PROJECT SUMMARY/ABSTRACT Cytokinesis is the final step in mitosis and facilitates the physical cleavage of one cell into two daughter cells. Animal cells achieve cytokinesis through the constriction of a cortical actomyosin contractile ring that forms around the cell equator between the segregating chromosomes. Failure of cytokinesis can lead to the formation of tetraploid cells that are thought to be an important intermediate in tumorigenesis. To ensure equal partitioning of the genetic material, contractile ring assembly is controlled by the anaphase spindle. The anaphase spindle sends two superimposed signals that pattern the contractility of the overlying cortex; a signal from the central spindle that forms between the separating chromosomes promotes contractility of the equatorial cortex, and a signal from the centrosomal microtubule asters suppresses contractility of the non-equatorial cortex. Recent work in C. elegans in my sponsor lab has implicated the mitotic kinase Aurora A in suppressing the accumulation of contractile ring proteins on the non-equatorial cortex. However, whether this function of Aurora A is conserved in human cells and the identity of the Aurora A target sites that mediate suppression of cortical contractility are currently unknown. In the proposed work, I will determine whether the role of Aurora A in patterning cortical contractility is conserved in human cells, use molecular replacement techniques in C. elegans to identify the targets of Aurora A-mediated suppression of cortical contractility, and determine how Aurora A suppression of contractility is integrated with central spindle promotion of contractility to pattern contractile ring formation. In Aim1, I will develop an assay to monitor the suppression of contractility on the non-equatorial cortex during cytokinesis in human cells and use it to determine if Aurora A has a conserved role in this process and whether ectopic targeting of Aurora A to the plasma membrane can suppress contractility. In Aim 2A, I will capitalize on the advantages the C. elegans embryo offers for molecular replacement experiments to perform an unbiased screen of cytokinesis regulators to identify the Aurora A target sites that mediate the ability of centrosomal asters to suppress cortical contractility and will test identified regulatory sites in human cells for conservation. In Aim 2B I will determine how Aurora A and central spindle-derived signals are integrated to allow for the precise specification of contractile ring location and dimensions. Collectively, this work will provide crucial insight into how Aurora A contributes to patterning cortical contractility in dividing cells. As inhibitors targeting Aurora A are currently in clinical trials as potential chemotherapeutic agents, understanding how the role of Aurora A in regulating contractility is related to its functions in tumorigenesis has the potential to impact therapeutic strategies in cancer.