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At least 19 recordsLinked to original sources
PubMed1977

[Partial disorganization of the anaphasic segregation of chromosomes in plant cells: combined actions of griseofulvin, producer of pluripolar anaphases and 2 ipecac alkaloids, producers of floating pole anaphases].

Anaphasis may be slightly checked by various treatments which however result in a normal chromosomic separation. Griseofulvin exerts a direct though partial influence on the mitotic apparatus, which entails "pluripolar anaphasis"; on the other hand Ipecac alkaloïds act indirectly and produce "floating poles anaphases". Treatments combining griseofulvin with cepheline or tubulosine show that there is never any synergy between the two processes. These results support our hypothesis that floating poles anaphases are not a sign of slight C-mitotic action but only come from a lag between the appearance/disappearance of microtubules and that of chromosomes during anaphasis.

Anaphase↗
PubMed2026

The Small but Versatile Cyclin-Dependent Kinase Subunit CKS: C. elegans CKS-1 Regulates Anaphase Onset and Is Required for Anaphase B During Oocyte Meiosis.

The cyclin-dependent kinase subunit (CKS) remains the least well-understood component of the tripartite cyclin-dependent kinase (CDK) complexes that specify the proper sequence of events required to duplicate and segregate genomes during eukaryotic cell division. Our recent investigation of CKS requirements during Caenorhabditis elegans oocyte meiosis I and II documents an essential role for CKS in the execution of anaphase B and expands the known range of CKS influence on cell cycle regulation to a third class of E3 ligases. Our findings also further document how C. elegans oocytes use very different mechanisms to progress through these two sequential cell divisions that ultimately produce a haploid oocyte. In this Think Again article, we discuss our findings as they relate to previous studies of CKS in different model systems.

Animals↗
PubMed1978

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

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.

Anaerobiosis↗
PubMed1979

Temperature effects on anaphase chromosome movement in the spermatocytes of two species of crane flies (Nephrotoma suturalis Loew and Nephrotoma ferruginea Fabricius).

Using phase-contrast cinemicrography on living crane fly (Nephrotoma suturalis Loew and Nephrotoma ferruginea Fabricius) spermatocytes, we have studied the effects of a range of temperatures (6--30 degrees C) on the anaphase I chromosome-to-pole movements of both autosomes and sex chromosomes. In contrast to previous work we have been able to study chromosome-to-pole velocities of autosomes without concurrent pole-to-pole elongation. In these cells we found that the higher the temperature, the faster was the autosomal chromosomes movement. From reviewing the literature we find that the general pattern of the effects of temperature on chromosome movement is similar whether or not pole-to-pole elongation occurs simultaneously with the chromosome-to-pole movement. Changes in cellular viscosities calculated from measurements of particulate Brownian movement do not seem to be able to account for the observed velocity differences due to temperature. Temperature effects on muscle contraction speed, flagellar beat frequency, ciliary beat frequency, granule flow in nerves, and chromosome movement have been compared, as have the activation energies for the rate-limiting steps in these motile systems: no distinction between possible mechanisms of force production is possible using these comparisons. The data show that even the different autosomes within single spermatocytes usually move at different speeds. These velocity differences cannot simply be related to chromosome size as the autosomes are visually indistinguishable. The sex chromosomes start their anaphase poleward movement after that of the autosomes, and move more slowly (by a factor of about 4), but their velocities appear to be affected by temperature in the same fashion as those of the autosomes. The interval between the onset of autosome anaphase and sex chromosome anaphase is also affected by temperature: the higher the temperature, the shorter the interval between the 2 stages. We have observed abnormalities in sex chromosome segregation, which may be due to temperature, but have not determined what the exact temperature shift conditions are that cause these abnormalities.

Anaphase↗
PubMed2026

Targeting KIFC1 to disrupt centrosome clustering and trigger anaphase catastrophe in small-cell lung cancer.

Supernumerary centrosomes are a hallmark of cancer. To maintain viability, cancer cells cluster these centrosomes during mitosis, enabling bipolar division similar to that of normal cells. Disruption of this centrosome clustering leads to multipolar anaphase and apoptosis (anaphase catastrophe), which selectively eliminates cancer cells harboring supernumerary centrosomes. In this context, because the motor protein KIFC1 contributes to centrosome clustering, we investigated whether targeting of this mechanism through KIFC1 inhibition could be exploited in small-cell lung cancer (SCLC), an aggressive malignancy with limited treatment options and poor prognosis. Through in silico and in vitro analyses, as well as IHC of clinical samples, we found that KIFC1 is overexpressed and that centrosome amplification occurs more frequently in SCLC compared with normal tissues and other cancer types. Pharmacological and genetic inhibition of KIFC1 disrupted the clustering of supernumerary centrosomes, triggered multipolar mitosis, and exerted antineoplastic effects in SCLC cells, with minimal effects on noncancerous cells. These findings were validated and extended in vivo using SCLC xenograft models. Finally, cotargeting KIFC1 and the centrosome duplication regulator PLK4 further enhanced growth suppression in SCLC cells. Together, these results suggest that disrupting centrosome clustering and triggering anaphase catastrophe via KIFC1 inhibition may represent a promising therapeutic strategy for SCLC.

