Publications by authors named "David W Severson"

100 Publications

Community acceptance of yeast interfering RNA larvicide technology for control of Aedes mosquitoes in Trinidad.

Authors:
Akilah T M Stewart Nikhella Winter Jessica Igiede Limb K Hapairai Lester D James Rachel Shui Feng Azad Mohammed David W Severson Molly Duman-Scheel

PLoS One 2020 14;15(8):e0237675. Epub 2020 Aug 14.

Eck Institute for Global Health, University of Notre Dame, Notre Dame, Indiana, United States of America.

RNA interference (RNAi), a technique used to investigate gene function in insects and other organisms, is attracting attention as a potential new technology for mosquito control. Saccharomyces cerevisiae (baker's yeast) was recently engineered to produce interfering RNA molecules that silence genes required for mosquito survival, but which do not correspond to genes in humans or other non-target organisms. The resulting yeast pesticides, which facilitate cost-effective production and delivery of interfering RNA to mosquito larvae that eat the yeast, effectively kill mosquitoes in laboratory and semi-field trials. In preparation for field evaluation of larvicides in Trinidad, a Caribbean island with endemic diseases resulting from pathogens transmitted by Aedes mosquitoes, adult residents living in the prospective trial site communities of Curepe, St. Augustine, and Tamana were engaged. Open community forums and paper surveys were used to assess the potential acceptability, societal desirability, and sustainability of yeast interfering RNA larvicides. These assessments revealed that Trinidadians have good working knowledge of mosquitoes and mosquito-borne illnesses. A majority of the respondents practiced some method of larval mosquito control and agreed that they would use a new larvicide if it were proven to be safe and effective. During the community engagement forums, participants were educated about mosquito biology, mosquito-borne diseases, and the new yeast larvicides. When invited to provide feedback, engagement forum attendees were strongly supportive of the new technology, raised few concerns, and provided helpful advice regarding optimal larvicide formulations, insecticide application, operational approaches for using the larvicides, and pricing. The results of these studies suggest that the participants are supportive of the potential use of yeast interfering RNA larvicides in Trinidad and that the communities assessed in this investigation represent viable field sites.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0237675PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7428178PMC
October 2020

Characterization of a dual-action adulticidal and larvicidal interfering RNA pesticide targeting the Shaker gene of multiple disease vector mosquitoes.

Authors:
Keshava Mysore Limb K Hapairai Longhua Sun Ping Li Chien-Wei Wang Nicholas D Scheel Alexandra Lesnik Jessica Igiede Max P Scheel Na Wei David W Severson Molly Duman-Scheel

PLoS Negl Trop Dis 2020 07 20;14(7):e0008479. Epub 2020 Jul 20.

Indiana University School of Medicine, Department of Medical and Molecular Genetics, South Bend, Indiana, United States of America.

The existing mosquito pesticide repertoire faces great challenges to sustainability, and new classes of pesticides are vitally needed to address established and emerging mosquito-borne infectious diseases. RNA interference- (RNAi-) based pesticides are emerging as a promising new biorational mosquito control strategy. In this investigation, we describe characterization of an interfering RNA pesticide (IRP) corresponding to the mosquito Shaker (Sh) gene, which encodes an evolutionarily conserved voltage-gated potassium channel subunit. Delivery of the IRP to Aedes aegypti adult mosquitoes in the form of siRNA that was injected or provided as an attractive toxic sugar bait (ATSB) led to Sh gene silencing that resulted in severe neural and behavioral defects and high levels of adult mortality. Likewise, when provided to A. aegypti larvae in the form of short hairpin RNA (shRNA) expressed in Saccharomyces cerevisiae (baker's yeast) that had been formulated into a dried inactivated yeast tablet, the yeast IRP induced neural defects and larval death. Although the Sh IRP lacks a known target site in humans or other non-target organisms, conservation of the target site in the Sh genes of multiple mosquito species suggested that it may function as a biorational broad-range mosquito insecticide. In support of this, the Sh IRP induced both adult and larval mortality in treated Aedes albopictus, Anopheles gambiae, and Culex quinquefasciatus mosquitoes, but was not toxic to non-target arthropods. These studies indicated that IRPs targeting Sh could one day be used in integrated biorational mosquito control programs for the prevention of multiple mosquito-borne illnesses. The results of this investigation also suggest that the species-specificity of ATSB technology, a new paradigm for vector control, could be enhanced through the use of RNAi-based pesticides.
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http://dx.doi.org/10.1371/journal.pntd.0008479DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7392347PMC
July 2020

Mating Competitiveness of Transgenic Aedes aegypti (Diptera: Culicidae) Males Against Wild-Type Males Reared Under Simulated Field Conditions.

Authors:
David S Kang Joanne M Cunningham Diane D Lovin Dave D Chadee David W Severson

J Med Entomol 2020 11;57(6):1775-1781

Department of Biological Sciences, University of Notre Dame, Notre Dame, IN.

Efforts directed at genetic modification of mosquitoes for population control or replacement are highly dependent on the initial mating success of transgenic male mosquitoes following their release into natural populations. Adult mosquito phenotypes are influenced by the environmental conditions experienced as larvae. Semifield studies conducted to date have not taken that under consideration when testing male mating fitness, and have compared mating success of males reared under identical environmental conditions. We performed pairwise mating challenges between males from a genetically modified laboratory strain (BF2) versus males from a recent Trinidad field isolate of Aedes aegypti (L.), a major vector of multiple arboviruses. We utilized larval density and nutrition to simulate environmental stress experienced by the Trinidad males and females. Our results indicated that environmental stress during larval development negatively influenced the competitiveness and reproductive success of males from the Trinidad population when paired with optimum reared BF2 males. Small (0.027 m3) and large (0.216 m3) trials were conducted wherein stressed or optimum Trinidad males competed with optimum BF2 males for mating with stressed Trinidad females. When competing with stress reared Trinidad males, optimum reared BF2 males were predominant in matings with stress reared Trinidad females, and large proportions of these females mated with males of both strains. When competing with optimum reared Trinidad males, no difference in mating success was observed between them and BF2 males, and frequencies of multiple matings were low. Our results indicate that future mating competition studies should incorporate appropriate environmental conditions when designing mating fitness trials of genetically modified males.
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http://dx.doi.org/10.1093/jme/tjaa111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7899268PMC
November 2020

Characterization of an adulticidal and larvicidal interfering RNA pesticide that targets a conserved sequence in mosquito G protein-coupled dopamine 1 receptor genes.

Authors:
Limb K Hapairai Keshava Mysore Longhua Sun Ping Li Chien-Wei Wang Nicholas D Scheel Alexandra Lesnik Max P Scheel Jessica Igiede Na Wei David W Severson Molly Duman-Scheel

Insect Biochem Mol Biol 2020 05 10;120:103359. Epub 2020 Mar 10.

