Three independent mechanisms of cell-cell adhesion function during development of Dictyostelium discoideum. The early adhesion system is mediated by a small protein, gp24, that first appears on the surface of cells several hours after initiation of development and preferentially accumulates in prestalk cells. There are three closely linked genes, csbA, csbB, and csbC, encoding gp24 that appear to be functionally redundant. Transformed cell lines in which one or two of these genes are deleted show alterations in early adhesion. Moreover, cells lacking csbC culminate only after a considerable delay and form gnarled fruiting bodies. Dr. Loomis will use homologous recombination to replace all three csb loci with a transformation vector carrying the pyr5-6 gene. The phenotype of the resulting strains will be analyzed in detail to determine the consequences to cell-cell adhesion and subsequent development. He will genetically rescue these triple deletion strains by transformation with a wild-type copy of one or more of the csb genes and then explore the molecular mechanism of adhesion by determining the functionality of variants generated by site specific mutagenesis. Using Restriction Enzyme Mediated Integration (REMI) to tag developmentally important genes, he will isolate and characterize other genes essential for cell-cell adhesion during early development.
