Abstract
BackgroundAedes aegypti mosquitoes are the main vectors of dengue viruses to humans. Understanding their biology and interactions with the pathogen are prerequisites for development of dengue transmission control strategies. Mosquito salivary glands are organs involved directly in pathogen transmission to vertebrate hosts. Information on the spatial distribution of gene expression in these organs is expected to assist in the development of novel disease control strategies, including those that entail the release of transgenic mosquitoes with impaired vector competence.ResultsWe report here the hybridization in situ patterns of 30 transcripts expressed in the salivary glands of adult Ae. aegypti females. Distinct spatial accumulation patterns were identified. The products of twelve genes are localized exclusively in the proximal-lateral lobes. Among these, three accumulate preferentially in the most anterior portion of the proximal-lateral lobe. This pattern revealed a salivary gland cell type previously undescribed in Ae. aegypti, which was validated by transmission electron microscopy. Five distinct gene products accumulate in the distal-lateral lobes and another five localize in the medial lobe. Seven transcripts are found in the distal-lateral and medial lobes. The transcriptional product of one gene accumulates in proximal- and distal-lateral lobes. Seven genes analyzed by quantitative PCR are expressed constitutively. The most abundant salivary gland transcripts are those localized within the proximal-lateral lobes, while previous work has shown that the distal-lateral lobes are the most active in protein synthesis. This incongruity suggests a role for translational regulation in mosquito saliva production.ConclusionsTransgenic mosquitoes with reduced vector competence have been proposed as tools for the control of dengue virus transmission. Expression of anti-dengue effector molecules in the distal-lateral lobes of Ae. aegypti salivary glands has been shown to reduce prevalence and mean intensities of viral infection. We anticipate greater efficiency of viral suppression if effector genes are expressed in all lobes of the salivary glands. Based on our data, a minimum of two promoters is necessary to drive the expression of one or more anti-dengue genes in all cells of the female salivary glands.
Highlights
Aedes aegypti mosquitoes are the main vectors of dengue viruses to humans
We report the hybridization in situ patterns of 30 genes expressed in the salivary glands of adult Ae. aegypti females, the identification of a new cell type located in the proximal portion of the lateral lobes, and discuss the application of such knowledge for enhancing efforts to interfere with dengue virus transmission
Hybridizations of digoxigenin-labeled anti-sense RNA to whole-mount salivary glands dissected from adult female mosquitoes showed that transcripts accumulate in specific lobes of the salivary gland
Summary
Aedes aegypti mosquitoes are the main vectors of dengue viruses to humans. Understanding their biology and interactions with the pathogen are prerequisites for development of dengue transmission control strategies. Mosquito salivary glands are organs involved directly in pathogen transmission to vertebrate hosts. Mosquito (Diptera, Culicidae) salivary glands have been studied extensively for their roles in blood feeding and pathogen transmission to vertebrate hosts. The salivary glands of adult female Ae. aegypti have a distinctive tri-lobed structure consisting of a single medial and two lateral lobes. The mosquito salivary glands produce and secrete molecules with diverse enzymatic, anti-hemostatic and antiinflammatory activities, which help in the acquisition of blood meals from vertebrate hosts, as well as for the digestion of sugar and nectar meals [15,18]. Mosquito saliva modulates vertebrate immune responses potentially increasing virus transmission, host susceptibility, viremia, disease progression and mortality [19,20,21]
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