scholarly journals Organization of Microtubules and Endoplasmic Reticulum During Mitosis and Cytokinesis in Wheat Meristems

1966 ◽  
Vol 1 (1) ◽  
pp. 109-120
Author(s):  
J. D. PICKETT-HEAPS ◽  
D. H. NORTHCOTE
Keyword(s):  
Endoplasmic Reticulum ◽  
Mitotic Spindle ◽  
Structural Changes ◽  
Preprophase Band ◽  
Cell Plate ◽  
Late Prophase ◽  
Daughter Cells ◽  
Initial Stage ◽  
Spindle Microtubules ◽  
Mother Cell Wall

The fine-structural changes accompanying mitosis in meristematic cells of the roots and coleoptile tissue of wheat have been studied. A band of microtubules encircling the nucleus appeared in the cytoplasm before the cells entered prophase. These microtubules were oriented at right angles to the direction of the mitotic spindle and were located at the position on the mother cell wall where the future cell plate dividing the daughter cells would have joined it. During prophase the number of microtubules in this preprophase band decreased and eventually disappeared, while microtubules were found to be aligned along the spindle axis. These spindle microtubules appeared as a cone-shaped array of units radiating from the polar zones of the spindle and passing very close tangentially to the nucleus. At late prophase they penetrated the disintegrating nuclear envelope and were seen between the chromosomes. During metaphase and anaphase many microtubules were present running throughout the length of the spindle, and others were found to be attached to chromosomes. Paired sister chromosomes were found joined to microtubules from opposite poles of the spindle. The position and orientation of the lamellae of the endoplasmic reticulum which invaded the spindle from the two poles was closely related to the position and alignment of the microtubules. During the formation of the cell plate vesicles were seen to be collected between the microtubules. As the vesicles fused to form the plate the microtubules were found only at its growing edge, where the vesicles were still being aligned. At the initial stage of its formation the microtubules passed right through the plate, but as it extended they appeared to end at the plate region. The results of the investigation are discussed in relation to the descriptions of mitosis and cytokinesis based on optical microscopy of living cells.

Symmetric and Asymmetric Mitosis and Cytokinesis in the Root Tip of Hydrocharis Morsus-Ranae L

1972 ◽  
Vol 11 (3) ◽  
pp. 723-737
Author(s):  
ELIZABETH G. CUTTER ◽  
CHING-YUAN HUNG
Keyword(s):  
Daughter Cell ◽  
Metaphase Plate ◽  
Cell Plate ◽  
Equatorial Region ◽  
Root Tip ◽  
Daughter Cells ◽  
Asymmetric Divisions ◽  
Spindle Microtubules ◽  
Asymmetric Mitosis ◽  
Dictyosome Vesicles

In the roots of Hydrocharis morsus-ranae, certain cells of the protoderm divide asymmetrically to form a small, highly cytoplasmic trichoblast proximally, and a larger, more vacuolate epidermal cell distally. The former develops as a root hair without further division; the latter divides several times to form ordinary epidermal cells. During mitosis, presumed dictyosome vesicles and fragments or sections of reticulated or serrate sheets of ER, aligned with the spindle microtubules, were observed among the chromosomes as early as metaphase, suggesting that the portions of ER were involved in formation of the cell plate or in some other function in the equatorial region. A pre-prophase band of microtubules was not observed. Asymmetric divisions differ from symmetric ones in the skewed orientation of the metaphase plate, the formation of a curved, rather wavy cell wall and the slightly greater vacuolation of one daughter cell. Less difference in the ultrastructure of the daughter cells resulting from an asymmetric division was observed in this rather slowly growing material than in other examples previously described in the literature.

scholarly journals Spindle microtubules generate tension-dependent changes in the distribution of inner kinetochore proteins

2011 ◽  
Vol 193 (1) ◽  
pp. 125-140 ◽  
Author(s):  
Aussie Suzuki ◽  
Tetsuya Hori ◽  
Tatsuya Nishino ◽  
Jiro Usukura ◽  
Atsushi Miyagi ◽  
...  
Keyword(s):  
Fluorescence Microscopy ◽  
Light Microscopy ◽  
Immunoelectron Microscopy ◽  
Mitotic Spindle ◽  
Structural Changes ◽  
Live Cell ◽  
Dynamic Interface ◽  
Spindle Microtubules ◽  
Kinetochore Region