Humans↗
PubMed1977

Behaviour of kinetochore fibres in Haemanthus katherinae during anaphase movements of chromosomes.

A laser light source along with a new method of preparing endosperm cells of Haemanthus katherinae for differential interference contrast (DIC) microscopy has led to increased visibility of kinetochore fibres. Little information is available concerning the behaviour of these fibres during anaphase in living cells. In metaphase, kinetochore fibres are seen as distinct bundles of microtubules, here referred to as 'filaments', extending from the kinetochore to the 'diffuse' pole. They possess an apparent globular substructure which corresponds to the moving 'particles or states' described previously from ciné films. In early anaphase, the filaments of each kinetochore fibre lose their parallel orientation characteristic of metaphase and splay out so that the more peripheral filaments intermingle with those of other kinetochore fibres. This process begins at the poles and proceeds as a wave toward the kinetochores as chromosomal movement progresses. This behaviour has been examined in relation to a number of proposed models for the mechanism of chromosome movement and has been found to place some constraints on some models but to be consistent with any model that hypothesizes that chromosomes move as a consequence of cumulative cohesive lateral interactions of microtubules.

Anaphase↗
PubMed2026

Viral inhibition of the anaphase promoting complex enhances replication by elevating nucleotide pools.

The anaphase promoting complex/cyclosome (APC/C) is a large, ubiquitin ligase and a central regulator of cell cycle progression. By targeting key substrates for degradation during mitosis and G1 phase, the APC/C coordinates metabolic fluctuations that occur during the cell cycle. A diverse range of viruses have convergently evolved mechanisms to bind and inhibit the APC/C; however, a molecular understanding for these interactions has never been demonstrated. Here, we use chicken anemia virus (CAV), a small single-stranded DNA virus encoding only three proteins, to demonstrate the importance of viral APC/C inhibition during replication. We show that the Vp3 protein of CAV inhibits the APC/C, causing a dramatic mitotic arrest during infection. The mutant virus lacking Vp3 is defective for replication and can be rescued by APC/C inhibition. Metabolomic profiling during CAV infection revealed that Vp3 expression mediates a broad increase in nucleotide pools. Moreover, viral inhibition of the APC/C resulted in stabilization of enzymes required for nucleotide biosynthesis. These findings suggest that the APC/C is a general target of many viruses to elevate nucleotide levels and facilitate viral genome replication.

Anaphase-Promoting Complex-Cyclosome↗
PubMed1977

On the mechanism of anaphase spindle elongation in Diatoma vulgare.

Central spindles from five dividing cells (one metaphase, three anaphase, and one telophase) of Diatoma vulgare were reconstructed from serial sections. Each spindle is made up of two half-spindles that are composed almost entirely of polar microtubules. A small percentage of continuous microtubules and free microtubules were present in every stage except telophase. The half-spindles interdigitate at the midregion of the central spindle, forming a zone of overlap where the microtubules from one pole intermingle with those of the other. At metaphase the overlap zone is fairly extensive, but as elongation proceeds, the spindle poles move apart and the length of the overlap decreases because fewer microtubules are sufficiently long to reach from the pole to the zone of interdigitation. At telophase, only a few tubules are long enough to overlap at the midregion. Concurrent with the decrease in the length of the overlap zone is an increase in the staining density of the intermicrotubule matrix at the same region. These changes in morphology can most easily be explained by assuming zone mechanochemical interaction between microtubules in the overlap zone which results in a sliding apart of the two half-spindles.

Eukaryota↗
PubMed1976

[Electron microscopic study of the nuclear membrane of SPEV cells during mitosis. II. Reconstruction of the nuclear membrane (anaphase and telophase)].

Reformation of the nuclear envelope of the PKLV cells starts in the early anaphase when numerous contacts between membranous elements and chromosomes become visible. The nuclear envelope reforms, first, on the periphery of chromosomes and in chromosome's centromeric regions, and later - in the telomeric regions. The latest reconstruction of nuclear envelope occurs in spaces where microtubules come up close to the "nuclei", The appearance of normal pore complexes in the late telophase is preceded by the appearance, in the early and middle telophase, of pores with unusual structure.

Cell Line↗
PubMed1976

[Kinetic study of the accumulation of anaphasic abnormalities in a synchronized population of meristematic root cells of Allium sativum L].

A population of meristematic root cells of Allium sativum L. is previously synchronized thanks to Hydroxyurea. When it reaches mitosis, this population undergoes the action of different antimetabolic drugs which slightly check the normal operating of the mitotic spindle without preventing chromosomic separation. In such conditions we can obtain from 30 to 50 slightly altered anaphasic cells out of 1000 cells. This is enough to allow us to contemplate the electronic microscope study of these abnormalities.

