The embryonic development of the Drosophila salivary glands provides several advantages for analysis of the genes involved in determination and differentiation. In the ectoderm of the germ band extended embryo, the glands begin development at a defined position which suggests the involvement of several known pattern regulating genes. Differentiation then occurs within a few hours, implying that there are few steps leading from commitment to differentiation. This proposal suggests methods to identify genes acting in the salivary glands at this early stage and to order them into a pathway for salivary gland development. Salivary gland marker genes will be identified using P-lacZ transposons that express beta-galactosidase in tissue specific patterns that include the salivary glands. Embryos homozygous for lethal transposon inserts will be examined for phenotypes that alter salivary gland development. For non-lethal inserts, mutations will be induced by imprecise transposon excision to test whether an adjacent gene is required for the development of salivary glands. For some inserts that are shown to be within or near to a gene that is important for salivary gland development, regions flanking the insert will be cloned by plasmid rescue and these regions searched for embryonic salivary gland transcripts. To get clues to gene function, exonic regions will be sequenced and examined for homology with known genes. Finally, mutations in required genes will be examined for effects on beta-galactosidase expression in several enhancer trap lines. Results form these tests will help define a pathway for embryonic salivary gland development. %%% Investigations of the genes that form patterns in early drosophila development have been spectacularly successful in solving the longstanding riddle of how a single fertilized egg cell develops the intricate and regular pattern that characterizes the mature embryo. This proposal is an attempt to extend those studies downstream to the actual formation of a differentiated organ, the salivary gland.
