Abstract
BackgroundIn insects, including Anopheles mosquitoes, Dscam (Down syndrome cell adhesion molecule) appears to be involved in phagocytosis of pathogens, and shows pathogen-specific splice-form expression between divergent pathogen (or parasite) types (e.g. between bacteria and Plasmodium or between Plasmodium berghei and Plasmodium falciparum). Here, data are presented from the first study of Dscam expression in response to genetic diversity within a parasite species.MethodsIn independent field and laboratory studies, a measure of Dscam splice-form diversity was compared between mosquitoes fed on blood that was free of P. falciparum to mosquitoes exposed to either single or mixed genotype infections of P. falciparum.ResultsSignificant increases in Anopheles gambiae Dscam (AgDscam) receptor diversity were observed in parasite-exposed mosquitoes, but only weak evidence that AgDscam diversity rises further upon exposure to mixed genotype parasite infections was found. Finally, a cluster of AgDscam exon 4 variants that become especially common during Plasmodium invasion was identified.ConclusionsWhile the data clearly indicate that AgDscam diversity increases with P. falciparum exposure, they do not suggest that AgDscam diversity rises further in response to increased parasite diversity.
Highlights
In insects, including Anopheles mosquitoes, Dscam (Down syndrome cell adhesion molecule) appears to be involved in phagocytosis of pathogens, and shows pathogen-specific splice-form expression between divergent pathogen types
31,920 unique splice forms of Dscam can be generated through the alternative splicing of 84 variable exons contained within three variable exon cassettes [30], and which could potentially contribute to a capability to distinguish between different genotypes of Plasmodium
For the field study, An. gambiae were membrane-fed on blood samples taken from gametocyte-carrying children, and RNA was harvested from the insects 24-hours postexposure, a time when parasites are traversing the midgut epithelium [30]. cDNAs were cloned and sequenced to identify specific Anopheles gambiae Dscam (AgDscam) gene variants expressed within insects fed from different blood samples
Summary
Significant increases in Anopheles gambiae Dscam (AgDscam) receptor diversity were observed in parasiteexposed mosquitoes, but only weak evidence that AgDscam diversity rises further upon exposure to mixed genotype parasite infections was found. A cluster of AgDscam exon 4 variants that become especially common during Plasmodium invasion was identified
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