[Fusion of Erwinia chrysanthemi spheroplasts in an electric fields]. / Sliianie sferoplastov Erwinia chrysanthemi v élektricheskom pole.

A new approach has been elaborated for electrofusion of Erwinia chrysanthemi spheroplasts. The new approach consists of superimposition of high voltage impulses on the pellet of tightly contacting cells in the course of centrifugation. The mixture of spheroplasts of two genetically marked strains was placed into the special centrifuge chambers and spinned for 15 min at 2500 g to get a compressed pellet between chamber electrodes. Three successive pulses of 6.6 kv/cm amplitude and 30 microseconds duration were applied to spheroplast pellet during centrifugation. Fusion products were viable and after plating on the surface of hypertonic medium regenerated to the rod forms. As a result, the hybrid clones carrying the markers of both parents were isolated.

[Principles of cytogenetic examination for detecting occupational hazards]. / Printsipy tsitogeneticheskogo obsledovaniia dlia vyiavleniia professional'nykh vrednostei.

The main principles are stated of carrying out a cytogenetic examination of human populations on the basis of critical analysis of data from literature and the authors' own experience in this field. The method for estimation of sister chromatid exchanges is shown expedient to be used together with the chromosome aberration analysis in carrying out cytogenetic examinations. Statistically ascertained approaches are adduced to select the necessary amount of persons examined in groups and the number of cells for analysis when using methods for estimation of sister chromatid exchanges and chromosome aberrations.

[Statistical analysis of the elimination of chromosome-type aberrations and the fate of the aberrant cells]. / Statisticheskii analiz éliminatsii aberratsii khromosomnogo tipa i sud'by aberrantnykh kletok.

The regularities of elimination of gamma-ray induced chromosome aberrations in human nonstimulated lymphocytes and the fate of aberrant cells have been studied. The cells at the first, second and third post-irradiation divisions were identified by the technique of differential staining of sister chromatids. A mathematical model has been suggested to describe the processes of formation, multiplication and death of the cells with dicentrics. This model has been shown to be in a good agreement with the experimental data. According to the model, the distribution of dicentrics among cells at the first and second mitoses follows the Poisson distribution. The analysis of the model has shown that the probability of divergence of two chromatids from one dicentric chromosome is equal 1/2, and that the acentric and monocentric types of chromosome aberrations have no influence upon cell survival in vitro. A method for empirical estimation of survival of other types of aberrations has been suggested. According to these estimates, the probabilities of transmission to the next mitosis are equal 2/3, 1 and 1/3 for paired fragments, ring chromosomes and interstitial deletions, respectively. It has been shown that approximately 1/4 of survived acentric structures can diverge to both daughter cells.

[Effect of thiophosphamide on the frequency of chromosome aberrations in cells heterozygous for ataxia-telangiectasia]. / Vliianie tiofosfamida na chastotu khromosonnykh aberratsii v kletkakh geterozigot po ataksii-teleangiéktazii.

Chromosome aberration rate in ataxia-teleangiectasia (AT) heterozygotes exposed to thiophosphamide in lymphocyte culture was compared to that in control donors. AT heterozygotes demonstrated an increased number of chromosome aberrations. The patterns of concentraion relationships in AT heterozygotes are depictable by the same equation as in control donors. However, the expected chromosome aberration rate in AT heterozygotes proved to be elevated, indicating the increased sensitivity of AT heterozygotes to the exposure to low doses of thiophosphamide, since no experimental differences were found in the spontaneous chromosome aberration rate between AT heterozygotes and control donors.

[Spontaneous level of sister chromosome exchanges and their distribution in human cells]. / Spontannyi uroven' sestrinskikh khromatidnykh obmenov i ikh raspredelenie po kletkam cheloveka.

