scholarly journals Novel roles of Kinesin-13 and Kinesin-8 during cell growth and division in the moss Physcomitrella patens

2019 ◽  
Author(s):  
Shu Yao Leong ◽  
Tomoya Edzuka ◽  
Gohta Goshima ◽  
Moé Yamada
Keyword(s):  
Cell Growth ◽  
Mitotic Spindle ◽  
Tip Growth ◽  
Physcomitrella Patens ◽  
Microtubule Dynamics ◽  
Chromosome Movement ◽  
Spindle Formation ◽  
Tip Cells ◽  
Null Mutants

AbstractKinesin-13 and -8 are well-known microtubule (MT) depolymerases that regulate MT length and chromosome movement in animal mitosis. While much is unknown about plant Kinesin-8, Arabidopsis and rice Kinesin-13 have been shown to depolymerise MTs in vitro. However, mitotic function of both kinesins has yet to be understood in plants. Here, we generated the complete null mutants in plants of Kinesin-13 and -8 in the moss Physcomitrella patens. Both kinesins were found to be non-essential for viability, but the Kinesin-13 knockout (KO) line had increased mitotic duration and reduced spindle length, whereas the Kinesin-8 KO line did not display obvious mitotic defects. Surprisingly, spindle MT poleward flux, for which Kinesin-13 is responsible for in animals, was retained in the absence of Kinesin-13. Concurrently, MT depolymerase activity of either moss kinesins could not be observed, with MT catastrophe inducing (Kinesin-13) or MT gliding (Kinesin-8) activity observed in vitro. Interestingly, both KO lines showed waviness in their protonema filaments, which correlated with positional instability of the MT foci in their tip cells. Taken together, the results suggest that plant Kinesin-13 and -8 have diverged in both mitotic function and molecular activity, acquiring new roles in regulating MT foci positioning for directed tip-growth.One sentence summaryThis study uncovered the roles of Kinesin-13 and Kinesin-8 in regulating microtubule dynamics for mitotic spindle formation and straight tip cell growth in the moss Physcomitrella patens

Regulation of Microtubule Assembly: The View From The End

2000 ◽  
Vol 6 (S2) ◽  
pp. 80-81
Author(s):  
L. Cassimeris ◽  
C. Spittle ◽  
M. Kratzer
Keyword(s):  
Chromosome Segregation ◽  
Mitotic Spindle ◽  
Dynamic Instability ◽  
Intrinsic Property ◽  
Microtubule Dynamics ◽  
Microtubule Assembly ◽  
Chromosome Movement ◽  
Spindle Formation ◽  
Associated Proteins

The mitotic spindle is responsible for chromosome movement during mitosis. It is composed of a dynamic array of microtubules and associated proteins whose assembly and constant turnover are required for both spindle formation and chromosome movement. Because microtubule assembly and turnover are necessary for chromosome segregation, we are studying how cells regulate microtubule dynamics. Microtubules are polarized polymers composed of tubulin subunits; they assemble by a process of dynamic instability where individual microtubules exist in persistent phases of elongation or rapid shortening with abrupt transitions between these two states. The switch from elongation to shortening is termed catastrophe, and the switch from shortening to elongation, rescue. Although dynamic instability is an intrinsic property of the tubulin subunits, cells use associated proteins to both speed elongation (∼ 10 fold) and regulate transitions.The only protein isolated to date capable of promoting fast polymerization consistent with rates in vivo is XMAP215, a 215 kD protein from Xenopus eggs.

scholarly journals The mitotic spindle protein CKAP2 potently increases formation and stability of microtubules

eLife ◽  
2022 ◽  
Vol 11 ◽  
Author(s):  
Thomas S McAlear ◽  
Susanne Bechstedt
Keyword(s):  
Cell Division ◽  
Growth Factor ◽  
Mitotic Spindle ◽  
Apparent Rate Constant ◽  
Microtubule Dynamics ◽  
Proliferation Marker ◽  
Microtubule Growth ◽  
Large Rearrangements ◽  
And Function

