On the right, a preblastoderm embryo is punctured for extraction and deposition of cytosol on the coverslip using a micropipette, thereby generating a series of embryo explants. (A) Schematic showing a Drosophila syncytial embryo immobilized to the coverslip and covered with a thin layer of halocarbon oil ready for time-lapse microscopy. Enabled by a novel experimental approach, our study illuminates an essential process of embryonic multicellularity.įeo, Klp3A, and Klp61F localization confirm antiparallel microtubule overlaps between asters of nonsister nuclei. We conclude that Feo and Klp3A cross-linking of antiparallel microtubule overlap generates a length-regulated mechanical link between neighboring microtubule asters.
A dimerization-deficient Feo abolishes nuclear separation in embryo explants, while the full-length protein rescues the genetic knockdown. A minimal internuclear distance is maintained in explants from control embryos but not from Feo-inhibited embryos, following micromanipulation-assisted repositioning. Germline knockdown causes irregular, less-dense nuclear delivery to the cell cortex and smaller distribution in ex vivo embryo explants. Here, we show that microtubule cross-linking by Feo and Klp3A is essential for nuclear distribution and internuclear distance maintenance in Drosophila. Contemporary hypotheses propose actomyosin-driven cytoplasmic movement transporting nuclei or repulsion of neighbor nuclei driven by microtubule motors. Mechanistic insight for nuclear positioning beyond cytoskeletal requirements is missing. The early insect embryo develops as a multinucleated cell distributing the genome uniformly to the cell cortex.