scholarly journals Mitosis in Barbulanympha. II. Dynamics of a two-stage anaphase, nuclear morphogenesis, and cytokinesis

1978 ◽  
Vol 77 (3) ◽  
pp. 655-684 ◽  
Author(s):  
S Inoué ◽  
H Ritter
Keyword(s):  
Nuclear Envelope ◽  
Morphological Change ◽  
Two Dimensional ◽  
Chromosome Movement ◽  
Central Spindle ◽  
Daughter Cells ◽  
Late Anaphase ◽  
Early Anaphase ◽  
Length Width ◽  
Anaphase B

Anaphase in Barbulanympha proceeds in two discrete steps. In anaphase-A, chromosomal spindle fibers shorten and chromosomes move to the stationary centrosomes. In anaphase-B, the central spindle elongates and ("telophasic") bouquets of chromosomes, with kinetochores still connected by the shortened chromosomal fibers to the centrosomes, are moved far apart. The length, width, and birefringence of the central spindle remain unchanged throughout anaphase-A. In anaphase-B, the central spindle elongates up to fivefold. During elongation, the peripheral fibers of the central spindle splay, first anteriorly and then laterally. The remaining central spindle progressively becomes thinner and the retardation decreases; however, the coefficient of birefringence stays approximately constant. The nuclear envelope persists throughout mitosis in Barbulanympha and the nucleus undergoes an intricate morphological change. In prophase, the nucleus engulfs the spindle; in early anaphase-A, the nuclear envelope forms a seam anterior to the spindle, the nucleus thus transforms into a complete sleeve surrounding the central spindle. In late anaphase-A, the middle of the seam opens up in a cleft as the lips part; in anaphase-B, the cleft expands posteriorly, progressively exposing the central spindle. Finally, the cleft partitions the nucleus into two. The nuclear envelope shows an apparent elasticity and two-dimensional fluidity. Localized, transient deformations of the nuclear envelope indicate poleward and counter-poleward forces acting on the kinetochores embedded in the envelope. These forces appear responsible for nuclear morphogenesis as well as anaphase chromosome movement. At the end of anaphase-B, the two rostrate Barbulanympha may swim apart of be poked apart into two daughter cells by another organism cohabiting the host's hindgut.

Mitosis in Mougeotia sp.

1972 ◽  
Vol 50 (9) ◽  
pp. 1811-1816 ◽  
Author(s):  
Carla W. Bech-Hansen ◽  
Larry C. Fowke
Keyword(s):  
Cell Wall ◽  
Electron Microscope ◽  
Nuclear Envelope ◽  
Short Distance ◽  
Late Anaphase ◽  
New Information ◽  
Early Anaphase

Combined light and electron microscope observations have provided new information concerning mitosis in Mougeotia. The distribution of microtubules during division suggests that intact wall microtubules moved at preprophase to form the spindle and returned to the cell wall at telophase. During metaphase and early anaphase, chromosomal microtubules were attached to distinct kinetochores; few interzonal microtubules were evident. The subsequent elongation of the spindle at late anaphase was accompanied by the appearance of numerous interzonal microtubules and the loss of the original nuclear envelope. The nucleoli dispersed during prophase and reformed at telophase. The wall septum appeared at prophase but extended only a short distance into the cell by telophase; microtubules were not associated with the developing septum.

scholarly journals Astral and spindle forces in PtK2 cells during anaphase B: a laser microbeam study

1993 ◽  
Vol 104 (4) ◽  
pp. 1207-1216 ◽  
Author(s):  
J.R. Aist ◽  
H. Liang ◽  
M.W. Berns
Keyword(s):  
Spindle Pole ◽  
Uv Laser ◽  
Central Spindle ◽  
Laser Microbeam ◽  
Spindle Poles ◽  
Pulling Forces ◽  
Early Anaphase ◽  
Anaphase B

Rat kangaroo kidney epithelium (PtK2) cells develop prominent asters and spindles during anaphase B of mitosis. It has been shown that severing the spindle at early anaphase B in living PtK1 cells results in a dramatic increase in the rate of pole-pole separation. This result suggested that the asters pull on the spindle poles, putting tension on the spindle, while the spindle acts as a governor, limiting the rate of pole separation. To further test these inferences, we used a UV-laser microbeam to damage one of the two asters in living PtK2 cells at early anaphase B and monitored the effects on individual spindle pole movements, pole-pole separation rates and astral microtubules (MTs). Irradiation at the estimated position of a centrosome greatly reduced its array of astral MTs and nearly stopped the movement of the irradiated pole, whereas the sister pole retained its normal array of astral MTs and actually accelerated. Control irradiations, either close to the estimated position of the centrosome or beside the spindle at the equator, had little or no effect on either spindle pole movements or astral MTs. These results support the inferences that during anaphase B in living PtK cells, the central spindle is under tension generated by pulling forces in the asters (presumably MT-mediated) and that the spindle generates counterforces that limit the rate of pole separation. The results also suggest that the central spindle in living PtK cells may be able to generate a pushing force.