Cells increase microtubule dynamics to make large rearrangements to their microtubule cytoskeleton during cell division. Changes in microtubule dynamics are essential for the formation and function of the mitotic spindle, and misregulation can lead to aneuploidy and cancer. Using in vitro reconstitution assays we show that the mitotic spindle protein Cytoskeleton-Associated Protein 2 (CKAP2) has a strong effect on nucleation of microtubules by lowering the critical tubulin concentration 100-fold. CKAP2 increases the apparent rate constant ka of microtubule growth by 50-fold and increases microtubule growth rates. In addition, CKAP2 strongly suppresses catastrophes. Our results identify CKAP2 as the most potent microtubule growth factor to date. These finding help explain CKAP2's role as an important spindle protein, proliferation marker, and oncogene.

Microtubules and microfilaments in tip growth: evidence that microtubules impose polarity on protonemal growth in Physcomitrella patens

1988 ◽  
Vol 89 (4) ◽  
pp. 533-540 ◽  
Author(s):  
J. H. DOONAN ◽  
D. J. COVE ◽  
C. W. LLOYD
Keyword(s):  
Tip Growth ◽  
Physcomitrella Patens ◽  
Cytochalasin D ◽  
Immunofluorescence Study ◽  
Apical Dome ◽  
High Concentrations ◽  
Cytoskeletal Elements ◽  
Drug Studies ◽  
Tip Cells ◽  
Cytoskeletal Drugs

In this study we compare the contributions of Factin and microtubules to tip growth in filamentous cells of the moss Physcomitrella patens. In tip growth, expansion seems to be restricted to the hemispherical apical dome. Cytoskeletal elements have been suspected, from drug studies, to be involved in this but electron microscopy has generally not confirmed the presence of an apical cytoskeleton. However, in a previous immunofluorescence study we reported that microtubules could be seen to focus upon the apical dome in tip cells of the moss P. patens. In the present investigation F-actin has also been detected at the apices of these cells. Anti-cytoskeletal drugs were therefore used to differentiate between the roles of actin filaments and microtubules in tip growth. At high concentrations (30μM), the herbicide cremart de-polymerized microtubules and caused tip swelling. F-actin was still present under such conditions but its fragmentation by cytochalasin D suppressed this herbicide-induced swelling. On its own, cytochalasin D arrested tip growth without causing swollen tips. At lower concentrations, cremart disorganized microtubules rather than causing their complete depolymerization. Under these conditions, new but swollen growing points were initiated along the filament. The addition of taxol to cremart-treated filaments tended to reduce swelling and to re-polarize outgrowth. With particular combinations of these drugs, multiple lateral out-growths were initiated in the vicinity of the nucleus. It is concluded: (1) that F-actin is present at the tips of Physcomitrella caulonemal apical cells; (2) that unfragmented F-actin is necessary for outgrowth; (3) that even disorganized microtubules permit some degree of outgrowth but that an unperturbed distribution of axial microtubules, focussing upon an apex, is essential in order to impose tubular shape and directionality upon expansion.

O-154 First mitotic spindle formation led by sperm centrosome-dependent microtubule organising centres may cause high incidence of zygotic division errors in humans

2021 ◽  
Vol 36 (Supplement_1) ◽  
Author(s):  
Y Kai ◽  
H Kawano ◽  
N Yamashita
Keyword(s):  
Mitotic Spindle ◽  
High Frequency ◽  
Live Cell Imaging ◽  
Cell Imaging ◽  
Immunofluorescence Assay ◽  
Live Cell ◽  
Microtubule Assembly ◽  
Cell Stage ◽  
Spindle Formation

