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PubMed2001

Analysis of cell division parameters and cell cycle gene expression during the cultivation of Arabidopsis thaliana cell suspensions.

Arabidopsis thaliana cell suspension cultures were characterized for the first time in detail in terms of biomass accumulation, cell division rate and cell cycle phase durations. Subsequently, this model system was used to follow the transcription profile of key cell cycle genes during a complete cultivation cycle. According to the calculated changes in the relative division rate over time, the cell cycle genes could be classified into four groups based on their transcriptional expression pattern. These differential patterns of gene expression are discussed with respect to the putative roles of the different cell cycle genes in the division cycle. Analysis of protein levels showed that mRNA levels did not correlate with protein levels in all cases. Results obtained in other systems, such as BY-2 cell suspensions or plants, confirm that cell suspension cultures of A. thaliana are suitable for the analysis of cell cycle regulation.

Arabidopsis↗
PubMed1998

Microbial asymmetric cell division: localization of cell fate determinants.

The genetic mechanisms that control asymmetric cell divisions--yielding progeny cells that differ from one another--have been conserved among prokaryotes, eukaryotic microbes, and higher organisms. All use the paradigm of regulatory protein localization as a way of translating genetic information into three-dimensional space.

Animals↗
PubMed1976

Action of rotenone and related respiratory inhibitors on mammalian cell division. 1 Cell kinetics and biochemical aspects.

Inhibitors of mitochondrial respiration, phosphorylation inhibitors, and uncoupling agents have been reported to delay or inhibit mitosis in cultured mammalian cells. Although the molecular mechanism by which mitosis is delayed in the presence of most respiratory inhibitors presumably involves lowered ATP production for mitotic requirements, one respiratory inhibitor, rotenone, was determined to arrest mitosis by an unrelated mechanism. Cell cycle kinetics studies, oxygen consumption measurements, and viscosity assays indicate that rotenone arrests cultured mammalian cells in mitosis by inhibiting spindle microtubule assembly by a mechanism analogous with colchicine, Colecemid and related antimitotic drugs. Amytal, which blocks electron transport at the same site as does rotenone, failed to arrest cell progression at mitosis. Rotenone delayed cell progression in all phases of the cell cycle, apparently as a direct result of respiration inhibition. Thus, rotenone appears to exert a dual function on events of the cell cycle.

Amobarbital↗
PubMed2005

Nitric oxide is required for, and promotes auxin-mediated activation of, cell division and embryogenic cell formation but does not influence cell cycle progression in alfalfa cell cultures.

It is now well established that nitric oxide (NO) serves as a signaling molecule in plant cells. In this paper experimental data are presented which indicate that NO can stimulate the activation of cell division and embryogenic cell formation in leaf protoplast-derived cells of alfalfa in the presence of auxin. It was found that various NO-releasing compounds promoted auxin-dependent division (as shown by incorporation of bromodeoxyuridine) of leaf protoplast-derived alfalfa cells. In contrast, application of NO scavenger or NO synthesis inhibitor inhibited the same process. Both the promotion and the inhibition of cell cycle activation correlated with the amount and activity of the cognate alfalfa p34cdc2 protein Medsa;CDKA;1,2. The effect of l-NG-monomethyl-L-arginine (L-NMMA) was transient, and protoplast-derived cells spending more than 3 days in culture become insensitive to the inhibitor as far as cell cycle progression was concerned. L-NMMA had no effect on the cell cycle parameters of cycling suspension-cultured cells, but had a moderate transient inhibitory effect on cells re-entering the cell cycle following phosphate starvation. Cycling cultured cells, however, could respond to NO, as indicated by the sodium nitroprusside (SNP)- and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO)-dependent accumulation of the ferritin protein. Based on these observations, it is hypothesized that L-NMMA-sensitive generation of NO is involved in the activation, but not the progression of the plant cell division cycle. In addition, SNP promoted and L-NMMA delayed the exogenous auxin [2,4-dichlorophenoxyacetic acid (2,4-D)] concentration-dependent formation of embryogenic cell clusters expressing the MsSERK1 gene; this further supports a link between auxin- and NO-dependent signaling pathways in plant cells.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1973

Bacterial cell division regulation: lysogenization of conditional cell division lon - mutants of Escherichia coli by bacteriophage.

The lon(-) mutants of Escherichia coli grow apparently normally except that, after temporary periods of inhibition of deoxyribonucleic acid synthesis, septum formation is specifically inhibited. Under these conditions, long, multinucleate, nonseptate filaments result. The lon(-) mutation also creates a defect such that wild-type bacteriophage lambda fails to lysogenize lon(-) mutants efficiently and consequently forms clear plaques on a lon(-) host. Two lines of evidence suggest that this failure probably results from interference with expression of the lambdacI gene, which codes for repressor, or with repressor action:-(i) when a lon(-) mutant was infected with a lambdacII, cIII, or c Y mutant, there was an additive effect between the lon(-) mutation and the lambdac mutations upon reduction of lysogenization frequency; and (ii) lon(-) mutants permitted the growth of the lambdacro(-) mutant under conditions in which the repressor was active. The isolation of lambda mutants (lambdatp) which gained the ability to form turbid plaques on lon(-) cells is also reported.

