Limits...
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.

Show MeSH

Related in: MedlinePlus

Targeting of the WNV Genome by RNAi at 7 and 14 Days Post Infection Is Correlated.(A) Count of reads aligning to each genome position at 7 and 14 days, n = 11,029, Spearman r = 0.7610, p<0.0001. (B) Count of abundant individual sequence reads in libraries obtained at 7 and 14 days, n = 433, Pearson R-squared = 0.03674, p<0.0001.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2698148&req=5

ppat-1000502-g004: Targeting of the WNV Genome by RNAi at 7 and 14 Days Post Infection Is Correlated.(A) Count of reads aligning to each genome position at 7 and 14 days, n = 11,029, Spearman r = 0.7610, p<0.0001. (B) Count of abundant individual sequence reads in libraries obtained at 7 and 14 days, n = 433, Pearson R-squared = 0.03674, p<0.0001.

Mentions: We then examined viRNAs that were apparently abundantly produced in mosquito midguts. At both 7 and 14 days the abundance of each unique read was calculated which ranged from 1 to 23 (Table 1). In order to assess whether the observed distribution of read abundance at both 7 and 14 days was significantly different than would be expected by chance, we conducted a permutation analysis. For each time point, n = 2544 (day 7) or n = 4419 (day 14) genomic positions were randomly sampled with replacement. The sampling procedure was repeated 100,000 times to obtain a theoretical distribution of read abundances, and this distribution was compared to the observed distribution by the Kolmorogov-Smirnov test (Figure 3). The observed abundance distribution was significantly different from the expectation (P<0.001 at 7 and 14 days). In addition, the intensity of viRNA targeting of each nucleotide of the genome was highly correlated at 7 and 14 days (Figure 4A). Further, a subset of viRNAs was detected at both sampled timepoints. The abundance of these “common” reads at 7 and 14 days was also highly correlated (Figure 4B).


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

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

Targeting of the WNV Genome by RNAi at 7 and 14 Days Post Infection Is Correlated.(A) Count of reads aligning to each genome position at 7 and 14 days, n = 11,029, Spearman r = 0.7610, p<0.0001. (B) Count of abundant individual sequence reads in libraries obtained at 7 and 14 days, n = 433, Pearson R-squared = 0.03674, p<0.0001.
© Copyright Policy
Related In: Results  -  Collection

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

ppat-1000502-g004: Targeting of the WNV Genome by RNAi at 7 and 14 Days Post Infection Is Correlated.(A) Count of reads aligning to each genome position at 7 and 14 days, n = 11,029, Spearman r = 0.7610, p<0.0001. (B) Count of abundant individual sequence reads in libraries obtained at 7 and 14 days, n = 433, Pearson R-squared = 0.03674, p<0.0001.
Mentions: We then examined viRNAs that were apparently abundantly produced in mosquito midguts. At both 7 and 14 days the abundance of each unique read was calculated which ranged from 1 to 23 (Table 1). In order to assess whether the observed distribution of read abundance at both 7 and 14 days was significantly different than would be expected by chance, we conducted a permutation analysis. For each time point, n = 2544 (day 7) or n = 4419 (day 14) genomic positions were randomly sampled with replacement. The sampling procedure was repeated 100,000 times to obtain a theoretical distribution of read abundances, and this distribution was compared to the observed distribution by the Kolmorogov-Smirnov test (Figure 3). The observed abundance distribution was significantly different from the expectation (P<0.001 at 7 and 14 days). In addition, the intensity of viRNA targeting of each nucleotide of the genome was highly correlated at 7 and 14 days (Figure 4A). Further, a subset of viRNAs was detected at both sampled timepoints. The abundance of these “common” reads at 7 and 14 days was also highly correlated (Figure 4B).

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