Blood of practically healthy donors of both sexes (27 females and 23 males) was cultured under the standard conditions during 96 hours. Bromodeoxyuridine (BUdR) was added at the final concentration of 10 mkg/ml 28 hours before harvesting. The slides were stained with acridine orange and Giemsa for differential staining of chromatids. In each culture sister chromatid exchanges (SCE) were analysed in 50 cells, and the part of cells undergoing the first, second and third mitoses at the time of harvesting, was calculated. According to the mean number of SCE per cell, the distribution of individuals was consistent with the normal law, the mean being 6.525 and standard deviation--0.956. A significant heterogeneity in the speed of cell cycle of cultures was observed. The coefficient of variation for the part of cells undergoing the first mitosis was 50%, for the cells in the second mitosis--15%, and for the cells in the third mitosis--154%. Correlation analysis showed a positive dependence of the mean level of SCF upon the age of a donor and upon the part of cells in the second mitosis in this individual. No reliable correlation of the SCE level with the donor's sex was observed. The distribution of cells, obtained from the culture of one individual, was best approximated by beta-distribution, and the distribution of cells obtained from the cultures of different individuals--by gamma-distribution. In both there was obtained a satisfactory approximation by Pearson's distribution of the 1 type, and significant deviations were found from the normal, Poison's and the negative binomial distribution. The conditions were found of similarity of empirical distribution of SCE in cells to the normal one. For that, it is not the value of SCE for a separate cell that should be used as a unit of measurement, but the mean from the values of frequencies for 5-10 cells. Hence, it was shown that for the evaluation of the mean frequency of SCE with the precision of 1 exchange in separate individuals it is necessary to analyse 40 cells, and to observe the 15% increase of spontaneous SCE level under the action of deleterious factors--8 individuals are enough to analyse.

[Individual variation in the frequency of chromosome aberrations under the influence of chemical mutagens. I. Inter-cultural and inter-individual variations in the effect of mutagens on human lymphocytes]. / Individual'nye variatsii chastoty khromosomnykh aberratsii pri deitvii khmicheskikh mutagenov. Soobshchenie I. Mezhkul'tural'nye i mezhindividual'nye variatsii pri deistvii mutagenov na limfotsity cheloveka

The study of the distribution law of human peripheral blood cultures for the sensitivity to thiophosphamide was performed. In the first experiment the blood from one person was used, in the second one the blood was used from different persons. "The percent of aberrant cells" and "the number of chromosome breaks per 100 cells" were scored. The distribution law of the cultures in all the experiments was found to be normal. Analysis of the variances on the percent of aberrant cells showed that the distribution law of the cultures received from one donor corresponded to the binomial one, and that of the cultures received from different donors--to the Poisson's one.

[Individual variations in the frequency of chromosome aberrations following exposure to chemical mutagens. III. Interindividual differences at different stages of the cell cycle]. / Individual'nye variatsii chastoty khromosomnykh aberratsii pri deistvii khimicheskikh mutagenov. Soobshchenie III. Mezhindividual'nye variatsii na raznykh stadiiakh kletochnogo tsikla.

The object of this investigation was the sensitivity to chemical mutagens of chromosomes of human lymphocytes obtained from different individuals. The distribution of individuals with respect to their sensitivity to fotrin and cytosine-arabinoside was studied. Tests for two characteristics were used, viz. "the percent of aberrant metaphases" and "the number of chrimosome breaks per 100 cells". It is shown by the statistical analysis, that the distribution does not depend on the stage of the cell cycle. The distribution of the individuals tested with respect to their sensitivity to mutagens was shown to be normal. Certain recommendations concerning the planning of experiments and the exposure of the experimental data are given by the authors.

[Mathematical modeling of the relationship between the cytogenetic effect and the concentration of the mutagen]. / Matematicheskoe modelirovanie zavisimosti tsitogeneticheskogo éffekta ot kontsentratsii mutagena

The effect of different concentrations of thiophosphamide on the culture of human leucocytes was investigated. Three mathematical models were studied, one of which, being satisfactory for describing the experimental data, was chosen. According to this model a quantity of aberrant cells changes with the concentration of thiophosphamide non-linearly and can be described according to the equation A=exp[-(KC+alpha)2], where A is a portion of normal cells, C - a concentration of a mutagen, K and alpha - the coefficients, while exp[-alpha2] is the control level of normal metaphases. The quantity of chromosome breaks per cell is described according to the equation X= exp [KC + +alpha)2]-1. The general view of the equation is constant for different phases of the cell cycle. It follows from the suggested model that the action of two molecules of an alkylating agent is necessary for the formation of a chromosome break. This is indicative of double-stranded structure of a chromosome in its section. It also follows from the suggested model that the action of thiophosphamide has no cut-off. Thiophosphamide induced chromatid aberrations during the G2 phase, therefore it is not a mutagen of the check action.