The kinetochore forms a dynamic interface with microtubules from the mitotic spindle. Live-cell light microscopy–based observations on the dynamic structural changes within the kinetochore suggest that molecular rearrangements within the kinetochore occur upon microtubule interaction. However, the source of these rearrangements is still unclear. In this paper, we analyze vertebrate kinetochore ultrastructure by immunoelectron microscopy (EM) in the presence or absence of tension from spindle microtubules. We found that the inner kinetochore region defined by CENP-A, CENP-C, CENP-R, and the C-terminal domain of CENP-T is deformed in the presence of tension, whereas the outer kinetochore region defined by Ndc80, Mis12, and CENP-E is not stretched even under tension. Importantly, based on EM, fluorescence microscopy, and in vitro analyses, we demonstrated that the N and C termini of CENP-T undergo a tension-dependent separation, suggesting that CENP-T elongation is at least partly responsible for changes in the shape of the inner kinetochore.

Centrosomes and mitotic spindle poles: a recent liaison?

2015 ◽  
Vol 43 (1) ◽  
pp. 13-18 ◽  
Author(s):  
Pavithra L. Chavali ◽  
Isabel Peset ◽  
Fanni Gergely
Keyword(s):  
Cell Division ◽  
Mitotic Spindle ◽  
Potential Benefit ◽  
Cell Types ◽  
Daughter Cells ◽  
Spindle Poles ◽  
Pericentriolar Material ◽  
Mitotic Spindle Assembly ◽  
Spindle Microtubules ◽  
Ordered Assembly

Centrosomes comprise two cylindrical centrioles embedded in the pericentriolar material (PCM). The PCM is an ordered assembly of large scaffolding molecules, providing an interaction platform for proteins involved in signalling, trafficking and most importantly microtubule nucleation and organization. In mitotic cells, centrosomes are located at the spindle poles, sites where spindle microtubules converge. However, certain cell types and organisms lack centrosomes, yet contain focused spindle poles, highlighting that despite their juxtaposition in cells, centrosomes and mitotic spindle poles are distinct physical entities. In the present paper, we discuss the origin of centrosomes and summarize their contribution to mitotic spindle assembly and cell division. We then describe the key molecular players that mediate centrosome attachment to mitotic spindle poles and explore why co-segregation of centrosomes and spindle poles into daughter cells is of potential benefit to organisms.

scholarly journals A comparison of the distribution of actin and tubulin in the mammalian mitotic spindle as seen by indirect immunofluorescence.

1977 ◽  
Vol 72 (3) ◽  
pp. 552-567 ◽  
Author(s):  
W Z Cande ◽  
E Lazarides ◽  
J R McIntosh
Keyword(s):  
Indirect Immunofluorescence ◽  
Mitotic Spindle ◽  
Metaphase Plate ◽  
Spindle Pole ◽  
Early Prophase ◽  
Chromosome Movement ◽  
Late Prophase ◽  
Small Ball ◽  
Nuclear Envelope Breakdown ◽  
Daughter Cells

Rabbit antibodies against actin and tubulin were used in an indirect immunofluorescence study of the structure of the mitotic spindle of PtK1 cells after lysis under conditions that preserve anaphase chromosome movement. During early prophase there is no antiactin staining associated with the mitotic centers, but by late prophase, as the spindle is beginning to form, a small ball of actin antigenicity is found beside the nucleus; After nuclear envelope breakdown, the actiactin stains the region around each mitotic center, and becomes organized into fibers that run between the chromosomes and the poles. Colchicine blocks this organization, but does not disrupt the staining at the poles. At metaphase the antiactin reveals a halo of ill-defined radius around each spindle pole and fibers that run from the poles to the metaphase plate. Antitubulin shows astral rays, fibers running from chromosomes to poles, and some fibers that run across the metaphase plate. At anaphase, there is a shortening of the antiactin-stained fibers, leaving a zone which is essentially free of actin-staining fluorescence between the separating chromosomes. Antitubulin stains the region between chromosomes and poles, but also reveals substantial fibers running through the zone between separating chromosomes. Cells fixed during cytokinesis show actin in the region of the cleavage furrow, while antitubulin reveals the fibrous spindle remnant that runs between daughter cells. These results suggest that actin is a component of the mammalian mitotic spindle, that the distribution of actin differs from that of tubulin and that the distributions of these two fibrous proteins change in different ways during anaphase.

