The influence of DNA content and nuclear volume on the frequency of radiation-induced chromosome aberrations in Bufo species

The frequency of chromosome aberrations was compared in X-irradiated blood lymphocytes of Bufo marinus, B. calamita and B. pardalis which have similar chromosome numbers (2n=22) and karyotypes but differ in chromosomal DNA content and nuclear volume. — For each species the yield, per cell of centric exchange aberrations (dicentrics+rings) and of deletions (interstitial and terminal) increased approximately as the 1.5th power of the dose. — The 55% higher chromosomal DNA content of B. pardalis compared with both B. marinus and B. calamita resulted in the same increase in the frequency of deletions as a 55% increase in radiation dose, approximately doubling the yield. Both factors probably lead to a similar increase in the frequency of primary lesions from which the deletions are derived. — In contrast, an increase in chromosomal DNA content did not result in a higher yield of dicentric and ring exchanges, probably because the greater nuclear volume of B. pardalis (twice that of the other species) offset the potential increase in exchanges by increasing the average distance between chromosomes and chromosome arms. The data support the hypothesis that, in order to be involved in exchange, chromosome regions must be close together at the time of irradiation. The frequency of deletions is unaffected by changes in nuclear volume.     

The influence of streptomycin on the frequency of induced chromosome aberrations

1. 1.
   P?sobení vysokými a? subletálními dosemi streptomycinu (0,5 m Mol, 1 m Mol) neindukovalo ?ádné pr?kazné zvý?ení frekvence chromosomálních aberací v metafázi a v anafázi a telofázi. Jediné pr?kazné zvý?ení frekvence aberantních anafází a telofází bylo zji?těno po p?sobení 1 m Mol streptomycinu (30°C, 48hod. restituce). Zvý?ení je hlavně podmíněno výskytem lagging chromosom? a bylo tedy výsledkem poruchy v?eténka a ne chromosomální aberací. To bylo prokázáno nepr?kazností zvý?ení frekvence aberantních metafází p?i stejném p?sobení. V diskusi jsou zd?razněny nevýhody hodnocení frekvence chromosomálních aberací v anafázi a telofázi.     
   
   

The effect of photosensitizing dyes on the 3H-thymidine incorporation of cells grown in vitro

The photodynamic inactivation of ³H-thymidine incorporation in mouse embryo (ME) and mouse L cells by acridine orange (AO), methylene blue (MB) or neutral red (NR) has been studied by estimating the number of nuclei capable of incorporating ³H-thymidine during a 24 h period following light exposure. In the dark NR and AO reduced the number of ME-nuclei incorporating ³H-thymidine but MB caused an increase in non-scheduled DNA synthesis. The dark effect on L cells was less but the photoinactivation of thymidine uptake was proportionally greater in these cells. Polyoma virus was shown to be capable of growing in cells whose thymidine uptake was reduced or completely stopped by photoinactivation with NR. However, if the NR damage was very great, or when AO was used to photosensitize cells, the synthesis of viral DNA was interfered with.     

The effect of frequency and grounding on whole-body absorption of humans in E-polarized radiofrequency fields

The radiofrequency absorption rates of five male human volunteers have been measured from 3 to 41 MHz. The subjects were exposed at about 10 microW /cm2 inside a very large transverse electromagnetic (TEM) cell and never absorbed more than 1 W. Both the EKH and EHK orientations were employed under both free-space and grounded conditions. Absorption rates for the EKH orientation exceed those of the EHK orientation by 40% in free space, but only by 6% when grounded. The absorption rates for the grounded men vary with frequency, f, as f1.9 from 3 to 25 MHz and then level off at peak. The free-space absorption rates vary as f1.7 from 3 to 18 MHz and as f2.9 from 18 to 41 MHz. The average measured absorption rates at 10 MHz exceed the average of the standard model calculations by a factor of three (for free space) or four (grounded). The average man, when exposed grounded in an EKH orientation to the maximum permitted exposure levels under ANSI standard C95 .1-1982, will absorb 0.58 +/- 0.14 W/kg over most of the 3 to 41-MHz frequency range. This slightly exceeds the whole-body maximum of 0.40 W/kg underlying the standard.     

The frequency of chromosome aberrations in a control population

Chromosome aberration frequencies in a group of new entrants and non-radiation workers from this establishment have been studied using both block-staining and G-banding techniques. Increased levels of chromosome exchanges were found in those with a previous history of occupational or medical exposure to potential clastogens and in smokers. The possibility of an age effect was suggested. The study emphasizes the problems encountered in obtaining suitable control levels for comparison with occupational studies of exposure to clastogens.     

The influence of post-treatment storage on the frequency of EMS-induced chromosomal aberrations in barley

Skladováním vysu?ených obilek po p?sobení EMS se zvy?uje frekvence chromozomálních aberací.     

Effect of fractionated exposure to carbon ions on the frequency of chromosome aberrations in tobacco root cells

The induction of chromosome aberrations in tobacco root tip cells was measured after exposure to either 18 MeV/n carbon ions or 2 MeV electrons. The RBE value for acute exposure was found to be about 10. Splitting the dose into two fractions did not produce any significant effect on the yield of aberrations following carbon-ion exposure, whereas a clear decrease was observed after exposure to electrons thereby indicating an induction/activation of error-free repair after the first fraction. Moreover, this decrease appeared to be independent of the types of chromosome aberrations. On the other hand, it was suggested that the lack of any significant effect on the yield of aberrations is either due to a lack of error-free repair or to a less efficient damage repair after exposure to carbon ions. Received: 26 February 2001 / Accepted: 28 June 2001     

The relationship between the spontaneous frequency of chromosome aberrations and the change in their frequency following mammography

Changes in chromosomal aberration rates, analysed for women 35-60 years of age exposed to 0.5-2 cGy during the mammography, suggested a relationship between the initial rates of chromosomal aberrations and those caused by the procedure. The spontaneous level of cytogenetic changes is assumed to be indicative of the degree of body radiosensitivity.     

