A novel role for cytokinesis proteins in acentrosomal spindle assembly and chromosome segregation in Drosophila oocytes. Arunika Das¹, Shital J. Shah², Kim S. McKim¹. 1) Waksman Institute, Rutgers University, NJ; 2) New Jersey Medical School, Newark.

   Accurate segregation of chromosomes is facilitated by the formation of a bipolar array of microtubules called the spindle. In mitotic spindle assembly, the centrosomes define the poles and organize the microtubules. In the oocytes of many animals, however, the centrosomes are absent and consequently it is poorly understood what organizes the bipolar spindle and directs the chromosomes to become attached to the microtubules, a process known as bi-orientation. Previous studies have shown that the chromosome passenger complex (CPC) is the master regulator of spindle assembly. The CPC is composed of four proteins, Incenp, Aurora B kinase, Survivin and Borealin. Unlike mitotic cells, where the CPC localizes to centromeres during metaphase, during meiotic metaphase it localizes in a ring around the chromosomes. This novel localization pattern is responsible for building a bipolar spindle and establishing bi-orientation. Our goal is to identify regulators of acentrosomal spindle assembly and CPC localization. An unbiased screen was performed based on synthetic lethal mutations with subito. Subito belongs to kinesin 6 family and is required for localizing the CPC to the ring in meiosis. We uncovered tumbleweed from this screen which is a regulator of cytokinesis like the CPC. We investigated other proteins in the cytokinesis pathway which interact with tum and the CPC. This study has revealed that Rho-1 and its downstream effector Sticky both regulate acentrosomal spindle assembly but do not seem to function in a similar manner. Sticky also helps to establish bi-orientation similar to the CPC. These results suggest that these proteins function in meiosis but may not act according to the pre-defined pathway. We are also testing several candidate genes like Haspin kinase, Tousled-like kinase and Shugoshin, which regulate CPC localization during mitosis. We have found that tlk regulates in spindle assembly and regulates CPC localization and homolog bi-orientation.