scholarly journals Mixing and matching nuclear envelope remodeling and spindle assembly strategies in the evolution of mitosis

2016 ◽  
Vol 41 ◽  
pp. 43-50 ◽  
Author(s):  
Maria Makarova ◽  
Snezhana Oliferenko
Keyword(s):  
Nuclear Envelope ◽  
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.

scholarly journals Experimental manipulation of the amount of tubulin available for assembly into the spindle of dividing sea urchin eggs.

1976 ◽  
Vol 70 (1) ◽  
pp. 75-85 ◽  
Author(s):  
G Sluder
Keyword(s):  
Nuclear Envelope ◽  
Sea Urchin ◽  
Maximum Rate ◽  
Spindle Assembly ◽  
Experimental Manipulation ◽  
Lytechinus Variegatus ◽  
Tubulin Polymerization ◽  
Treated Cell ◽  
Sea Urchin Eggs ◽  
Nuclear Envelope Breakdown

Spindle assembly is studied in the eggs of the sea urchin Lytechinus variegatus by experimentally varying the amount of polymerizable tubulin within the egg. Aliquots of fertilized eggs from the same female are individually pulsed for 1-6 min with 1 X 10(-6) M Colcemid at least 20 min before first nuclear envelope breakdown. This treatment inactivates a portion of the cellular tubulin before the spindle is formed. Upon entering mitosis, treated eggs form functional spindles that are reduced in length and birefringent retardation but not width. With increased exposure to Colcemid, the length and retardation of the metaphase spindles are progressively reduced. Similar results are obtained by pulsing the eggs with Colcemid before fertilization, which demonstrates that the tubulin found in unfertilized sea urchin eggs is later used in spindle formation. Spindles, once assembled, are responsive to increases in the amount of polymerizable tubulin within the cell. Rapid increases in the amount of polymerizable tubulin within a Colcemid-treated cell can be experimentally effected by irradiating the cells with 366-nm light. This treatment photochemically inactivates the Colcemid, thereby freeing the tubulin to polymerize. Upon irradiation, the small prometaphase spindles of Colcemid-treated cells immediately increase in length and retardation. In these irradiated cells, spindle length and retardation increase as much as four times faster than they do during prometaphase for normal spindles. This suggests that the rate of the normal prometaphase increase in retardation and spindle size may be determined by factors other than the maximum rate of tubulin polymerization in the cell.

scholarly journals Assembly of Caenorhabditis elegans acentrosomal spindles occurs without evident microtubule-organizing centers and requires microtubule sorting by KLP-18/kinesin-12 and MESP-1

2016 ◽  
Vol 27 (20) ◽  
pp. 3122-3131 ◽  
Author(s):  
Ian D. Wolff ◽  
Michael V. Tran ◽  
Timothy J. Mullen ◽  
Anne M. Villeneuve ◽  
Sarah M. Wignall
Keyword(s):  
Caenorhabditis Elegans ◽  
High Resolution ◽  
Nuclear Envelope ◽  
Spindle Assembly ◽  
Cell Types ◽  
High Resolution Imaging ◽  
Spindle Formation ◽  
Mixed Polarity ◽  
Resolution Imaging ◽  
Meiosis I

Although centrosomes contribute to spindle formation in most cell types, oocytes of many species are acentrosomal and must organize spindles in their absence. Here we investigate this process in Caenorhabditis elegans, detailing how acentrosomal spindles form and revealing mechanisms required to establish bipolarity. Using high-resolution imaging, we find that in meiosis I, microtubules initially form a “cage-like” structure inside the disassembling nuclear envelope. This structure reorganizes so that minus ends are sorted to the periphery of the array, forming multiple nascent poles that then coalesce until bipolarity is achieved. In meiosis II, microtubules nucleate in the vicinity of chromosomes but then undergo similar sorting and pole formation events. We further show that KLP-18/kinesin-12 and MESP-1, previously shown to be required for spindle bipolarity, likely contribute to bipolarity by sorting microtubules. After their depletion, minus ends are not sorted outward at the early stages of spindle assembly and instead converge. These proteins colocalize on microtubules, are interdependent for localization, and can interact, suggesting that they work together. We propose that KLP-18/kinesin-12 and MESP-1 form a complex that functions to sort microtubules of mixed polarity into a configuration in which minus ends are away from the chromosomes, enabling formation of nascent poles.