Indiana University School of Medicine, Department of Medical and Molecular Genetics, Raclin-Carmichael Hall, 1234 Notre Dame Ave., South Bend, IN, 46617, USA; The University of Notre Dame Eck Institute for Global Health, Notre Dame, IN, 46556, USA; The University of Notre Dame Department of Biological Sciences, Galvin Life Sciences, Notre Dame, IN, 46556, USA. Electronic address:

G protein-coupled receptors (GPCRs), key regulators of a variety of critical biological processes, are attractive targets for insecticide development. Given the importance of these receptors in many organisms, including humans, it is critical that novel pesticides directed against GPCRs are designed to be species-specific. Here, we present characterization of an interfering RNA pesticide (IRP) targeting the mosquito GPCR-encoding dopamine 1 receptor (dop1) genes. A small interfering RNA corresponding to dop1 was identified in a screen for IRPs that kill Aedes aegypti during both the adult and larval stages. The 25 bp sequence targeted by this IRP is conserved in the dop1 genes of multiple mosquito species, but not in non-target organisms, indicating that it could function as a biorational mosquito insecticide. Aedes aegypti adults treated through microinjection or attractive toxic sugar bait delivery of small interfering RNA corresponding to the target site exhibited severe neural and behavioral defects and high levels of adult mortality. Likewise, A. aegypti larval consumption of dried inactivated yeast tablets prepared from a Saccharomyces cerevisiae strain engineered to express short hairpin RNA corresponding to the dop1 target site resulted in severe neural defects and larval mortality. Aedes albopictus and Anopheles gambiae adult and larval mortality was also observed following treatment with dop1 IRPs, which were not toxic to non-target arthropods. The results of this investigation indicate that dop1 IRPs can be used for species-specific targeting of dop1 GPCRs and may represent a new biorational strategy for control of both adult and larval mosquitoes.
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http://dx.doi.org/10.1016/j.ibmb.2020.103359DOI Listing
May 2020

Changing patterns in the distribution of the Mayaro virus vector Haemagogus species in Trinidad, West Indies.

Authors:
Renee Ali Azad Mohammed Jayaraj Jayaraman Naresh Nandram Rachel Shui Feng Raul Diosany Lezcano Roshan Seeramsingh Brent Daniel Diane D Lovin David W Severson Adesh Ramsubhag

Acta Trop 2019 Nov 25;199:105108. Epub 2019 Jul 25.

Department of Life Sciences, Faculty of Science & Technology, The University of the West Indies, St. Augustine Campus, Trinidad and Tobago. Electronic address:

The Mayaro virus disease (MAYVD) is an emerging mosquito borne zoonosis that was first reported on the island of Trinidad in 1954. The viral agent for this disease is known to presently be endemic to Central and South America. The enzootic cycle of the Mayaro virus (MAYV) is not fully characterized, though primates are thought to be the main reservoir with Haemagogus species of mosquitoes as the primary vector. This virus has been responsible for several sporadic cases of infections and limited outbreaks, but it is postulated that the MAYVD will become a major epidemic in the future, following in the steps of the recent pandemics caused by Chikungunya and Zika viruses. Mitigating possible major outbreaks of MAYVD in the future would require effective strategies for vector control, for which knowledge on the ecology and distribution of the Haemagogus mosquitoes would be vitally important. In Trinidad, Haemagogus species have only been reported in the northwestern peninsula of the island based on studies up to 1995. However, no recent investigations have been completed to determine the status of this important vector on the island. The aim of this study was to investigate the current spatial distribution of Haemagogus species in the island of Trinidad, West Indies. Adult Haemagogus (Hag.) mosquitoes and larvae were surveyed during a twenty-month period using human bait trapping and ovitraps in major forested areas on the island. Mosquito species were identified using classical taxonomic keys. Haemagogus species were widespread and found in all forest types surveyed. Hag. janthinomys (85.7%) was the most widely distributed and dominant species on the island. Lower levels of Hag. leucocelaneus (7.3%), Hag. equinus (6.4%) and Hag. celeste (0.6%) were also collected. Overall, the proportion of mosquitoes collected in the wet season (June-December) was 3.5 times more than in the dry season (January-May). Mangroves, young secondary forests, semi-evergreen and evergreen forest types had relatively high mean abundance levels of Haemagogus species as compared to deciduous and montane forests. Proximity analysis suggests that population settlements within a 1 km buffer of the forest peripherals may be at risk for any emerging arboviral disease associated with these mosquito vectors. Haemagogus species showed a much wider distribution in Trinidad as compared to previous reports from up to 20 years ago and were prevalent in areas with no known presence of non-human primates. Since the MAYV has been previously implicated in causing infections in vertebrate hosts like rodents, birds and small mammals, the findings of this study suggest that there may be alternative hosts and reservoirs of this virus in the sylvatic cycle in Trinidad, other than primates. This has significant epidemiological implications for mosquito-borne viral infections in the region.
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http://dx.doi.org/10.1016/j.actatropica.2019.105108DOI Listing
November 2019

Identification of Host Blood Meals of Mosquitoes (Diptera: Culicidae) Collected at the Aripo Savannas Scientific Reserve in Trinidad, West Indies.

Authors:
David S Kang Ray Martinez Aliya Hosein Rachel Shui Feng Lester James Diane D Lovin Joanne M Cunningham Cally S T Miller Matthew W Eng Dave D Chadee David W Severson

J Med Entomol 2019 10;56(6):1734-1738

Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN.

Surveillance for blood-fed female mosquitoes was performed between August 2015 and February 2016 at sites along the periphery of the Aripo Savannas Environmentally Reserve (ASSR) located in northeastern Trinidad, West Indies. We collected engorged female mosquitoes representing 13 species. DNA extractions from dissected abdomens were subjected to PCR amplification with three primer pairs targeting the mitochondrial cytochrome oxidase I and cytochrome b gene sequences. High-quality sequence information and host identification were obtained for 42 specimens representing eight mosquito species with at least one primer combination. A broad range of vertebrates including humans were identified, but the majority were nonhuman mammals, both domestic and wild. Domestic dogs were the most common host and may represent potential sentinel species for monitoring local enzootic arbovirus activity in Trinidad. Culex declarator Dyer and Knab and Culex nigripalpus Theobald were the most common blood-fed mosquito species comprising 79.1% of the total number identified. These species obtained blood meals from birds, nonhuman mammals, and human hosts, and therefore pose significant risks as potential bridge vectors for epizootic arbovirus transmission in the ASSR area as well as other sylvan areas in Trinidad. These data represent the first such results for Trinidad.
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http://dx.doi.org/10.1093/jme/tjz113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182913PMC
October 2019

Characterization of a broad-based mosquito yeast interfering RNA larvicide with a conserved target site in mosquito semaphorin-1a genes.