Abstract Study question Why do multinucleated blastomeres appear at high frequency in two-cell-stage embryos in humans? Summary answer Failure in microtubule assembly during the first mitotic spindle body formation by sperm centrosome-dependent microtubule organising centres (MTOCs) may lead to chromosomal instability. What is known already Unlike that in mice, multinucleated blastomeres appear at high frequency in two-cell-stage embryos in humans. However, the underlying mechanism remains elusive. In mice, multiple acentriolar MTOCs appear around the male and female pronuclei after pronuclear disappearance and contribute to dual-spindle formation, engulfing each parental chromosome. This spindle formation may ensure an error-free division, keeping the chromosomes stable during the first cleavage, as observed in mice, but it is unclear whether a similar mechanism exists in humans. Study design, size, duration To examine how sperm centrosomes contribute to MTOC formation in humans, two types of 3PN zygotes derived fromeither conventional in vitro fertilization (c-IVF, n = 30) or intracytoplasmic sperm injection (ICSI, n = 10) were used. The zygotes were collected from October 2018 to January 2020. MTOC and mitotic spindle formation at consecutive stages of development during the first cleavage were analysed under static and dynamic conditions using immunofluorescence assay and fluorescent live-cell imaging. Participants/materials, setting, methods Under ethics approval, 3PN zygotes were donated by infertile couples undergoing c-IVF or ICSI cycles at the Yamashita Shonan Yume Clinic in Japan. All participants provided informed consent. Immunofluorescence assay was performed using antibodies against α-tubulin, pericentrin, and H3K9me3 after fixation with MTSB-XF solution. Fluorescent live-cell imaging was performed using TagGFP2-H2B mRNA (chromosome marker) and FusionRed-MAP4 mRNA (microtubule marker). Main results and the role of chance Immunofluorescence revealed that while 3PN zygotes derived from c-IVF showed four pericentrin dots, those derived from ICSI exhibited two pericentrin dots. In pro-metaphase, an independent group of chromosomes derived from each pronucleus and MTOCs were formed by the sperm centrosome at the core. Microtubules from each MTOC extended toward the chromosomes in the early metaphase; a quadrupolar spindle was formed in the c-IVF-derived zygotes, and a bipolar spindle was formed in the ICSI-derived zygotes by the MTOCs at the zygote apex after chromosome alignment. In pro-metaphase, the microtubules extended from the MTOCs to the nearest chromosome. Since microtubule assembly was found on oocyte-derived chromosomes, we hypothesised that whether a chromosome is surrounded by microtubules depends on the location of the MTOCs, irrespective of its origin. Live-cell imaging of histone H2B and MAP4 revealed that four MTOCs appeared around the three pronuclei just before the disappearance of the pronuclear membrane; microtubules then extended from the MTOCs toward the chromosomes, beginning to form a mitotic spindle as the chromosomes moved to the centre of the oocyte. Interestingly, one of the three assembled chromosome groups showed no microtubule assembly in the pro-metaphase. Similar results were obtained in all six 3PN zygotes subjected. Limitations, reasons for caution We demonstrated the high risk of developing bare chromosomes not surrounded by microtubules during the formation of the first mitotic spindle, using human tripronuclear zygotes. However, owing to unavailability of normal fertilized oocytes for this study because of the clinical use, we were unable to confirm this in normal zygotes. Wider implications of the findings Although two sperm centrosome-dependent MTOCs are expected to be formed in normal fertilized oocytes, these MTOCs are not sufficient to completely enclose physically separated female and male chromosomes with the microtubules. This explains the high frequency of zygotic division errors that lead to unstable human chromosomes. Trial registration number not applicable

Mitotic Spindle Dysfunction Promotes Genomic Instability In Marrow Failure

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 880-880 ◽  
Author(s):  
Katie Lombardo ◽  
Jason Stumpff ◽  
Susan Parkhurst ◽  
Linda Wordeman ◽  
Akiko Shimamura
Keyword(s):  
Genomic Instability ◽  
Mitotic Spindle ◽  
Conflicts Of Interest ◽  
Bone Marrow Failure ◽  
Microtubule Dynamics ◽  
Published Data ◽  
Hematopoietic Progenitor ◽  
Microtubule Stability ◽  
Cd34 Cells

