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A more recent version of this article appeared on May 1, 2006
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Submitted on August 30, 2005
Revised on January 12, 2006
Accepted on February 6, 2006
*Cell Dynamics Group, Temasek Life Sciences Laboratory, 117604 Singapore, Singapore;
Department of Biological Sciences, National University of Singapore, 117543 Singapore, Singapore;
The Boulder Laboratory for 3-D Electron Microscopy of Cells, Department of MCD Biology, University of Colorado, Boulder, CO 80309
Monitoring Editor: Tim Stearns
Microtubule-organizing centers (MTOCs) concentrate microtubule nucleation, attachment and bundling factors and thus restrict formation of microtubule arrays in spatial and temporal manner. How MTOCs appear remains an exciting question in cell biology. Here we show that the TACC-related protein, Mia1p/Alp7p, functions in emergence of large MTOCs in interphase fission yeast cells. We found that Mia1p was a microtubule-binding protein that preferentially localized to the minus ends of microtubules and was associated with the sites of microtubule attachment to the nuclear envelope. Cells lacking Mia1p exhibited less microtubule bundles. Microtubules could be nucleated and bundled but were frequently released from the nucleation sites in mia1
cells. Mia1p was required for stability of microtubule bundles and persistent utilization of nucleation sites both in interphase and post-anaphase array dynamics. The
-tubulin-rich material was not organized in large perinuclear or microtubule-associated structures in mia1
cells. Interestingly, absence of microtubules in dividing wild type cells prevented appearance of large
-tubulin rich MTOC structures in daughters. When microtubule polymerization was allowed, MTOCs were efficiently assembled de novo. We propose a model where MTOC emergence is a self-organizing process requiring the continuous association of microtubules with nucleation sites.
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