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Spindle Poles (spindle + pole)
Terms modified by Spindle Poles Selected AbstractsLive-cell analysis of mitotic spindle formation in taxol-treated cellsCYTOSKELETON, Issue 8 2008Jessica E. Hornick Abstract Taxol functions to suppress the dynamic behavior of individual microtubules, and induces multipolar mitotic spindles. However, little is known about the mechanisms by which taxol disrupts normal bipolar spindle assembly in vivo. Using live imaging of GFP-, tubulin expressing cells, we examined spindle assembly after taxol treatment. We find that as taxol-treated cells enter mitosis, there is a dramatic re-distribution of the microtubule network from the centrosomes to the cell cortex. As they align there, the cortical microtubules recruit NuMA to their embedded ends, followed by the kinesin motor HSET. These cortical microtubules then bud off to form cytasters, which fuse into multipolar spindles. Cytoplasmic dynein and dynactin do not re-localize to cortical microtubules, and disruption of dynein/dynactin interactions by over-expression of p50 "dynamitin" does not prevent cytaster formation. Taxol added well before spindle poles begin to form induces multipolarity, but taxol added after nascent spindle poles are visible,but before NEB is complete,results in bipolar spindles. Our results suggest that taxol prevents rapid transport of key components, such as NuMA, to the nascent spindle poles. The net result is loss of mitotic spindle pole cohesion, microtubule re-distribution, and cytaster formation. Cell Motil. Cytoskeleton 2008. © 2008 Wiley-Liss, Inc. [source] Dynamics of the endoplasmic reticulum during early development of Drosophila melanogasterCYTOSKELETON, Issue 3 2003Yves Bobinnec Abstract In this study, we analyze for the first time endoplasmic reticulum (ER) dynamics and organization during oogenesis and embryonic divisions of Drosophila melanogaster using a Protein Disulfide Isomerase (PDI) GFP chimera protein. An accumulation of ER material into the oocyte takes place during the early steps of oogenesis. The compact organization of ER structures undergoes a transition to an expanded reticular network at fertilization. At the syncytial stage, this network connects to the nuclear envelope as each nucleus divides. Time-lapse confocal microscopy on PDI transgenic embryos allowed us to characterize a rapid redistribution of the ER during the mitotic phases. The ER network is massively recruited to the spindle poles in prophase. During metaphase most of the ER remains concentrated at the spindle poles and shortly thereafter forms several layers of membranes along the ruptured nuclear envelope. Later, during telophase an accumulation of ER material occurs at the spindle equator. We also analyzed the subcellular organization of the ER network at the ultrastructural level, allowing us to corroborate the results from confocal microscopy studies. This dynamic redistribution of ER suggests an unexpected regulatory function for this organelle during mitosis. Cell Motil. Cytoskeleton 54:217,225, 2003. © 2003 Wiley-Liss, Inc. [source] Spindle pole fragmentation due to proteasome inhibitionJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2005Anka G. Ehrhardt During interphase, the centrosome concentrates cell stress response molecules, including chaperones and proteasomes, into a proteolytic center. However, whether the centrosome functions as proteolytic center during mitosis is not known. In this study, cultured mammalian cells were treated with the proteasome inhibitor MG 132 and spindle morphology in mitotic cells was characterized in order to address this issue. Proteasome inhibition during mitosis leads to the formation of additional asters that cause the assembly of multipolar spindles. The cause of this phenomenon was investigated by inhibiting microtubule-based transport and protein synthesis. These experimental conditions prevented the formation of supernumerary asters during mitosis. In addition, the expression of dsRed without proteasome inhibition led to the fragmentation of spindle poles. These experiments showed that the formation of extra asters depends on intact microtubule-based transport and protein synthesis. These results suggest that formation of supernumerary asters is due to excessive accumulation of proteins at the spindle poles and consequently fragmentation of the centrosome. Together, this leads to the conclusion that the centrosome functions as proteolytic center during mitosis and proteolytic activity at the spindle poles is necessary for maintaining spindle pole integrity. © 2005 Wiley-Liss, Inc. [source] Role of AMPK throughout meiotic maturation in the mouse oocyte: Evidence for promotion of polar body formation and suppression of premature activationMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 10 2010Stephen M. Downs Abstract This study was conducted to assess the role of AMPK in regulating meiosis in mouse oocytes from the germinal vesicle stage to metaphase II. Exposure of mouse cumulus cell-enclosed oocytes (CEO) and denuded oocytes (DO) during spontaneous maturation in vitro to AMPK-activating agents resulted in augmentation of the rate and frequency of polar body formation. Inhibitors of AMPK had an opposite, inhibitory effect. In addition, the AMPK inhibitor, compound C (Cmpd C) increased the frequency of oocyte activation. The stimulatory action of the AMPK-activating agent, AICAR, and the inhibitory action of Cmpd C were diminished if exposure was delayed, indicating an early action of AMPK on polar body formation. The frequency of spontaneous and Cmpd C-induced activation in CEO was reduced as the period of hormonal priming was increased, and AMPK stimulation eliminated the activation response. Immunostaining of oocytes with antibody to active AMPK revealed an association of active kinase with chromatin, spindle poles, and midbody during maturation. Immunolocalization of the ,1 catalytic subunit of AMPK showed an association with condensed chromatin and the meiotic spindle but not in the spindle poles or midbody; ,2 stained only diffusely throughout the oocyte. These data suggest that AMPK is involved in a regulatory capacity throughout maturation and helps promote the completion of meiosis while suppressing premature activation. Mol. Reprod. Dev. 77:888,899, 2010. © 2010 Wiley-Liss, Inc. [source] A CH domain-containing N terminus in NuMA?PROTEIN SCIENCE, Issue 10 2002Maria Novatchkova Abstract Nuclear mitotic apparatus protein (NuMA) is an essential vertebrate component in organizing microtubule ends at spindle poles. The NuMA-dynactin/dynein motor multiprotein complex not only explains the transport of NuMA along spindle fibers but also is linked to the process of microtubule focusing. The interaction sites of NuMA to dynein/dynactin have not been mapped. In the yet functionally uncharacterized N terminus of NuMA, we predict a calponin-homology (CH) domain, a motif with binding activity for actin-like molecules. We substantiate the primary sequence analysis-based prediction with secondary structure and fold recognition analysis, and we propose the N-terminal CH domain of NuMA as a likely interaction site for actin-related protein 1 (Arp1) protein of the dynactin/dynein complex. [source] Golgi biogenesis in simple eukaryotesCELLULAR MICROBIOLOGY, Issue 3 2007Cynthia Y. He Summary The accurate duplication of cellular organelles is important to ensure propagation through successive generations. The semi-conserved replication of DNA and DNA-containing organelles has been well studied, but the mechanisms used to duplicate most other organelles remain elusive. These include the centrosomes, which act as microtubule organizing centres during interphase and orient the mitotic spindle poles during mitosis. Centrosomes can also act as basal bodies, nucleating the growth of cilia or flagella. Even less understood are the mechanisms used to duplicate membrane-bound organelles that do not contain DNA. These include organelles involved in the secretory pathway such as the endoplasmic reticulum and the Golgi apparatus. This review will summarize the current knowledge of Golgi biogenesis in simple eukaryotic organisms, in particular, two protozoan parasites, Toxoplasma gondii and Trypanosoma brucei. [source] | ||||||||||