THE MICROTUBULE MOTOR CYTOPLASMIC DYNEIN IS REQUIRED FOR SPINDLE ORIENTATION DURING GERMLINE CELL DIVISIONS AND OOCYTE DIFFERENTIATION IN DROSOPHILA

During animal development cellular differentiation is often preceded b y an asymmetric cell division whose polarity is determined by the orie ntation of the mitotic spindle. In the fruit fly, Drosophila melanogas ter, the oocyte differentiates in a 16-cell syncytium that arises from a cystoblast which undergoes 4 synchronous divisions with incomplete cytokinesis. During these divisions, spindle orientation is highly ord ered and is thought to impart a polarity to the cyst that is necessary for the subsequent differentiation of the oocyte. Using mutations in the Drosophila cytoplasmic dynein heavy chain gene, Dhc64C, we show th at cytoplasmic dynein is required at two stages of oogenesis. Early in oogenesis, dynein mutations disrupt spindle orientation in dividing c ysts and block oocyte determination. The localization of dynein in mit otic cysts suggests spindle orientation is mediated by the microtubule motor cytoplasmic dynein. Later in oogenesis, dynein function is nece ssary for proper differentiation, but does not appear to participate i n morphogen localization within the oocyte. These results provide evid ence for a novel developmental role for the cytoplasmic dynein motor i n cellular determination and differentiation.