scholarly journals Studies on the Endoplasmic Reticulum

1960 ◽  
Vol 7 (1) ◽  
pp. 167-180 ◽  
Author(s):  
Keith R. Porter ◽  
Raul D. Machado
Keyword(s):  
Endoplasmic Reticulum ◽  
Nuclear Envelope ◽  
Phase Contrast ◽  
Cell Plate ◽  
Middle Zone ◽  
Root Tips ◽  
Late Prophase ◽  
Polar Caps ◽  
Interphase Cells ◽  
And Behavior

Cells of onion and garlic root tips were examined under the electron and phase contrast microscopes after fixation in KMnO4. Special attention was focused on the distribution and behavior of the endoplasmic reticulum (ER) during the several phases of mitosis. Slender profiles, recognized as sections through thin lamellar units of the ER (most prominent in KMnO4-fixed material), are distributed more or less uniformly in the cytoplasm of interphase cells and show occasional continuity with the nuclear envelope. In late prophase the nuclear envelope breaks down and its remnants plus cytoplasmic elements of the ER, which are morphologically identical, surround the spindle in a zone from which mitochondria, etc., are excluded. During metaphase these ER elements persist and concentrate as two separate systems in the polar caps or zones of the spindle. At about this same time they begin to proliferate and to invade the ends of the spindle. The invading lamellar units form drape-like partitions between the anaphase chromosomes. In late anaphase, their advancing margins reach the middle zone of the spindle and begin to fray out. Finally, in telophase, while elements of the ER in the poles of the spindle coalesce around the chromosomes to form the new envelope, the advancing edges of those in the middle zone reticulate at the level of the equator to form a close lattice of tubular elements. Within this, which is identified as the phragmoplast, the earliest signs of the cell plate appear in the form of small vesicles. These subsequently grow and fuse to complete the separation of the two protoplasts. Other morphological units apparently participating in mitosis are described. Speculation is provided on the equal division or not of the nuclear envelope and the contribution the envelope fragments make to the ER of the new cell.

scholarly journals The mitotic spindle mediates inheritance of the Golgi ribbon structure

2009 ◽  
Vol 184 (3) ◽  
pp. 391-397 ◽  
Author(s):  
Jen-Hsuan Wei ◽  
Joachim Seemann
Keyword(s):  
Mitotic Spindle ◽  
Daughter Cell ◽  
Daughter Cells ◽  
Spindle Poles ◽  
Golgi Membranes ◽  
Ribbon Structure ◽  
Golgi Ribbon

The mammalian Golgi ribbon disassembles during mitosis and reforms in both daughter cells after division. Mitotic Golgi membranes concentrate around the spindle poles, suggesting that the spindle may control Golgi partitioning. To test this, cells were induced to divide asymmetrically with the entire spindle segregated into only one daughter cell. A ribbon reforms in the nucleated karyoplasts, whereas the Golgi stacks in the cytoplasts are scattered. However, the scattered Golgi stacks are polarized and transport cargo. Microinjection of Golgi extract together with tubulin or incorporation of spindle materials rescues Golgi ribbon formation. Therefore, the factors required for postmitotic Golgi ribbon assembly are transferred by the spindle, but the constituents of functional stacks are partitioned independently, suggesting that Golgi inheritance is regulated by two distinct mechanisms.

Fyn Accelerates M Phase Progression by Promoting the Assembly of Mitotic Spindle Microtubules

2015 ◽  
Vol 117 (4) ◽  
pp. 894-903 ◽  
Author(s):  
Mai Okamoto ◽  
Yuji Nakayama ◽  
Ayana Kakihana ◽  
Ryuzaburo Yuki ◽  
Noritaka Yamaguchi ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
M Phase ◽  
Phase Progression ◽  
Spindle Microtubules

scholarly journals An actin network is present in the cytoplasm throughout the cell cycle of carrot cells and associates with the dividing nucleus.

