During the first meiotic division, homologous chromosomes linked by chiasmata interact with the spindle microtubules and segregate to opposite poles. Defects in this process lead to aneuploidy in the fertilized egg and have serious consequences on development, often resulting in death of the developing embryo. In humans, aneuploidy is a leading cause of spontaneous abortions and infertility in women. If aneuploids do survive, they manifest with diseases such as Down's, Tumer's or Klinefelter's syndrome. In many organisms, including humans and flies, the female meiotic spindle lacks centrioles and the classical microtubule-organizing center at the poles. The centrosomes and their constituent proteins are usually thought to organize bipolar spindles and therefore, in female meiosis, spindle pole organization must occur by a novel mechanism. By utilizing the powerful genetic and cytological techniques available in studies involving Drosophila melanogaster females, it is our long-term goal to elucidate the mechanism by which acentrosomal meiotic spindles form and how they function to segregate the chromosomes. We have found that the subito (sub) gene is required for bipolar spindle formation and homolog segregation during female meiosis in Drosophila. The findings that sub encodes a kinesin-like motor protein and is required during early embryogenesis and male meiosis has stimulated several new experiments. The aims of this study are to identify the role of SUB in spindle formation and understand how the meiotic spindle forms and functions to segregate chromosomes in the absence of centrosomes. A combination of genetic, immunological and cytological techniques will be used to illuminate the functions of SUB. These studies will investigate three critical areas of spindle biology by: 1) determining the subcellular localization of the sub protein in meiotic spindles and characterize how SUB interacts with the microtubules, 2) determining what other proteins interacts with SUB, and 3) using live imaging techniques to investigate the mechanism of spindle pole formation through a real time analysis of meiosis and mitosis in wild-type and mutants. The results of these studies will provide insights into the mechanisms of spindle formation and homolog segregation during meiosis and mitosis.