The long term objective of the research proposed is to understand how the precise arrays of different cell types within an organism are generated. The question will be addressed by utilizing the legs of the Drosophila melanogaster adult as a model system. The leg bristle pattern is established in part through the functions of two genes 'hairy' and 'achaete'. In most leg segments, achaete is expressed in eight longitudinal stripes corresponding to the primordia of the bristle rows. 'Hairy' is expressed in four longitudinal stripes located between every other pair of achaete stripes and corresponding to the primordia of bristleless cuticle. The periodic expression of 'achaete' is established in part through the function of 'hairy' which represses 'achaete' expression within its domains of expression and defines one boundary of each 'achaete' longitudinal stripe. Since 'hairy' is expressed in a spatially restricted pattern that is required for the patterning of two different pattern elements, bristleless and bristled cuticle, a study of the regulation of 'hairy' expression should provide insight into the mechanisms by which leg pattern is generated. We will investigate both cis- and trans-regulatory mechanisms involved in the production of the 'hairy' leg longitudinal stripes of expression. The cis-regulatory elements that gorvern expression of the 'hairy' leg longitudinal stripes of expression will be located by both transgenic and genetic approaches. This region will be dissected to identify the minimal elements necessary for producing the 'hairy' leg stripes and to determine whether the 'hairy' leg longitudinal stripes are regulated independently or in concert. A comparative analysis of the 'hairy' leg cis- regulatory elements from Drosophila melanogaster and Drosophila virilis will be performed to identify conserved regions that may correspond to binding sites for trans- regulatory proteins. The potential function of these sequences will be tested by a mutational analysis. The possible roles of the segment polarity genes in patterning 'hairy' leg expression will be investigated by monitoring 'hairy' expression in: a) leg discs homozygous mutant for adult viable or temperature-sensitive allele segment polarity alleles, b) leg discs mosaic for null segment polarity alleles produced by FLP mediated recombination, c) leg discs misexpressing certain segment polarity genes. In addition a comparison of the 'hairy' leg stripes of expression with segment polarity gene expression will be performed. In summary, a study of the the genetic regulation of 'hairy' in the leg disc should be an excellent opportunity to learn how periodicity is generated in a cellular field and for comparison of the mechanisms for generation of striped expression in two different developmental fields.