1987 ◽  
Vol 105 (1) ◽  
pp. 387-395 ◽  
Author(s):  
J A Traas ◽  
J H Doonan ◽  
D J Rawlins ◽  
P J Shaw ◽  
J Watts ◽  
...  
Keyword(s):  
Mitotic Spindle ◽  
Three Dimensional ◽  
Preprophase Band ◽  
Alternative Methods ◽  
Cell Periphery ◽  
Actin Network ◽  
Suspension Cells ◽  
Daucus Carota L ◽  
Culture Cells ◽  
Transvacuolar Strands

We have studied the F-actin network in cycling suspension culture cells of carrot (Daucus carota L.) using rhodaminyl lysine phallotoxin (RLP). In addition to conventional fixation with formaldehyde, we have used two different nonfixation methods before adding RLP: extracting cells in a stabilizing buffer; inducing transient pores in the plasma membrane with pulses of direct current (electroporation). These alternative methods for introducing RLP revealed additional features of the actin network not seen in aldehyde-fixed cells. The three-dimensional organization of this network in nonflattened cells was demonstrated by projecting stereopairs derived from through-focal series of computer-enhanced images. F-actin is present in interphase cells in four interconnected configurations: a meshwork surrounding the nucleus; thick cables in transvacuolar strands and deep in the cytoplasm; a finer network of bundles within the cortical cytoplasm; even finer filaments that run in ordered transverse array around the cell periphery. The actin network is organized differently during division but it does not disappear as do the cortical microtubules. RLP stains a central filamentous cortical band as the chromatin begins to condense (preprophase); it stains the mitotic spindle (as recently shown by Seagull et al. [Seagull, R. W., M. Falconer, and C. A. Weerdenburg, 1987, J. Cell Biol., 104:995-1004] for aldehyde fixed suspension cells) and the cytokinetic apparatus (as shown by Clayton, L., and C. W. Lloyd, 1985, Exp. Cell Res., 156:231-238). However, it is now shown that an additional network of F-actin persists in the cytoplasm throughout division associating in turn with the preprophase band, the mitotic spindle, and the cytokinetic phragmoplast.

The Xenopus protein kinase pEg2 associates with the centrosome in a cell cycle-dependent manner, binds to the spindle microtubules and is involved in bipolar mitotic spindle assembly

1998 ◽  
Vol 111 (5) ◽  
pp. 557-572 ◽  
Author(s):  
C. Roghi ◽  
R. Giet ◽  
R. Uzbekov ◽  
N. Morin ◽  
I. Chartrain ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Protein Kinase ◽  
Mitotic Spindle ◽  
Cultured Cells ◽  
Dependent Manner ◽  
Egg Extracts ◽  
Pericentriolar Material ◽  
Spindle Microtubules ◽  
Cycle Dependent

By differential screening of a Xenopus laevis egg cDNA library, we have isolated a 2,111 bp cDNA which corresponds to a maternal mRNA specifically deadenylated after fertilisation. This cDNA, called Eg2, encodes a 407 amino acid protein kinase. The pEg2 sequence shows significant identity with members of a new protein kinase sub-family which includes Aurora from Drosophila and Ipl1 (increase in ploidy-1) from budding yeast, enzymes involved in centrosome migration and chromosome segregation, respectively. A single 46 kDa polypeptide, which corresponds to the deduced molecular mass of pEg2, is immunodetected in Xenopus oocyte and egg extracts, as well as in lysates of Xenopus XL2 cultured cells. In XL2 cells, pEg2 is immunodetected only in S, G2 and M phases of the cell cycle, where it always localises to the centrosomal region of the cell. In addition, pEg2 ‘invades’ the microtubules at the poles of the mitotic spindle in metaphase and anaphase. Immunoelectron microscopy experiments show that pEg2 is located precisely around the pericentriolar material in prophase and on the spindle microtubules in anaphase. We also demonstrate that pEg2 binds directly to taxol stabilised microtubules in vitro. In addition, we show that the presence of microtubules during mitosis is not necessary for an association between pEg2 and the centrosome. Finally we show that a catalytically inactive pEg2 kinase stops the assembly of bipolar mitotic spindles in Xenopus egg extracts.

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