Different Stages Of Cell Division Research Articles

Bundling of Microtubules by Motor and Tail Domains of a Kinesin-like Calmodulin-Binding Protein from Arabidopsis: Regulation by Ca2+/Calmodulin

Kinesin-like calmodulin-binding protein (KCBP), a novel kinesin-like protein from plants, is unique among kinesins and kinesin-like proteins in having a calmodulin-binding domain adjacent to its motor domain. KCBP localizes to mitotic microtubule (MT) arrays including the preprophase band, the spindle apparatus, and the phragmoplast, suggesting a role for KCBP in establishing these MT arrays by bundling MTs. To determine if KCBP bundles MTs, we expressed C-terminal motor and N-terminal tail domains of KCBP, and used the purified proteins in MT bundling assays. The 1.5 C protein with the motor and calmodulin-binding domains induced MT bundling. The 1.5 C-induced bundles were dissociated in the presence of Ca2+/calmodulin. Similar results were obtained with a 1.4 C protein, which lacks much of the coiled-coil region present in 1.5 C protein and does not form dimers. The N-terminal tail of KCBP, which contains an ATP-independent MT binding site, is also capable of bundling MTs. These results, together with the KCBP localization data, suggest the involvement of KCBP in establishing mitotic MT arrays during different stages of cell division and that Ca2+/calmodulin regulates the formation of these MT arrays.

The effects of elevated temperature on chiasma formation in Locusts migratoria

Individuals from an inbred laboratory stock of Locusta migratoria were subjected to 40° C heat treatments. These involved both constant 40° C treatment and shorter periods of 5, 4, 3, or 2 days at the high temperature followed by a return to the lower temperature of 30° C. Chiasma frequency analyses revealed that a total of four different effects could be produced by the heat treatments at different stages of cell division: two of the effects involved increases and two involved decreases. Similar, though not identical, effects have also been obtained in the locus Schistocerca gregaria. The similarities and differences in the responses shown by these two species are compared and contrasted.

Influence of cell-wall thickness on cell division: electron microscopic study with Bacillus cereus.

Bacillus cereus that had been exposed to chloramphenicol for 0 and 90 min synthesized walls whose thickness increased with time. These cells were washed and resuspended in fresh growth medium. Cell division was examined by electron microscopy. In untreated cells, a slight invagination of the cytoplasmic membrane with deposit of cross-wall material marked the onset of cell division. The cross wall grew inward until the septum was about [Formula: see text] completed. This was followed by splitting and bifurcation of the outer edge of the cross wall, which in turn separated the peripheral wall scars. Cross-wall penetration with further splitting continued until the daughter cells were completely partitioned. The peripheral wall scars that were located at the junction of peripheral and end walls at the time of cell separation indicated that the zone of cell division was probably not a region of active cell elongation. In cells treated with chloramphenicol for 90 min, cross-wall initiation and completion all occurred beneath a thickened peripheral wall. The circumferential portion of the peripheral wall at the zone of cell division appeared to be responsible for the hindrance of cell separation. This thick layer subsequently severed at three or four sites to allow the separation of daughter cells. For cells that had initiated cross-wall invagination at the time when chloramphenicol was added, accumulation of a large amount of cross-wall material at the zone of cell division was observed. Upon removal of the antibiotic, cells abandoned the old and initiated a new dividing site. For cells that had already completed cross-wall formation at the time of chloramphenicol treatment, the increase in wall thickness did not appear to interfere with cell separation. Models for the different stages of cell division in all these bacteria were presented.

Chemotherapy of tumors with continuous intravenous infusion of cytostatics

Sixty patients with advanced incurable cancer have been treated with continuous intravenous infusion with different anticancer drugs. The aim of the experiment was to reach prolonged high blood level of cytotoxic agents, to inhibit the growth of the whole cell population during the different stages of cell division. The study has confirmed that prolonged infusion of anticancer drugs affects both toxicity and therapeutic response. This suggests the use of the technique of prolonged intravenous infusion as the first «step» treatment in cancer chemotherapy.

The effect of X-radiation on fumarase activity during different stages of cell division in Tetrahymena pyriformis GL

1. 1. Tetrahymena pyriformis GL was grown in a two per cent solution of proteose peptone. 2. 2. Synchronous division was induced by the temperature flux method. 3. 3. The fumarase activity was tested at different stages of cell division in irradiated and non-irradiated cultures. 4. 4. There was a significant ( P < 0.05) difference in fumarase activity in all cases between the irradiated and non-irradiated determinations. 5. 5. A comparison of the enzymatic activity in the controls of each stage with the activity of the stages immediately preceding and following showed a significant ( P < 0.05) difference in all cases with the exception of the step from stage III to stage V. 6. 6. A comparison of the enzymatic activity in the experimentals of each stage with the activity of the stages immediately preceding and following showed a significant ( P < 0.05) difference in all cases. 7. 7. Ionizing radiation was found to inhibit fumarase activity. 8. 8. The highest rate of enzyme activity was found in the interphase stage of cell division. 9. 9. This acceleration of enzymatic activity is thought to be the result of an attempt of the organisms to replenish the energy needed to carry on the processes of cell division. 10. 10. The enzymatic activity was increased by the addition of phosphate ions. 11. 11. Basic and acid dyestuffs had toxic effects on the enzyme. 12. 12. An enlargement of the cells following exposure to ionizing radiation was noted.

The effect of ultraviolet radiation on succinic dehydrogenase activity during different stages of cell division

1. 1. T. pyriformis GL was grown in a chemically defined medium. 2. 2. Synchronous division was induced by the temperature flux method. 3. 3. The succinic dehydrogenase activity was tested in both control and irradiated cultures of each stage of division. 4. 4. The enzymatic activity of those control organisms tested immediately after shock treatment and those tested 150 minutes after shock treatment (stages II and VII) was inhibited when compared to the normal control (stage I). 5. 5. In the same two stages (II and VII), radiation caused a significant acceleration of activity. 6. 6. We feel that this acceleration of enzymatic activity may be the result of an attempt on the part of the organisms to recover from the lethal effects of radiation.

The Effects of Temperature on the Durations of the Different Stages of Cell Division in the Root-tip

A new technique for determining the durations of the different phases of division is described. It is shown that at 15° C. the mean durations of the several phases in the root-tip of the pea are as follows: interphase 23 hours; prophase 2 hours; metaphase 25 minutes; anaphase 5 minutes; telophase 22 minutes. The effects of different temperatures have been determined, and it is shown that all stages are accelerated by an increase in temperature from 15° to 25° C, the ratios of the durations at the two temperatures being about 2-o or slightly less. It is suggested that since interphase is the longest stage of the division cycle, in terms of growth effects on this stage are the most significant.

Experimental studies on nuclear and cell division

During several seasons extensive experiments were made on the segmenting eggs of Crepidula plana. These experiments included a study of the influence on nuclear and cell division of hypertonic and hypotonic sea water, of ether, alcohol, etc., of the lack of oxygen, of the electric current, and of pressure and shaking. The following general conclusions may be drawn from this work:1. Under the same treatment the effects may be extremely varied, owing, probably, to the different stages of cell division acted upon.2. A dividing cell is much more easily disturbed or rendered abnormal than is a resting one; the mitotic figure in particular is very easily altered and most of the abnormalities observed arise from this source.3. The earlier stages of cleavage are much more easily altered than are the later ones.4. Certain general abnormalities occur after the most varied treatment, e. g., the general results both of concentration and of dilution of sea water are to produce polyasters and to prevent the cleavage of...