Abstract

Cell division is a fundamental biological event that underlies the growth and development of all organisms. Because human and fission yeast (Schizosaccharomyces pombe) cells divide symmetrically through constriction of the actomyosin ring, fission yeast provides an ideal model system to reveal conserved cell cycle properties. In fission yeast, an evolutionarily conserved protein, Mid1, plays a critical role in organizing the early steps of contractile ring formation. Mid1 functions as a scaffold to bridge the cell cortex with the contractile ring. Cells lacking mid1 form off-centered, highly disorganized ring structures and exhibit severe cell division defects. Our previous research demonstrates that cyclin-dependent kinase, Cdc2, and the polo-like kinase, Plo1, directly phosphorylate Mid1. This phosphorylation event potentially functions in Mid1 regulation. To examine Mid1 phospho-regulation, phospho-site mutants were generated at the endogenous mid1 locus. Phosophorylation sites on Mid1 were mutated to alanine to prevent potential phosphorylation and strains containing this mutation were examined for cell cycle defects. Interestingly, phospho-site mutants progressed through mitosis significantly faster than wild-type cells. Current studies focus on the consequence of treating phospho-site mutants with microtubule and actin destabilizing agents.