Authors:
Keshava Mysore Ping Li Chien-Wei Wang Limb K Hapairai Nicholas D Scheel Jacob S Realey Longhua Sun David W Severson Na Wei Molly Duman-Scheel

Parasit Vectors 2019 May 22;12(1):256. Epub 2019 May 22.

Department of Medical and Molecular Genetics, Indiana University School of Medicine, South Bend, IN, USA.

Background: RNA interference (RNAi), which has facilitated functional characterization of mosquito neural development genes such as the axon guidance regulator semaphorin-1a (sema1a), could one day be applied as a new means of vector control. Saccharomyces cerevisiae (baker's yeast) may represent an effective interfering RNA expression system that could be used directly for delivery of RNA pesticides to mosquito larvae. Here we describe characterization of a yeast larvicide developed through bioengineering of S. cerevisiae to express a short hairpin RNA (shRNA) targeting a conserved site in mosquito sema1a genes.

Results: Experiments conducted on Aedes aegypti larvae demonstrated that the yeast larvicide effectively silences sema1a expression, generates severe neural defects, and induces high levels of larval mortality in laboratory, simulated-field, and semi-field experiments. The larvicide was also found to induce high levels of Aedes albopictus, Anopheles gambiae and Culex quinquefasciatus mortality.

Conclusions: The results of these studies indicate that use of yeast interfering RNA larvicides targeting mosquito sema1a genes may represent a new biorational tool for mosquito control.
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http://dx.doi.org/10.1186/s13071-019-3504-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6532267PMC
May 2019

Characterization of a yeast interfering RNA larvicide with a target site conserved in the synaptotagmin gene of multiple disease vector mosquitoes.

Authors:
Keshava Mysore Ping Li Chien-Wei Wang Limb K Hapairai Nicholas D Scheel Jacob S Realey Longhua Sun Joseph B Roethele David W Severson Na Wei Molly Duman-Scheel

PLoS Negl Trop Dis 2019 05 20;13(5):e0007422. Epub 2019 May 20.

Indiana University School of Medicine, Department of Medical and Molecular Genetics, South Bend, IN, United States of America.

New mosquito control strategies are vitally needed to address established and emerging arthropod-borne infectious diseases. Here we describe the characterization of a yeast interfering RNA larvicide that was developed through the genetic engineering of Saccharomyces cerevisiae (baker's yeast) to express a short hairpin RNA targeting the Aedes aegypti synaptotagmin (Aae syt) gene. The larvicide effectively silences the Aae syt gene, causes defects at the larval neural synapse, and induces high rates of A. aegypti larval mortality in laboratory, simulated-field, and semi-field trials. Conservation of the interfering RNA target site in multiple mosquito species, but not in humans or other non-target species, suggested that it may function as a broad-range mosquito larvicide. In support of this, consumption of the yeast interfering RNA larvicide was also found to induce high rates of larval mortality in Aedes albopictus, Anopheles gambiae, and Culex quinquefasciatus mosquito larvae. The results of these studies suggest that this biorational yeast interfering RNA larvicide may represent a new intervention that can be used to combat multiple mosquito vectors of human diseases.
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http://dx.doi.org/10.1371/journal.pntd.0007422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6544322PMC
May 2019

QTL Determining Diel Flight Activity in Male Culex pipiens Mosquitoes.

Authors:
Paul V Hickner Akio Mori Samuel S C Rund Aaron D Sheppard Joanne M Cunningham Dave D Chadee Giles E Duffield David W Severson

J Hered 2019 05;110(3):310-320

Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN.

Members of the Culex pipiens complex differ in physiological traits that facilitate their survival in diverse environments. Assortative mating within the complex occurs in some regions where autogenous (the ability to lay a batch of eggs without a blood meal) and anautogenous populations are sympatric, and differences in mating behaviors may be involved. For example, anautogenous populations mate in flight/swarms, while autogenous populations often mate at rest. Here, we characterized flight activity of males and found that anautogenous strain males were crepuscular, while autogenous strain males were crepuscular and nocturnal, with earlier activity onset times. We conducted quantitative trait locus (QTL) mapping to explore the genetic basis of circadian chronotype (crepuscular vs. crepuscular and nocturnal) and time of activity onset. One major-effect QTL was identified for chronotype, while 3 QTLs were identified for activity onset. The highest logarithm of the odds (LOD) score for the chronotype QTL coincides with a chromosome 3 marker that contains a 15-nucleotide indel within the coding region of the canonical clock gene, cryptochrome 2. Sequencing of this locus in 7 different strains showed that the C-terminus of CRY2 in the autogenous forms contain deletions not found in the anautogenous forms. Consequently, we monitored activity in constant darkness and found males from the anautogenous strain exhibited free running periods of ~24 h while those from the autogenous strain were ~22 h. This study provides novel insights into the genetic basis of flight behaviors that likely reflect adaptation to their distinct ecological niches.
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http://dx.doi.org/10.1093/jhered/esz003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6503456PMC
May 2019

Genome-Wide Transcriptome Profiling Reveals Genes Associated with Meiotic Drive System of .

Authors:
Dongyoung Shin Susanta K Behura David W Severson

Insects 2019 Jan 10;10(1). Epub 2019 Jan 10.

Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.

is an important mosquito vector of several arboviruses, including dengue, yellow fever, Zika, and Chikungunya, which cause significant human morbidity and mortality globally. In certain populations of this mosquito, a native meiotic drive system causes abnormal spermatogenesis that results in highly male-biased progenies from some matings. Although the basic genetics and cytogenetics of the drive mechanism were elucidated, very little is known on a transcriptome level about how the meiotic drive phenotype is expressed in individual males. To address this question, we conducted a whole-genome microarray expression study of testes from a meiotic-drive-carrying strain (T37) in comparison with testes from a non-drive-carrying strain (RED). Based on bioinformatics analyses of the microarray data, we identified 209 genes associated with the meiotic drive phenotype that were significantly differentially expressed between the two strains. -means cluster analysis revealed nine clusters, in which genes upregulated in T37 testes were assigned to five clusters and genes downregulated in T37 testes were assigned to four clusters. Our data further revealed that genes related to protein translation, phosphorylation, and binding, as well as to G-protein-coupled receptor (GPCR) and peptidase activities, are differentially upregulated in testes from males with the meiotic drive genotype. Based on pathway analysis of these differentially expressed genes, it was observed that the glycosylphosphatidylinositol (GPI)-anchor biosynthesis pathway may play a role in the meiotic drive system. Overall, this investigation enhances our understanding of whole-genome gene expression associated with the meiotic drive system in .
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http://dx.doi.org/10.3390/insects10010025DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6358845PMC
January 2019

Preparation and Use of a Yeast shRNA Delivery System for Gene Silencing in Mosquito Larvae.

