Salivary polytene chromosome map of Anopheles darlingi, the main vector of neotropical malaria

Physical Mapping of the Anopheles (Nyssorhynchus) darlingi Genomic Scaffolds

The genome assembly of Anopheles darlingi consists of 2221 scaffolds (N50 = 115,072 bp) and has a size spanning 136.94 Mbp. This assembly represents one of the smallest genomes among Anopheles species. Anopheles darlingi genomic DNA fragments of ~37 Kb were cloned, end-sequenced, and used as probes for fluorescence in situ hybridization (FISH) with salivary gland polytene chromosomes. In total, we mapped nine DNA probes to scaffolds and autosomal arms. Comparative analysis of the An. darlingi scaffolds with homologous sequences of the Anopheles albimanus and Anopheles gambiae genomes identified chromosomal rearrangements among these species. Our results confirmed that physical mapping is a useful tool for anchoring genome assemblies to mosquito chromosomes.

Vector-Focused Approaches to Curb Malaria Transmission in the Brazilian Amazon: An Overview of Current and Future Challenges and Strategies

In Brazil, malaria transmission is mostly confined to the Amazon, where substantial progress has been made towards disease control in the past decade. Vector control has been historically considered a fundamental part of the main malaria control programs implemented in Brazil. However, the conventional vector-control tools have been insufficient to control or eliminate local vector populations due to the complexity of the Amazonian rainforest environment and ecological features of malaria vector species in the Amazon, especially Anopheles darlingi. Malaria elimination in Brazil and worldwide eradication will require a combination of conventional and new approaches that takes into account the regional specificities of vector populations and malaria transmission dynamics. Here we present an overview on both conventional and novel promising vector-focused tools to curb malaria transmission in the Brazilian Amazon. If well designed and employed, vector-based approaches may improve the implementation of malaria-control programs, particularly in remote or difficult-to-access areas and in regions where existing interventions have been unable to eliminate disease transmission. However, much effort still has to be put into research expanding the knowledge of neotropical malaria vectors to set the steppingstones for the optimization of conventional and development of innovative vector-control tools.

The Development of Cytogenetic Maps for Malaria Mosquitoes

Anopheline mosquitoes are important vectors of human malaria. Next-generation sequencing opens new opportunities for studies of mosquito genomes to uncover the genetic basis of a Plasmodium transmission. Physical mapping of genome sequences to polytene chromosomes significantly improves reference assemblies. High-resolution cytogenetic maps are essential for anchoring genome sequences to chromosomes as well as for studying breakpoints of chromosome rearrangements and chromatin protein localization. Here we describe a detailed pipeline for the development of high-resolution cytogenetic maps using polytene chromosomes of malaria mosquitoes. We apply this workflow to the refinement of the cytogenetic map developed for Anopheles beklemishevi.

A standard photomap of the ovarian nurse cell chromosomes for the dominant malaria vector in Europe and Middle East Anopheles sacharovi

Background

Anopheles sacharovi is a dominant malaria vector species in South Europe and the Middle East which has a highly plastic behaviour at both adult and larval stages. Such plasticity has prevented this species from eradication by several anti-vector campaigns. The development of new genome-based strategies for vector control will benefit from genome sequencing and physical chromosome mapping of this mosquito. Although a cytogenetic photomap for chromosomes from salivary glands of An. sacharovi has been developed, no cytogenetic map suitable for physical genome mapping is available.

Methods

Mosquitoes for this study were collected at adult stage in animal shelters in Armenia. Polytene chromosome preparations were prepared from ovarian nurse cells. Fluorescent in situ hybridization (FISH) was performed using PCR amplified probes.

Results

This study constructed a high-quality standard photomap for polytene chromosomes from ovarian nurse cells of An. sacharovi. Following the previous nomenclature, chromosomes were sub-divided into 39 numbered and 119 lettered sub-divisions. Chromosomal landmarks for the chromosome recognition were described. Using FISH, 4 PCR-amplified genic probes were mapped to the chromosomes. The positions of the probes demonstrated gene order reshuffling between An. sacharovi and Anopheles atroparvus which has not been seen cytologically. In addition, this study described specific chromosomal landmarks that can be used for the cytotaxonomic diagnostics of An. sacharovi based on the banding pattern of its polytene chromosomes.

Conclusions

This study constructed a high-quality standard photomap for ovarian nurse cell chromosomes of An. sacharovi and validated its utility for physical genome mapping. Based on the map, cytotaxonomic features for identification of An. sacharovi have been described. The cytogenetic map constructed in this study will assist in creating a chromosome-based genome assembly for this mosquito and in developing cytotaxonomic tools for identification of other species from the Maculipennis group.

Anopheles darlingi polytene chromosomes: revised maps including newly described inversions and evidence for population structure in Manaus

Salivary gland polytene chromosomes of 4th instar Anopheles darlingi Root were examined from multiple locations in the Brazilian Amazon. Minor modifications were made to existing polytene photomaps. These included changes to the breakpoint positions of several previously described paracentric inversions and descriptions of four new paracentric inversions, two on the right arm of chromosome 3 and two on the left arm of chromosome 3 that were found in multiple locations. A total of 18 inversions on the X (n = 1) chromosome, chromosome 2 (n = 7) and 3 (n = 11) were scored for 83 individuals from Manaus, Macapá and Porto Velho municipalities. The frequency of 2Ra inversion karyotypes in Manaus shows significant deficiency of heterozygotes (p < 0.0009). No significant linkage disequilibrium was found between inversions on chromosome 2 and 3. We hypothesize that at least two sympatric subpopulations exist within the An. darlingi population at Manaus based on inversion frequencies.