Abstract Abstract 880 Shwachman-Diamond syndrome (SDS) is an autosomal recessively inherited disorder associated with bone marrow failure and leukemia predisposition. The majority of patients harbor biallelic mutations in the SBDS gene. The SBDS protein has been implicated in several cellular functions including ribosome biogenesis and microtubule stabilization during mitosis. We have previously found that SBDS deficiency results in multipolar spindles, centrosome amplification and aneuploidy, implicating a role for SBDS in cell division. The mechanism by which SBDS functions to ensure proper spindle assembly and DNA segregation during mitosis remains unknown. Here we present evidence that SBDS functions to promote mitotic spindle stability both by directly modifying microtubule dynamics and through a microtubule crosslinking activity. Importantly, the microtubule stabilizing effects of SBDS appear to be essential for the growth and differentiation of hematopoietic progenitor cells. Specifically, we found that SBDS deficiency resulted in shortened mitotic spindle length and decreased spindle acetylation, a marker of microtubule stability. The loss of microtubule stability in the absence of SBDS function may be due to changes in microtubule dynamics or reduction in microtubule crosslinking activity, as we found that addition of recombinant purified wild-type SBDS to polymerized microtubules in vitro increases their polymerization rate and strongly promotes microtubule bundling. Interestingly, recombinant patient-derived missense mutant SBDS proteins showed a marked decrease in their microtubule bundling ability. To assess whether spindle destabilization contributes to marrow failure, we modeled hematopoiesis in the absence of SBDS in vitro. When SBDS expression was knocked down in human CD34+ cells, proliferation, differentiation, and hematopoietic progenitor colony formation were impaired, consistent with published data on primary marrow from SDS patients. The addition of taxol at concentrations that significantly impaired hematopoiesis in control CD34+ cells resulted in stable to improved hematopoiesis in the SBDS-deficient CD34+ cells. Based on these data, we hypothesize that spindle destabilization by SBDS loss promotes genomic instability, which in turn, contributes to marrow failure and leukemia predisposition. Disclosures: No relevant conflicts of interest to declare.

scholarly journals In vitro reconstitution of branched microtubule nucleation

2019 ◽  
Author(s):  
Ammarah Tariq ◽  
Lucy Green ◽  
J Charles G. Jeynes ◽  
Christian Soeller ◽  
James G. Wakefield
Keyword(s):  
Mitotic Spindle ◽  
Eukaryotic Cell ◽  
Synthetic Approach ◽  
Dependent Manner ◽  
Spindle Formation ◽  
In Vitro Reconstitution ◽  
A Cell ◽  
One Step ◽  
Cycle Dependent

AbstractEukaryotic cell division requires the mitotic spindle, a microtubule (MT)-based structure which accurately aligns and segregates duplicated chromosomes. The dynamics of spindle formation are determined primarily by correctly localising the MT nucleator, γ-Tubulin Ring Complex (γ-TuRC)1-4, within the cell. A conserved MT-associated protein complex, Augmin, recruits γ-TuRC to pre-existing spindle MTs, amplifying their number, in an essential cellular phenomenon termed “branched” MT nucleation5-9. Here, we purify endogenous, GFP-tagged Augmin and γ-TuRC from Drosophila embryos to near homogeneity using a novel one-step affinity technique. We demonstrate that, in vitro, while Augmin alone does not affect Tubulin polymerisation dynamics, it stimulates γ-TuRC-dependent MT nucleation in a cell cycle-dependent manner. We also assemble and visualise the MT-Augmin-γ-TuRC-MT junction using light microscopy. Our work therefore conclusively reconstitutes branched MT nucleation. It also provides a powerful synthetic approach with which to investigate the emergence of cellular phenomena, such as mitotic spindle formation, from component parts.

