Studies on the cell wall of Chlorella I. Quantitative changes in cell wall polysaccharides during the cell cycle of Chlorella ellipsoidea

1. 1. The cell wall of Chlorella ellipsoidea was fractionated intotwo components, alkali-soluble hemicellulose and alkali-insoluble"rigid wall". The former was composed of several neutral sugars,i.e. rhamnose, xylose, arabinose, mannose and galactose, andthe latter had glucosamine as a main constituent sugar.
2. 2.Quantitative changes in both hemicellulose and "rigid wall"contents during the cell cycle were followed using synchronouslygrown cells. The two cell wall components showed markedly differentchanges. Hemicellulose increased in proportion to the enlargementof the cell surface area in the growing phase, while the "rigidwall" remained almost constant in this phase. The "rigid wall"increased only in the reproduction phase—the time of autosporeformation.

(Received September 26, 1977; )     

Chromatin changes during the cell cycle.

Considerable progress has recently been made in elucidating the biochemical mechanisms regulating changes in chromatin structure during all stages of the cell cycle. Although anticipated, the apparently ubiquitous role played by phosphorylation/dephosphorylation reactions in modulating these changes is, nonetheless, remarkable.     

Stepwise accumulation of autoregulated enzyme activities during the cell cycle of the eucaryote Chlorella

Although the allocyclic X chromosome of the mouse frequently appears heteropycnotic, showing chromatid apposition, the feature is not necessarily consistent in conventionally stained metaphases. In contrast, the quinacrine mustard fluorescence and acetic saline Giemsa techniques unambiguously delineate the asynchronously replicating, allocyclic X in most metaphase spreads prepared from 6.5–7.5 days old female embryos, where the allocyclic X is characterized by bright fluorescence over the entire length with two faintly dark bands in the lower middle regions. The same X shows heavy staining by the ASG technique, resulting in less conspicuous banding pattern as compared with its isocyclic homologue. The above features are confirmed in adult bone marrow cells and primary fibroblast culture of the lung derived from the adult female as well as the 18-day-old embryo, though the frequency of cells with an identifiable allocyclic X decreases to some extent. Length measurement demonstrates that the allocyclic X is slightly shorter than the isocyclic one.     

Bone cell elasticity and morphology changes during the cell cycle

The mechanical properties of cells are reported to be regulated by a range of factors including interactions with the extracellular environment and other cells, differentiation status, the onset of pathological states, as well as the intracellular factors, for example, the cytoskeleton. The cell cycle is considered to be a well-ordered sequence of biochemical events. A number of processes reported to occur during its progression are inherently mechanical and, as such, require mechanical regulation. In spite of this, few attempts have been made to investigate the putative regulatory role of the cell cycle in mechanobiology. In the present study, Atomic Force Microscopy (AFM) was employed to investigate the elastic modulus of synchronised osteoblasts. The data obtained confirm that osteoblast elasticity is regulated by cell cycle phase; specifically, cells in S phase were found to have a modulus approximately 1.7 times that of G1 phase cells. Confocal microscopy studies revealed that aspects of osteoblast morphology, namely F-actin expression, were also modulated by the cell cycle, and tended to increase with phase progression from G0 onwards. The data obtained in this study are likely to have implications for the fields of tissue- and bio-engineering, where prior knowledge of cell mechanobiology is essential for the effective replacement and repair of tissue. Furthermore, studies focused on biomechanics and the biophysical properties of cells are important in the understanding of the onset and progression of disease states, for example cancer at the cellular level. Our study demonstrates the importance of the combined use of traditional and relatively novel microscopy techniques in understanding mechanical regulation by crucial cellular processes, such as the cell cycle.     

再议细胞周期中染色体、DNA的数量变化规律

对核质不同步分裂时染色体、DNA数量变化规律进行了补充,对染色体、DNA在细胞核中的数量变化进行了分析,并绘制曲线加以比较。     

Intracellular pH changes during the cell cycle in Tetrahymena.

The equilibrium distribution of 5,5-dimethyloxazoladine 2,4-dione (DMO) between intra- and extracellular volume was used to estimate intracellular pH (pHi) in Tetrahymena pyiformis. In control experiments, DMO was found to equilibrate rapidly in response to a pH gradient. Under normal growth conditions, pHi was constant over a finite range of external pH, being maintained near pH 7.1 over the external pH range 5.2 to 7.3. This same range of external pH was also optimal for growth. pHi was monitored during the cell cycle of a synchronous population of T. pyriformis GL. The cells were synchronized either by starvation/refeeding or heat shock. Under both conditions, there were two alkaline shifts of approximately 0.4 pH units per cell cycle. These shifts in pH retained a constant remporal relationship to S phase and were not affected by changes in the time, duration, or magnitude of cytokinesis.     