scholarly journals EFFECTORS OF THE SPINDLE ASSEMBLY CHECKPOINT BUT NOT THE MITOTIC EXIT NETWORK ARE CONFINED WITHIN THE NUCLEUS OF SACCHAROMYCES CEREVISIAE

2018 ◽  
Author(s):  
Lydia R Heasley ◽  
Jennifer G DeLuca ◽  
Steven M Markus
Keyword(s):  
Nuclear Envelope ◽  
Mammalian Cells ◽  
Spindle Assembly Checkpoint ◽  
Spindle Assembly ◽  
Mitotic Checkpoint ◽  
Mitotic Exit ◽  
Cell Cycle Checkpoints ◽  
Anaphase Promoting Complex ◽  
Mitotic Exit Network ◽  
And Function

The Spindle Assembly Checkpoint (SAC) prevents erroneous chromosome segregation by delaying mitotic progression when chromosomes are incorrectly attached to the mitotic spindle. This delay is mediated by Mitotic Checkpoint Complexes (MCCs), which assemble at unattached kinetochores and repress the activity of the Anaphase Promoting Complex/Cyclosome (APC/C). The cellular localizations of MCCs are likely critical for proper SAC function, yet remain poorly defined. We recently demonstrated that in mammalian cells, in which the nuclear envelope disassembles during mitosis, MCCs diffuse throughout the spindle region and cytoplasm. Here, we employed binucleate yeast zygotes to examine the localization dynamics of SAC effectors required for MCC assembly and function in budding yeast, in which the nuclear envelope remains intact throughout mitosis. Our findings indicate that in yeast MCCs are confined to the nuclear compartment and excluded from the cytoplasm during mitosis. In contrast, we find that effectors of the Mitotic Exit Network (MEN) - a pathway that initiates disassembly of the anaphase spindle only when it is properly oriented - are in fact freely exchanged between multiple nuclei within a shared cytoplasm. Our study provides insight into how cell cycle checkpoints have evolved to function in diverse cellular contexts.

scholarly journals Dissection of the NUP107 nuclear pore subcomplex reveals a novel interaction with spindle assembly checkpoint protein MAD1 in Caenorhabditis elegans

2012 ◽  
Vol 23 (5) ◽  
pp. 930-944 ◽  
Author(s):  
Eduardo Ródenas ◽  
Cristina González-Aguilera ◽  
Cristina Ayuso ◽  
Peter Askjaer
Keyword(s):  
Caenorhabditis Elegans ◽  
Nuclear Envelope ◽  
Molecular Mechanisms ◽  
Spindle Assembly Checkpoint ◽  
Protein Import ◽  
Spindle Assembly ◽  
Nucleocytoplasmic Transport ◽  
Nuclear Pore ◽  
Nuclear Pore Complexes ◽  
Pore Complexes

Nuclear pore complexes consist of several subcomplexes. The NUP107 complex is important for nucleocytoplasmic transport, nuclear envelope assembly, and kinetochore function. However, the underlying molecular mechanisms and the roles of individual complex members remain elusive. We report the first description of a genetic disruption of NUP107 in a metazoan. Caenorhabditis elegans NUP107/npp-5 mutants display temperature-dependent lethality. Surprisingly, NPP-5 is dispensable for incorporation of most nucleoporins into nuclear pores and for nuclear protein import. In contrast, NPP-5 is essential for proper kinetochore localization of NUP133/NPP-15, another NUP107 complex member, whereas recruitment of NUP96/NPP-10C and ELYS/MEL-28 is NPP-5 independent. We found that kinetochore protein NUF2/HIM-10 and Aurora B/AIR-2 kinase are less abundant on mitotic chromatin upon NPP-5 depletion. npp-5 mutants are hypersensitive to anoxia, suggesting that the spindle assembly checkpoint (SAC) is compromised. Indeed, NPP-5 interacts genetically and physically with SAC protein MAD1/MDF-1, whose nuclear envelope accumulation requires NPP-5. Thus our results strengthen the emerging connection between nuclear pore proteins and chromosome segregation.