Comparative analysis of the frequency and type of chromosomal aberrations in somatic cells in maternal-fetal infections

Fetal infections have high specific gravity in the structure of perinatal diseases and mortality. The gravity of infection processes in pregnancies and degree of fetal pathology are not correlated. Latent asymptomatic forms of pregnant's diseases can often be the cause of the congenital malformations and fetal death. We present here results of the analysis of the frequencies and types of chromosome aberrations in pregnancies with latent infections. The chromosome structure damages, mainly chromatide-type aberrations, were registered with higher frequency in the studied group.     

Differentiation of the colon endocrine cells in mucosal epithelium of humans and some vertebrate animals

By electron microscopy, the mucosal epithelium of a distal part of the intestine of humans and other vertebrates (Rana temporaria, Lacerta vivipara, Columba livia, rabbit, rat, pig, cow) was examined. On the basis of the variety of cellular structure and the level of specialization of the involved elements a common regularity of ways of differentiation of endocrine cells was revealed. The updating of endocrine cells basically occurs as a result of differentiation of cambial cells through intermediate pre-enteroendocrine forms. Reorganization of exocrine epithelial cells is accomplished through "mixed" exo-endocrine cells. At the lower vertebrate animals the "mixed" cells are met much more frequently than in mammals, including man. In humans the greatest quantity of these cells is observed in the intra-uterine period of development and in cases of pathology. Ways of cytogenesis in endocrine cells are differently manfested in the course of ontogenesis and under broken ability to live.     

Increase in the frequency of gamma-ray induced chromosomal aberrations in mammalian cells by post-treatment with novobiocin

The effect of novobiocin (an inhibitor of DNA topoisomerase and polymerase) on the frequency of chromosomal aberrations was examined in Chinese hamster V79 cells irradiated with gamma-rays in the plateau phase of growth and subcultured in the presence of novobiocin until the first mitosis after irradiation. Novobiocin alone affected cell survival, DNA synthesis and the mitotic frequency of unirradiated cells in a dose-dependent manner, without causing any significant increase in the frequency of chromosome- or chromatid-type aberrations. The frequency of chromosome-type aberrations induced by gamma-radiation was not influenced by novobiocin at 200 microM, but the frequency of chromosome deletions (but not rings and dicentrics) showed a two-fold increase when 300 microM novobiocin was present. Irradiation produced a low level of chromatid-type aberrations and post-treatment with novobiocin at concentrations greater than 100 microM significantly increased the frequency of chromatid gaps and breaks. The results support the idea that different radiation-induced lesions lead to chromosome- as opposed to chromatid-type aberrations.     

The frequency of chromosome aberrations in rat bone marrow cells in the late period after a single uptake of tritium

A prolonged self-maintenance of haemopoietic tissue cells with stable chromosome rearrangements following a single intake of tritium oxide in the amount of 24 MBq/g of body weight (absorbed dose of 11 Gy) is shown. Mutant cells revealed long after the radionuclide exposure are descendants of stem-cell precursors, bearing stable chromosome aberrations during the period of formation of radiation injury after the radionuclide administration.     

The synergistic effect of aphidicolin on the yield of X-ray-induced chromosome aberrations throughout the cell cycle in JU56 cells

The effect of a 2-h post-treatment with aphidicolin at a dose sufficient to inhibit DNA synthesis on the yield of X-ray-induced chromosomal aberrations throughout the cell cycle was measured. Exposure to aphidicolin during and after irradiation brought about an increase in exchanges in cells irradiated in G2, in sister unions only in cells irradiated in S, and in all chromosome aberration types (fragments, sister unions, and dicentrics) in cells irradiated in G1. It is suggested that, during G1 and G2 but not during S inhibiting the repair enzyme alpha-polymerase brings about the conversion of some X-ray-induced DNA lesions to double-strand which can then take part in aberrations.     

The effect of in vitro heating on the distribution of nuclear matrix polypeptides in HeLa cells

The in situ nuclear matrix was obtained from HeLa cells. After permeabilization with nonionic detergent, the resulting structures were incubated for 1h at 37°C to determine whether or not such an incubation might result in the redistribution of nuclear polypetides which resisted extraction with buffers of high-ionic strength (1.6 M NaCl or 0.25 M (NH₄)2SO₄ as well as DNase I digestion. Using indirect immunofluorescence experiments and monoclonal antibodies we show that heating to 37° C changes the distribution of a 160 kDa protein previously shown to be a component of the inner matrix network. On the other hand, a 125 kDa polypeptide was not affected at all by the incubation. Our results clearly indicate that the inclusion of a 37°C incubation (for example during digestion with DNase I) in the protocol to obtain the in situ nuclear matrix can result in the formation of in vitro artifacts.     

Chromosome aberrations caused by the effect of ultrasound in the meristematic cells ofvicia faba

In our present work the formation of chromosome aberrations has been studied in dependence on the tima interval between sonication and fixation of the primary root tips of Vicia faba. Maximum occurrence of aberrations was recorded immediately after sonication. The results of our experiments pointed to the fact that the frequency of the induced changes was independent on the sonic waves intensity within the range of 0-2—3-0 W/cm² and on ultrasond treatment duration within the range of 1—20 min. Studies of the distribution of chromosome abnormalities caused by ultrasound between the large and small chromosomes of theVicia faba meristematic cells in various time intervals showed that the frequency of the aberrations in both chromosome groups was proportional to its total metaphase lengths. Analysis of the type of aberrations observed in various time intervals after sonication indicated the simultaneous formation of chromosome and chromatide abnormalities.