Mitosis in the rice blast fungus and its possible implications for pathogenic variability

1985 ◽  
Vol 63 (6) ◽  
pp. 1129-1134 ◽  
Author(s):  
K. V. S. R. Kameswar Row ◽  
J. R. Aist ◽  
J. P. Crill
Keyword(s):  
Nuclear Envelope ◽  
High Frequency ◽  
Spindle Pole Body ◽  
Rice Blast Fungus ◽  
Spindle Pole ◽  
Central Spindle ◽  
Pole Body ◽  
Spindle Pole Bodies ◽  
Pathogenic Variability ◽  
Anaphase B

Mitosis in Pyricularia oryzae was reexamined, using both living and stained specimens. During prophase, the spindle pole body becomes quiescent and separates into two parts. The nucleolus disperses as chromosomes become visible. At metaphase, the spindle pole bodies are situated at the ends of the intranuclear spindle to which the chromosomes are attached at different points along its length. Anaphase A disjunction of chromatids is asynchronous; consequently, lagging chromosomes are typical. Anaphase B involves a marked elongation of the central spindle as first one incipient daughter nucleus and then the other migrates out of the original, intact nuclear envelope. During telophase, the central spindle and remainder of the nuclear envelope disappear, the chromatin returns to the dispersed state, and the nucleolus reappears. Contrary to earlier reports, mitosis in P. oryzae is virtually identical with that now known to be typical for other Ascomycetes, such as Ceratocystis and Nectria. The high frequency of pathogenic variability in P. oryzae could result from aneuploidy, and several mechanisms by which aneuploidy could arise are postulated.

scholarly journals The Drosophila kinesin-like protein KLP3A is a midbody component required for central spindle assembly and initiation of cytokinesis.

1995 ◽  
Vol 129 (3) ◽  
pp. 709-723 ◽  
Author(s):  
B C Williams ◽  
M F Riedy ◽  
E V Williams ◽  
M Gatti ◽  
M L Goldberg
Keyword(s):  
Motor Protein ◽  
Spindle Assembly ◽  
Male Meiosis ◽  
Cleavage Furrow ◽  
Critical Component ◽  
Central Spindle ◽  
Late Anaphase ◽  
Spindle Elongation ◽  
Anaphase B ◽  
Kinesin Superfamily

We describe here a new member of the kinesin superfamily in Drosophila, KLP3A (Kinesin-Like-Protein-at-3A). The KLP3A protein localizes to the equator of the central spindle during late anaphase and telophase of male meiosis. Mutations in the KLP3A gene disrupt the interdigitation of microtubules in spermatocyte central spindles. Despite this defect, anaphase B spindle elongation is not obviously aberrant. However, cytokinesis frequently fails after both meiotic divisions in mutant testes. Together, these findings strongly suggest that the KLP3A presumptive motor protein is a critical component in the establishment or stabilization of the central spindle. Furthermore, these results imply that the central spindle is the source of signals that initiate the cleavage furrow in higher cells.

scholarly journals Functional implications of cold-stable microtubules in kinetochore fibers of insect spermatocytes during anaphase.

1980 ◽  
Vol 85 (3) ◽  
pp. 853-865 ◽  
Author(s):  
E D Salmon ◽  
D A Begg
Keyword(s):  
Dynamic Equilibrium ◽  
Chromosome Movement ◽  
Temperature Dependent ◽  
Abrupt Changes ◽  
Functional Implications ◽  
Early Anaphase ◽  
Physiological Pathways ◽  
Cold Stability ◽  
Rate Limiting ◽  
Steady State Balance

In normal anaphase of crane fly spermatocytes, the autosomes traverse most of the distance to the poles at a constant, temperature-dependent velocity. Concurrently, the birefringent kinetochore fibers shorten while retaining a constant birefringent retardation (BR) and width over most of the fiber length as the autosomes approach the centrosome region. To test the dynamic equilibrium model of chromosome poleward movement, we abruptly cooled or heated primary spermatocytes of the crane fly Nephrotoma ferruginea (and the grasshopper Trimerotropis maritima) during early anaphase. According to this model, abrupt cooling should induce transient depolymerization of the kinetochore fiber microtubules, thus producing a transient acceleration in the poleward movement of the autosomal chromosomes, provided the poles remain separated. Abrupt changes in temperature from 22 degrees C to as low as 4 degrees C or as high as 31 degrees C in fact produced immediate changes in chromosome velocity to new constant velocities. No transient changes in velocity were observed. At 4 degrees C (10 degrees C for grasshopper cells), chromosome movement ceased. Although no nonkinetochore fiber BR remained at these low temperatures, kinetochore fiber BR had changed very little. The cold stability of the kinetochore fiber microtubules, the constant velocity character of chromosome movement, and the observed Arrhenius relationship between temperature and chromosome velocity indicate that a rate-limiting catalyzed process is involved in the normal anaphase depolymerization of the spindle fiber microtubules. On the basis of our birefringence observations, the kinetochore fiber microtubules appear to exist in a steady-state balance between comparatively irreversible, and probably different, physiological pathways of polymerization and depolymerization.

