Functional characterisation of selected alleles in natural populations of Drosophila melanogaster

Drosophila melanogaster initially endemic to Africa colonized the rest of the world around 10,000 years ago. These migrant populations had to adapt to new environments (e.g.: temperature, seasonal variations) and were thus under selection. Using hitchhiking mapping, three regions of the X chromosome were shown to have undergone a selective sweep associated with the habitat expansion of Drosophila melanogaster. The more detailed study of one of them revealed that two fragments containing the neighbouring genes cramped (crm) and synthaxin4 (syx4) show the strongest reduction in variability in non-African Drosophila (7.8 and 8.1 fold). Four substitutions not observed in African flies have been fixed in European flies in cramped (crm) and syntaxin4 (syx4). Preliminary results show that crm is differentially expressed in African and European flies, while no differences were found for syx4 . crm represents therefore a promising candidate. It is a member of the Polycomb group genes well known for their roles in the maintenance of the expression pattern of developmental genes. Population genetic approaches do not provide further information on which mutation (s) has (have) caused the selective advantage. The goal of this project is to test functionally the effects of these substitutions using drosophila genetics and in particular transgenesis. The expression profile of European and African crm alleles will be characterise in detail using both real-time PCR and in situ hybridization. Furthermore, we will attempt to characterize the effect of different crm alleles by studying the interaction with other Polycomb group genes. Finally, we will characterize the binding properties of different Crm alleles. In order to identify the beneficial mutation(s), transgenic flies baring different combinations of the candidate alleles will be tested.