Summary Cytokinesis, the physical separation of one cell into two daughter cells, is the final stage of cell division, and although it is the least well understood, it is central to development and tissue homeostasis. Correctly timing cytokinesis so that it occurs only after chromosome replication and segregation is necessary to prevent catastrophic genomic instability, and accordingly, cytokinesis is strictly regulated in concert with other cell cycle events. Using a powerful model organism, the fission yeast Schizosaccharomyces pombe, my lab has conducted pioneering research to identify proteins essential for cytokinesis and to learn how the myriad proteins that comprise the cell division machinery are coordinated to ensure the exquisite spatial and temporal control of cell division. We propose to continue our work pursuing fundamental questions in this field using a multi-disciplinary approach in two directions. In one direction, we will tackle how CK1 protein kinases are able to inhibit cytokinesis during a delay in spindle assembly by pursuing their regulation. We will determine whether CK1 activity is regulated by cell cycle cues. Understanding CK1 regulation in the context of the mitotic checkpoint will establish general mechanisms of regulation for this enzyme family, which are conserved, multifunctional kinases with roles in numerous human diseases. In a second direction, we will advance our understanding of the assembly and architecture of the contractile ring using a combination of microscopy, biochemistry, and genetics. We will continue to build our knowledge of the major scaffold of the contractile ring, the F-BAR protein Cdc15, by defining how it oligomerizes on the plasma membrane, and how other contractile ring components including the phosphatase calcineurin are organized on the Cdc15 scaffold. These focused mechanistic studies will be complemented with proteomic and genetic screens designed to establish a functional interaction network of contractile ring components. Together, these studies will have a major impact for understanding how cytokinesis is orchestrated in eukaryotic species from yeast to humans.