scholarly journals Localized accumulation of tubulin during semi-open mitosis in the Caenorhabditis elegans embryo

2012 ◽  
Vol 23 (9) ◽  
pp. 1688-1699 ◽  
Author(s):  
Hanako Hayashi ◽  
Kenji Kimura ◽  
Akatsuki Kimura
Keyword(s):  
Caenorhabditis Elegans ◽  
Nuclear Envelope ◽  
Mitotic Spindle ◽  
Fluorescence Recovery After Photobleaching ◽  
Spindle Assembly ◽  
Small Gtpase ◽  
Microtubule Assembly ◽  
C Elegans ◽  
Nuclear Envelope Breakdown ◽  
Mitotic Spindle Assembly

The assembly of microtubules inside the cell is controlled both spatially and temporally. During mitosis, microtubule assembly must be activated locally at the nascent spindle region for mitotic spindle assembly to occur efficiently. In this paper, we report that mitotic spindle components, such as free tubulin subunits, accumulated in the nascent spindle region, independent of spindle formation in the Caenorhabditis elegans embryo. This accumulation coincided with nuclear envelope permeabilization, suggesting that permeabilization might trigger the accumulation. When permeabilization was induced earlier by knockdown of lamin, tubulin also accumulated earlier. The boundaries of the region of accumulation coincided with the remnant nuclear envelope, which remains after nuclear envelope breakdown in cells that undergo semi-open mitosis, such as those of C. elegans. Ran, a small GTPase protein, was required for tubulin accumulation. Fluorescence recovery after photobleaching analysis revealed that the accumulation was accompanied by an increase in the immobile fraction of free tubulin inside the remnant nuclear envelope. We propose that this newly identified mechanism of accumulation of free tubulin—and probably of other molecules—at the nascent spindle region contributes to efficient assembly of the mitotic spindle in the C. elegans embryo.

scholarly journals Centrosome Maturation and Mitotic Spindle Assembly in C. elegans Require SPD-5, a Protein with Multiple Coiled-Coil Domains

2002 ◽  
Vol 3 (5) ◽  
pp. 673-684 ◽  
Author(s):  
Danielle R. Hamill ◽  
Aaron F. Severson ◽  
J.Clayton Carter ◽  
Bruce Bowerman
Keyword(s):  
Mitotic Spindle ◽  
Coiled Coil ◽  
Spindle Assembly ◽  
C Elegans ◽  
Mitotic Spindle Assembly

scholarly journals The C. elegans RSA Complex Localizes Protein Phosphatase 2A to Centrosomes and Regulates Mitotic Spindle Assembly

Cell ◽  
2007 ◽  
Vol 128 (1) ◽  
pp. 115-127 ◽  
Author(s):  
Anne-Lore Schlaitz ◽  
Martin Srayko ◽  
Alexander Dammermann ◽  
Sophie Quintin ◽  
Natalie Wielsch ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Spindle Assembly ◽  
C Elegans ◽  
Phosphatase 2A ◽  
Mitotic Spindle Assembly

scholarly journals β-importins Tnpo-SR and Cadmus and the small GTPase Ran promote ovarian cyst formation in Drosophila

2021 ◽  
Author(s):  
Allison N. Beachum ◽  
Taylor D. Hinnant ◽  
Anna E. Williams ◽  
Amanda M. Powell ◽  
Elizabeth T. Ables
Keyword(s):  
Germ Cells ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Cyst Formation ◽  
Small Gtpase ◽  
Undifferentiated Cells ◽  
Egg Chambers ◽  
Mitotic Spindle Assembly ◽  
Cyst Development ◽  
Oocyte Selection

