Site-Directed φC31-Mediated Integration and Cassette Exchange in Anopheles Vectors of Malaria

Functional genomic analysis and related strategies for genetic control of malaria rely on validated and reproducible methods to accurately modify the genome of Anopheles mosquitoes. Amongst these methods, the φC31 system allows precise and stable site-directed integration of transgenes, or the substitution of integrated transgenic cassettes via recombinase-mediated cassette exchange (RMCE). This method relies on the action of the Streptomyces φC31 bacteriophage integrase to catalyze recombination between two specific attachment sites designated attP (derived from the phage) and attB (derived from the host bacterium). The system uses one or two attP sites that have been integrated previously into the mosquito genome and attB site(s) in the donor template DNA. Here we illustrate how to stably modify the genome of attP-bearing Anopheles docking lines using two plasmids: an attB-tagged donor carrying the integration or exchange template and a helper plasmid encoding the φC31 integrase. We report two representative results of φC31mediated site-directed modification: the single integration of a transgenic cassette in An. stephensi and RMCE in An. gambiae mosquitoes. φC31-mediated genome manipulation offers the advantage of reproducible transgene expression from validated, fitness neutral genomic sites, allowing comparative qualitative and quantitative analyses of phenotypes. The site-directed nature of the integration also substantially simplifies the validation of the single insertion site and the mating scheme to obtain a stable transgenic line. These and other characteristics make the φC31 system an essential component of the genetic toolkit for the transgenic manipulation of malaria mosquitoes and other insect vectors

A comparative view on sex differentiation and gametogenesis genes in lungfish and coelacanths

none8siGonadal sex differentiation andreproductionare the keys totheperpetuationof favorable gene combinations andpositively selected traits. In vertebrates, several gonad development features that differentiate tetrapods and fishes are likely to be, at least in part, related to the water-to-land transition. The collection of information from basal sarcopterygians, coelacanths, and lungfishes, is crucial to improve our understanding of the molecular evolution of pathways involved in reproductive functions, since these organisms are generally regarded as “living fossils” and as the direct ancestors of tetrapods. Here, we report for the first time the characterization of >50 genes related to sex differentiation and gametogenesis in Latimeria menadoensis and Protopterus annectens. Although the expression profiles of most genes is consistent with the intermediate position of basal sarcopterygians between actinopterygian fish and tetrapods, their phylogenetic placement and presence/absence patterns often reveal a closer affinity to the tetrapod orthologs. On the other hand, particular genes, for example, the male gonad factor gsdf (Gonadal Soma-Derived Factor), provide examples of ancestral traits sharedwith actinopterygians,which disappeared in the tetrapod lineage.openMaria Assunta Biscotti, Mateus Contar Adolfi, Marco Barucca, Mariko Forconi, Alberto Pallavicini, Marco Gerdol, Adriana Canapa, Manfred SchartlBiscotti, Maria Assunta; Contar Adolfi, Mateus; Barucca, Marco; Forconi, Mariko'; Pallavicini, Alberto; Gerdol, Marco; Canapa, Adriana; Schartl, Manfre

New insecticide screening platforms indicate that Mitochondrial Complex I inhibitors are susceptible to cross-resistance by mosquito P450s that metabolise pyrethroids

Fenazaquin, pyridaben, tolfenpyrad and fenpyroximate are Complex I inhibitors offering a new mode of action for insecticidal malaria vector control. However, extended exposure to pyrethroid based products such as long-lasting insecticidal nets (LLINs) has created mosquito populations that are largely pyrethroid-resistant, often with elevated levels of P450s that can metabolise and neutralise diverse substrates. To assess cross-resistance liabilities of the Complex I inhibitors, we profiled their susceptibility to metabolism by P450s associated with pyrethroid resistance in Anopheles gambiae (CYPs 6M2, 6P3, 6P4, 6P5, 9J5, 9K1, 6Z2) and An. funestus (CYP6P9a). All compounds were highly susceptible. Transgenic An. gambiae overexpressing CYP6M2 or CYP6P3 showed reduced mortality when exposed to fenpyroximate and tolfenpyrad. Mortality from fenpyroximate was also reduced in pyrethroid-resistant strains of An. gambiae (VK7 2014 and Tiassalé 13) and An. funestus (FUMOZ-R). P450 inhibitor piperonyl butoxide (PBO) significantly enhanced the efficacy of fenpyroximate and tolfenpyrad, fully restoring mortality in fenpyroximate-exposed FUMOZ-R. Overall, results suggest that in vivo and in vitro assays are a useful guide in the development of new vector control products, and that the Complex I inhibitors tested are susceptible to metabolic cross-resistance and may lack efficacy in controlling pyrethroid resistant mosquitoes

Functional genetic validation of key genes conferring insecticide resistance in the major African malaria vector

