Hemolytic C-type lectin CEL-III from sea cucumber expressed in transgenic mosquitoes impairs malaria parasite development

Site-specific integration and expression of an anti-malarial gene in transgenic Anopheles gambiae significantly reduces Plasmodium infections

Diseases transmitted by mosquitoes have a devastating impact on global health and this is worsening due to difficulties with existing control measures and climate change. Genetically modified mosquitoes that are refractory to disease transmission are seen as having great potential in the delivery of novel control strategies. Historically the genetic modification of insects has relied upon transposable elements which have many limitations despite their successful use. To circumvent these limitations the Streptomyces phage phiC31 integrase system has been successfully adapted for site-specific transgene integration in insects. Here, we present the first site-specific transformation of Anopheles gambiae, the principal vector of human malaria. Mosquitoes were initially engineered to incorporate the phiC31 targeting site at a defined genomic location. A second phase of genetic modification then achieved site-specific integration of Vida3, a synthetic anti-malarial gene. Expression of Vida3, specifically in the midgut of bloodfed females, offered consistent and significant protection against Plasmodium yoelii nigeriensis, reducing average parasite intensity by 85%. Similar protection was observed against Plasmodium falciparum in some experiments, although protection was inconsistent. In the fight against malaria, it is imperative to establish a broad repertoire of both anti-malarial effector genes and tissue-specific promoters for their expression, enabling those offering maximum effect with minimum fitness cost to be identified. In the future, this technology will allow effective comparisons and informed choices to be made, potentially leading to complete transmission blockade.

Choosing anti-Plasmodium molecules for genetically modifying mosquitoes: focus on peptides

In the wake of the development of insecticide resistance in mosquitoes, novel strategies for halting malaria transmission are being developed. These include the genetic modification (GM) of mosquitoes to become incompetent vectors. Although mosquito GM technologies are progressing rapidly, the rationale behind choosing anti-parasite molecules to be expressed by mosquitoes has received less attention. Here, questions are explored that that should be addressed during the strategic selection of these anti-Plasmodium molecules, focusing on antimicrobial peptides. Properties that will enhance the likelihood of success are discussed, and the need to plan an initial strategy to eliminate molecules that cause fitness costs to the mosquito is considered. Effector molecules with proven anti-sporogonic stage activity are reviewed, and the activity of a selection of these molecules is detailed.

Flying vaccinator; a transgenic mosquito delivers a Leishmania vaccine via blood feeding

'Flying vaccinator' is the concept of using genetically engineered hematophagous insects to deliver vaccines. Here we show the generation of a transgenic anopheline mosquito that expresses the Leishmania vaccine candidate, SP15, fused to monomeric red fluorescent protein (mDsRed) in its salivary glands. Importantly, mice bitten repeatedly by the transgenic mosquitoes raised anti-SP15 antibodies, indicating delivery of SP15 via blood feeding with its immunogenicity intact. Thus, this technology makes possible the generation of transgenic mosquitoes that match the original concept of a 'flying vaccinator'. However, medical safety issues and concerns about informed consent mitigate the use of the 'flying vaccinator' as a method to deliver vaccines. We propose that this expression system could be applied to elucidate saliva-malaria sporozoite interactions.

Gene structure and expression of nanos (nos) and oskar (osk) orthologues of the vector mosquito, Culex quinquefasciatus

The products of the maternal-effect genes, nanos (nos) and oskar (osk), are important for the development of germ cells in insects. Furthermore, these genes have been proposed as candidates for donating functional DNA regulatory sequences for use in gene drive systems to control transmission of mosquito-borne pathogens. The nos and osk genes of the cosmopolitan vector mosquito, Culex quinquefasciatus, encode proteins with domains common to orthologues found in other mosquitoes. Expression analyses support the conclusion that the role of these genes is conserved generally among members of the nematocera. Hybridization in situ analyses reveal differences in mRNA distribution in early embryos in comparison with the cyclorraphan, Drosophila melanogaster, highlighting a possible feature in the divergence of the clades each insect represents.