Do or die: how selfishness might help eradicate malaria 30/07/07. By the Wellcome Trust In the fight against insect-borne diseases such as malaria, the use of insects with diminished capability to spread disease is a major potential weapon.

If such disease-resistant insects were released into the wild population, however, there would be no guarantee that they could outcompete and replace their normal, disease-carrying relatives.

Now, a team from the California Institute of Technology has found a method that could ensure that modified insects quickly dominate the natural population. The idea comes from a genetic element called Medea (maternal-effect dominant embryonic arrest), which is seen in a type of flour beetle. This element selects for its own survival: maternal Medea produces a lethal toxin that kills all the mother's eggs unless they have inherited the Medea element themselves, which allows them to produce an antidote.

In this study, which involved fruit flies, the 'toxin' was two microRNAs that silence a gene vital for development in fly embryos. The embryos only survived if they inherited Medea and therefore had the 'antidote' - in this case, an extra copy of the silenced gene, immune to the RNA.

Tests in the lab showed that the Medea element quickly spread throughout the fly population; when flies carrying Medea were mated with wild-type flies, all flies carried Medea after ten generations. Further work is needed to see whether this system could work in mosquitoes, the vectors of malaria. Researchers hope that coupling the Medea element to a malaria resistance gene will allow resistant mosquitoes to spread throughout, and eventually to dominate, the population.

References

Chen CH et al. A synthetic maternal-effect selfish genetic element drives population replacement in Drosophila. Science 2007;316(5824):597-600. Abstract