Aedes aegypti genomics

The mosquito, Aedes aegypti, is the primary, worldwide arthropod vector for the yellow fever and dengue viruses. As it is also one of the most tractable mosquito species for laboratory studies, it has been and remains one of the most intensively studied arthropod species. This has resulted in the development of detailed genetic and physical maps for Ae. aegypti and considerable insight into its genome organization. The research community is well-advanced in developing important molecular tools that will facilitate a whole genome sequencing effort. This includes generation of BAC clone end sequences, physical mapping of selected BAC clones and generation of EST sequences. Whole genome sequence information for Ae. aegypti will provide important insight into mosquito chromosome evolution and allow for the identification of genes and gene function. These functions may be common to all mosquitoes or perhaps unique to individual species, possibly specific to host-seeking and blood-feeding behaviors, as well as the innate immune response to pathogens encountered during blood-feeding. This information will be invaluable to the global effort to develop novel strategies for preventing arthropod-borne disease transmission.     

Aedes aegypti ferritin.

Diseases transmitted by hematophagous (blood-feeding) insects are responsible for millions of human deaths worldwide. In hematophagous insects, the blood meal is important for regulating egg maturation. Although a high concentration of iron is toxic for most organisms, hematophagous insects seem unaffected by the iron load in a blood meal. One means by which hematophagous insects handle this iron load is, perhaps, by the expression of iron-binding proteins, specifically the iron storage protein ferritin. In vertebrates, ferritin is an oligomer composed of two types of subunits called heavy and light chains, and is part of the constitutive antioxidant response. Previously, we found that the insect midgut, a main site of iron load, is also a primary site of ferritin expression and that, in the yellow fever mosquito, Aedes aegypti, the expression of the ferritin heavy-chain homologue (HCH) is induced following blood feeding. We now show that the expression of the Aedes ferritin light-chain homologue (LCH) is also induced with blood-feeding, and that the genes of the LCH and HCH are tightly clustered. mRNA levels for both LCH- and HCH-genes increase with iron, H2O2 and hemin treatment, and the temporal expression of the genes is very similar. These results confirm that ferritin could serve as the cytotoxic protector in mosquitoes against the oxidative challenge of the bloodmeal. Finally, although the Aedes LCH has no iron responsive element (IRE) at its 5'-untranslated region (UTR), the 5'-UTR contains several introns that are alternatively spliced, and this alternative splicing event is different from any ferritin message seen to date.     

Ammonia metabolism in Aedes aegypti

We investigated the mechanisms by which Aedes aegypti mosquitoes are able to metabolize ammonia. When females were given access to solutions containing NH(4)Cl or to a blood meal, hemolymph glutamine and proline concentrations increased markedly, indicating that ammonium/ammonia can be removed from the body through the synthesis of these two amino acids. The importance of glutamine synthetase was shown when an inhibitor of the enzyme was added to the meal causing the glutamine concentration in hemolymph to decrease significantly, while the proline concentration increased dramatically. Unexpectedly, we found an important role for glutamate synthase. When mosquitoes were fed azaserine, an inhibitor of glutamate synthase, the glutamine concentration increased and the proline concentration decreased significantly. This confirms the presence of glutamate synthase in mosquitoes and suggests that this enzyme contributes to the production of glutamate for proline synthesis. Several key enzymes related to ammonium/ammonia metabolism showed activity in homogenates of mosquito fat body and midgut. The mosquito genes encoding glutamate dehydrogenase, glutamine synthetase, glutamate synthase, pyrroline-5-carboxylate synthase were cloned and sequenced. The mRNA expression patterns of these genes were examined by a real-time RT-PCR in fat body and midgut. The results show that female mosquitoes have evolved efficient mechanisms to detoxify large loads of ammonium/ammonia.     

Trisomy in Aedes aegypti.

A trisomic (2n=6+1) pupa of the yellow fever mosquito Aedes aegypti has been found. The trisomy involved chromosome 3 which is intermediate in size between 1 and 2. The extra chromosome formed a univalent or a trivalent during meiosis.     

