In Drosophila embryos, salivary glands arise from a thickened placode of cells in the ventral part of the labial segment. After the placode forms, its cells are invaginated to form a simple tubular gland. Within three hours the cells of the gland are already differentiated and producing abundant, secreted products. This simple example of organogenesis provides opportunities to examine the interaction between genes that establish the overall pattern of the embryo and those that direct tissue specific development. Dr. Beckendorf's experiments have focussed on the role of embryonic pattern forming genes in choosing the location of the salivary placodes and initiation salivary gland development. The goal of the current proposal is to identify additional genes that act downstream from the pattern forming genes to direct the morphogenesis and differentiation of the glands. Three independent approaches will be used to identify these new genes: analyzing enhancer trap lines, screening deficiency mutant embryos for salivary defects, and searching for downstream targets of the transcription factor encoded by the for head gene. These methods should identify a new set of genes that will help him characterize specific steps in salivary development. Because of the short time between initial determination and differentiation, he hopes eventually to identify many, if not all, of the intervening steps in salivary development.
