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RNAi targeting of West Nile virus in mosquito midguts promotes virus diversification.

Brackney DE, Beane JE, Ebel GD - PLoS Pathog. (2009)

Bottom Line: Our data demonstrate that WNV infection in orally exposed vector mosquitoes induces the RNAi pathway and that regions of the WNV genome that are more intensely targeted by RNAi are more likely to contain point mutations compared to weakly targeted regions.These results suggest that, under natural conditions, positive selection of WNV within mosquitoes is stronger in regions highly targeted by the host RNAi response.Further, they provide a mechanistic basis for the relative importance of mosquitoes in driving WNV diversification.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM, USA.

ABSTRACT
West Nile virus (WNV) exists in nature as a genetically diverse population of competing genomes. This high genetic diversity and concomitant adaptive plasticity has facilitated the rapid adaptation of WNV to North American transmission cycles and contributed to its explosive spread throughout the New World. WNV is maintained in nature in a transmission cycle between mosquitoes and birds, with intrahost genetic diversity highest in mosquitoes. The mechanistic basis for this increase in genetic diversity in mosquitoes is poorly understood. To determine whether the high mutational diversity of WNV in mosquitoes is driven by RNA interference (RNAi), we characterized the RNAi response to WNV in the midguts of orally exposed Culex pipiens quinquefasciatus using high-throughput, massively parallel sequencing and estimated viral genetic diversity. Our data demonstrate that WNV infection in orally exposed vector mosquitoes induces the RNAi pathway and that regions of the WNV genome that are more intensely targeted by RNAi are more likely to contain point mutations compared to weakly targeted regions. These results suggest that, under natural conditions, positive selection of WNV within mosquitoes is stronger in regions highly targeted by the host RNAi response. Further, they provide a mechanistic basis for the relative importance of mosquitoes in driving WNV diversification.

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Related in: MedlinePlus

viRNA Coverage of WNV Genome at 7 and 14 Days Post Infection.Complete genome of WNV showing the intensity of viRNA coverage at each nucleotide of the genome at 7 (A) and 14 (B) days postfeeding. Reads originating from the positive strand are shown in blue, above the axis, and those originating from the negative strand are shown in red, below the axis. Particular regions appear to be preferentially targeted by the RNAi response, including the 5′ aspect of the C coding region and the 3′ non-coding region. Peaks are generally higher at 14 than 7 days post infection (dpi), with notable exceptions in NS2a, at the NS4b/NS5 junction and the 3′-UTR. Both positive and negative polarity RNA is targeted by viRNAs generated in mosquito midgut cells. At 14 dpi, although true for both 7 and 14 dpi, the focus of viRNA targeting in the C coding sequence (C) is characterized by a relatively intense targeting of the negative strand compared to the 3′-UTR (D). Notably, well documented imperfect stem-loops and other critical functional RNA structures within the 3′-UTR do not appear to be intensely targeted by the RNAi response.
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ppat-1000502-g002: viRNA Coverage of WNV Genome at 7 and 14 Days Post Infection.Complete genome of WNV showing the intensity of viRNA coverage at each nucleotide of the genome at 7 (A) and 14 (B) days postfeeding. Reads originating from the positive strand are shown in blue, above the axis, and those originating from the negative strand are shown in red, below the axis. Particular regions appear to be preferentially targeted by the RNAi response, including the 5′ aspect of the C coding region and the 3′ non-coding region. Peaks are generally higher at 14 than 7 days post infection (dpi), with notable exceptions in NS2a, at the NS4b/NS5 junction and the 3′-UTR. Both positive and negative polarity RNA is targeted by viRNAs generated in mosquito midgut cells. At 14 dpi, although true for both 7 and 14 dpi, the focus of viRNA targeting in the C coding sequence (C) is characterized by a relatively intense targeting of the negative strand compared to the 3′-UTR (D). Notably, well documented imperfect stem-loops and other critical functional RNA structures within the 3′-UTR do not appear to be intensely targeted by the RNAi response.

Mentions: To assess positional and regional differences in the intensity of viRNA targeting of the WNV genome in mosquito midguts, the frequency of viRNA reads mapping to each nucleotide in the WNV genome was computed (Figure 2A). Inspection of these results revealed (A) an asymmetric distribution of viRNAs across the genome with some regions being highly targeted and others weakly or not targeted and (B) that peaks in the frequency distribution of hits along the genome at 7 days were also apparent at 14 days, although peaks at 14 days tended to be higher, with some exceptions.


RNAi targeting of West Nile virus in mosquito midguts promotes virus diversification.

