9418119 Kuhn It is proposed to establish by immunocytochemistry the precise embryonic expression patterns for genes required in the tail region of Drosophila melangaster. A hierarchy of gene function will be established by examining how null mutants for the different genes affect the distribution patterns of genes expressed in different regions of the tail. The normal embryonic segment/parasegment distribution patterns for the genes will be compared to the expression patterns of the same genes in the larval genital disc in order to determine the extent to which each embryonic tail segment contributes to the sexually dimorphic genital disc. Clonal analysis will be used to define the segment borders in the genital disc and in the adult genitalia. Finally, the adult transformations caused by mutant genes with homeotic phenotypes will be examined to establish how each gene contributes to the identity of the adult tail region. Since null mutants for all of these genes are early lethals, the homeotic transformations will be studied by mitotic recombination in clones of mutant cells. %%% Drosophila melanogaster provides a superb animal model for studying the gene network required to take the animal from a single cell to a differentiated multicellular organism. The goal of this study is to determine how the early acting pair rule genes, segment polarity genes, homeotic selector genes and other genes with homeotic phenotypes contribute to formation of the tail segments (defined as abdominal segments A8 through A11). Whereas the segmental organization of the thorax and anterior abdomen is morphologically delineated in the Drosophila larva and adult, tail segments lack such well-defined boundaries. Thus, the organization of the tail region has been difficult to decipher. Results from these studies will help us understand how the Drosophila tail segments form and how the segments have been genetically modified through evolutionary time into the specialized female and male genitalia. The lesson s learned in Drosophila may provide some insights into how some of these same genes developmentally interact in the tail region of more complex organisms where they are also expressed. ***