Meshing Method of High Precision FEM in Large Complex Structural Simulations

2012 ◽  
Vol 195-196 ◽  
pp. 701-704
Author(s):  
Yan Hua Xue ◽  
Zhi Guang Wang ◽  
Xiao Hong Li ◽  
Xin Jiang
Keyword(s):  
Finite Element ◽  
Complex Structure ◽  
Width Ratio ◽  
Two Dimensional ◽  
Element Analysis ◽  
Large Complex ◽  
Mesh Density ◽  
Length Width ◽  
Complex Structural ◽  
Dimensional Element

Shing is playing an important role in the large complex structural FEM simulations; it has a direct effect on calculating precision of structural simulations. For increasing the calculation accuracy and analysis accuracy of complex structure, the finite element meshing problems is proposed on the finite element analysis of large complicated structures. The effects caused by element type, mesh density and intergradations on calculating precision are studied and discussed. A research argues that with length-width ratio of 1~2 and length-thickness ration of 1.5~4.5 of two-dimensional rectangular element, the quality of meshing method of two-dimensional element is above normal. As the height of one-dimensional element is equal to the sum of reinforcing rib height of outer panel and half the thickness of panel, more accurate results can be obtained.

When rDNA transcription is arrested during mitosis, UBF is still associated with non-condensed rDNA

1997 ◽  
Vol 110 (19) ◽  
pp. 2429-2440 ◽  
Author(s):  
J. Gebrane-Younes ◽  
N. Fomproix ◽  
D. Hernandez-Verdun
Keyword(s):  
Secondary Constriction ◽  
Three Dimensional ◽  
Ribosomal Gene ◽  
Rdna Transcription ◽  
Transcription Machinery ◽  
Late Anaphase ◽  
Early Anaphase ◽  
Dimensional Distribution ◽  
Open Question ◽  
Kinetics Of

The mechanisms that control inactivation of ribosomal gene (rDNA) transcription during mitosis is still an open question. To investigate this fundamental question, the precise timing of mitotic arrest was established. In PtK1 cells, rDNA transcription was still active in prophase, stopped in prometaphase until early anaphase, and activated in late anaphase. Because rDNA transcription can still occur in prophase and late anaphase chromosomes, the kinetics of rDNA condensation during mitosis was questioned. The conformation of the rDNA was analyzed by electron microscopy from the G2/M transition to late anaphase in the secondary constriction, the chromosome regions where the rDNAs are clustered. Whether at transcribing or non-transcribing stages, non-condensed rDNA was observed in addition to axial condensed rDNA. Thus, the persistence of this non-condensed rDNA during inactive transcription argues in favor of the fact that mitotic inactivation is not the consequence of rDNA condensation. Analysis of the three-dimensional distribution of the rDNA transcription factor, UBF, revealed that it was similar at each stage of mitosis in the secondary constriction. In addition, the colocalization of UBF with non-condensed rDNA was demonstrated. This is the first visual evidence of the association of UBF with non-condensed rDNA. As we previously reported that the rDNA transcription machinery remained assembled during mitosis, the colocalization of rDNA fibers with UBF argues in favor of the association of the transcription machinery with certain rDNA copies even in the absence of transcription. If this hypothesis is correct, it can be assumed that condensation of rDNA as well as dissociation of the transcription machinery from rDNA cannot explain the arrest of rDNA transcription during mitosis. It is proposed that modifications of the transcription machinery occurring in prometaphase could explain the arrest of transcription, while reverse modifications in late anaphase could explain activation.

scholarly journals Regulating chromosomal movement by the cochaperone FKB-6 ensures timely pairing and synapsis

2017 ◽  
Vol 216 (2) ◽  
pp. 393-408 ◽  
Author(s):  
Benjamin Alleva ◽  
Nathan Balukoff ◽  
Amy Peiper ◽  
Sarit Smolikove
Keyword(s):  
Nuclear Envelope ◽  
Chromosome Pairing ◽  
Meiotic Prophase ◽  
Homologous Chromosome ◽  
Strand Break ◽  
Crossing Over ◽  
Chromosome Movement ◽  
Microtubule Network ◽  
Homologous Chromosome Pairing ◽  
Proper Movement

