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Logo of bmcgenoBioMed Centralsearchsubmit a manuscriptregisterthis articleBMC Genomics
 
BMC Genomics. 2009; 10: 551.
Published online Nov 21, 2009. doi:  10.1186/1471-2164-10-551
PMCID: PMC2799440
Candidate genes revealed by a genome scan for mosquito resistance to a bacterial insecticide: sequence and gene expression variations
Aurélie Bonin,corresponding author#1 Margot Paris,#1 Guillaume Tetreau,#1 Jean-Philippe David,1 and Laurence Després1
1Laboratoire d'Ecologie Alpine, CNRS-UMR 5553, Université Joseph Fourier, BP 53, 38041 Grenoble cedex 09, France
corresponding authorCorresponding author.
#Contributed equally.
Aurélie Bonin: abonin/at/indiana.edu; Margot Paris: margot.paris/at/e.ujf-grenoble.fr; Guillaume Tetreau: guillaume.tetreau/at/e.ujf-grenoble.fr; Jean-Philippe David: jean-philippe.david/at/ujf-grenoble.fr; Laurence Després: laurence.despres/at/ujf-grenoble.fr
Received July 25, 2009; Accepted November 21, 2009.
Abstract
Background
Genome scans are becoming an increasingly popular approach to study the genetic basis of adaptation and speciation, but on their own, they are often helpless at identifying the specific gene(s) or mutation(s) targeted by selection. This shortcoming is hopefully bound to disappear in the near future, thanks to the wealth of new genomic resources that are currently being developed for many species. In this article, we provide a foretaste of this exciting new era by conducting a genome scan in the mosquito Aedes aegypti with the aim to look for candidate genes involved in resistance to Bacillus thuringiensis subsp. israelensis (Bti) insecticidal toxins.
Results
The genome of a Bti-resistant and a Bti-susceptible strains was surveyed using about 500 MITE-based molecular markers, and the loci showing the highest inter-strain genetic differentiation were sequenced and mapped on the Aedes aegypti genome sequence. Several good candidate genes for Bti-resistance were identified in the vicinity of these highly differentiated markers. Two of them, coding for a cadherin and a leucine aminopeptidase, were further examined at the sequence and gene expression levels. In the resistant strain, the cadherin gene displayed patterns of nucleotide polymorphisms consistent with the action of positive selection (e.g. an excess of high compared to intermediate frequency mutations), as well as a significant under-expression compared to the susceptible strain.
Conclusion
Both sequence and gene expression analyses agree to suggest a role for positive selection in the evolution of this cadherin gene in the resistant strain. However, it is unlikely that resistance to Bti is conferred by this gene alone, and further investigation will be needed to characterize other genes significantly associated with Bti resistance in Ae. aegypti. Beyond these results, this article illustrates how genome scans can build on the body of new genomic information (here, full genome sequence and MITE characterization) to finally hold their promises and help pinpoint candidate genes for adaptation and speciation.
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