COPI-mediated membrane trafficking is required for cytokinesis in Drosophila male meiotic divisions

The coatomer protein complex, COPI, mediates retrograde vesicle transport from the Golgi apparatus to the ER. Here, we investigated the meiotic phenotype of Drosophila melanogaster spermatocytes expressing dsRNA of 52 genes encoding membrane-trafficking-related factors. We identified COPI as an essential factor for male meiosis. In Drosophila male meiotic divisions, COPI is localized in the ER-Golgi intermediate compartment of tER-Golgi units scattered throughout the spermatocyte cytoplasm. Prior to chromosome segregation, the vesicles assemble at the spindle pole periphery through a poleward movement, mediated by minus-end motor dynein along astral microtubules. At the end of each meiotic division, COPI-containing vesicles are equally partitioned between two daughter cells. Our present data strongly suggest that spermatocytes possess a regulatory mechanism for equal inheritance of several types of membrane vesicles. Using testis-specific knockdown of COPI subunits or the small GTPase Arf or mutations of the gamma COP gene, we examined the role of COPI in male meiosis. COPI depletion resulted in the failure of cytokinesis, through disrupted accumulation of essential proteins and lipid components at the cleavage furrow region. Furthermore, it caused a reduction in the number of overlapping central spindle microtubules, which are essential for cytokinesis. Drosophila spermatocytes construct ER-based intracellular structures associated with astral and spindle microtubules. COPI depletion resulted in severe disruption of these ER-based structures. Thus, we propose that COPI plays an important role in Drosophila male meiosis, not only through vesicle transport to the cleavage furrow region, but also through the formation of ER-based structures.