Nuclear and cytoplasmic dynamics of sperm penetration, pronuclear formation and microtubule organization during fertilization and early preimplantation development in the human

1995 ◽  
Vol 1 (5) ◽  
pp. 429-461 ◽  
Author(s):  
Jonathan Van Blerkom ◽  
Patrick Davis ◽  
John Merriam ◽  
Jane Sinclair
Keyword(s):  
Mitotic Spindle ◽  
Microtubule Organization ◽  
Cytoplasmic Microtubule ◽  
Spindle Formation ◽  
Sperm Tail ◽  
Relative Contribution ◽  
Human Fertilization ◽  
Sperm Penetration ◽  
Principal Piece

Abstract This report describes spatial and temporal aspects of sperm penetration and intracytoplasmic migration, pronuclear evolution and the specificity of presyngamic opposition, stage-specific changes in cytoskeletal organization and the relative contribution of maternal and paternal components to mitotic spindle formation. These studies involved observations of living human oocytes during conventional insemination in vitro and after intracytoplasmic deposition of spermatozoa, analysis of chromatin organization and distribution during pronuclear evolution, and detection of actin and α-, rβ- and γ-tubulin by confocal immuno-fluorescence microscopy. Immature and mature oocytes, penetrated but unfertilized oocytes, fertilized but arrested eggs, and cleavage-stage embryos from normal and dispermic fertilizations were examined. The results demonstrate that sperm nuclear migration to the maternal perinuclear region is rapid and linear, occurs in the absence of a detectable cytoskeletal system and appears to be assisted by an unusual configuration of the sperm tail principal piece which results from either retained intracytoplasmic motility or the process by which the sperm tail is progressively incorporated into the oocyte. Our findings also show a specificity of pronuclear alignment that is associated with a polarized distribution of both maternal and paternal chromatin, and with the position of the sperm centrosome and the presence of microtubules nucleated from this structure. The results also indicate that a maternal microtubule nucleating capacity is present in the immature oocyte but is apparently inactive until spindle formation. The poles of the first mitotic spindle appear to be derived from the sperm centrosome, although some maternal contribution cannot be excluded. The sperm tail and centrosome persist in a single cell through the cleavage stages, and the latter serves as a prominent site of cytoplasmic microtubule nucleation. The results provide a detailed understanding of the cellular and nuclear morphodynamics of the human fertilization process and indicate subtle defects that may be responsible for early developmental failure.

Centrosome Aberrations, Disturbed Mitotic Spindle Formation and G1 Arrest in Normal and Leukemic Cells Treated with the SRC/ABL Inhibitor Dasatinib.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2167-2167
Author(s):  
Alice Fabarius ◽  
Michelle Giehl ◽  
Alwin Kraemer ◽  
Oliver Frank ◽  
Martin C. Mueller ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Cell Lines ◽  
Mitotic Spindle ◽  
Cell Cycle Progression ◽  
Dermal Fibroblasts ◽  
G1 Arrest ◽  
Osteosarcoma Cell ◽  
Cycle Progression ◽  
Spindle Formation

