mosquitoes by vertical transmission) or indirectly (from one vertebrate to another by mosquito-borne transmission).

Methodology/principal findings: RVFV was serially passaged in BHK21 (hamster) or Aag2 (Aedes aegypti) cells, or in alternation between the two cell types. After 30 passages, these single host-passaged viruses lost their virulence and induced protective effects against a challenge with a virulent virus. Large deletions in the NSs gene that encodes the virulence factor were detectable from the 15(th) serial passage onwards in BHK21 cells and from the 10(th) passage in Aag2 cells. The phosphoprotein NSs is not essential to viral replication allowing clones carrying deletions in NSs to predominate as they replicate slightly more rapidly. No genetic changes were found in viruses that were passaged alternately between arthropod and vertebrate cells. Furthermore, alternating passaged viruses presenting complete NSs gene remained virulent after 30 passages.

Conclusions/significance: Our results strongly support the view that alternating replication is necessary to maintain the virulence factor carried by the NSs phosphoprotein.

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Related in: MedlinePlus

Experimental strategy to test RVFV evolution in vitro.The parental P strain virus was subjected to 30 serial passages in BHK21 cells or Aag2 cells, or 30 passages that alternated between BHK21 and Aag2 cells, using a multiplicity of infection (MOI) of 0.1 PFU/cell. The fitness of P (the parental strain), Z30Alt (bulk harvest at the 30th alternating passage in BHK21 and Aag2 cells), Z30B (bulk harvest at the 30th serial passage in BHK21 cells), Z30A (bulk harvest at the 30th serial passage in Aag2 cells), Z30BC (a clone isolated after the 30th serial passage in BHK21 cells) and Z30AC (a clone isolated after the 30th serial passage in Aag2 cells) were tested by inoculation into mice. Genetic changes were detected by sequencing the NSs gene carrying the virulence factor.
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pntd-0001156-g001: Experimental strategy to test RVFV evolution in vitro.The parental P strain virus was subjected to 30 serial passages in BHK21 cells or Aag2 cells, or 30 passages that alternated between BHK21 and Aag2 cells, using a multiplicity of infection (MOI) of 0.1 PFU/cell. The fitness of P (the parental strain), Z30Alt (bulk harvest at the 30th alternating passage in BHK21 and Aag2 cells), Z30B (bulk harvest at the 30th serial passage in BHK21 cells), Z30A (bulk harvest at the 30th serial passage in Aag2 cells), Z30BC (a clone isolated after the 30th serial passage in BHK21 cells) and Z30AC (a clone isolated after the 30th serial passage in Aag2 cells) were tested by inoculation into mice. Genetic changes were detected by sequencing the NSs gene carrying the virulence factor.

Mentions: Figure 1 describes the strategy adopted to test the hypothesis that an alternating host cycle constrains the evolution of RVFV.


Host alternation is necessary to maintain the genome stability of rift valley fever virus.

Moutailler S, Roche B, Thiberge JM, Caro V, Rougeon F, Failloux AB - PLoS Negl Trop Dis (2011)

Experimental strategy to test RVFV evolution in vitro.The parental P strain virus was subjected to 30 serial passages in BHK21 cells or Aag2 cells, or 30 passages that alternated between BHK21 and Aag2 cells, using a multiplicity of infection (MOI) of 0.1 PFU/cell. The fitness of P (the parental strain), Z30Alt (bulk harvest at the 30th alternating passage in BHK21 and Aag2 cells), Z30B (bulk harvest at the 30th serial passage in BHK21 cells), Z30A (bulk harvest at the 30th serial passage in Aag2 cells), Z30BC (a clone isolated after the 30th serial passage in BHK21 cells) and Z30AC (a clone isolated after the 30th serial passage in Aag2 cells) were tested by inoculation into mice. Genetic changes were detected by sequencing the NSs gene carrying the virulence factor.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3101185&req=5

pntd-0001156-g001: Experimental strategy to test RVFV evolution in vitro.The parental P strain virus was subjected to 30 serial passages in BHK21 cells or Aag2 cells, or 30 passages that alternated between BHK21 and Aag2 cells, using a multiplicity of infection (MOI) of 0.1 PFU/cell. The fitness of P (the parental strain), Z30Alt (bulk harvest at the 30th alternating passage in BHK21 and Aag2 cells), Z30B (bulk harvest at the 30th serial passage in BHK21 cells), Z30A (bulk harvest at the 30th serial passage in Aag2 cells), Z30BC (a clone isolated after the 30th serial passage in BHK21 cells) and Z30AC (a clone isolated after the 30th serial passage in Aag2 cells) were tested by inoculation into mice. Genetic changes were detected by sequencing the NSs gene carrying the virulence factor.
Mentions: Figure 1 describes the strategy adopted to test the hypothesis that an alternating host cycle constrains the evolution of RVFV.

Bottom Line: This genetic stability is assumed to result from a fitness trade-off imposed by host alternation, which constrains arbovirus genome evolution.The phosphoprotein NSs is not essential to viral replication allowing clones carrying deletions in NSs to predominate as they replicate slightly more rapidly.Our results strongly support the view that alternating replication is necessary to maintain the virulence factor carried by the NSs phosphoprotein.

View Article: PubMed Central - PubMed

Affiliation: Molecular Genetics of Bunyavirus, Department of Virology, Institut Pasteur, Paris, France.

ABSTRACT

Background: Most arthropod-borne viruses (arboviruses) are RNA viruses, which are maintained in nature by replication cycles that alternate between arthropod and vertebrate hosts. Arboviruses appear to experience lower rates of evolution than RNA viruses that replicate in a single host. This genetic stability is assumed to result from a fitness trade-off imposed by host alternation, which constrains arbovirus genome evolution. To test this hypothesis, we used Rift Valley fever virus (RVFV), an arbovirus that can be transmitted either directly (between vertebrates during the manipulation of infected tissues, and between mosquitoes by vertical transmission) or indirectly (from one vertebrate to another by mosquito-borne transmission).

Methodology/principal findings: RVFV was serially passaged in BHK21 (hamster) or Aag2 (Aedes aegypti) cells, or in alternation between the two cell types. After 30 passages, these single host-passaged viruses lost their virulence and induced protective effects against a challenge with a virulent virus. Large deletions in the NSs gene that encodes the virulence factor were detectable from the 15(th) serial passage onwards in BHK21 cells and from the 10(th) passage in Aag2 cells. The phosphoprotein NSs is not essential to viral replication allowing clones carrying deletions in NSs to predominate as they replicate slightly more rapidly. No genetic changes were found in viruses that were passaged alternately between arthropod and vertebrate cells. Furthermore, alternating passaged viruses presenting complete NSs gene remained virulent after 30 passages.

Conclusions/significance: Our results strongly support the view that alternating replication is necessary to maintain the virulence factor carried by the NSs phosphoprotein.

Show MeSH
Related in: MedlinePlus