Resistance in to members of all 4 major classes (pyrethroids, carbamates, organochlorines, and organophosphates) of public health insecticides limits effective control of malaria transmission in Africa. Increase in expression of detoxifying enzymes has been associated with insecticide resistance, but their direct functional validation in is still lacking. Here, we perform transgenic analysis using the GAL4/UAS system to examine insecticide resistance phenotypes conferred by increased expression of the 3 genes-, , and -most often found up-regulated in resistant We report evidence in that organophosphate and organochlorine resistance is conferred by overexpression of GSTE2 in a broad tissue profile. Pyrethroid and carbamate resistance is bestowed by similar overexpression, and confers only pyrethroid resistance when overexpressed in the same tissues. Conversely, such overexpression increases susceptibility to the organophosphate malathion, presumably due to conversion to the more toxic metabolite, malaoxon. No resistant phenotypes are conferred when either gene overexpression is restricted to the midgut or oenocytes, indicating that neither tissue is involved in insecticide resistance mediated by the candidate P450s examined. Validation of genes conferring resistance provides markers to guide control strategies, and the observed negative cross-resistance due to gives credence to proposed dual-insecticide strategies to overcome pyrethroid resistance. These transgenic -resistant lines are being used to test the "resistance-breaking" efficacy of active compounds early in their development

Small-Cage Laboratory Trials of Genetically-Engineered Anopheline Mosquitoes

Control of mosquito-borne pathogens using genetically-modified vectors has been proposed as a promising tool to complement conventional control strategies. CRISPR-based homing gene drive systems have made transgenic technologies more accessible within the scientific community. Evaluation of transgenic mosquito performance and comparisons with wild-type counterparts in small laboratory cage trials provide valuable data for the design of subsequent field cage experiments and experimental assessments to refine the strategies for disease prevention. Here, we present three different protocols used in laboratory settings to evaluate transgene spread in anopheline mosquito vectors of malaria. These include inundative releases (no gene-drive system), and gene-drive overlapping and non-overlapping generation trials. The three trials vary in a number of parameters and can be adapted to desired experimental settings. Moreover, insectary studies in small cages are part of the progressive transition of engineered insects from the laboratory to open field releases. Therefore, the protocols described here represent invaluable tools to provide empirical values that will ultimately aid field implementation of new technologies for malaria elimination

Site-Directed φC31-Mediated Integration and Cassette Exchange in Anopheles Vectors of Malaria.

Functional genomic analysis and related strategies for genetic control of malaria rely on validated and reproducible methods to accurately modify the genome of Anopheles mosquitoes. Amongst these methods, the φC31 system allows precise and stable site-directed integration of transgenes, or the substitution of integrated transgenic cassettes via recombinase-mediated cassette exchange (RMCE). This method relies on the action of the Streptomyces φC31 bacteriophage integrase to catalyze recombination between two specific attachment sites designated attP (derived from the phage) and attB (derived from the host bacterium). The system uses one or two attP sites that have been integrated previously into the mosquito genome and attB site(s) in the donor template DNA. Here we illustrate how to stably modify the genome of attP-bearing Anopheles docking lines using two plasmids: an attB-tagged donor carrying the integration or exchange template and a helper plasmid encoding the φC31 integrase. We report two representative results of φC31-mediated site-directed modification: the single integration of a transgenic cassette in An. stephensi and RMCE in An. gambiae mosquitoes. φC31-mediated genome manipulation offers the advantage of reproducible transgene expression from validated, fitness neutral genomic sites, allowing comparative qualitative and quantitative analyses of phenotypes. The site-directed nature of the integration also substantially simplifies the validation of the single insertion site and the mating scheme to obtain a stable transgenic line. These and other characteristics make the φC31 system an essential component of the genetic toolkit for the transgenic manipulation of malaria mosquitoes and other insect vectors

Using the GAL4-UAS System for Functional Genetics in Anopheles gambiae

The bipartite GAL4-UAS system is a versatile and powerful tool for functional genetic analysis. The essence of the system is to cross transgenic 'driver' lines that express the yeast transcription factor GAL4 in a tissue specific manner, with transgenic 'responder' lines carrying a candidate gene/RNA interference construct whose expression is controlled by Upstream Activation Sequences (UAS) that bind GAL4. In the ensuing progeny, the gene or silencing construct is thus expressed in a prescribed spatiotemporal manner, enabling the resultant phenotypes to be assayed and gene function inferred. The binary system enables flexibility in experimental approaches to screen phenotypes generated by transgene expression in multiple tissue-specific patterns, even if severe fitness costs are induced. We have adapted this system for Anopheles gambiae, the principal malaria vector in Africa. In this article, we provide some of the common procedures used during GAL4-UAS analysis. We describe the An. gambiae GAL4-UAS lines already generated, as well as the cloning of new responder constructs for upregulation and RNAi knockdown. We specify a step by step guide for sexing of mosquito pupae to establish genetic crosses, that also includes screening progeny to follow inheritance of fluorescent gene markers that tag the driver and responder insertions. We also present a protocol for clearing An. gambiae embryos to study embryonic development. Finally, we introduce potential adaptions of the method to generate driver lines through CRISPR/Cas9 insertion of GAL4 downstream of target genes