GNBP domain of Anopheles darlingi: are polymorphic inversions and gene variation related to adaptive evolution?

Anopheles darlingi is the main malaria vector in humans in South America. In the Amazon basin, it lives along the banks of rivers and lakes, which responds to the annual hydrological cycle (dry season and rainy season). In these breeding sites, the larvae of this mosquito feed on decomposing organic and microorganisms, which can be pathogenic and trigger the activation of innate immune system pathways, such as proteins Gram-negative binding protein (GNBP). Such environmental changes affect the occurrence of polymorphic inversions especially at the heterozygote frequency, which confer adaptative advantage compared to homozygous inversions. We mapped the GNBP probe to the An. darlingi 2Rd inversion by fluorescent in situ hybridization (FISH), which was a good indicator of the GNBP immune response related to the chromosomal polymorphic inversions and adaptative evolution. To better understand the evolutionary relations and time of divergence of the GNBP of An. darlingi, we compared it with nine other mosquito GNBPs. The results of the phylogenetic analysis of the GNBP sequence between the species of mosquitoes demonstrated three clades. Clade I and II included the GNBPB5 sequence, and clade III the sequence of GNBPB1. Most of these sequences of GNBP analyzed were homologous with that of subfamily B, including that of An. gambiae (87 %), therefore suggesting that GNBP of An. darling belongs to subfamily B. This work helps us understand the role of inversion polymorphism in evolution of An. darlingi.

Phylogenetic analysis of the GST family in Anopheles (Nyssorhynchus) darlingi

Anopheles darlingi Root, 1926 and Anopheles gambiae (Diptera: Culicidae) are the most important human malaria vectors in South America and Africa, respectively. The two species are estimated to have diverged 100 million years ago. Studies on the phylogenetics and evolution of gene sequences, such as glutathione S-transferase (GST) in disease-transmitting mosquitoes are scarce. The sigma class GST (KC890767) from the transcriptome of An. darlingi captured in the Brazilian Amazon was studied by in silico hybridization, and mapped to chromosome 3 of An. gambiae. The sigma class GST of An. darlingi was used for phylogenetic analyses to understand the GST base composition of the most recent common ancestor between An. darlingi, Anopheles gambiae, Aedes aegypti and Culex quinquefasciatus. The GST (KC890767) of An. darlingi was studied to generate the main divergence branches using a Neighbor-Joining and bootstrapping approaches to confirm confidence levels on the tree nodes that separate the An. darlingi and other mosquito species. The results showed divergence between An. gambiae, Ae. Aegypti, Cx. quinquefasciatus, and Phlebotomus papatasi as outgroup, and the homology relationship between sigma class GST of An. darlingi and GSTS1_1 gene of An. gambiae was valuable for phylogenetic and evolutionary studies.

The genome of Anopheles darlingi, the main neotropical malaria vector

Anopheles darlingi is the principal neotropical malaria vector, responsible for more than a million cases of malaria per year on the American continent. Anopheles darlingi diverged from the African and Asian malaria vectors ∼100 million years ago (mya) and successfully adapted to the New World environment. Here we present an annotated reference A. darlingi genome, sequenced from a wild population of males and females collected in the Brazilian Amazon. A total of 10 481 predicted protein-coding genes were annotated, 72% of which have their closest counterpart in Anopheles gambiae and 21% have highest similarity with other mosquito species. In spite of a long period of divergent evolution, conserved gene synteny was observed between A. darlingi and A. gambiae. More than 10 million single nucleotide polymorphisms and short indels with potential use as genetic markers were identified. Transposable elements correspond to 2.3% of the A. darlingi genome. Genes associated with hematophagy, immunity and insecticide resistance, directly involved in vector–human and vector–parasite interactions, were identified and discussed. This study represents the first effort to sequence the genome of a neotropical malaria vector, and opens a new window through which we can contemplate the evolutionary history of anopheline mosquitoes. It also provides valuable information that may lead to novel strategies to reduce malaria transmission on the South American continent. The A. darlingi genome is accessible at www.labinfo.lncc.br/index.php/anopheles-darlingi.

Chromosomal localization of actin genes in the malaria mosquito Anopheles darlingi

Physical and genetic maps have been used for chromosomal localization of genes in vectors of infectious diseases. The availability of polytene chromosomes in malaria mosquitoes provides a unique opportunity to precisely map genes of interest. We report the physical mapping of two actin genes on polytene chromosomes of the major malaria vector in the Amazon, Anopheles darlingi (Diptera: Culicidae). Clones with actin gene sequences were obtained from a cDNA library constructed from RNA isolated from adult females and males of An. darlingi. Each of the two clones was mapped to a unique site on chromosomal arm 2L in subdivisions 21A (clone pl05-A04) and 23B (clone pl17-G06). The obtained results, together with previous mapping data, provide a suitable basis for comparative genomics and for establishing chromosomal homologies among major malaria vectors.