9306704 Botas One of the least understood problems in Drosophila developmental genetics is the specification of segmental identity by homeotic selector genes. What are the functions of target genes of homeoproteins? What are the specific control elements through which homeoproteins exert their identity functions? What are the molecular bases for the phenomena of phenotypic suppression? By addressing these questions, this work will provide insight into how homeotic selector genes control morphogenesis. decapentaplegic (dpp) is under homeotic control. dpp expression in parasegment 7 of the embryonic visceral mesoderm (vm) requires normal function of Ultrabithorax (Ubx); in addition, ectopic expression of Ubx leads to ectopic expression of dpp. Ubx protein (UBX) binds to the dpp site in polytene chromosomes. A 600 base pare dpp enhancer (vm-en), identified by immunoprecipitation with purified UBX, confers regulation by Ubx in the vm. Two adjacent UBX binding sites in vm- en have been defined by DNAse I footprinting. Sequences in vm-en required for enhancer function will be defined by deletion analysis. Site directed mutagenesis will be carried out to determine: 1) the function of UBX binding sites in vivo and 2) whether UBX regulates dpp directly. Lack of function mutations in either Ubx or dpp disrupt midgut morphogenesis by causing the lack of the second midgut constriction. A vm-en dpp transgene able to rescue this mutant dpp phenotype has been constructed. This transgene will be used to investigate directly the role of specific vm-en sequences, including the UBX binding sites, in midgut morphogenesis. abdominal-A (abd-A) completely represses dpp in parasegment 8 of the vm. This repression is also conferred by vm-en but is not a consequence of abd-A repressing Ubx. Hence, the vm-en is an ideal tool to investigate a general phenomena of epistasis among homeotic proteins known as phenotypic suppression. A 450- base pair dpp embryonic ectoderm enhancer (ee-en) has also been identified by immunoprecipitation with UBX and the possible function of dpp in PNS development and the roles of ee-en and its homeodomain binding sites will be studied. The investigation of the control of segment-specific morphogenesis by Drosophila homeoproteins is likely to be of general interest because of the evolutionary conservation of homeotic/Hox genes from Drosophila to humans. The control of segment specific functions of dpp by homeotic genes is particularly relevant because many proteins of the TGF-beta family have been implicated in a variety of essential developmental functions in vertebrates. ***
