Project Summary / Abstract Pattern formation, the spatial organization of cells of different types, is central to the development and function of metazoans. Pattern formation also occurs in microbial communities such as biofilms and colonies. For example, pattern formation is manifested by localization of different cell types to different regions of a microbial community. Formation of these patterns requires communication between individual cells, and so the first organisms to communicate were likely microorganisms within communities. From this perspective, the most ancient and fundamental mechanisms of communication on earth evolved, and still exist, in simple microorganisms. Here we propose that in the model genetic organism, Saccharomyces cerevisiae, this communication involves secreted metabolites that serve as cell-cell signals. A variety of evidence suggests that this type of communication is important in healthy and diseased human tissues. Yeast colonies are ideal for investigating pattern formation and the cell-cell signals that underlie these patterns. Two advantages of this organism are its facile genetics and the depth of knowledge we have regarding this particular species. Yeast colonies contain a thick layer of meiotic cells at the top of the colony supported by an underlying layer of feeder cells. Feeder cells are so named because they provide metabolites to the upper colony layer. A sharp boundary forms between these two layers. The focus of the proposed research is the mechanism of differential partitioning-- a change in the relative allocation of the colony, the ratio of meiotic cells: feeder cells, in response to environment (food, temperature, etc.). We propose that communities adapt to their environment by differential partitioning. Our specific aims are to determine: 1) the role of signaling pathways and their target transcription factors in regulating differential partitioning in response to environmental cues, 2) the role of secreted metabolites as a type of cell-cell communication that controls this partitioning. To achieve these aims, we will utilize several approaches. First, we will use flow cytometry to distinguish different colony subpopulations, corresponding to different cell fates, and how environmental cues and genetic mutations drive the relative allocation of these subpopulation. Second, we will determine the temporal/spatial expression of genes within colonies using fluorescent-tagged proteins and colony sectioning. Third, we will identify and characterize metabolites serving as cell-cell signals that control colony organization. The proposed research has potential connections to broader biological topics that are difficult to study in other organisms. These include biofilm pattern formation, which contributes to the pathogenicity of some yeast species, the effects of environment on development, and the role of secreted metabolites in regulating multicellular functions.