Profiling gene expression in spermatogenesis in model and pest insects

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A major challenge for modern agriculture is to control pest species while minimising the adverse consequences to the environment. Insect pests cause significant economic damage, either by eating the crop or reducing quality such that the crop is not marketable. Insects also act as disease vectors, transmitting human and animal pathogens as well as plant diseases. The Sterile Insect Technique (SIT) is an effective, species-specific and environmentally friendly method for controlling pest populations. SIT involves releasing millions of sterile insects over a wide area to mate with the native insects that are present. Native females that mate with the sterile males produce non viable offspring, leading to a decline in the target pest population. In classical SIT, insects are sterilised with irradiation which reduces the competitiveness of the released insects and is too damaging to be applied to many insect species. Oxitec, the industrial partner for this research project, has demonstrated that major improvements are possible through the use of genetically engineered insects. The genetically engineered insects carry an easily identifiable marker (so they can be distinguished from wild animals), can be readily sorted into males vs females and produce inviable offspring unless fed a dietary supplement (in the factory). Ideally the released flies would be inherently male sterile. Also ideally the sperm from factory-reared released males would be marked so it would be possible to easily discern whether any particular wild female had mated with a wild male or a released male. The fruit fly Drosophila melanogaster is a harmless insect that has been a mainstay of genetics research for the last century. Research on Drosophila as a model organism has informed research in human disease biology as well as in understanding the biology of pest insects. In Drosophila we can express any gene we like in almost any cell, with the notable exception of certain spermatogenesis stages. Analysis of gene function in Drosophila spermatogenesis has been hampered by our lack of ability to express genes at will during this process. Many genes are expressed during sperm production, and, while significant progress has been made in determining their functions, more sophisticated genetic manipulation techniques will greatly facilitate further functional analyses. In this project we will investigate gene expression patterns in various stages of sperm formation in the model insect Drosophila melanogaster and in two insect pests, Ceratitis capitata (Mediterranean fruit fly) and Aedes aegypti (Yellow fever mosquito). We will dissect the testes and determine gene expression profiles at various stages of the sperm production process for all three species. The data from Drosophila will extend our current understanding to give much more stage specific information. For the pest insect species our project will be first genome scale analysis of gene expression in spermatogenesis. At the end of the project we will have generated profiles of gene expression levels during spermatogenesis in the three species. We will have defined the precise transcript structures of many testis-expressed genes, thus our data will inform genome annotations for all three species. We will select some testis-expressed genes for further validation, and will generate lines of insects that allow us to express any gene of our choice specifically in the cells of the testes. This will facilitate both the basic research of the academic lab (and other Drosophila labs worldwide) and the applied research of the industrial partner in developing sterile male insects for population control strategies.