ABSTRACTGerm cells undergo mitotic expansion via incomplete cytokinesis, forming cysts of undifferentiated cells that remain interconnected prior to meiotic initiation, through mechanisms that are not well-defined. In somatic cells, Ras-related nuclear protein (Ran) spatiotemporally regulates mitotic spindle assembly, cleavage furrow formation and abscission. Here, we identify Ran and β-importins as critical regulators of cyst development in the Drosophila ovary. Depletion of Ran or the β-importins Tnpo-SR and cadmus disrupts oocyte selection and results in egg chambers with variable numbers of germ cells, suggesting abnormal cyst development and cyst fragmentation. We demonstrate that Ran, Tnpo-SR, and Cadmus regulate key cellular processes during cyst formation, including cell cycle dynamics, fusome biogenesis, and ring canal stability, yet do so independently of mitotic spindle assembly. Further, Tnpo-SR and Cadmus control cyclin accumulation and suppress cytokinesis independent of Ran-GTP, suggesting that β-importins sequester protein cargos that normally promote the mitotic-to-meiotic transition. Our data demonstrates that Ran and β-importins are critical for germ cell cyst formation, a role that is likely conserved in other organisms.SUMMARY STATEMENTRan and two β-importins function coordinately to promote oocyte selection and cyst development in the Drosophila ovary.

scholarly journals Functional Overlap of Microtubule Assembly Factors in Chromatin-Promoted Spindle Assembly

2009 ◽  
Vol 20 (11) ◽  
pp. 2766-2773 ◽  
Author(s):  
Aaron C. Groen ◽  
Thomas J. Maresca ◽  
Jesse C. Gatlin ◽  
Edward D. Salmon ◽  
Timothy J. Mitchison
Keyword(s):  
Mitotic Spindle ◽  
Animal Cell ◽  
Spindle Assembly ◽  
Functional Redundancy ◽  
The Other ◽  
Microtubule Assembly ◽  
Microtubule Polymerization ◽  
Egg Extract ◽  
Assembly Factors ◽  
Mitotic Spindle Assembly

Distinct pathways from centrosomes and chromatin are thought to contribute in parallel to microtubule nucleation and stabilization during animal cell mitotic spindle assembly, but their full mechanisms are not known. We investigated the function of three proposed nucleation/stabilization factors, TPX2, γ-tubulin and XMAP215, in chromatin-promoted assembly of anastral spindles in Xenopus laevis egg extract. In addition to conventional depletion-add back experiments, we tested whether factors could substitute for each other, indicative of functional redundancy. All three factors were required for microtubule polymerization and bipolar spindle assembly around chromatin beads. Depletion of TPX2 was partially rescued by the addition of excess XMAP215 or EB1, or inhibiting MCAK (a Kinesin-13). Depletion of either γ-tubulin or XMAP215 was partially rescued by adding back XMAP215, but not by adding any of the other factors. These data reveal functional redundancy between specific assembly factors in the chromatin pathway, suggesting individual proteins or pathways commonly viewed to be essential may not have entirely unique functions.

scholarly journals Microtubule Assembly and Pole Coalescence: Early Steps in C. elegans Oocyte Meiosis I Spindle Assembly

2020 ◽  
Author(s):  
Chien-Hui Chuang ◽  
Aleesa J. Schlientz ◽  
Jie Yang ◽  
Bruce Bowerman
Keyword(s):  
Molecular Mechanisms ◽  
Spindle Assembly ◽  
Nuclear Lamina ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Bipolar Structure ◽  
C Elegans ◽  
Nuclear Envelope Breakdown ◽  
Oocyte Meiosis ◽  
Meiosis I

ABSTRACTHow oocytes assemble bipolar meiotic spindles in the absence of centrosomes as microtubule organizing centers remains poorly understood. We have used live cell imaging in C. elegans to investigate requirements for the nuclear lamina and for conserved regulators of microtubule dynamics during oocyte meiosis I spindle assembly, assessing these requirements with respect to recently identified spindle assembly steps. We show that the nuclear lamina is required for microtubule bundles to form a cage-like structure that appears shortly after oocyte nuclear envelope breakdown and surrounds the oocyte chromosomes, although bipolar spindles still assembled in its absence. Although two conserved regulators of microtubule nucleation, RAN-1 and γ-tubulin, are not required for bipolar spindle assembly, both contribute to normal levels of spindle-associated microtubules and spindle assembly dynamics. Finally, the XMAP215 ortholog ZYG-9 and the nearly identical minus-end directed kinesins KLP-15/16 are required for proper assembly of the early cage-like structure of microtubule bundles, and for early spindle pole foci to coalesce into a bipolar structure. Our results provide a framework for assigning molecular mechanisms to recently described steps in C. elegans oocyte meiosis I spindle assembly.

