First Steps towards Underdominant Genetic Transformation of Insect Populations

Abstract

The idea of introducing genetic modifications into wild populations of insects to stop them from spreading diseases is more than 40 years old. Synthetic disease refractory genes have been successfully generated for mosquito vectors of dengue fever and human malaria. Equally important is the development of population transformation systems to drive and maintain disease refractory genes at high frequency in populations. We demonstrate an underdominant population transformation system in Drosophila melanogaster that has the property of being both spatially self-limiting and reversible to the original genetic state. Both population transformation and its reversal can be largely achieved within as few as 5 generations. The described genetic construct {Ud} is composed of two genes; (1) a UAS-RpL14.dsRNA targeting RNAi to a haploinsufficient gene RpL14 and (2) an RNAi insensitive RpL14 rescue. In this proof-of-principle system the UAS-RpL14.dsRNA knock-down gene is placed under the control of an Actin5c-GAL4 driver located on a different chromosome to the {Ud} insert. This configuration would not be effective in wild populations without incorporating the Actin5c-GAL4 driver as part of the {Ud} construct (or replacing the UAS promoter with an appropriate direct promoter). It is however anticipated that the approach that underlies this underdominant system could potentially be applied to a number of species.

Evolutionary biology and genetic techniques for insect control

“…; Reeves et al. ). The likelihood of population allele replacement depends upon the initial frequency of introduction and does not require that both wild‐type and introduced homozygotes have equal fitness, just that both their fitnesses are greater than the heterozygote.…”

“…However, a recent study successfully developed proof of principle in D. melanogaster (Reeves et al. ). The expression of a Minute locus was knocked down in heterozygotes.…”

Evolution of Resistance Against CRISPR/Cas9 Gene Drive

“…Ongoing efforts to transfer the Medea system from flour beetles to other insects have, thus far, fallen short (Chen et al 2007;Akbari et al 2014). Underdominance systems have also been developed (Altrock et al 2010;Akbari et al 2013;Reeves et al 2014), but these are slow-spreading systems that require multiple releases of large numbers of male transgenic insects. The use of Wolbachia-mediated strategies have perhaps been most successful (Lambrechts et al 2015).…”

Transgene Biocontainment Strategies for Molecular Farming

“…This was achieved using a genetic construct to encode for two genes: the first encodes for a RNAi knockdown of the WT version of the gene Rpl14; the second gene is a refactored version of Rpl4 such that it isn't susceptible to RNAi knockdown. When the engineered organism was mated with WT flies there was a marked fitness reduction in the heterozygotes (Reeves et al, 2014). However, in order to be effective for biocontainment the underdominance must result in total sterility or death of the hybrids.…”