Authors:
Keshava Mysore Limb K Hapairai Na Wei Jacob S Realey Nicholas D Scheel David W Severson Molly Duman-Scheel

Methods Mol Biol 2019 ;1858:213-231

Department of Medical and Molecular Genetics, Indiana University School of Medicine, South Bend, IN, USA.

The mosquito genome projects facilitated research in new facets of mosquito biology, including functional genetic studies in the dengue and Zika virus vector Aedes aegypti and the primary African malaria vector Anopheles gambiae. RNA interference (RNAi) has facilitated gene silencing experiments in both of these disease vector mosquito species and could one day be applied as a new method of vector control. Here, we describe a procedure for the genetic engineering of Saccharomyces cerevisiae (baker's yeast) that express short hairpin RNA (shRNA) corresponding to mosquito target genes of interest. Following cultivation, which facilitates inexpensive propagation of shRNA, the yeast is inactivated and prepared in a ready-to-use dry tablet formulation that is fed to mosquito larvae. Ingestion of the yeast tablets results in effective larval target gene silencing. This technically straightforward and affordable technique may be applicable to a wide variety of mosquito species and potentially to other arthropods that feed on yeast.
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http://dx.doi.org/10.1007/978-1-4939-8775-7_15DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7202713PMC
July 2019

A transcriptomic survey of the impact of environmental stress on response to dengue virus in the mosquito, Aedes aegypti.

Authors:
David S Kang Martin S Barron Diane D Lovin Joanne M Cunningham Matthew W Eng Dave D Chadee Jun Li David W Severson

PLoS Negl Trop Dis 2018 06 11;12(6):e0006568. Epub 2018 Jun 11.

Department of Biological Sciences, University of Notre Dame, Notre Dame, IN, United States of America.

Populations of Aedes aegypti naturally exhibit variable susceptibility to dengue viruses. This natural variation can be impacted by nutritional stress resulting from larval-stage crowding, indicating the influence of environment components on the adult mosquito immune response. In particular, larval crowding was previously shown to reduce the susceptibility of adult females of a Trinidad field isolate of A. aegypti to the dengue serotype 2 (JAM1409) virus. Here, we present the first whole transcriptome study to address the impact of environmental stress on A. aegypti response to dengue virus. We examined expression profiles of adult females resulting from crowded and optimum reared larvae from the same Trinidad isolate at two critical early time points-3 and 18 hours post dengue virus infected blood meal. We exposed specimens to either a dengue or naïve blood meal, and then characterized the response in ten gene co-expression modules based on their transcriptional associations with environmental stress and time. We further analyzed the top 30 hub or master regulatory genes in each of the modules, and validated our results via qRT-PCR. These hub genes reveal which functions are critical to the mechanisms that confer dengue virus refractoriness or susceptibility to stress conditioned A. aegypti, as well as the time points at which they are most important.
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http://dx.doi.org/10.1371/journal.pntd.0006568DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6013235PMC
June 2018

Multifaceted functional implications of an endogenously expressed tRNA fragment in the vector mosquito Aedes aegypti.

Authors:
Matthew W Eng Anthony Clemons Casey Hill Roberta Engel David W Severson Susanta K Behura

PLoS Negl Trop Dis 2018 01 24;12(1):e0006186. Epub 2018 Jan 24.

Department of Biological Sciences and Eck institute for Global Health, University of Notre Dame, Notre Dame, Indiana, United States of America.

The mosquito Aedes aegypti is the primary vector of human arboviral diseases caused by dengue, chikungunya and Zika viruses. Many studies have shown the potential roles of small RNA molecules such as microRNA, small interfering RNA and PIWI-interacting RNA in vector mosquitoes. The function of tRNA fragments (tRF), the newly discovered class of small RNAs, in mosquitoes is not known. In this study, we show that specific tRFs are expressed in significantly differential manner between males and females of Ae. aegypti strains. Specific tRFs also show differential response during developmental transition from larvae to adults, as well as after blood feeding of adult females. The expression pattern of tRFs upon blood feeding varied depending upon if the blood contained dengue virus, and also if the females were treated with antibiotic prior to feeding to cleanse of the gut bacteria. Our findings show that a single tRF derived from the precursor sequences of a tRNA-Gly was differentially expressed between males and females, developmental transitions and also upon blood feeding by females of two laboratory strains that vary in midgut susceptibility to dengue virus infection. The multifaceted functional implications of this specific tRF suggest that biogenesis of small regulatory molecules from a tRNA can have wide ranging effects on key aspects of Ae. aegypti vector biology.
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http://dx.doi.org/10.1371/journal.pntd.0006186DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783352PMC
January 2018

Origin of a High-Latitude Population of in Washington, DC.

Authors:
Andrea Gloria-Soria Andrew Lima Diane D Lovin Joanne M Cunningham David W Severson Jeffrey R Powell

Am J Trop Med Hyg 2018 02 14;98(2):445-452. Epub 2017 Dec 14.

Yale University, New Haven, Connecticut.

An overwintering population of has been documented in the Capitol Hill neighborhood of Washington, DC, since 2011. Mitochondrial cytochrome oxidase I () sequence data presented in a previous study traced the origin to the New World. Here, we use microsatellite and 14,071 single nucleotide polymorphisms along with mitochondrial DNA (mtDNA) sequences on Washington samples and samples from potential sources to further narrow the origin of this population. Genetically, Washington are closest to populations in Florida, meaning this is the most likely source. Florida experienced the first mosquito-borne transmission of dengue in the United States after decades of absence of this disease, as well as local transmission of chikungunya and Zika in recent years. This suggests that the Capitol Hill, Washington, DC population of is capable of transmitting viruses such as dengue, chikungunya, and Zika in modern US city environments.
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http://dx.doi.org/10.4269/ajtmh.17-0676DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5929211PMC
February 2018

Yeast interfering RNA larvicides targeting neural genes induce high rates of Anopheles larval mortality.

Authors:
Keshava Mysore Limb K Hapairai Longhua Sun Elizabeth I Harper Yingying Chen Kathleen K Eggleson Jacob S Realey Nicholas D Scheel David W Severson Na Wei Molly Duman-Scheel

Malar J 2017 Nov 13;16(1):461. Epub 2017 Nov 13.

Dept. of Medical and Molecular Genetics, Indiana University School of Medicine, 1234 Notre Dame Avenue, South Bend, IN, 46530, USA.

Background: Although larviciding can reduce the number of outdoor biting malaria vector mosquitoes, which may help to prevent residual malaria transmission, the current larvicide repertoire is faced with great challenges to sustainability. The identification of new effective, economical, and biorational larvicides could facilitate maintenance and expansion of the practice of larviciding in integrated malaria vector mosquito control programmes. Interfering RNA molecules represent a novel class of larvicides with untapped potential for sustainable mosquito control. This investigation tested the hypothesis that short interfering RNA molecules can be used as mosquito larvicides.