Brackney DE, Beane JE, Ebel GD - PLoS Pathog. (2009)

viRNA Coverage of WNV Genome at 7 and 14 Days Post Infection.Complete genome of WNV showing the intensity of viRNA coverage at each nucleotide of the genome at 7 (A) and 14 (B) days postfeeding. Reads originating from the positive strand are shown in blue, above the axis, and those originating from the negative strand are shown in red, below the axis. Particular regions appear to be preferentially targeted by the RNAi response, including the 5′ aspect of the C coding region and the 3′ non-coding region. Peaks are generally higher at 14 than 7 days post infection (dpi), with notable exceptions in NS2a, at the NS4b/NS5 junction and the 3′-UTR. Both positive and negative polarity RNA is targeted by viRNAs generated in mosquito midgut cells. At 14 dpi, although true for both 7 and 14 dpi, the focus of viRNA targeting in the C coding sequence (C) is characterized by a relatively intense targeting of the negative strand compared to the 3′-UTR (D). Notably, well documented imperfect stem-loops and other critical functional RNA structures within the 3′-UTR do not appear to be intensely targeted by the RNAi response.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2698148&req=5

ppat-1000502-g002: viRNA Coverage of WNV Genome at 7 and 14 Days Post Infection.Complete genome of WNV showing the intensity of viRNA coverage at each nucleotide of the genome at 7 (A) and 14 (B) days postfeeding. Reads originating from the positive strand are shown in blue, above the axis, and those originating from the negative strand are shown in red, below the axis. Particular regions appear to be preferentially targeted by the RNAi response, including the 5′ aspect of the C coding region and the 3′ non-coding region. Peaks are generally higher at 14 than 7 days post infection (dpi), with notable exceptions in NS2a, at the NS4b/NS5 junction and the 3′-UTR. Both positive and negative polarity RNA is targeted by viRNAs generated in mosquito midgut cells. At 14 dpi, although true for both 7 and 14 dpi, the focus of viRNA targeting in the C coding sequence (C) is characterized by a relatively intense targeting of the negative strand compared to the 3′-UTR (D). Notably, well documented imperfect stem-loops and other critical functional RNA structures within the 3′-UTR do not appear to be intensely targeted by the RNAi response.
Mentions: To assess positional and regional differences in the intensity of viRNA targeting of the WNV genome in mosquito midguts, the frequency of viRNA reads mapping to each nucleotide in the WNV genome was computed (Figure 2A). Inspection of these results revealed (A) an asymmetric distribution of viRNAs across the genome with some regions being highly targeted and others weakly or not targeted and (B) that peaks in the frequency distribution of hits along the genome at 7 days were also apparent at 14 days, although peaks at 14 days tended to be higher, with some exceptions.

Bottom Line: Our data demonstrate that WNV infection in orally exposed vector mosquitoes induces the RNAi pathway and that regions of the WNV genome that are more intensely targeted by RNAi are more likely to contain point mutations compared to weakly targeted regions.These results suggest that, under natural conditions, positive selection of WNV within mosquitoes is stronger in regions highly targeted by the host RNAi response.Further, they provide a mechanistic basis for the relative importance of mosquitoes in driving WNV diversification.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, University of New Mexico School of Medicine, Albuquerque, NM, USA.

ABSTRACT
West Nile virus (WNV) exists in nature as a genetically diverse population of competing genomes. This high genetic diversity and concomitant adaptive plasticity has facilitated the rapid adaptation of WNV to North American transmission cycles and contributed to its explosive spread throughout the New World. WNV is maintained in nature in a transmission cycle between mosquitoes and birds, with intrahost genetic diversity highest in mosquitoes. The mechanistic basis for this increase in genetic diversity in mosquitoes is poorly understood. To determine whether the high mutational diversity of WNV in mosquitoes is driven by RNA interference (RNAi), we characterized the RNAi response to WNV in the midguts of orally exposed Culex pipiens quinquefasciatus using high-throughput, massively parallel sequencing and estimated viral genetic diversity. Our data demonstrate that WNV infection in orally exposed vector mosquitoes induces the RNAi pathway and that regions of the WNV genome that are more intensely targeted by RNAi are more likely to contain point mutations compared to weakly targeted regions. These results suggest that, under natural conditions, positive selection of WNV within mosquitoes is stronger in regions highly targeted by the host RNAi response. Further, they provide a mechanistic basis for the relative importance of mosquitoes in driving WNV diversification.

Show MeSH
Related in: MedlinePlus