scholarly journals Nucleosome functions in spindle assembly and nuclear envelope formation

BioEssays ◽  
2015 ◽  
Vol 37 (10) ◽  
pp. 1074-1085 ◽  
Author(s):  
Christian Zierhut ◽  
Hironori Funabiki
Keyword(s):  
Nuclear Envelope ◽  
Spindle Assembly ◽  
Nuclear Envelope Formation

scholarly journals Nucleolar Separation from Chromosomes during Aspergillus nidulans Mitosis Can Occur Without Spindle Forces

2009 ◽  
Vol 20 (8) ◽  
pp. 2132-2145 ◽  
Author(s):  
Leena Ukil ◽  
Colin P. De Souza ◽  
Hui-Lin Liu ◽  
Stephen A. Osmani
Keyword(s):  
Nuclear Envelope ◽  
Aspergillus Nidulans ◽  
Mitotic Spindle ◽  
Spindle Assembly Checkpoint ◽  
Spindle Assembly ◽  
Physical Separation ◽  
Nucleolar Structure ◽  
Nucleolar Organizing Regions ◽  
Nucleolar Proteins ◽  
Nucleolar Segregation

How the nucleolus is segregated during mitosis is poorly understood and occurs by very different mechanisms during closed and open mitosis. Here we report a new mechanism of nucleolar segregation involving removal of the nucleolar-organizing regions (NORs) from nucleoli during Aspergillus nidulans mitosis. This involves a double nuclear envelope (NE) restriction which generates three NE-associated structures, two daughter nuclei (containing the NORs), and the nucleolus. Therefore, a remnant nucleolar structure can exist in the cytoplasm without NORs. In G1, this parental cytoplasmic nucleolus undergoes sequential disassembly releasing nucleolar proteins to the cytoplasm as nucleoli concomitantly reform in daughter nuclei. By depolymerizing microtubules and mutating spindle assembly checkpoint function, we demonstrate that a cycle of nucleolar “segregation” can occur without a spindle in a process termed spindle-independent mitosis (SIM). During SIM physical separation of the NOR from the nucleolus occurs, and NE modifications promote expulsion of the nucleolus to the cytoplasm. Subsequently, the cytoplasmic nucleolus is disassembled and rebuilt at a new site around the nuclear NOR. The data demonstrate the existence of a mitotic machinery for nucleolar segregation that is normally integrated with mitotic spindle formation but that can function without it.

scholarly journals Two-step interphase microtubule disassembly aids spindle morphogenesis

2017 ◽  
Author(s):  
Nunu Mchedlishvili ◽  
Helen K. Matthews ◽  
Adam Corrigan ◽  
Buzz Baum
Keyword(s):  
Nuclear Envelope ◽  
Cell Shape ◽  
Spindle Assembly ◽  
Microtubule Cytoskeleton ◽  
Nuclear Compartment ◽  
Step Process ◽  
Mitotic Entry ◽  
Microtubule Stability ◽  
Compartment Boundary ◽  
Mitotic Cells

AbstractEntry into mitosis triggers profound changes in cell shape and cytoskeletal organisation. Here, by studying microtubule remodelling in human flat mitotic cells, we identify a two-step process of interphase microtubule disassembly. First, a microtubule stabilizing protein, Ensconsin, is inactivated in prophase as a consequence of its phosphorylation downstream of Cdk1/CyclinB. This leads to a reduction in interphase microtubule stability that may help to fuel the growth of centrosomally-nucleated microtubules. The peripheral interphase microtubules that remain are then rapidly lost as the concentration of tubulin heterodimers falls following dissolution of the nuclear compartment boundary. Finally, we show that a failure to destabilize microtubules in prophase leads to the formation of microtubule clumps, which interfere with spindle assembly. Overall, this analysis highlights the importance of the stepwise remodelling of the microtubule cytoskeleton, and the significance of permeabilization of the nuclear envelope in coordinating the changes in cellular organisation and biochemistry that accompany mitotic entry.

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.

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