The kdr-bearing haplotype and susceptibility to Plasmodium falciparum in Anopheles gambiae: genetic correlation and functional testing

Abstract

BackgroundMembers of the Anophelesgambiae species complex are primary vectors of human malaria in Africa. It is known that a large haplotype shared between An. gambiae and Anophelescoluzzii by introgression carries point mutations of the voltage-gated sodium channel gene para, including the L1014F kdr mutation associated with insensitivity to pyrethroid insecticides. Carriage of L1014F kdr is also correlated with higher susceptibility to infection with Plasmodium falciparum. However, the genetic mechanism and causative gene(s) underlying the parasite susceptibility phenotype are not known.MethodsMosquitoes from the wild Burkina Faso population were challenged by feeding on natural P. falciparum gametocytes. Oocyst infection phenotypes were determined and were tested for association with SNP genotypes. Candidate genes in the detected locus were prioritized and RNAi-mediated gene silencing was used to functionally test for gene effects on P. falciparum susceptibility.ResultsA genetic locus, Pfin6, was identified that influences infection levels of P. falciparum in mosquitoes. The locus segregates as a ~3 Mb haplotype carrying 65 predicted genes including the para gene. The haplotype carrying the kdr allele of para is linked to increased parasite infection prevalence, but many single nucleotide polymorphisms on the haplotype are also equally linked to the infection phenotype. Candidate genes in the haplotype were prioritized and functionally tested. Silencing of para did not influence P. falciparum infection, while silencing of a predicted immune gene, serine protease ClipC9, allowed development of significantly increased parasite numbers.ConclusionsGenetic variation influencing Plasmodium infection in wild Anopheles is linked to a natural ~3 megabase haplotype on chromosome 2L that carries the kdr allele of the para gene. Evidence suggests that para gene function does not directly influence parasite susceptibility, and the association of kdr with infection may be due to tight linkage of kdr with other gene(s) on the haplotype. Further work will be required to determine if ClipC9 influences the outcome of P. falciparum infection in nature, as well as to confirm the absence of a direct influence by para.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-015-0924-8) contains supplementary material, which is available to authorized users.

Epigenetic regulation of Plasmodium falciparum clonally variant gene expression during development in Anopheles gambiae

“…coluzzii and An. gambiae are both natural malaria vectors in the study area of Burkina Faso but they differ in their susceptibility to infection40. Consequently, if there is selection by the mosquito immune system for the expression of a specific var gene we may expect a differential response between the two species in terms of var gene expression.…”

A bibliometric analysis of literature on malaria vector resistance: (1996 – 2015)

“…Point mutations in mosquitos described as Knockdown resistance (kdr) was extensively investigated to understand the molecular aspects of Anopheles mosquito resistance. Knockdown resistance (kdr) is the most common form of insecticide resistance and has been reported in many African and Asian countries [20,81,[95][96][97][98][99][100][101][102][103][104]. One of the top cited articles also discussed the role of voltage gated sodium channels in insecticide resistance.…”

Evolution of GOUNDRY, a cryptic subgroup of Anopheles gambiae s.l., and its impact on susceptibility to Plasmodium infection

“…As 12 GOUNDRY genomes is not a large enough sample size for association testing, we obtained SNP genotype data for 274 GOUNDRY individuals who had also been phenotyped in a Plasmodium infection experiment as part of an independent study (Mitri et al 2015). Full details of Illumina SNP chip assay design and data collection and infection experiments are available in that publication but will be summarized here.…”

“…Inbreeding is known to have detrimental effects on various phenotypes, including resistance to parasite infection (Hamilton et al 1990;Luong et al 2007). To test whether inbreeding in GOUNDRY increases intrinsic susceptibility to P. falciparum infection in this group, we studied a larger panel of 274 GOUNDRY females that were experimentally infected with local wild isolates of P. falciparum and genotyped at 1436 SNPs across the genome (Mitri et al 2015). After filtering, we estimated inbreeding coefficients with the program ngsF (Vieira et al 2013) information).…”

“…To identify the evolutionary origins, age and degree of genetic isolation from other genetic subgroups of GOUNDRY, we analysed full genome data from GOUNDRY and multiple closely related Anopheles species as well as SNP chip and phenotype data from an independent study (Mitri et al 2015). We estimate the demographic history of GOUNDRY and its potential importance for Plasmodium infections and identify a putative, novel X-linked chromosomal inversion in GOUNDRY that may be a barrier to gene flow with closely related subgroups.…”