A Mira-GFP screen : looking for missing genes in bicoid mRNA localisation

During Drosophila oogenesis, bicoid mRNA is localised to the anterior of the oocyte, where it is translated after egg deposition to pattern the head. However, only a few genes involved in the bcd mRNA localisation have been identified in classic genetic screens. In this thesis, I describe a genetic screen for suppressors of Miranda-GFP, which was designed to identify missing genes required for the bcd mRNA localisation. Mira is not endogenously expressed during oogenesis. However, when Mira-GFP is expressed in the female germ line, the resulting embryos show a maternal-effect lethal bicaudal phenotype. oskar mRNA is localised to both anterior and posterior ends of these embryos and co-localises with Staufen to both ends of the oocyte. Stau is double-strand RNA binding protein and is required for osk and bcd mRNA localisation during oogenesis and asymmetrical prospero mRNA localisation in neuroblasts. Mira functions as an adaptor to couple Stau/pros mRNA to the basal side of neuroblasts. Mutants in genes required for bcd mRNA localisation, such as exuperantia and swallow, suppress the Mira-GFP bicaudal phenotype. Osk mRNA diffuses from the anterior of these oocytes in a similar way to bcd mRNA, indicating that Mira-GFP couples Stau/osk mRNA to the anterior localisation pathway. I further confirmed this by showing that the anterior localisation of Mira-GFP is microtubule-dependent, like bcd mRNA. In order to find genes required for bcd mRNA localisation, I performed a screen for dominant suppressors of the Mira-GFP bicaudal phenotype. I have identified and characterised a number of interesting mutants from this screen, and have shown that several of them cause defects in bcd mRNA localisation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo