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NEWS AND VIEWSOrganizing cytoplasmic microtubules: no nucleus, no problemTetsuya Horio and Takashi TodaCorrect organization of a polarised microtubule array is vital for eukaryotic cells. Microtubule organizing centers (MTOCs) are generally believed to have an essential role in this process. However, two papers published in this issue have demonstrated that in fission yeast, interphase microtubules can self-organize in anucleate cells lacking any authentic MTOC.MTOCs are thought to nucleate the majority of microtubules and thus have a dominant role in organizing the microtubule arrays. Artificially removing centrosomes, the major MTOCs in animal cells, does result in disruption of the interphase cytoplasmic array of the microtubules. However, the microtubules in these cells eventually form asters, which can assemble functional spindles1. It is also well established that mitotic bipolar spindles can self-organize in the absence of centrosomes2. In addition, organized acentrosomal microtubules in interphase have been observed in many systems3. Although there is evidence that microtubules self-organize without centrosomes, the lack of experimental tools have made it difficult to analyse where these microtubules are initially nucleated and whether they exhibit the same properties as centrosomal microtubules.In fission yeast, several arrays of interphase cytoplasmic microtubules run in parallel along the longitudinal axis of the cell. In a single microtubule array, bundles of a few microtubules are oriented in an anti-parallel manner with their plus ends towards the tip of the cell and overlapping in the middle of the cell at their minus ends. Three types of cytoplasmic MTOCs are known to exist. The first is the spindle pole body (SPB), which is considered to be equivalent to the centrosome of animal cells. During interphase, SPBs are located outside the nuclear membrane and nucleate some of the cytoplasmic microtubules. The second type is the eMTOC (equatorial MTOC) that is formed transiently at the cell equator in late mitotic phase. eMTOCs release cytoplasmic microtubules after mitosis, subsequently disappear and are only re-established in the next cell cycle. The third type are called iMTOCs (interphase MTOCs) and they predominantly localise to the outer surface of the nuclear Normal celliMTOCsAnucleate cellBinucleate cellCell in late mitosis CytokinesisFigure 1 Microtubule organizing centers in fission yeast and generation of anucleate cells. Schematic representation of the organization of the microtubules in a normal cell. Three types of MTOCs...