Cell Division↗
PubMed1996

An ultradian clock controls locomotor behaviour and cell division in isolated cells of Paramecium tetraurelia.

An ultradian clock operates in fast growing cells of the large ciliate, Paramecium tetraurelia. The period of around 70 minutes is well temperature-compensated over the temperature range tested, i.e. between 18 degrees C and 33 degrees C. The Q10 between 18 degrees C and 27 degrees C is 1.08; above 27 degrees C there is a slight overcompensation. The investigation of individual cells has revealed that two different cellular functions are under temporal control by this ultradian clock. First, locomotor behaviour, which is an alternation between a phase of fast swimming with only infrequent turning, and a phase of slow swimming with frequent spontaneous changes of direction. In addition, the ultradian clock is involved in the timing of cell division. Generation times are not randomly distributed, but occur in well separated clusters. At all of the six temperatures tested, the clusters are separated by around 70 minutes which corresponds well to the period of the locomotor behaviour rhythm at the respective temperatures. Whereas the interdivision times were gradually lengthened both above and below the optimum growth temperature, the underlying periodicity remained unaffected. Also cells of different clonal age had identical periods, suggesting that neither the differences in DNA content, not other changes associated with ageing in Paramecium have an effect on the clock. A constant phase relationship was observed between the rhythm in locomotor behaviour and the time window for cell division; this strongly suggests that the same ultradian clock exerts temporal control over both processes.

Animals↗
PubMed1984

Relationship between ascorbic acid and cell division.

Proliferating cells require large amounts of ascorbic acid to reach cell division. The decrease in ascorbic acid caused by adding lycorine, an inhibitor of ascorbic acid biosynthesis, induces profound inhibition of cell division: the cell cycle is arrested in G1 and G2 phase, more than 90% of the cells being accumulated in G1 after some time. The effect of lycorine on mitotic index (MI) has been reversed by increasing experimentally the concentration of ascorbic acid in tissues. Ascorbic acid control on cell division is found to be specific, since isoascorbic acid is wholly ineffective. It is suggested that the principal role of ascorbic acid in the cell cycle may be related to its action in controlling the synthesis of hydroxyproline-containing proteins, which can be essential requirements for development of G1 and G2.

Alkaloids↗
PubMed1995

Asymmetric segregation of Numb and Prospero during cell division.

A cell can divide asymmetrically by specifically segregating a determinant into one of its daughter cells. The Numb protein is a candidate for such a determinant in the asymmetric cell divisions of the developing Drosophila nervous system. Numb is a membrane-associated protein that localizes asymmetrically during cell division and segregates into one daughter cell, where it is required for the specification of the correct cell fate. Here we show that a nuclear protein, Prospero, translocates to the membrane at the beginning of cell division and colocalizes with Numb throughout mitosis, suggesting a common mechanism for asymmetric segregation. Numb and Prospero localization is coupled to mitosis and tightly correlated with the position of one of the two centrosomes. In contrast to centrosome positioning, however, Numb and Prospero localization is independent of microtubules. Cytochalasin D treatment suggests that the process is also independent of actin. We propose that there is an organizer of asymmetric cell division which provides positional information for both the orientation of the mitotic spindle and asymmetric localization of Numb and Prospero.

Actins↗
PubMed1997

A novel prespore-cell-inducing factor in Dictyostelium discoideum induces cell division of prespore cells.

In Dictyostelium discoideum strain V12M2, at a very low cell density (approximately 10(2) cells/cm2), most amoebae differentiate into prespore cells in a salt solution containing cAMP if an adequately diluted conditioned medium (CM) is provided (Oohata, A. A. (1995) Differentiation 59, 283-288). This finding suggests the presence of factor(s) released into the medium that are involved in inducing prespore cell differentiation. In the present study, we report the presence of two types of factors that function synergistically in prespore cell induction; one is a heat-stable and dialysable factor(s) and the other is a heat-labile and non-dialysable factor termed psi (psi) factor (prespore-inducing factor). We purified and characterized the psi factor. Its relative molecular mass was determined to be 106x10(3) Mr by SDS-PAGE and 180x10(3) Mr by gel filtration HPLC, respectively. These results indicate that psi factor exists as a dimer under native conditions. In addition to inducing prespore cell differentiation, psi factor induced cell division of prespore cells in submerged culture. Our results suggest that psi factor plays important roles not only in prespore cell differentiation but also in the progress of the cell cycle in the prespore pathway in normal development.

Animals↗
PubMed1991

Reduction in lactate accumulation correlates with differentiation-induced terminal cell division of leukemia cells.

