809 Phospho-regulation of the anillin-related scaffolding protein, Mid1


cell division, fission yeast




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 cytokinesis properties. In fission yeast, an evolutionarily conserved protein, Mid1, plays a critical role in organizing the early steps of contractile ring formation and 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 cytokinesis defects. Coincident with its cortical accumulation, Mid1 becomes hyper-phosphorylated. Our previous research demonstrates that cyclin-dependent kinase, Cdc2, and the polo-like kinase, Plo1, directly phosphorylate Mid1. In addition to consensus phosphorylation motifs for Plo1 and Cdc2, Mid1 contains several RXXS motifs, which fits the phosphorylation consensus sequence for Sid2 kinase. Sid2 is the most downstream kinase in the SIN signaling cascade, which signals from the spindle pole body to trigger constriction of the contractile ring. To examine Mid1 phospho-regulation, phospho-site mutants were generated at the endogenous mid1 locus and examined for cell division 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.

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