PldB, a Putative Phospholipase D Homologue, Mediates Quorum Sensing in Dictyostelium discoideum Development

PldB, a Putative Phospholipase D Homologue, Mediates Quorum Sensing in Dictyostelium discoideum Development by Yi Chen Adviser: Derrick Brazill, Ph.D. Quorum sensing, the ability to measure the local cell density, is required for animal cells to achieve proper cell growth, differentiation and development. However, because of the genetic intractability of mammalian cells, we study quorum sensing in the genetically pliable unicellular eukaryote Dictyostelium discoideum. D. discoideum cells live as individual cells under vegetative conditions. Starvation sets off development to a multicellular organism. But cells won’t develop unless enough cells are under starvation conditions. Approximately 10 cells are needed to form a fruiting body, the final stage of the development. When starved, cells are able to calculate the concentration of surrounding starving cells by simultaneously secreting and sensing a glycoprotein named conditioned medium factor (CMF). A high density of starving cells results in a high level of CMF, which allows cell aggregation and development. Here, we describe the role of a putative phospholipase D (PLD) homologue, PldB, in quorum sensing pathways. PldB is present during early development when quorum sensing is occurring as well as in later development. pldB ̄ cells can aggregate at low cell density. This phenotype is cell autonomous. Cells overexpressing pldB are unable to aggregate or form fruiting bodies even at high cell density. These observations imply that PldB is involved in quorum