A detailed analysis of the expression of the Drosophila melanogaster sox70D gene during embryonic development in wild type and mutant embryos with both antibody and nucleic acid probes will characterise the role of this gene in development in terms of segmentation and neurogenesis. Conclusions from these experiments will be confirmed and extended by utilising transgenic lines in which the sox70D gene is ectopically expressed. A genetic screen for genes which interact with sox70D will be initiated by screening for suppressers and enhancers of the dominant D phenotype associated with the gene. These experiments will elucidate the role of a Sox gene in development and provide indications as to the type of gene products that Sox proteins interact with. This information will be applicable to the study of mammalian Sox genes where an description of the molecular pathways these genes are involved in is difficult to obtain.