Global genetic diversity of Aedes aegypti

Mosquitoes, especially Aedes aegypti, are becoming important models for studying invasion biology. We characterized genetic variation at 12 microsatellite loci in 79 populations of Ae. aegypti from 30 countries in six continents, and used them to infer historical and modern patterns of invasion. Our results support the two subspecies Ae. aegypti formosus and Ae. aegypti aegypti as genetically distinct units. Ae. aegypti aegypti populations outside Africa are derived from ancestral African populations and are monophyletic. The two subspecies co‐occur in both East Africa (Kenya) and West Africa (Senegal). In rural/forest settings (Rabai District of Kenya), the two subspecies remain genetically distinct, whereas in urban settings, they introgress freely. Populations outside Africa are highly genetically structured likely due to a combination of recent founder effects, discrete discontinuous habitats and low migration rates. Ancestral populations in sub‐Saharan Africa are less genetically structured, as are the populations in Asia. Introduction of Ae. aegypti to the New World coinciding with trans‐Atlantic shipping in the 16th to 18th centuries was followed by its introduction to Asia in the late 19th century from the New World or from now extinct populations in the Mediterranean Basin. Aedes mascarensis is a genetically distinct sister species to Ae. aegypti s.l. This study provides a reference database of genetic diversity that can be used to determine the likely origin of new introductions that occur regularly for this invasive species. The genetic uniqueness of many populations and regions has important implications for attempts to control Ae. aegypti, especially for the methods using genetic modification of populations.     

Aedes aegypti midgut remodeling during metamorphosis

The Aedes aegypti midgut is restructured during metamorphosis; its epithelium is renewed by replacing the digestive and endocrine cells through stem or regenerative cell differentiation. Shortly after pupation (white pupae) begins, the larval digestive cells are histolized and show signs of degeneration, such as autophagic vacuoles and disintegrating microvilli. Simultaneously, differentiating cells derived from larval stem cells form an electron-dense layer that is visible 24 h after pupation begins. Forty-eight hours after pupation onset, the differentiating cells yield an electron-lucent cytoplasm rich in microvilli and organelles. Dividing stem cells were observed in the fourth instar larvae and during the first 24 h of pupation, which suggests that stem cells proliferate at the end of the larval period and during pupation. This study discusses various aspects of the changes during midgut remodeling for pupating A. aegypti.     

Midgut bacterial dynamics in Aedes aegypti

In vector mosquitoes, the presence of midgut bacteria may affect the ability to transmit pathogens. We have used a laboratory colony of Aedes aegypti as a model for bacterial interspecies competition and show that after a blood meal, the number of species (culturable on Luria-Bertani agar) that coexist in the midgut is low and that about 40% of the females do not harbor any cultivable bacteria. We isolated species belonging to the genera Bacillus, Elizabethkingia, Enterococcus, Klebsiella, Pantoea, Serratia, and Sphingomonas, and we also determined their growth rates, antibiotic resistance, and ex vivo inhibition of each other. To investigate the possible existence of coadaptation between midgut bacteria and their host, we fed Ae.?aegypti cohorts with gut bacteria from human, a frog, and two mosquito species and followed the bacterial population growth over time. The dynamics of the different species suggests coadaptation between host and bacteria, and interestingly, we found that Pantoea stewartii isolated from Ae.?aegypti survive better in Ae.?aegypti as compared to P.?stewartii isolated from the malaria mosquito Anopheles gambiae.     

Utilization of larval and pupal detritus by Aedes aegypti and Aedes albopictus

The utilization of detritus sources by mosquito larvae during development may significantly affect adult life history traits and mosquito population growth. Many studies have shown invertebrate carcasses to be an important detritus source in larval habitats, but little is known regarding how invertebrate carcasses are utilized by mosquito larvae. We conducted two studies to investigate the rate of detritus consumption and its effect on larval development and life history traits. Overall, we found that Aedes aegypti and Aedes albopictus larvae rapidly consumed larval detritus, while pupal detritus was consumed at a significantly slower rate. We also found that the consumption of larval detritus significantly increased larval survivorship and decreased male development time but did not significantly influence female development time or pupal cephalothorax length for either sex. Our results suggest that the direct consumption of larval detritus can support the production of adults in larval habitats that lack allochthonous detritus inputs or where such organic inputs are insufficient. These studies indicate that different forms of invertebrate detritus are utilized in distinct ways by mosquito larvae, and therefore different forms of invertebrate detritus may have distinct effects on larval development and adult life history traits.     