Abstract Multitargeted ABL inhibitors have been developed to simultaneously inhibit various pathways associated with proliferation in BCR-ABL+ diseases. Dasatinib (Bristol Myers Squibb) is a potent inhibitor targeting ABL, SRC, and other tyrosine kinases. SRC kinases are required for progression through the initial phase of mitosis. Centrosomes play a fundamental role in mitotic spindle organization, chromosome segregation and genetic stability. We sought to evaluate the activity of dasatinib on proliferation, centrosome status, spindle formation, and cell cycle progression in vitro and in vivo. Normal human dermal fibroblasts (NHDF), Chinese hamster embryonal fibroblasts (CHE), and the human osteosarcoma cell line U2OS were treated with serial concentrations (1nM-10μM) of dasatinib for 3 weeks. Effects of dasatinib were compared with data achieved with the ABL inhibitors imatinib (Novartis, 5–20μM) and nilotinib (Novartis, 0.5–20μM), the specific SRC inhibitor PP2 (Calbiochem-Novabiochem, 0.1–2μM), the ABL/LYN inhibitor INNO-406 (Innovive, 0.1–2μM), and solvent control. Bone marrow and peripheral blood samples from 18 patients (pts, 10 m, 8 f; median age 57 yrs, range 26–75) treated with dasatinib (70mg bid) after imatinib failure for a median of 11 mo (range, 3–16) were investigated. 17 pts had chronic myeloid leukemia (CML) in chronic phase. One patient suffered from a gastrointestinal stromal tumor. For comparison, 3 untreated CML pts and 3 healthy individuals were evaluated. Cell proliferation was determined in liquid culture incubated with serial dilutions of the inhibitor. Centrosome morphology and spindle formation were evaluated after pericentrin and α-tubulin staining, respectively. Cell cycle progression was analyzed by FACS and expression of EG5 by immunofluorescence microscopy. Dasatinib induced a G1 cell cycle arrest in all cell lines tested and in pts associated with a shift to 1n DNA ploidy and absence of EG5 as a marker for G2 phase/mitosis. In vitro, centrosomal aberrations and delay of spindle formation were observed in a dose dependent fashion. In pts, centrosome alterations were found in a median of 17% (range, 10–15) of cells. Disturbed spindle formation was observed in 9/18 pts. In comparison, incubation with imatinib and nilotinib was associated with centrosome aberrations but not with defects of spindle formation and G1 arrest. PP2 induced S-phase arrest; centrosome aberrations were observed at higher dosages (1–2 μM) only, spindle formation was not affected. INNO-406 was associated with both centrosome aberrations and disturbed spindle formation. In pharmacological doses, proliferation of BCR-ABL neg. cell lines was inhibited after dasatinib treatment, but not after incubation with imatinib, nilotinib, PP2, or INNO-406. In conclusion, dasatinib blocks the G1/S transition and thereby inhibits cell growth in normal and neoplastic cells. In addition, it induces both centrosomal and spindle aberrations. Effects of dasatinib are not based on SRC inhibition alone but may be associated with the combination of SRC and ABL inhibition or with non-specific effects on multiple kinases. Therefore, dasatinib should be defined as a cytostatic drug with a strong targeted component resulting in a preferential inhibition of cells harboring a specific target, like BCR-ABL.

scholarly journals In vitroeffects of 2‐methoxyestradiol on MCF‐12A and MCF‐7 cell growth, morphology and mitotic spindle formation

2008 ◽  
Vol 26 (5) ◽  
pp. 632-642 ◽  
Author(s):  
Catherina Van Zijl ◽  
Mona‐Liza Lottering ◽  
Francois Steffens ◽  
Annie Joubert
Keyword(s):  
Cell Growth ◽  
Mitotic Spindle ◽  
Growth Morphology ◽  
Spindle Formation ◽  
Mcf 7

scholarly journals Nup98 regulates bipolar spindle assembly through association with microtubules and opposition of MCAK

2011 ◽  
Vol 22 (5) ◽  
pp. 661-672 ◽  
Author(s):  
Marie K. Cross ◽  
Maureen A. Powers
Keyword(s):  
Nuclear Pore Complex ◽  
Mitotic Spindle ◽  
Spindle Assembly ◽  
Microtubule Dynamics ◽  
Nuclear Pore ◽  
Bipolar Spindle ◽  
Terminal Domain ◽  
C Terminus ◽  
Mitotic Spindle Assembly

During mitosis, the nuclear pore complex is disassembled and, increasingly, nucleoporins are proving to have mitotic functions when released from the pore. We find a contribution of the nucleoporin Nup98 to mitotic spindle assembly through regulation of microtubule dynamics. When added to Xenopus extract spindle assembly assays, the C-terminal domain of Nup98 stimulates uncontrolled growth of microtubules. Conversely, inhibition or depletion of Nup98 leads to formation of stable monopolar spindles. Spindle bipolarity is restored by addition of purified, recombinant Nup98 C-terminus. The minimal required region of Nup98 corresponds to a portion of the C-terminal domain lacking a previously characterized function. We show association between this region of the C-terminus of Nup98 and both Taxol-stabilized microtubules and the microtubule-depolymerizing mitotic centromere–associated kinesin (MCAK). Importantly, we demonstrate that this domain of Nup98 inhibits MCAK depolymerization activity in vitro. These data support a model in which Nup98 interacts with microtubules and antagonizes MCAK activity, thus promoting bipolar spindle assembly.

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