Novel developmental functions of the Drosophila SOX gene Dichaete

All multicellular life begins as a single cell---the fertilised egg, from which the adult organism develops. As a general priniciple, as embryos progess through development, changes in cellular status seem to be effected by cell specific transcription factors which regulate specific gene subsets.;The SOX (Sry box) family of transcription factors are one such developmentally important class of transcription factors, consisting of twenty mammalian proteins that each contain a single High Mobility Group (HMG) DNA binding domain that is >50% homologous to that of Sry, the mammalian testes determining factor. SOX proteins are multi-functional developmental regulators that sequence specifically bind DNA, and can function both as classical transcription factors and as architectural components of chromatin (Kiefer et al. 2007, Lefebvre et al. 2007).;We have been modeling SOX gene function using the Drosophila SOX gene Dichaete (D). D has similar biochemical properties to mammalian SOX proteins, and is essential for embryonic segmentation and cell fate specification (Ma et al. 1998, Russell et al. 1996). In this thesis I detail novel functions of D in oogenesis and adult olfactory system development.;Chapter two details D expression and function during oogenesis in Drosophila. We show that D is transiently expressed in the oocyte cytoplasm from region 2 of the germarium through stage 8. We demonstrate that D protein can bind gurken mRNA, which was mislocalised in D mutant egg chambers. These studies contribute to our understanding of the establishment of dorsal/ventral polarity and significantly detail a cytoplasmic role for SOX proteins in binding mRNA (Mukherjee et al., 2006).;Chapter three details the expression and function of D in the adult Drosophila nervous system. I show that D is prominently expressed in a mixture of excitatory and inhibitory local neurons (LNs) and central complex ring neurons. Hypomorphic D alleles were generated, and the mutant brains exhibited misplacement and mistargeting of specific olfactory projection neurons. These data greatly enhance our understanding of the development of neuronal connectivity in a discrete neural map represented by the fly antennal lobe, and represent a detailed report of SOX gene expression in the adult brain.