Transposable elements (TEs) are proposed as a basis for developing drive systems to spread pathogen resistance genes through vector mosquito populations. The use of transcriptional and translational control DNA elements from genes expressed specifically in the insect germ line to mediate transposition offers possibilities for mitigating some of the concerns about transgene behavior in the target vector species and eliminating effects on nontarget organisms. Here, we describe the successful use of the promoter and untranslated regions from the nanos (nos) orthologous gene of the yellow fever mosquito, Aedes aegypti, to control sex-and tissuespecific expression of exogenously derived mariner MosI transposase-encoding DNA. Transgenic mosquitoes expressed transposase mRNA in abundance near or equal to the endogenous nos transcript and exclusively in the female germ cells. In addition, MosI mRNA was deposited in developing oocytes and localized and maintained at the posterior pole during early embryonic development. Importantly, four of five transgenic lines examined were capable of mobilizing a second MosI transgene into the mosquito genome, indicating that functional transposase was being produced. Thus, the nos control sequences show promise as part of a TE-based gene drive system. dengue ͉ gene drive ͉ transposon

Genetic strategies for controlling malaria transmission based on engineering pathogen resistance in Anopheles mosquitoes are being tested in a number of animal models. A key component is the effector molecule and the efficiency with which it reduces parasite transmission. Single-chain antibodies (scFvs) that bind the circumsporozoite protein of the avian parasite, Plasmodium gallinaceum, can reduce mean intensities of sporozoite infection of salivary glands by two to four orders of magnitude in transgenic Aedes aegypti. Significantly, mosquitoes with as few as 20 sporozoites in their salivary glands are infectious for a vertebrate host, Gallus gallus. Although scFvs hold promise as effector molecules, they will have to reduce mean intensities of infection to zero to prevent parasite transmission and disease. We conclude that similar endpoints must be reached with human pathogens if we are to expect an effect on disease transmission.

The excision of specific DNA sequences from integrated transgenes in insects permits the dissection in situ of structural elements that may be important in controlling gene expression. Furthermore, manipulation of potential control elements in the context of a single integration site mitigates against insertion site influences of the surrounding genome. The cre-loxP site-specific recombination system has been used successfully to remove a marker gene from transgenic yellow fever mosquitoes, Aedes aegypti. A total of 33.3% of all fertile families resulting from excision protocols showed evidence of cre-loxP-mediated site-specific excision. Excision frequencies were as high as 99.4% within individual families. The cre recombinase was shown to precisely recognize loxP sites in the mosquito genome and catalyze excision. Similar experiments with the FLP/FRT site-specific recombination system failed to demonstrate excision of the marker gene from the mosquito chromosomes.