Microsoft word - alphey.doc

Dominant lethal systems for genetic control of mosquito populations

Luke Alphey1, Céline Vass, Hoang Kim Phuc, Peng Gong, Matthew Epton, Morten Andreasen and
Helen White-Cooper
Dept. of Zoology, University of Oxford, South Parks Road, Oxford OX1 2PS, UK
1: corresponding author, email: [email protected]
Recent advances in insect genetic engineering have opened up new possibilities in the genetic control
of insect vectors of human diseases. Key advances include the genetic transformation of Aedes,
Anopheles and Culex mosquitoes, and the sequencing of the Anopheles gambiae genome. We are
currently attempting to engineer repressible dominant lethal genes or genetic systems into
mosquitoes, using Aedes aegypti as our model mosquito and Drosophila melanogaster as our genetic
test-bed. The primary applied goal of the programme is to develop usable area-wide population
control methods based on the Sterile Insect Technique, an approach we call RIDL (Release of Insects
carrying a Dominant Lethal)1,2. For this purpose, we are attempting to develop genetic systems with
the following properties:
Genetic marker:
A genetic marker is useful not only to isolate the initial transformant, but also to discriminate
between released and wild adults in a mass-release program without having to resort to PCR or other
molecular methods. Therefore, a marker that can be readily scored in adults would be helpful. Our
present marker, DsRed2 under the control of the Drosophila Actin5C promoter comes close to this; it
is easily scored in live larvae and pupae of Aedes aegypti, and in dissected adults. If only males are
released, the requirement for an adult marker may be less important.
Repressible dominant lethality (non-sex-specific)
An area-wide control program based on mass-release of mosquitoes would preferably not release
large numbers of biting females. Some form of sex-separation is therefore required. For Anopheles
mosquitoes, this will presumably require a genetic sexing mechanism (see below), but for Aedes
aegypti physical sex separation based on pupal size can be very effective, as shown in trial
programmes in the 1970’s. A critical problem with SIT-type control methods for mosquitoes is
sterilisation. Early trials found that pupal irradiation compromised the adults, while adult irradiation
is problematic. Chemosterilisation was used instead, but greater concern about toxic residues would
make this difficult today. Use of a strain homozygous for a non-sex-specific dominant lethal can
potentially overcome this problem2,3. We are therefore attempting to construct such strains, using the
tetracycline-repressible gene expression system4 to allow us to repress the lethal effect with dietary
tetracycline. This programme has achieved some success, and I will report on our progress so far.
Genetic sexing mechanisms
In many cases it is important to release only males, rather than a mixed population of males and
females. There are two main reasons for this: the adult females may be hazardous and/or co-
releasing females may inhibit dispersal of males. While physical sex-separation methods are
available for Aedes aegypti, this is not the case for other important mosquito species. We are
therefore developing sexing methods based on the use of sex-specific promoters, sex-specific
splicing and/or sex-specific effector molecules.
Alphey, L. & Andreasen, M. H. Dominant lethality and insect population control. Mol. Biochem. Parasitol. 121,
173-178 (2002).
Thomas, D., Donnelly, C., Wood, R. & Alphey, L. Insect population control using a dominant, repressible,
lethal genetic system. Science 287, 2474-2476 (2000).
Horn, C. & Wimmer, E. A transgene-based, embryo-specific lethality system for insect pest management. Nat.
Biotech. 21, 64-70 (2003).
Gossen, M. & Bujard, H. Tight control of gene expression in mammalian cells by tetracycline- responsive
promoters. Proc Natl Acad Sci U S A 89, 5547-51 (1992).

Source: http://skonops.imbb.forth.gr/embo_meeting/abstracts/transposons-transgenesis/Alphey.pdf