Results: A small interfering RNA (siRNA) screen for larval lethal genes identified siRNAs corresponding to the Anopheles gambiae suppressor of actin (Sac1), leukocyte receptor complex member (lrc), and offtrack (otk) genes. Saccharomyces cerevisiae (baker's yeast) was engineered to produce short hairpin RNAs (shRNAs) for silencing of these genes. Feeding larvae with the engineered yeasts resulted in silenced target gene expression, a severe loss of neural synapses in the larval brain, and high levels of larval mortality. The larvicidal activities of yeast interfering RNA larvicides were retained following heat inactivation and drying of the yeast into user-friendly tablet formulations that induced up to 100% larval mortality in laboratory trials.

Conclusions: Ready-to-use dried inactivated yeast interfering RNA larvicide tablets may someday be an effective and inexpensive addition to malaria mosquito control programmes and a valuable, biorational tool for addressing residual malaria transmission.
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http://dx.doi.org/10.1186/s12936-017-2112-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5683233PMC
November 2017

Lure-and-Kill Yeast Interfering RNA Larvicides Targeting Neural Genes in the Human Disease Vector Mosquito Aedes aegypti.

Authors:
Limb K Hapairai Keshava Mysore Yingying Chen Elizabeth I Harper Max P Scheel Alexandra M Lesnik Longhua Sun David W Severson Na Wei Molly Duman-Scheel

Sci Rep 2017 10 16;7(1):13223. Epub 2017 Oct 16.

Indiana University School of Medicine, Department of Medical and Molecular Genetics, South Bend, IN, USA.

New mosquito control strategies are vitally needed to address established arthropod-borne infectious diseases such as dengue and yellow fever and emerging diseases such as Zika and chikungunya, all of which are transmitted by the disease vector mosquito Aedes aegypti. In this investigation, Saccharomyces cerevisiae (baker's yeast) was engineered to produce short hairpin RNAs (shRNAs) corresponding to the Aedes aegypti orthologs of fasciculation and elongation protein zeta 2 (fez2) and leukocyte receptor cluster (lrc) member, two genes identified in a recent screen for A. aegypti larval lethal genes. Feeding A. aegypti with the engineered yeasts resulted in silenced target gene expression, disrupted neural development, and highly significant larval mortality. Larvicidal activities were retained following heat inactivation and drying of the yeast into tabular formulations that induced >95% mortality and were found to attract adult females to oviposit. These ready-to-use inactivated yeast interfering RNA tablets may one day facilitate the seamless integration of this new class of lure-and-kill species-specific biorational mosquito larvicides into integrated mosquito control programs.
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http://dx.doi.org/10.1038/s41598-017-13566-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5643370PMC
October 2017

Larval stress alters dengue virus susceptibility in Aedes aegypti (L.) adult females.

Authors:
David S Kang Yehonatan Alcalay Diane D Lovin Joanne M Cunningham Matthew W Eng Dave D Chadee David W Severson

Acta Trop 2017 Oct 23;174:97-101. Epub 2017 Jun 23.

Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, 46556 USA. Electronic address:

In addition to genetic history, environmental conditions during larval stages are critical to the development, success and phenotypic fate of the Aedes aegypti mosquito. In particular, previous studies have shown a strong genotype-by-environment component to adult mosquito body size in response to optimal vs stressed larval conditions. Here, we expand upon those results by investigating the effects of larval-stage crowding and nutritional limitation on the susceptibility of a recent field isolate of Aedes aegypti to dengue virus serotype-2. Interestingly, female mosquitoes from larvae subjected to a stressed regime exhibited significantly reduced susceptibility to disseminated dengue infection 14days post infection compared to those subjected to optimal regimes. Short term survivorship post-infected blood feeding was not significantly different. As with body size, dengue virus susceptibility of a mosquito population is determined by a combination of genetic and environmental factors and is likely maintained by balancing selection. Here, we provide evidence that under different environmental conditions, the innate immune response of field-reared mosquitoes exhibits a large range of phenotypic variability with regard to dengue virus susceptibility. Further, as with body size, our results suggest that mosquitoes reared under optimal laboratory conditions, as employed in all mosquito-pathogen studies to date, may not always be realistic proxies for natural populations.
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http://dx.doi.org/10.1016/j.actatropica.2017.06.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5571755PMC
October 2017

Genome Investigations of Vector Competence in Aedes aegypti to Inform Novel Arbovirus Disease Control Approaches.

Authors:
David W Severson Susanta K Behura

Insects 2016 Oct 30;7(4). Epub 2016 Oct 30.

Division of Animal Sciences, University of Missouri, Columbia, MO 65211, USA.

Dengue (DENV), yellow fever, chikungunya, and Zika virus transmission to humans by a mosquito host is confounded by both intrinsic and extrinsic variables. Besides virulence factors of the individual arboviruses, likelihood of virus transmission is subject to variability in the genome of the primary mosquito vector, . The "vectorial capacity" of varies depending upon its density, biting rate, and survival rate, as well as its intrinsic ability to acquire, host and transmit a given arbovirus. This intrinsic ability is known as "vector competence". Based on whole transcriptome analysis, several genes and pathways have been predicated to have an association with a susceptible or refractory response in to DENV infection. However, the functional genomics of vector competence of is not well understood, primarily due to lack of integrative approaches in genomic or transcriptomic studies. In this review, we focus on the present status of genomics studies of DENV vector competence in as limited information is available relative to the other arboviruses. We propose future areas of research needed to facilitate the integration of vector and virus genomics and environmental factors to work towards better understanding of vector competence and vectorial capacity in natural conditions.
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http://dx.doi.org/10.3390/insects7040058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5198206PMC
October 2016

Apoptosis-related genes control autophagy and influence DENV-2 infection in the mosquito vector, Aedes aegypti.

Authors:
Matthew W Eng Madeleine N van Zuylen David W Severson

Insect Biochem Mol Biol 2016 09 12;76:70-83. Epub 2016 Jul 12.

Eck Institute for Global Health and Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA. Electronic address:

The mosquito Aedes aegypti is the primary urban vector for dengue virus (DENV) worldwide. Insight into interactions occurring between host and pathogen is important in understanding what factors contribute to vector competence. However, many of the molecular mechanisms for vector competence remain unknown. Our previous global transcriptional analysis suggested that differential expression of apoptotic proteins is involved in determining refractoriness vs susceptibility to DENV-2 infection in Ae. aegypti females following a DENV-infected blood meal. To determine whether DENV-refractory Ae. aegypti showed more robust apoptosis upon infection, we compared numbers of apoptotic cells from midguts of refractory and susceptible strains and observed increased numbers of apoptotic cells in only the refractory strain upon DENV-2 infection. Thereafter, we manipulated apoptosis through dsRNA interference of the initiator caspase, Aedronc. Unexpectedly, dsAedronc-treated females showed both decreased frequency of disseminated infection and decreased virus titer in infected individuals. Insect caspases have also previously been identified as regulators of the cellular recycling process known as autophagy. We observed activation of autophagy in midgut and fat body tissues following a blood meal, as well as programmed activation of several apoptosis-related genes, including the effector caspase, Casps7. To determine whether autophagy was affected by caspase knockdown, we silenced Aedronc and Casps7, and observed reduced activation of autophagy upon silencing. Our results provide evidence that apoptosis-related genes are also involved in regulating autophagy, and that Aedronc may play an important role in DENV-2 infection success in Ae. aegypti, possibly through its regulation of autophagy.
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http://dx.doi.org/10.1016/j.ibmb.2016.07.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5010484PMC
September 2016

High-throughput cis-regulatory element discovery in the vector mosquito Aedes aegypti.

