Abstract
BackgroundSouthern house mosquito Culex quinquefasciatus belongs to the C. pipiens cryptic species complex, with global distribution and unclear taxonomy. Mosquitoes of the complex can transmit human and animal pathogens, such as filarial worm, West Nile virus and avian malarial Plasmodium. Physical gene mapping is crucial to understanding genome organization, function, and systematic relationships of cryptic species, and is a basis for developing new vector control strategies. However, physical mapping was not established previously for Culex due to the lack of well-structured polytene chromosomes.MethodsInbreeding was used to diminish inversion polymorphism and asynapsis of chromosomal homologs. Identification of larvae of the same developmental stage using the shape of imaginal discs allowed achievement of uniformity in chromosomal banding pattern. This together with high-resolution phase-contrast photography enabled the development of a cytogenetic map. Fluorescent in situ hybridization was used for gene mapping.ResultsA detailed cytogenetic map of C. quinquefasciatus polytene chromosomes was produced. Landmarks for chromosome recognition and cytological boundaries for two inversions were identified. Locations of 23 genes belonging to 16 genomic supercontigs, and 2 cDNA were established. Six supercontigs were oriented and one was found putatively misassembled. The cytogenetic map was linked to the previously developed genetic linkage groups by corresponding positions of 2 genetic markers and 10 supercontigs carrying genetic markers. Polytene chromosomes were numbered according to the genetic linkage groups.ConclusionsThis study developed a new standard cytogenetic photomap of the polytene chromosomes for C. quinquefasciatus and was applied for the fine-scale physical mapping. It allowed us to infer chromosomal position of 1333 of annotated genes belonging to 16 genomic supercontigs and find orientation of 6 of these supercontigs; the new cytogenetic and previously developed genetic linkage maps were integrated based on 12 matches. The map will further assist in finding chromosomal position of the medically important and other genes, contributing into improvement of the genome assembly. Better assembled C. quinquefasciatus genome can serve as a reference for studying other vector species of C. pipiens complex and will help to resolve their taxonomic relationships. This, in turn, will contribute into future development of vector and disease control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-015-0912-4) contains supplementary material, which is available to authorized users.
Highlights
Southern house mosquito Culex quinquefasciatus belongs to the C. pipiens cryptic species complex, with global distribution and unclear taxonomy
A standard photographic map of C. quinquefasciatus JHB polytene chromosomes In order to develop a cytogenetic map for the polytene chromosomes of C. quinquefasciatus we examined salivary glands, Malpighian tubules, and gastric cecum of 4th instar larvae, pupae and adults, for the presence of polytene chromosomes using lacto-aceto-orcein staining
Any genes of interest such as of medical importance and others can be located using physical mapping and placed on the map. This way a detailed fine-scale physical map can be produced by ordering and orienting more genomic supercontigs, and this data will improve the genome assembly. This map is a basis for identifying polymorphic inversions in natural populations of the C. quinquefasciatus
Summary
Southern house mosquito Culex quinquefasciatus belongs to the C. pipiens cryptic species complex, with global distribution and unclear taxonomy. The southern house mosquito Culex quinquefasciatus Say 1823 is a primary vector of several human and animal pathogens: A) lymphatic filarial worm Wuchereria bancrofti, which causes elephantiasis of limbs and genitalia, causing life-long disabilities; B) West Nile virus and several other encephalitis-causing arboviruses which can be deadly; C) Avian malarial Plasmodium, which makes Culex a good model for studying malaria transmission. The burden of these diseases is enormous, with millions of people affected, and even more at risk. As a required framework against which phenotypes and genotypes can be associated in population studies, it can form an improved basis for the development of new vector control and disease prevention strategies
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