Lactate accumulation in the medium and glucose utilization decreased during the induction of in vitro differentiation of mouse erythroleukemia (MEL) and human myeloid leukemia (HL-60) cells. The decrease in lactate accumulation occurred as early as 24 h after inducer treatment was initiated and occurred prior to the decrease in glucose utilization. The decrease in lactate accumulation was greater than that predicted by the decrease in glucose utilization, i.e., the ratio of glucose used glycolytically, as measured by lactate accumulation, to glucose used in other pathways ('glycolytic ratio') markedly decreased during differentiation in these cell lines. Differentiation correlated with the abrogation of the high levels of lactate accumulation first described by Warburg as characteristic of some transformed and neoplastic cells. Studies on both parental and differentiation-resistant variant MEL cell lines indicated that the changes in lactate accumulation were not dependent on the changes in glucose utilization and could be dissociated from them. Moreover, the changes in lactate accumulation only occurred in cells able to undergo differentiation-induced terminal cell division. This regulatable expression of lactate accumulation in MEL and HL-60 cells in vitro may make them useful model systems for the elucidation of the molecular mechanisms controlling lactate formation in malignant cells.

Acetamides↗
PubMed1999

Coordination of cell growth with cell division.

Proliferating cells must increase their mass coordinately with cell division. Recent evidence suggests that coupling of cell growth with cell division might be achieved by making synthesis of activators of cell division particularly sensitive to the capacity of the cell's protein synthesis machinery.

Animals↗
PubMed1983

Studies on cell division in mammalian cells. VII. A temperature-sensitive cell line abnormal in centriole separation and chromosome movement.

A temperature-sensitive Syrian hamster mutant cell line, ts-745, exhibiting novel mitotic events has been isolated. The cells show normal growth and mitosis at 33 degrees C, the permissive temperature. At the nonpermissive temperature of 39 degrees C, mitotic progression becomes aberrant. Metaphase cells and those cells still able to form a metaphase configuration continue through and complete normal cell division. However, cells exposed to 39 degrees C for longer than 15 min can not form a normal metaphase spindle. Instead, the chromosomes are distributed in a spherical shell, with microtubules (MT) radiating to the chromosomes from four closely associated centrioles near the center of the cell. The cells progress from the spherical monopolar state to other monopolar orientations conical in appearance with four centrioles in the apex region. Organized chromosome movement is present, from the spherical shell state to the asymmetrical orientations. Chromosomes remain in the metaphase configuration without chromatid separation. Prometaphase chromosome congression appears normal, as the chromosomes and MT form a stable monopolar spindle, but bipolar spindle formation is apparently blocked in a premetaphase state. When returned from 39 degrees to 33 degrees C, the defective phenotype is readily reversible. At 39 degrees C, the mitotic abnormality lasts 3-5 h, followed by reformation of a single nucleus and cell flattening in an interphase-like state. Subsequent cell cycle events appear to occur, as the cells duplicate chromosomes and initiate a second round of abnormal mitosis. Cell cycle traversion continues for at least 5 d in some cells despite abnormal mitosis resulting in cells accumulating several hundred chromosomes.

Animals↗
PubMed1985

Protease induction of hemoglobin synthesis but not terminal cell division in K562 cells.

Several protease preparations of varied specificity increased hemoglobin levels in K562 cells. These are the first enzymes shown to stimulate this process in these cells. Hemin, at a concentration at which it did not act as a potent inducer of hemoglobin production, was found to synergistically stimulate induction by proteases. As seen in some other cell types, six different protease preparations also stimulated K562 cell yield. Hemin did not enhance the protease stimulation of cell yield, but was, instead, slightly inhibitory. Trypsin was one of the most potent inducers of the proteases tested. A combination of trypsin with a "synergistic" concentration of hemin did not decrease the size of K562 cells during induction of hemoglobin production, suggesting that these cells were not irreversibly differentiated nor induced to terminal cell division by this treatment. This was supported, although not proven, by an assay that demonstrated no progressive decrease in the rate of cell multiplication associated with the induction of hemoglobin synthesis.

Animals↗
PubMed2002

Auxin efflux carrier activity and auxin accumulation regulate cell division and polarity in tobacco cells.

Division and growth of most types of in vitro-cultured plant cells require an external source of auxin. In such cultures, the ratio of external to internal auxin concentration is crucial for the regulation of the phases of the standard growth cycle. In this report the internal concentration of auxin in suspension-cultured cells of Nicotiana tabacum L., strain VBI-0, was manipulated either (i) by increasing 10-fold the normal concentration of 1-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid in the external medium; or (ii) by addition 1-N-naphthylphthalamic acid (NPA; an inhibitor of auxin efflux and of auxin efflux carrier traffic). Both treatments delayed the onset of cell division for 6-7 days without loss of cell viability. In both cases, cell division activity subsequently resumed coincident with a reduction in the ability of cells to accumulate [(3)H]NAA from an external medium. Following renewed cell division, a significant proportion of the NPA-treated cells but not those grown at high auxin concentration, exhibited changes in the orientation of new cell divisions and loss of polarity. We conclude that cell division, but not cell elongation, is prevented when the internal auxin concentration rises above a critical threshold value and that the directed traffic of auxin efflux carriers to the plasma membrane may regulate the orientation of cell divisions.

2,4-Dichlorophenoxyacetic Acid↗