34 research outputs found
Targeting sex determination for genetic control of the malaria mosquito
No full textMalaria is a devastating disease that causes more than 400,000 deaths each year, primarily in underprivileged regions of sub-Saharan Africa. During the last two decades, mortality caused by the disease has been reduced by half, largely driven by coordinated vector control based on the use of insecticides and bed nets. Nevertheless, the declining trend in malaria cases appears to have stalled recently and there is a growing concern that new interventions will be needed to reach widespread malaria elimination. Gene drive systems are potentially transformative in this endeavour because they allow rapid, self-sustaining and species-specific control of the mosquito vector through the limited release of genetically modified mosquitoes. While proof-of-principle studies have demonstrated the feasibility of the approach, none of them have managed to fulfil the requirements needed to progress in field or semi-field testing, largely due to strong fitness costs and genetic resistance to gene drive. This thesis describes the first gene drive system demonstrated to spread in caged populations of Anopheles gambiae mosquitoes, unimpeded by resistance or fitness constraints. By targeting an ultra-conserved locus in the gene doublesex, this strategy is able to thwart target site resistance in caged experiments whilst driving complete population suppression through the conversion of genetic females to sterile intersex. In this thesis, I demonstrate complete population elimination of caged populations from single releases of gene drive mosquitoes using a 12.5% initial allele release frequency, and crucially, I demonstrate its effectiveness in large cage semi-field conditions designed to reveal complex behaviours otherwise absent in small scale testing. The complete suppression of vector populations using a gene system is a landmark achievement and brings the gene drive technology closer to be implemented in the wild to complement current interventions against malaria.Open Acces
Assessing the acoustic behaviour of Anopheles gambiae (s.l.) dsxF mutants: implications for vector control
No full textHigh-resolution transcriptional profiling of Anopheles gambiae spermatogenesis reveals mechanisms of sex chromosome regulation.
No full textAlthough of high priority for the development of genetic tools to control malaria-transmitting mosquitoes, only a few germline-specific regulatory regions have been characterised to date and the presence of global regulatory mechanisms, such as dosage compensation and meiotic sex chromosome inactivation (MSCI), are mostly assumed from transcriptomic analyses of reproductive tissues or whole gonads. In such studies, samples include a significant portion of somatic tissues inevitably complicating the reconstruction of a defined transcriptional map of gametogenesis. By exploiting recent advances in transgenic technologies and gene editing tools, combined with fluorescence-activated cell sorting and RNA sequencing, we have separated four distinct cell lineages from the Anopheles gambiae male gonads: premeiotic, meiotic (primary and secondary spermatocytes) and postmeiotic. By comparing the overall expression levels of X-linked and autosomal genes across the four populations, we revealed a striking transcriptional repression of the X chromosome coincident with the meiotic phase, classifiable as MSCI, and highlighted genes that may evade silencing. In addition, chromosome-wide median expression ratios of the premeiotic population confirmed the absence of dosage compensation in the male germline. Applying differential expression analysis, we highlighted genes and transcript isoforms enriched at specific timepoints and reconstructed the expression dynamics of the main biological processes regulating the key stages of sperm development and maturation. We generated the first transcriptomic atlas of A. gambiae spermatogenesis that will expand the available toolbox for the genetic engineering of vector control technologies. We also describe an innovative and multidimensional approach to isolate specific cell lineages that can be used for the targeted analysis of other A. gambiae organs or transferred to other medically relevant species and model organisms
A male-biased sex-distorter gene drive for the human malaria vector Anopheles gambiae
No full textOnly female insects transmit diseases such as malaria, dengue and Zika; therefore, control methods that bias the sex ratio of insect offspring have long been sought. Genetic elements such as sex-chromosome drives can distort sex ratios to produce unisex populations that eventually collapse, but the underlying molecular mechanisms are unknown. We report a male-biased sex-distorter gene drive (SDGD) in the human malaria vector Anopheles gambiae. We induced super-Mendelian inheritance of the X-chromosome-shredding I-PpoI nuclease by coupling this to a CRISPR-based gene drive inserted into a conserved sequence of the doublesex (dsx) gene. In modeling of invasion dynamics, SDGD was predicted to have a quicker impact on female mosquito populations than previously developed gene drives targeting female fertility. The SDGD at the dsx locus led to a male-only population from a 2.5% starting allelic frequency in 10-14 generations, with population collapse and no selection for resistance. Our results support the use of SDGD for malaria vector control
Cross-species Y chromosome function between malaria vectors of the Anopheles gambiae species complex
No full textY chromosome function, structure and evolution is poorly understood in many species, including the Anopheles genus of mosquitoes-an emerging model system for studying speciation that also represents the major vectors of malaria. While the Anopheline Y had previously been implicated in male mating behavior, recent data from the Anopheles gambiae complex suggests that, apart from the putative primary sex-determiner, no other genes are conserved on the Y. Studying the functional basis of the evolutionary divergence of the Y chromosome in the gambiae complex is complicated by complete F1 male hybrid sterility. Here, we used an F1 × F0 crossing scheme to overcome a severe bottleneck of male hybrid incompatibilities that enabled us to experimentally purify a genetically labeled A. gambiae Y chromosome in an A. arabiensis background. Whole genome sequencing (WGS) confirmed that the A. gambiae Y retained its original sequence content in the A. arabiensis genomic background. In contrast to comparable experiments in Drosophila, we find that the presence of a heterospecific Y chromosome has no significant effect on the expression of A. arabiensis genes, and transcriptional differences can be explained almost exclusively as a direct consequence of transcripts arising from sequence elements present on the A. gambiae Y chromosome itself. We find that Y hybrids show no obvious fertility defects, and no substantial reduction in male competitiveness. Our results demonstrate that, despite their radically different structure, Y chromosomes of these two species of the gambiae complex that diverged an estimated 1.85 MYA function interchangeably, thus indicating that the Y chromosome does not harbor loci contributing to hybrid incompatibility. Therefore, Y chromosome gene flow between members of the gambiae complex is possible even at their current level of divergence. Importantly, this also suggests that malaria control interventions based on sex-distorting Y drive would be transferable, whether intentionally or contingent, between the major malaria vector species
Natural infection of C. elegans by an oomycete reveals a new pathogen-specific immune response
No full textIn its natural habitat, the nematode Caenorhabditis elegans encounters a plethora of other organisms, including many that are pathogenic [ 1 ; 2]. The study of interactions between C. elegans and various pathogens has contributed to characterizing key mechanisms of innate immunity [ 2; 3 ; 4]. However, how C. elegans recognizes different pathogens to mount pathogen-specific immune responses remains still largely unknown [ 3; 5; 6; 7 ; 8]. Expanding the range of known C. elegans-infecting pathogens and characterizing novel pathogen-specific immune responses are key steps toward answering this question. We report here that the oomycete Myzocytiopsis humicola is a natural pathogen of C. elegans, and we describe its infection strategy. We identify a new host immune response to pathogen exposure that involves induction of members of a previously uncharacterized gene family encoding chitinase-like (CHIL) proteins. We demonstrate that this response is highly specific against M. humicola and antagonizes the infection. We propose that CHIL proteins may diminish the ability of the oomycete to infect by hindering pathogen attachment to the host cuticle. This work expands our knowledge of natural eukaryotic pathogens of C. elegans and introduces a new pathosystem to address how animal hosts recognize and respond to oomycete infections
