Cell division is a universal cellular process responsible for the proliferation and differentiation of cells. After the chromosomes are faithfully segregated during mitosis, cells undergo cytokinesis, where one cell divides into two. Cytokinesis in many eukaryotes requires a structure known as the contractile ring, which contains actin, myosin and many other proteins assembled just beneath the plasma membrane. In this thesis, I present my studies on the function and organization of this ring. I used the powerful genetically tractable model organism the fission yeast Schizosaccharomyces pombe to study these processes in cytokinesis. First, I showed that one function of the cytokinetic ring is to regulate the assembly of the septum cell wall in a curvature dependent manner, suggesting a mechanosensitive mechanism. Second, I analyzed the substructure organization of the proteins within the ring, showing that ring proteins are arranged in clusters and in different layers. Finally, in a collaborative project, I studied the arrangement of chromosomes within the nucleus, and identified a protein required for linking centromeres to the spindle pole body at the nuclear envelope.

In general, my thesis provides new insights into the spatial mechanisms of cytokinesis and chromosome organization.