scholarly journals Microtubule assembly and pole coalescence: early steps in Caenorhabditiselegans oocyte meiosis I spindle assembly

Biology Open ◽  
2020 ◽  
Vol 9 (6) ◽  
pp. bio052308
Author(s):  
Chien-Hui Chuang ◽  
Aleesa J. Schlientz ◽  
Jie Yang ◽  
Bruce Bowerman
Keyword(s):  
Molecular Mechanisms ◽  
Spindle Assembly ◽  
Nuclear Lamina ◽  
Spindle Pole ◽  
Microtubule Assembly ◽  
Bipolar Structure ◽  
C Elegans ◽  
Nuclear Envelope Breakdown ◽  
Oocyte Meiosis ◽  
Meiosis I

ABSTRACTHow oocytes assemble bipolar meiotic spindles in the absence of centrosomes as microtubule organizing centers remains poorly understood. We have used live cell imaging in Caenorhabditis elegans to investigate requirements for the nuclear lamina and for conserved regulators of microtubule dynamics during oocyte meiosis I spindle assembly, assessing these requirements with respect to recently identified spindle assembly steps. We show that the nuclear lamina is required for microtubule bundles to form a peripheral cage-like structure that appears shortly after oocyte nuclear envelope breakdown and surrounds the oocyte chromosomes, although bipolar spindles still assembled in its absence. Although two conserved regulators of microtubule nucleation, RAN-1 and γ-tubulin, are not required for bipolar spindle assembly, both contribute to normal levels of spindle-associated microtubules and spindle assembly dynamics. Finally, the XMAP215 ortholog ZYG-9 and the nearly identical minus-end directed kinesins KLP-15/16 are required for proper assembly of the early cage-like structure of microtubule bundles, and for early spindle pole foci to coalesce into a bipolar structure. Our results provide a framework for assigning molecular mechanisms to recently described steps in C. elegans oocyte meiosis I spindle assembly.

scholarly journals Chromosomes initiate spindle assembly upon experimental dissolution of the nuclear envelope in grasshopper spermatocytes.

1995 ◽  
Vol 131 (5) ◽  
pp. 1125-1131 ◽  
Author(s):  
D Zhang ◽  
R B Nicklas
Keyword(s):  
Nuclear Envelope ◽  
Essential Role ◽  
Spindle Assembly ◽  
Microtubule Assembly ◽  
Chromosomal Protein ◽  
Spindle Microtubule ◽  
Late Prophase ◽  
Spindle Formation ◽  
Bipolar Spindle

Chromosomes are known to enhance spindle microtubule assembly in grasshopper spermatocytes, which suggested to us that chromosomes might play an essential role in the initiation of spindle formation. Chromosomes might, for example, activate other spindle components such as centrosomes and tubulin subunits upon the breakdown of the nuclear envelope. We tested this possibility in living grasshopper spermatocytes. We ruptured the nuclear envelope during prophase, which prematurely exposed the centrosomes to chromosomes and nuclear sap. Spindle assembly was promptly initiated. In contrast, assembly of the spindle was completely inhibited if the nucleus was mechanically removed from a late prophase cell. Other experiments showed that the trigger for spindle assembly is associated with the chromosomes; other constituents of the nucleus cannot initiate spindle assembly in the absence of the chromosomes. The initiation of spindle assembly required centrosomes as well as chromosomes. Extracting centrosomes from late prophase cells completely inhibited spindle assembly after dissolution of the nuclear envelope. We conclude that the normal formation of a bipolar spindle in grasshopper spermatocytes is regulated by chromosomes. A possible explanation is an activator, perhaps a chromosomal protein (Yeo, J.-P., F. Alderuccio, and B.-H. Toh. 1994a. Nature (Lond.). 367: 288-291), that promotes and stabilizes the assembly of astral microtubules and thus promotes assembly of the spindle.

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