Effect of static magnetic fields on the budding of yeast cells

The effect of static magnetic fields on the budding of single yeast cells was investigated using a magnetic circuit that was capable of generating a strong magnetic field (2.93 T) and gradient (6100 T² m^?1). Saccharomyces cerevisiae yeast cells were grown in an aqueous YPD agar in a silica capillary under either a homogeneous or inhomogeneous static magnetic field. Although the size of budding yeast cells was only slightly affected by the magnetic fields after 4 h, the budding angle was clearly affected by the direction of the homogeneous and inhomogeneous magnetic fields. In the homogeneous magnetic field, the budding direction of daughter yeast cells was mainly oriented in the direction of magnetic field B. However, when subjected to the inhomogeneous magnetic field, the daughter yeast cells tended to bud along the axis of capillary flow in regions where the magnetic gradient, estimated by B(dB/dx), were high. Based on the present experimental results, the possible mechanism for the magnetic effect on the budding direction of daughter yeast cells is theoretically discussed. Bioelectromagnetics 31:622–629, 2010. © 2010 Wiley‐Liss, Inc.     

The distribution of chromatin in budding yeast cells

Summary and conclusions A critical examination of well fixed yeast cells killed at different states in the growth cycle shows that the distribution of chromatin in the yeast cell varies depending on the stage in the growth cycle. Our data support the view (1) that the spindle is intravacuolar, (2) that mitosis occurs on the spindle, (3) that the chromosomes spin out after mitosis to extend into the vacuole, (4) that a large nucleolus appears in the nuclear vacuole of rapidly growing wellnourshed cells, and (5) that in the presence of adequate amounts of phosphate and otherwise favorable conditions the chromosomes are covered with metaphosphate. This work has been supported by grants from the National Cancer Institute of the National Institutes of Health, Public Health Service C-2140 and from the Illinois Division of the American Cancer Society.     

Age-related changes in the physiological state of budding yeast cells

Biochemical and physiological changes occurring during the relative ageing of budding yeast cells were studied. In contrast to scar-free daughter cells the scar-bearing mother cells display a longer G1 phase of the cell cycle, synthesize RNA more slowly, consume oxygen more rapidly, possess a higher saturation constant K_s, and their cell walls are less resistant to mechanical strain.     

Dependence of the radiosensitivity of yeast cells on the LET of radiations. Experiments on haploid cells

The previously developed model was used to study the dependence of radiosensitivity (D0(-1) of Saccharomyces cerevisiae (the wild type and radiosensitive mutant) on linear energy transfer (LET) of ionizing radiation. D0(-1) (L) of haploid yeasts was shown to be associated, to a certain extent, with the capacity of radiation damages repair. As to the wild-type cells, the above function was represented by a curve showing a maximum, while a descending curve was characteristic of the radiosensitive mutant cells deficient in radiation damages repair. The influence of the repair processes on cell radiosensitivity decreased with increasing LET.     

Sociobiology of the budding yeast

Social theory has provided a useful framework for research with microorganisms. Here I describe the advantages and possible risks of using a well-known model organism, the unicellular yeast Saccharomyces cerevisiae, for sociobiological research. I discuss the problems connected with clear classification of yeast behaviour based on the fitness-based Hamilton paradigm. Relevant traits include different types of communities, production of flocculins, invertase and toxins, and the presence of apoptosis.     

Electro-fusion of haploid Saccharomyces yeast cells of identical mating type

Yeast protoplasts from the haploid strains 21 a and 111a were exposed to an inhomogeneous alternating field (about 1 kV/cm, 2 MHz). Due to dielectrophoretic aggregation two or more cells with close membrane contact are formed between the electrodes. Cell fusion was observed by application of two field pulses (11 kV/cm, 7 s duration) applied at an interval of 1 s. The intensity of the field pulses is sufficiently high to induce reversible electrical breakdown at membrane sites oriented in the field direction. After a 8 to 14 days incubation period on selection medium two types of fusion products could be isolated: 1) Hybrids with a haploid constitution, respiratory-competent and auxotrophic for histidine. 2) Cells with a diploid cell size and prototrophic for histidine. The genetic analysis for mating types and auxotrophic markers show that in the second case plasmogamy followed by karyogamy had occurred.     