Antimetabolites↗
PubMed1979

Role of spindle microtubules in the control of cell cycle timing.

Sea urchin eggs are used to investigate the involvement of spindle microtubules in the mechanisms that control the timing of cell cycle events. Eggs are treated for 4 min with Colcemid at prophase of the first mitosis. No microtubules are assembled for at least 3 h, and the eggs do not divide. These eggs show repeated cycles of nuclear envelope breakdown (NEB) and nuclear envelope reformation (NER). Mitosis (NEB to NER) is twice as long in Colcemid-treated eggs as in the untreated controls. Interphase (NER to NEB) is the same in both. Thus, each cycle is prolonged entirely in mitosis. The chromosomes of treated eggs condense and eventually split into separate chromatids which do not move apart. This "canaphase" splitting is substantially delayed relative to anaphase onset in the control eggs. Treated eggs are irradiated after NEB with 366-nm light to inactivate the Colcemid. This allows the eggs to assemble normal spindles and divide. Up to 14 min after NEB, delays in the start of microtubule assembly give equal delays in anaphase onset, cleavage, and the events of the following cell cycle. Regardless of the delay, anaphase follows irradiation by the normal prometaphase duration. The quantity of spindle microtubules also influences the timing of mitotic events. Short Colcemid treatments administered in prophase of second division cause eggs to assemble small spindles. One blastomere is irradiated after NEB to provide a control cell with a normal-sized spindle. Cells with diminished spindles always initiate anaphase later than their controls. Telophase events are correspondingly delayed. This work demonstrates that spindle microtubules are involved in the mechanisms that control the time when the cell will initiate anaphase, finish mitosis, and start the next cell cycle.

Animals↗
PubMed1979

Micromanipulation studies of chromosome movement. I. Chromosome-spindle attachment and the mechanical properties of chromosomal spindle fibers.

We have used micromanipulation to study the attachment of chromosomes to the spindle and the mechanical properties of the chromosomal spindle fibers. Individual chromosomes can be displaced about the periphery of the spindle, in the plane of the metaphase plate, without altering the structure of the spindle or the positions of the nonmanipulated chromosomes. From mid-prometaphase through the onset of anaphase, chromosomes resist displacement toward either spindle pole, or beyond the spindle periphery. In anaphase a chromosome can be displaced either toward its spindle pole or laterally, beyond the periphery of the spindle; however, the chromosome resists displacement away from the spindle pole. When an anaphase half-bivalent is displaced toward its spindle pole, it stops migrating until the nonmanipulated half-bivalents reach a similar distance from the pole. The manipulated half-bivalent then resumes its poleward migration at the normal anaphase rate. No evidence was found for mechanical attachments between separating half-bivalents in anaphase. Our observations demonstrate that chromosomes are individually anchored to the spindle by fibers which connect the kinetochores of the chromosomes to the spindle poles. These fibers are flexible, much less extensible than the chromosomes, and are to pivot about their attachment points. While the fibers are able to support a tensile force sufficient to stretch a chromosome, they buckle when subjected to a compressive force. Preliminary evidence suggests that the mechanical attachment fibers detected with micromanipulation correspond to the birefringent chromosomal spindle fibers observed with polarization microscopy.

Animals↗
PubMed1979

Tubulin and calmodulin. Effects of microtubule and microfilament inhibitors on localization in the mitotic apparatus.

Indirect immunofluorescence was used to determine the distribution of calmodulin in the mitotic apparatus of rat kangaroo PtK2 and Chinese hamster ovary (CHO) cells. The distribution of calmodulin in PtK2 cells was compared to the distribution of tubulin, also as revealed by indirect immunofluorescence. During mitosis, calmodulin was found to be a dynamic component of the mitotic apparatus. Calmodulin first appeared in association with the forming mitotic apparatus during midprophase. In metaphase and anaphase, calmodulin was found between the spindle poles and the chromosomes. While tubulin was found in the interzonal region throughout anaphase, calmodulin appeared in the interzone region only at late anaphase. The interzonal calmodulin of late anaphase condensed during telophase into two small regions, one on each side of the midbody. Calmodulin was not detected in the cleavage furrow. In view of the differences in the localization of calmodulin, tubulin, and actin in the mitotic apparatus, experiments were designed to determine the effects of various antimitotic drugs on calmodulin localization. Cytochalasin B, an inhibitor of actin microfilaments, had no apparent effect on calmodulin or tubulin localization in the mitotic apparatus of CHO cells. Microtubule inhibitors, such as colcemid and N2O, altered the appearance of tubulin- and calmodulin-specific fluorescence in mitotic CHO cells. Cold temperature (0 degrees C) altered tubulin-specific fluorescence of metaphase PtK2 cells but did not alter calmodulin-specific fluorescence. From these studies, it is concluded that calmodulin is more closely associated with the kinetichore-to-pole microtubules than other components of the mitotic apparatus.

Animals↗