Fig. 6.

Different strategies for mitosis deployed in eukaryotes. A During closed mitosis, often observed in fungi, the mitotic spindle assembles within the nucleus. Spindle pole bodies (pink; see also Fig. 5) are integrated within the nuclear envelope (yellow) and nucleate microtubules (green) that attach and segregate the duplicated chromatids (blue) within the boundaries of an intact nuclear envelope. Nuclear pore complexes (red–orange) integrated in the nuclear envelope remain intact and functional during this process. B–D Some types of mitosis are neither strictly closed nor strictly open. In the filamentous fungus Aspergillus nidulans, but also female germline stem cells of Drosophila, the nuclear envelope remains intact during mitosis, but nuclear pore complexes partially disassemble so that tubulin monomers diffuse into the nucleus and polymerize to microtubules (B). By contrast, entry of Drosophila early embryos into mitosis is accompanied by a partial breakdown of the nuclear envelope, but with large fractions of the nuclear envelope including nuclear pore complexes remaining intact (C). In many organisms and cell types, as e.g. in Caenorhabditis elegans early embryos, upon entry into mitosis polar openings form in the nuclear envelope, which allow microtubules nucleated from cytoplasmic centrosomes to reach, attach and segregate the duplicated chromatids (D). E During open mitosis seen in many vertebrate cells and in plants, the nuclear envelope including nuclear pore complexes dis- and reassemble during mitosis to allow the formation of a cytosolic spindle apparatus formed by centrosome-nucleated microtubules (see also Fig. 5)