Comparative analysis of cytokinesis in budding yeast, fission yeast and animal cells

Cytokinesis is a temporally and spatially regulated process through which the cellular constituents of the mother cell are partitioned into two daughter cells, permitting an increase in cell number. When cytokinesis occurs in a polarized cell it can create daughters with distinct fates. In eukaryotes, cytokinesis is carried out by the coordinated action of a cortical actomyosin contractile ring and targeted membrane deposition. Recent use of model organisms with facile genetics and improved light-microscopy methods has led to the identification and functional characterization of many proteins involved in cytokinesis. To date, this analysis indicates that some of the basic components involved in cytokinesis are conserved from yeast to humans, although their organization into functional machinery that drives cytokinesis and the associated regulatory mechanisms bear species-specific features. Here, we briefly review the current status of knowledge of cytokinesis in the budding yeast Saccharomyces cerevisiae, the fission yeast Schizosaccharomyces pombe and animal cells, in an attempt to highlight both the common and the unique features. Although these organisms diverged from a common ancestor about a billion years ago, there are eukaryotes that are far more divergent. To evaluate the overall evolutionary conservation of cytokinesis, it will be necessary to include representatives of these divergent branches. Nevertheless, the three species discussed here provide substantial mechanistic diversity.     

Dependence of the nucleoside effect on linear energy transfer.

L929 cells were irradiated by cyclotron-produced neutrons and by 14.8 MeV monoenergetic neutrons. For comparison cells were also irradiated by 60Co gamma rays. Following irradiation cells were treated by an equimolar solution of deoxyribonucleosides, and the effect on cell survival measured. Results show that nucleoside treatment was efficient after low-LET irradiation: gamma ray survival curves were altered by deoxyribonucleosides in terms of significantly increased extrapolation numbers only, but without Do change. Cells irradiated by neutrons from either of the two sources did not respond to nucleoside treatment, and consequently their survival curves remained unaltered. These results show that the nucleoside effect does occur after low-LET irradiation, but apparently not following high-LET irradiation. Since deoxyribonucleosides as well as other cell breakdown products are released in irradiated and necrotic tumours due to massive cell destruction, such a nucleoside effect could possibly enhance the cell survival and thus effect the result of radiotherapy. Absence of the nucleoside effect in case of high-LET irradiation may therefore be an additional potential gain from neutrons in radiotherapy.     

On the revised concept of linear energy transfer

The quantities linear energy transfer or restricted linear energy transfer are utilized in calculations that link absorbed dose to the fluence distribution of a radiation field. The computations provide approximations to absorbed dose in terms of the intermediate quantity cema or reduced cema. With the definition of the restricted linear energy transfer,L , given in ICRU Report 33, the approximation remains imperfect. This study deals with the resulting need for a modified definition ofL , as proposed in a draft report of ICRU. Essential differences between the old and the new definitions are demonstrated. The changed definition permits a rigorous formulation of the dependence between fluence and absorbed dose.     

The role of glutathione in natural and modified radioresistance of yeast cells

A study was made of the dependence of different natural and modified radioresistance upon glutathione content of yeast cells (Saccharomyces cerevisiae and Pichia guilliermondii). It was shown that glutathione was only involved in the formation of natural radioresistance in Saccharomyces cerevisiae cells. It was also shown that the increase in the radioresistance of yeast cells under the effect of 2-amino-2-thiazoline was accompanied by the increase in the level of total glutathione in them.     

The role of the repair of double-stranded DNA breaks in the radioresistance of yeast cells

The role of DNA double-strand break (DSB) repair in radioresistance of Saccharomyces cerevisiae G1 cells is discussed. The contribution of rapid and slow DNA DSB repair to radioresistance of diploid yeast has been estimated. The contribution of the DNA DSB repair involving no homologous chromosome interaction is shown to be insignificant in comparison with the recombinational repair. The rapid DNA DSB repair efficiency calculation method based on the proposed yeast radiation inactivation model is given. The calculations are in a satisfactory agreement with the experimental data. Possible mechanisms of radiation induction of lethal sectoring in yeast are discussed. This phenomenon is supposed to be due to the DNA DSB processing during vegetative division of irradiated cells. A general scheme of radiation inactivation of yeast cells is proposed.     

The centromere of budding yeast

Stable maintenance of genetic information during meiosis and mitosis is dependent on accurate chromosome transmission. The centromere is a key component of the segregational machinery that couples chromosomes with the spindle apparatus. Most of what is known about the structure and function of the centromeres has been derived from studies on yeast cells. In Saccharomyces cerevisiae, the centromere DNA requirements for mitotic centromere function have been defined and some of the proteins required for an active complex have been identified. Centromere DNA and the centromere proteins form a complex that has been studied extensively at the chromatin level. Finally, recent findings suggest that assembly and activation of the centromere are integrated in tethe cell cycle.     

Demonstration of a septal pore in budding Candida albicans yeast cells

Electron microscopy of Candida albicans yeast cells grown in a peptone glucose broth at 37 degrees C revealed pores in the septum identical in appearance to those already described in the hyphal form of the fungus. The presence of septal pores in yeast cells may explain apparently synchronous post-septation events in parent and daughter cells, and emphasizes the close structural similarities between different morphological forms of C. albicans.