Authors:
Susanta K Behura Joseph Sarro Ping Li Keshava Mysore David W Severson Scott J Emrich Molly Duman-Scheel

BMC Genomics 2016 05 10;17:341. Epub 2016 May 10.

Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN, 46556, USA.

Background: Despite substantial progress in mosquito genomic and genetic research, few cis-regulatory elements (CREs), DNA sequences that control gene expression, have been identified in mosquitoes or other non-model insects. Formaldehyde-assisted isolation of regulatory elements paired with DNA sequencing, FAIRE-seq, is emerging as a powerful new high-throughput tool for global CRE discovery. FAIRE results in the preferential recovery of open chromatin DNA fragments that are not bound by nucleosomes, an evolutionarily conserved indicator of regulatory activity, which are then sequenced. Despite the power of the approach, FAIRE-seq has not yet been applied to the study of non-model insects. In this investigation, we utilized FAIRE-seq to profile open chromatin and identify likely regulatory elements throughout the genome of the human disease vector mosquito Aedes aegypti. We then assessed genetic variation in the regulatory elements of dengue virus susceptible (Moyo-S) and refractory (Moyo-R) mosquito strains.

Results: Analysis of sequence data obtained through next generation sequencing of FAIRE DNA isolated from A. aegypti embryos revealed >121,000 FAIRE peaks (FPs), many of which clustered in the 1 kb 5' upstream flanking regions of genes known to be expressed at this stage. As expected, known transcription factor consensus binding sites were enriched in the FPs, and of these FoxA1, Hunchback, Gfi, Klf4, MYB/ph3 and Sox9 are most predominant. All of the elements tested in vivo were confirmed to drive gene expression in transgenic Drosophila reporter assays. Of the >13,000 single nucleotide polymorphisms (SNPs) recently identified in dengue virus-susceptible and refractory mosquito strains, 3365 were found to map to FPs.

Conclusion: FAIRE-seq analysis of open chromatin in A. aegypti permitted genome-wide discovery of CREs. The results of this investigation indicate that FAIRE-seq is a powerful tool for identification of regulatory DNA in the genomes of non-model organisms, including human disease vector mosquitoes.
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http://dx.doi.org/10.1186/s12864-016-2468-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4862039PMC
May 2016

Multiple QTL Determine Dorsal Abdominal Scale Patterns in the Mosquito Aedes aegypti.

Authors:
Akio Mori Yoshio Tsuda Masahiro Takagi Yukiko Higa David W Severson

J Hered 2016 09 29;107(5):438-44. Epub 2016 Apr 29.

From the Department of Biological Sciences and Eck Institute for Global Health, University of Notre Dame, Notre Dame, IN 46556 (Mori and Severson); and Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan (Tsuda, Takagi, and Higa).

The mosquito, Aedes aegypti (L.) originated in Sub-Saharan Africa as a dark form sylvan species (A. aegypti formosus). Evolution of A. aegypti aegypti type form as a human commensal facilitated its colonization of most semitropical and tropical areas. We investigated the genetic basis for abdominal white scale presence that represents the diagnostic for sylvan A. aegypti formosus (scales absent), from type form (scales present) and A. aegypti queenslandensis form (dense scaling). We performed quantitative trait locus (QTL) mapping using 3 criteria for scale patterns among 192 F1 intercross progeny from matings between a queenslandensis type and an aegypti type form. Results identified 3 QTL determining scale patterns and indicated that classification criteria impact robustness of QTL LOD support. Dark- and light-colored forms exist in sympatry, but vary in multiple phenotypic characteristics, including preferences for vertebrate host, oviposition container, house-entering behavior, and dengue vector competence. Markers associated with 2 QTL regions reflected major reductions in recombination frequencies compared with the standard type form linkage map, suggestive of inversion polymorphisms associated with observed linkage disequilibrium between type-specific characteristics. Understanding the genic basis for differences in A. aegypti forms could inform efforts to develop new mosquito and arboviral disease control strategies.
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http://dx.doi.org/10.1093/jhered/esw027DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4925163PMC
September 2016

Identification of a major Quantitative Trait Locus determining resistance to the organophosphate temephos in the dengue vector mosquito Aedes aegypti.

Authors:
Marcelo H S Paiva Diane D Lovin Akio Mori Maria A V Melo-Santos David W Severson Constância F J Ayres

Genomics 2016 Jan 11;107(1):40-8. Epub 2015 Nov 11.

Departamento de Entomologia, Centro de Pesquisas Aggeu Magalhães, Fundação Oswaldo Cruz, Av. Professor Moraes Rego, s/n - Campus da UFPE - Cidade Universitária, Recife, PE50740-465, Brazil. Electronic address:

Organophosphate insecticides (OP) have extensively been used to control mosquitoes, such as the vector Aedes aegypti. Unfortunately, OP resistance has hampered control programs worldwide. We used Quantitative Trait Locus (QTL) mapping to evaluate temephos resistance in two F1 intercross populations derived from crosses between a resistant Ae. aegypti strain (RecR) and two susceptible strains (MoyoD and Red). A single major effect QTL was identified on chromosome 2 of both segregating populations, named rtt1 (resistance to temephos 1). Bioinformatics analyses identified a cluster of carboxylesterase genes (CCE) within the rtt1 interval. qRT-PCR demonstrated that different CCEs were up-regulated in F2 resistant individuals from both crosses. However, none exceeded the 2-fold expression. Primary mechanisms for temephos resistance may vary between Ae. aegypti populations, yet also appear to support previous findings suggesting that multiple linked esterase genes may contribute to temephos resistance in the RecR strain as well as other populations.
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http://dx.doi.org/10.1016/j.ygeno.2015.11.004DOI Listing
January 2016

siRNA-Mediated Silencing of doublesex during Female Development of the Dengue Vector Mosquito Aedes aegypti.

Authors:
Keshava Mysore Longhua Sun Michael Tomchaney Gwyneth Sullivan Haley Adams Andres S Piscoya David W Severson Zainulabeuddin Syed Molly Duman-Scheel

PLoS Negl Trop Dis 2015 Nov 6;9(11):e0004213. Epub 2015 Nov 6.