Innate immune response of Aedes aegypti

Insects are able to protect themselves from invasion by pathogens by a rapid and potent arsenal of inducible immune peptides. This fast, extremely effective response is part of the innate immunity exhibited by all insects and many invertebrates, and shows striking similarities with the innate immune response of vertebrates. In Aedes aegypti invasion of the hemocoel by bacteria elicits the production of defensins, cecropins, a peptide active only against Gram-negative bacteria, and several other peptides that we are now characterizing. However, not all insects utilize the same peptides in the same concentrations, which may reflect the pathogens to which they may have been exposed through evolutionary time. These protective measures we see in mosquitoes are the current state of the evolution of a rapid immune response that has contributed to the success of insects in inhabiting essentially every niche on earth. The molecules involved in the response of Aedes aegypti to pathogens, and the potential role of these peptides against eukaryotic parasites ingested and transmitted by mosquitoes are discussed.     

白纹伊蚊和埃及伊蚊经卵传递登革病毒的研究

白纹伊蚊和埃及伊蚊通过吸食病毒液或叮吸有病毒血症的小鸡血后,能感染登革１－４型病毒,并能在蚊体内增殖,对感染雌蚊了１和子２代幼虫,雌性或雄性成虫４５５９只,分１０１批进行了病毒检测,白纹伊蚊子１代的批阳性率;登革１型为１０％（１／１０）２型为２２．２２％（２／９）３型为３３．３３％（４／１２）,４型为２８．９５％（１１／３８）登革１～４型的最低子代感染率依次主国０．２０％,０．７１％,０．７０％和     

白纹伊蚊和埃及伊蚊对基孔肯雅病毒的易感性和传播性的研究

用４株基孔肯雅病毒经口感染白纹伊蚊和埃及伊蚊,进行了易感性和传播性的研究。结果表明,这两种蚊虫对基孔肯雅病毒易感。无论白纹伊蚊或埃及伊蚊,感染后第５－６天即可通过吸血将病毒传播给乳鼠,至第８－１３天,传播率可高达５５．５５％－１００％。感染蚊亦可经叮咬将病毒传播给小鸡。埃及伊蚊的易感性和传播率高于白纹伊蚊。实验还发现,不同来源毒株之间存在一定差异,如分离自云南白纹伊蚊的Ｍ８１株的感染率和传播率均高于其它毒株。这些结果表明,白纹伊蚊和埃及伊蚊在基孔肯雅病毒的保存和传播中起重要作用。     

Temporal genetic stability of Stegomyia aegypti (= Aedes aegypti) populations

The mosquito Stegomyia aegypti (= Aedes aegypti) (Diptera: Culicidae) is the primary vector of viruses that cause yellow fever, dengue and Chikungunya fever. In the absence of effective vaccines, the reduction of these diseases relies on vector control strategies. The success of these strategies is tightly linked to the population dynamics of target populations. In the present study, 14 collections from St. aegypti populations separated by periods of 1–13 years were analysed to determine their temporal genetic stability. Although temporal structure is discernible in most populations, the degree of temporal differentiation is dependent on the population and does not obscure the geographic structure of the various populations. The results suggest that performing detailed studies in the years prior to and after population reduction‐ or modification‐based control interventions at each target field site may be useful in assessing the probability of success.     

Aedes aegypti peroxidase gene characterization and developmental expression

The functions of insect peroxidases include detoxification, stabilization of extracellular matrices, and possible involvement in insect immunity. The current study describes the isolation of a peroxidase gene, AePox, and its cDNA from the mosquito, Aedes aegypti. AePox codes for a protein that is homologous to various heme-peroxidases from vertebrates and invertebrates, with highest identity to Drosophila melanogaster peroxidase (62%). Sequence comparison identified several functionally and structurally conserved domains in the mosquito peroxidase, including a heme environment, a calcium binding site, and five possible disulfide bridges. These results imply that AePOX may likely have a similar structure and catalytic mechanism as those described for the mammalian myeloperoxidase superfamily. Expression studies demonstrate that AePox is transcribed in mosquito larvae and pupae, but not in adults, in ovaries, or in early embryos. However, AePOX protein is present in all mosquito stages and possibly has a maturation process that is similar to that of human myeloperoxidase. Unlike most human peroxidases, the AePox gene contains a TATA box and an ecdysone response element (EcRE).