In the last step of cell division, a process called cytokinesis, the mother cell splits into two daughter cells. During cytokinesis a contractile actin-myosin ring forms beneath the plasma membrane around the cell equator. To coordinate cytokinesis with chromosome segregation, the contractile ring assembles in response to signals from the mitotic spindle. A stimulatory signal promotes cortical contractility by activating RhoA at the cell equator. At the same time, an inhibitory signal emanating from the centrosomal microtubule asters suppresses contractility at the cell poles. Attempts to identify the molecular basis of the inhibitory signal have been hindered by the absence of a robust assay. To address this problem, we established an assay for aster-based suppression of contractility in the C. elegans embryo. Using this assay, we identified TPXL-1, the homologue of TPX2, to be essential for aster-based clearing of contractile ring proteins from the cell poles. TPXL-1 is an aurora A kinase activator that localizes to the centrosomal microtubule asters. In tpxl-1 mutant embryos the kinetochore microtubules are extremely short, which results in a short mitotic spindle at anaphase onset. To determine whether the short mitotic spindle or tpxl-1 depletion itself causes defects in aster-based suppression, we increased spindle length in tpxl-1 mutants by depleting the kinetochore component hcp-4. Rescuing spindle length in tpxl-1 mutants did not rescue the defects in aster-based suppression, suggesting that TPXL-1 has a direct role in this process. We are currently testing whether aster-based clearing of contractile ring proteins depends on the ability of TPXL-1 to activate aurora A kinase. In summary, we identified the first molecular component of the aster-based mechanism that supports contractile ring assembly by inhibiting the accumulation of contractile ring proteins at the cell poles.