Department of Medical and Molecular Genetics, Indiana University School of Medicine, South Bend, Indiana, United States of America.

The development of sex-specific traits, including the female-specific ability to bite humans and vector disease, is critical for vector mosquito reproduction and pathogen transmission. Doublesex (Dsx), a terminal transcription factor in the sex determination pathway, is known to regulate sex-specific gene expression during development of the dengue fever vector mosquito Aedes aegypti. Here, the effects of developmental siRNA-mediated dsx silencing were assessed in adult females. Targeting of dsx during A. aegypti development resulted in decreased female wing size, a correlate for body size, which is typically larger in females. siRNA-mediated targeting of dsx also resulted in decreased length of the adult female proboscis. Although dsx silencing did not impact female membrane blood feeding or mating behavior in the laboratory, decreased fecundity and fertility correlated with decreased ovary length, ovariole length, and ovariole number in dsx knockdown females. Dsx silencing also resulted in disruption of olfactory system development, as evidenced by reduced length of the female antenna and maxillary palp and the sensilla present on these structures, as well as disrupted odorant receptor expression. Female lifespan, a critical component of the ability of A. aegypti to transmit pathogens, was also significantly reduced in adult females following developmental targeting of dsx. The results of this investigation demonstrate that silencing of dsx during A. aegypti development disrupts multiple sex-specific morphological, physiological, and behavioral traits of adult females, a number of which are directly or indirectly linked to mosquito reproduction and pathogen transmission. Moreover, the olfactory phenotypes observed connect Dsx to development of the olfactory system, suggesting that A. aegypti will be an excellent system in which to further assess the developmental genetics of sex-specific chemosensation.
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http://dx.doi.org/10.1371/journal.pntd.0004213DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4636264PMC
November 2015

Evidence for an Overwintering Population of Aedes aegypti in Capitol Hill Neighborhood, Washington, DC.

Authors:
Andrew Lima Diane D Lovin Paul V Hickner David W Severson

Am J Trop Med Hyg 2016 Jan 2;94(1):231-5. Epub 2015 Nov 2.

Disease Carrying Insects Program, Fairfax County Health Department, Fairfax, Virginia; Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana; Eck Institute for Global Health, University of Notre Dame, Notre Dame, Indiana

Aedes aegypti is an invasive, highly anthropophilic mosquito and a major vector for dengue and chikungunya. Population persistence in the continental United States is reportedly limited to southward of the average 10°C winter isotherm, which in the east, bisects Alabama, Mississippi, Georgia, and South Carolina. We report on summer collections and genotypic analyses of Ae. aegypti collected in the Capitol Hill neighborhood in Washington, DC (WDC). Analysis of a 441-bp fragment of the mitochondrial cytochrome oxidase I gene sequence identified the same two haplotype sequences during 2011-2014, and placed these within two discrete groups known to be derived from lineages resident in the Americas. Analysis of 10 microsatellite loci for specimens collected during 2011-2014 revealed no evidence for introgression of new alleles across years. Overall, our data support a conclusion that this represents a resident WDC population, likely maintained during winter months in a subterranean habitat that facilitates year-round survival.
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http://dx.doi.org/10.4269/ajtmh.15-0351DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4710436PMC
January 2016

Inheritance of Resistance to Deltamethrin in Aedes aegypti (Diptera: Culicidae) From Cuba.

Authors:
María Magdalena Rodríguez Daymi Hurtado David W Severson Juan A Bisset

J Med Entomol 2014 Nov 1;51(6):1213-9. Epub 2014 Nov 1.

Department of Vector Control, Institute of Tropical Medicine "Pedro Kourí" Cuba, A. Postal 601, Marianao 13, Ciudad de La Habana, Cuba.

The development of pyrethroid resistance in Aedes aegypti (L) (Diptera: Culicidae) is a serious concern because major A. aegypti control programs are predominantly based on pyrethroid use during epidemic disease outbreaks. Research about the genetic basis for pyrethroid resistance and how it is transmitted among mosquito populations is needed. The objective of this study was to determine how deltamethrin resistance is inherited in the Cuban A. aegypti-resistant reference strain. Here, a field population of A. aegypti from Santiago de Cuba (SAN-F14), subjected to 14 generations of selection for high deltamethrin resistance level (91.25×), was used to prepare reciprocal F1 and backcross progeny with the insecticide-susceptible Rockefeller strain. Bioassays with larvae were performed according to World Health Organization guidelines. The activities of metabolic enzymes were assayed through synergist and biochemical tests. The null hypothesis of the parallelism test between the two probit regression lines of the reciprocal F1 (susceptible females × resistant males and vice versa) was not rejected at the 5% significance level (P = 0.42), indicating autosomal inheritance. The LC50 response of both F1 progenies to deltamethrin was elevated but less than the highly resistant SAN-F14 strain. DLC values for the F1 progenies were 0.91 and 0.87, respectively, suggesting that deltamethrin resistance in the SAN-F14 strain is inherited as an autosomal incompletely dominant trait, involving at least two factors, which implies a faster development of deltamethrin resistance in larvae and lost product effectiveness. Metabolic enzymes including esterases and cytochrome P-450 monooxygenases but not glutathione-S-transferases were involved in deltamethrin resistance in larvae.
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http://dx.doi.org/10.1603/ME13237DOI Listing
November 2014

Correction: Mitotic-Chromosome-Based Physical Mapping of the Culex quinquefasciatus Genome.

Authors:
Anastasia N Naumenko Vladimir A Timoshevskiy Nicholas A Kinney Alina A Kokhanenko Becky S deBruyn Diane D Lovin Vladimir N Stegniy David W Severson Igor V Sharakhov Maria V Sharakhova

PLoS One 2015 8;10(5):e0127565. Epub 2015 May 8.

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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0127565PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4425355PMC
May 2016

Chitosan/interfering RNA nanoparticle mediated gene silencing in disease vector mosquito larvae.

Authors:
Xin Zhang Keshava Mysore Ellen Flannery Kristin Michel David W Severson Kun Yan Zhu Molly Duman-Scheel

J Vis Exp 2015 Mar 25(97). Epub 2015 Mar 25.