Synthetic rates of chloroplast and cytoplasmic ribosomal ribonucleic acids during the cell cycle of Chlorella

By feeding radioisotopic precursors of RNA ([5-³H]uracil and[5-³H]uridine) to cells of Chlorella ellipsoidea at variousstages in the cell cycle effected by autotrophic synchronousculture, we examined synthetic rates of the chloroplast andthe cytoplasmic ribosomal ribonucleic acids (chl-rRNA and cyt-rRNA,respectively). The net incorporation of the precursors intochl-rRNA was higher than that into cyt-rRNA in the early stagesof the cell cycle, and vice versa in the late stages. The specificactivity of chl-rRNA was extremely high, and this phenomenonwas likely to be intrinsic to small cells at the start of thecell cycle under autotrophic conditions, namely, cell-cyclestagespecific. We conclude that algal cells grown autotrophicallysynthesize chl-rRNA at a distinctly higher rate than cyt-rRNAin the early stages of the cell cycle. (Received July 21, 1978; )     

Flash-induced oxygen yield sequences during the life cycle of Chlorella

(i) The pattern of O₂ flash yields in the first 4 hours of the life cycle cannot be described by the simple Kok model without additional assumptions. (ii) The miss coefficient in the mature cells in significantly higher than that in the autospores, its change occurring at the expense of the single-hit coefficient . Computer simulation yielded values of 0.29 and 0.23 and values of 0.66 and 0.72 in the light and dark, respectively. (iii) The onset of light at the beginning of the cycle drastically changes the equilibrium distribution of the S states in the dark; the ratio S₀/S₁ increases from 30/70 to 50/50 in 1 h, and is restored not earlier than in the 6th hour. (iv) In the presence of 1 mmol/l p-benzoquinone, the alga shows pronounced and long-lasting oscillations in the O₂ yield sequences, independently of the time of the life cycle. This means that the O₂-evolving system itself is always present and equally efficient throughout the life cycle. Limits imposed on its activity (mainly in the first 4 hours) are clearly of an external nature. The redox potential of the inner thylakoid space is presumably involved.Abbreviations BQ p-benzoquinone - DCIP 2,6-dichlorophenolindophenol - OES oxygen-evolving system - PS photosystem     

Directionality of F-actin cables changes during the fission yeast cell cycle

Longitudinal F-actin cables are thought to be important for transporting materials for polarized cell growth in fission yeast. We show that most F-actin in the cables is oriented such that the barbed end faces the nearest cell tip during interphase; however, this directionality is reversed during mitosis. These orientations of F-actin ensure proper transport of materials to growing sites during these cell-cycle stages.     

Dynamic changes in the subcellular localization of Drosophila beta-sarcoglycan during the cell cycle

One of the proposed roles of sarcoglycan is to stabilize dystrophin glycoprotein complexes in muscle sarcolemma. Involvement in signal transduction has also been proposed and abnormalities in some sarcoglycan genes are known to be responsible for muscular dystrophy. While characterization of sarcoglycans in muscle has been performed, little is known about its functions in the non-muscle tissues in which mammalian sarcoglycans are expressed. Here, we investigated temporal and spatial expression patterns of Drosophila beta-sarcoglycan (dScgbeta) during development by immunohistochemistry. In addition to almost ubiquitous expression in various tissues and organs, as seen for its mammalian counterpart, anti-dScgbeta staining data of embryos, eye imaginal discs, and salivary glands demonstrated cytoplasmic localization during S phase in addition to plasma membrane staining. Furthermore we found that subcellular localization of dScgbeta dramatically changes during mitosis through possible association with tubulin. These observations point to a complex role of sarcoglycans in non-muscle tissues.     

The course of respiration during the life cycle of Chlorella cells

Endogenous and glucose respiration were studied during the life history of Chlorella pyrenoidosa. A generalized picture of the course of respiration during the life cycle is suggested. At the liberation of daughter cells from the wall of the mother cell, or soon after, the respiration rate reaches its lowest level. If the daughter cells are placed in light the respiration rate rapidly increases with time, soon reaches a maximum, and then declines slowly. Two factors are important in the initial increase—the early developmental stage of the cells and the influence of light. In autotrophically developing algae the parts played by developmental processes and by light have not been separated. Direct activation of respiratory enzymes by light, in addition to the level of respiratory substrate, cannot be excluded. The decline of respiration rate over most of the cell history seems to have no connection with light and is probably bound to the developmental processes per se. Darkening the suspension interrupts growth and induces liberation of daughter cells, with concomitant faster decrease in respiration rate. The rate of respiration of small daughter cells decreases in darkness only slowly with time. Illumination seems necessary to bring these cells back to a high level of respiratory activity.     

Endothelial cell subpopulations in vitro: cell volume, cell cycle, and radiosensitivity

Vascular endothelial cells (EC) are important clinical targets of radiation and other forms of free radical/oxidant stresses. In this study, we found that the extent of endothelial damage may be determined by the different cytotoxic responses of EC subpopulations. The following characteristics of EC subpopulations were examined: 1) cell volume; 2) cell cycle position; and 3) cytotoxic indexes for both acute cell survival and proliferative capacity after irradiation (137Cs, gamma, 0-10 Gy). EC cultured from bovine aortas were separated by centrifugal elutriation into subpopulations of different cell volumes. Through flow cytometry, we found that cell volume was related to the cell cycle phase distribution. The smallest EC were distributed in G1 phase and the larger cells were distributed in either early S, middle S, or late S + G2M phases. Cell cycle phase at the time of irradiation was not associated with acute cell loss. However, distribution in the cell cycle did relate to cell survival based on proliferative capacity (P less than 0.01). The order of increasing radioresistance was cells in G1 (D0 = 110 cGy), early S (135 cGy), middle S (145 cGy), and late S + G2M phases (180 cGy). These findings 1) suggest an age-related response to radiation in a nonmalignant differentiated cell type and 2) demonstrate EC subpopulations in culture.