669B Poster - 10. Cell biology: Cytoskeleton, organelles and trafficking
Friday April 08, 2:00 PM - 4:00 PM

Authors:
Lingkun Gu; Mo Weng

Affiliation: University of Nevada, Las Vegas

Keywords:
i. cellular organelles; d. compartments and boundaries

Nuclei are often actively positioned for specialized cellular functions or developmental purposes and failures in correct positioning can lead to dysfunctions and defects. Early embryos of Drosophila melanogaster are tasked with positioning hundreds of nuclei because the embryogenesis begins with 13 synchronized nuclear divisions within a syncytium. Although nuclei initially localize in the anterior half of the embryo, during nuclear cycle 4-6, they are evenly spread along the anterior-posterior axis in an actomyosin-dependent process called axial expansion. Then, during cycle 7-9, nuclei migrate and distribute evenly in the syncytial cortex, followed by the last four nuclear divisions. The even nuclear spacing ensures that cells of similar sizes are generated during the cleavage stage. However, the molecular mechanisms of axial expansion and cortical migration are still poorly understood. Here, we identify a plasma membrane-associated kinase gilgamesh (gish) as an important player in this complex process. gish-depleted embryos show defects in axial expansion: nuclear spreading to the posterior half of the embryo is delayed and the nuclei preferentially localize to the anterior half. Interestingly, the nuclei also show premature localization to the syncytial cortex, suggesting gish may be involved in the positioning of active myosin or in a mechanism that balances myosin-induced cytoplasmic flow. During the last four nuclear divisions on the cortex, gish depletion leads to defects in mitotic furrow formation, which further disrupts nuclear spacing and is accompanied by desynchronization of the nuclear cycle. In summary, we show that gish is required for the even positioning of nuclei in fly syncytium at multiple stages.