Department of Medical and Molecular Genetics, Indiana University School of Medicine; Eck Institute for Global Health, University of Notre Dame; Department of Biological Sciences, University of Notre Dame;

Vector mosquitoes inflict more human suffering than any other organism-and kill more than one million people each year. The mosquito genome projects facilitated research in new facets of mosquito biology, including functional genetic studies in the primary African malaria vector Anopheles gambiae and the dengue and yellow fever vector Aedes aegypti. RNA interference- (RNAi-) mediated gene silencing has been used to target genes of interest in both of these disease vector mosquito species. Here, we describe a procedure for preparation of chitosan/interfering RNA nanoparticles that are combined with food and ingested by larvae. This technically straightforward, high-throughput, and relatively inexpensive methodology, which is compatible with long double stranded RNA (dsRNA) or small interfering RNA (siRNA) molecules, has been used for the successful knockdown of a number of different genes in A. gambiae and A. aegypti larvae. Following larval feedings, knockdown, which is verified through qRT-PCR or in situ hybridization, can persist at least through the late pupal stage. This methodology may be applicable to a wide variety of mosquito and other insect species, including agricultural pests, as well as other non-model organisms. In addition to its utility in the research laboratory, in the future, chitosan, an inexpensive, non-toxic and biodegradable polymer, could potentially be utilized in the field.
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http://dx.doi.org/10.3791/52523DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4401390PMC
March 2015

Insecticide Resistance and Metabolic Mechanisms Involved in Larval and Adult Stages of Aedes aegypti Insecticide-Resistant Reference Strains from Cuba.

Authors:
Juan Andrés Bisset María Magdalena Rodríguez Leydis French David W Severson Gladys Gutiérrez Daymi Hurtado Ilario Fuentes

J Am Mosq Control Assoc 2014 Dec;30(4):298-304

1  Institute of Tropical Medicine Pedro Kourí-Vector Control, Autopista Novia del Mediodia Km 61/2 La Habana, Havana City 10400, Cuba.

Studies were conducted to compare levels of insecticide resistance and to determine the metabolic resistance mechanisms in larval and adult stages of Aedes aegypti from Cuba. Three insecticide-resistant reference strains of Ae. aegypti from Cuba were examined. These strains were derived from a Santiago de Cuba strain isolated in 1997; it was previously subjected to a strong selection for resistance to temephos (SAN-F6), deltamethrin (SAN-F12), and propoxur (SAN-F13) and routinely maintained in the laboratory under selection pressure up to the present time, when the study was carried out. In addition, an insecticide-susceptible strain was used for comparison. The insecticide resistance in larvae and adults was determined using standard World Health Organization methodologies. Insecticide resistance mechanisms were determined by biochemical assays. The esterases (α EST and β EST) and mixed function oxidase (MFO) activities were significantly higher in adults than in the larvae of the three resistant strains studied. The association of resistance level with the biochemical mechanism for each insecticide was established for each stage. The observed differences between larval and adult stages of Ae. aegypti in their levels of insecticide resistance and the biochemical mechanisms involved should be included as part of monitoring and surveillance activities in Ae. aegypti vector control programs.
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http://dx.doi.org/10.2987/14-6431.1DOI Listing
December 2014

Mitotic-chromosome-based physical mapping of the Culex quinquefasciatus genome.

Authors:
Anastasia N Naumenko Vladimir A Timoshevskiy Nicholas A Kinney Alina A Kokhanenko Becky S deBruyn Diane D Lovin Vladimir N Stegniy David W Severson Igor V Sharakhov Maria V Sharakhova

PLoS One 2015 13;10(3):e0115737. Epub 2015 Mar 13.

Department of Entomology and Fralin Life Science Institute, Virginia Tech, Blacksburg, Virginia, United States of America; Institute of Biology and Biophysics, Tomsk State University, Tomsk, Russia.

The genome assembly of southern house mosquito Cx. quinquefasciatus is represented by a high number of supercontigs with no order or orientation on the chromosomes. Although cytogenetic maps for the polytene chromosomes of this mosquito have been developed, their utilization for the genome mapping remains difficult because of the low number of high-quality spreads in chromosome preparations. Therefore, a simple and robust mitotic-chromosome-based approach for the genome mapping of Cx. quinquefasciatus still needs to be developed. In this study, we performed physical mapping of 37 genomic supercontigs using fluorescent in situ hybridization on mitotic chromosomes from imaginal discs of 4th instar larvae. The genetic linkage map nomenclature was adopted for the chromosome numbering based on the direct positioning of 58 markers that were previously genetically mapped. The smallest, largest, and intermediate chromosomes were numbered as 1, 2, and 3, respectively. For idiogram development, we analyzed and described in detail the morphology and proportions of the mitotic chromosomes. Chromosomes were subdivided into 19 divisions and 72 bands of four different intensities. These idiograms were used for mapping the genomic supercontigs/genetic markers. We also determined the presence of length polymorphism in the q arm of sex-determining chromosome 1 in Cx. quinquefasciatus related to the size of ribosomal locus. Our physical mapping and previous genetic linkage mapping resulted in the chromosomal assignment of 13% of the total genome assembly to the chromosome bands. We provided the first detailed description, nomenclature, and idiograms for the mitotic chromosomes of Cx. quinquefasciatus. Further application of the approach developed in this study will help to improve the quality of the southern house mosquito genome.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0115737PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4358980PMC
March 2016

Whole transcriptome responses among females of the filariasis and arbovirus vector mosquito Culex pipiens implicate TGF-β signaling and chromatin modification as key drivers of diapause induction.

Authors:
Paul V Hickner Akio Mori Erliang Zeng John C Tan David W Severson

Funct Integr Genomics 2015 Jul 30;15(4):439-47. Epub 2015 Jan 30.

Eck Institute for Global Health and Department of Biological Sciences, University of Notre Dame, 107C Galvin Life Sciences, Notre Dame, IN, 46556, USA,

Culex pipiens mosquitoes are important disease vectors inhabiting temperate zones, worldwide. The seasonal reduction in temperature and photoperiod accompanying late summer and early fall prompts female mosquitoes to enter diapause, a stage of developmental arrest and physiological conditioning that enhances survival during the winter months. To investigate the molecular mechanisms underlying diapause induction, we used custom whole transcriptome microarrays to identify differences in gene expression following exposure to nondiapause (long days, 25 °C) and diapause-inducing (short days, 18 °C) environmental conditions. Using a two-way ANOVA, we identified 1130 genes that were differentially expressed. We used the expression of these genes across three time points to construct a gene co-expression network comprising five modules. Genes in modules 1, 2, and 3 were largely up-regulated, while genes in modules 4 and 5 were down-regulated when compared to nondiapause conditions. Pathway enrichment analysis of the network modules revealed some potential regulatory mechanisms driving diapause induction. Module 1 was enriched for genes in the TGF-ß and Wnt signaling pathways; module 2 was enriched for genes involved in insect hormone biosynthesis, specifically, ecdysone synthesis; module 3 was enriched for genes involved in chromatin modification; and module 5 was enriched for genes in the circadian rhythm pathway. Our results suggest that TGF-β signaling and chromatin modification are key drivers for the integration of environmental signals into the diapause induction phase in C. pipiens mosquitoes.
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http://dx.doi.org/10.1007/s10142-015-0432-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4492872PMC
July 2015