The ability to sense and respond to nutrient levels in the environment is essential for the survival of organisms. One strategy employed by single cells is exemplified by Dictyostelium, which survives a food shortage by initiating a simple, yet elegant, developmental program resulting in the formation of spores. How do Dictyostelium detect that food has become limiting and then initiate their developmental program? The available data indicate that they sense changes in the levels of an uncharacterized secreted factor(s) that allow them to monitor the ratio of Dictyostelium cells to their food source, bacteria. Failure to secret this factor(s) results in a lack of response to a loss of food, and the cells do not develop spores. A Dictyostelium mutant that fails to initiate the developmental cycle because it does not secrete the critical factor(s) required for monitoring food levels has been identified. This mutant is a useful tool that will be exploited to identify the factor(s) that triggers the onset of development in Dictyostelium. Two aims will be pursued: (1) A biochemical approach will be used to isolate and fully characterize the factor; (2) The molecular basis for the mutant phenotype will be determined. The mutant gene encodes a novel type of myosin. The role of this motor protein in the secretion of a critical developmental factor will be investigated. The successful completion of this project should provide fundamentally important information about how Dictyostelium employs a secreted factor(s) to initiate development and the role of a unique myosin in the process. Identification of this triggering mechanism should then serve as a paradigm for how secreted factors are used to monitor an organism's environment as well as initiate key developmental processes. This project will provide research training for post-doctoral associates, graduate students, and undergraduates.