In meiotic prophase I, homologous chromosome pairing is promoted through chromosome movement mediated by nuclear envelope proteins, microtubules, and dynein. After proper homologue pairing has been established, the synaptonemal complex (SC) assembles along the paired homologues, stabilizing their interaction and allowing for crossing over to occur. Previous studies have shown that perturbing chromosome movement leads to pairing defects and SC polycomplex formation. We show that FKB-6 plays a role in SC assembly and is required for timely pairing and proper double-strand break repair kinetics. FKB-6 localizes outside the nucleus, and in its absence, the microtubule network is altered. FKB-6 is required for proper movement of dynein, increasing resting time between movements. Attenuating chromosomal movement in fkb-6 mutants partially restores the defects in synapsis, in agreement with FKB-6 acting by decreasing chromosomal movement. Therefore, we suggest that FKB-6 plays a role in regulating dynein movement by preventing excess chromosome movement, which is essential for proper SC assembly and homologous chromosome pairing.

Nuclear division in the marine dinoflagellate Oxyrrhis marina

1986 ◽  
Vol 85 (1) ◽  
pp. 161-175
Author(s):  
X.P. Gao ◽  
J.Y. Li
Keyword(s):  
Nuclear Envelope ◽  
Phylogenetic Relationships ◽  
Nuclear Division ◽  
Metaphase Plate ◽  
Active Role ◽  
Ultrastructural Changes ◽  
Interphase Nuclei ◽  
Oxyrrhis Marina ◽  
Two Stages ◽  
Anaphase B

The nuclear division of Oxyrrhis marina is a very distinct one among the mitoses of dinoflagellates that have been studies. Using synchronized populations, we have investigated the ultrastructural changes in this nuclear division. In interphase, nuclei can be classified into two groups on the basis of the shapes of the chromosomes. Y- and U-shaped chromosomes have been observed in both types of interphase nuclei. By prophase the nucleus becomes oval, many nuclear plaques appear on the nuclear envelope, and many microtubules radiate from these nuclear plaques within the nucleus. Metaphase can be identified by the characteristic arrangement of the chromosomes; an equatorial metaphase plate is absent. As in many higher organisms, anaphase includes two stages: anaphase A and anaphase B. During anaphase A the nucleus does not apparently elongate and the chromosomes migrate towards the poles by a combination of the shortening of the chromosome-associated microtubules and the elongation of those located between daughter chromosomes. During anaphase B the nucleus elongates to about twice its former length. This elongation may result from growth of the interzonal nuclear envelope. Dividing nucleoli are associated with microtubules, which suggests that microtubules may play an active role in the division of the nucleolus. The evolution of mitosis and the phylogenetic relationships between Oxyrrhis, typical dinoflagellates and Syndinium are discussed.

Cytochemical Adenosinetriphosphatase in Plant Root Meristem

1968 ◽  
Vol 3 (3) ◽  
pp. 423-436
Author(s):  
NORMA SHIFRIN ◽  
L. LEVINE
Keyword(s):  
Atpase Activity ◽  
Root Meristem ◽  
Plant Root ◽  
Root Tip ◽  
Chromosome Movement ◽  
Nuclear Membranes ◽  
Late Anaphase ◽  
Rnase Treatment ◽  
Mitotic Cells

Root tip meristems were stained to demonstrate ATPase activity by two different methods, with general agreement in localization but not specificity, and with emphasis on mitotic cells. In interphase, ATPase was localized in nucleoli and nuclear membranes, with lesser activity in the nuclear substance. In prophase, chromosomes were outlined by ATPase stain which gradually declined in intensity at prometaphase, becoming least evident in metaphase. Staining activity increased again in anaphase, and remained high in telophase. In prometaphase, anaphase and late anaphase--early telophase, the ATPase was concentrated in a fibril which appeared to coil around the chromosomes. The ATPase fibril was thinnest at metaphase and shorter and thicker at telophase. In addition, granules formed in association with the coils of the fibril in late anaphase and early telophase. Later on, these granules may have fused and contributed to nucleolar reformation. The ATPase never localized in the chromosomal fibre nor in any other region of the spindle. RNA generally localized like ATPase, but ATPase loci were unchanged after ribonuclease (RNase) treatment. Because of certain similarities between ATPase and argentaffin localization, some relationship between the nucleolus and ATPase is suggested. A mechanochemical transducing role is postulated for the ATPase, because cytochemical properties were like those of ATPase in the A-band of myofibrillae, and because other changes in it could be correlated with chromosome movement.

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