DSSS - When 1+1 is 1: Mechanisms of cell-cell fusion in the fission yeast

Sexual reproduction is ubiquitous amongst eukaryotes. This requires alternation of cell-cell (gamete) fusion and genome reduction through meiosis. My lab has been using the yeast sexual reproduction pathway to study how cells polarize to find a mate and mount a fusion reaction. In the fission yeast Schizosaccharomyces pombe, sexual reproduction occurs between P and M cells, which communicate through pheromone-GPCR-MAPK signaling, driving the formation of cell pairs. Transition from gametes to zygote involves local cell wall digestion at the point of gamete contact, while preserving cell integrity. We have shown that cell-cell fusion requires the actin fusion focus, an aster-like assembly of linear actin filaments assembled by the formin Fus1, which concentrates both signaling molecules and secretory vesicles carrying cell wall digestion enyzmes. I will present our recent work exploring the molecular mechanisms of formation of the actin fusion focus, which require both formation of a formin biomolecular condensate and cytoskeletal focusing through formin-myosin feedback. I will also describe our progress in understanding the roles of local MAPK and PAK signaling for cells to pierce their cell wall once and only once.