Mechanisms contributing to non-recovery of translocations induced in meiotic cells

A cytological analysis of 22 and 7 autosomal (2;3) translocations induced, respectively, in mature and immature oocytes of Drosophila melanogaster appeared to be random in the distribution of the breaks. This finding is contrary to that expected if, as suggested by the mechanism of directed disjunction, the chromosomes involved in interchange at the centric region tended to be distributed to opposite poles at division I of meiosis. In each arm, the breaks were distributed more or less at random between the centromere and the telomere. However, in the translocations from the immature oocytes, the break-telomere distances of the segments interchanged showed a positive correlation, indicating that translocations induced in meiotic prophase and having a highly disproportionate length of segments interchanged are prone to be eliminated at division II by non-random disjunction of heteromorphic dyads.     

Protoplasmic Incompatibility and Cell Lysis in PODOSPORA ANSERINA. I. Genetic Investigations on Mutations of a Novel Modifier Gene That Suppresses Cell Destruction

The distribution of chromosomal aberrations between and within chromosomes of male D, melanogaster somatic cells after treatment with UV has been analyzed. -- Distribution of the breaks between chromosomes was largely nonrandom since we found a higher aberration frequency than that expected on the Y chromosome. Moreover, within the chromosomes the aberrations are clustered in the pericentromeric heterochromatic regions. The above distribution is compared with that of the breaks induced by X rays and methyl-methane-sulphonate (MMS) which were distributed in a different pattern.     

Distribution of the points of breaks in radiation-induced chromosome rearrangements along the polytene chromosomes of Anopheles messeae

Distribution of 431 rearrangement breaks induced by X-ray treatment in polytene chromosomes of Anopheles messeae was studied. No differences were revealed in the distribution pattern of inversion and translocation breaks. The frequency both of inversion and translocation breaks is much greater in the distal parts of autosomes than in the proximal ones. Within autosomes, breaks are grouped in a number of subdivisions. The points of breaks are Non-randomly distributed. The causes for this non-randomness are discussed.     

THE INFLUENCE OF PLANTING DATE AND MANURING ON THE INCIDENCE OF VIRUS DISEASES IN POTATO CROPS

Field experiments with Majestic potatoes were made over six years at Rothamsted to test the effects of varying date of planting and manuring on the yield of tubers and the incidence of the aphid-transmitted leaf roll and Y (rugose mosaic) viruses. Yield was increased by early planting, and by all the manures, especially dung. Early planting also usually increased the incidence of virus disease. Different manures had different effects on disease incidence; the average results from all comparisons showed the largest increase in incidence of both viruses from the use of dung; sulphate of ammonia increased the incidence of leaf roll, and muriate of potash that of rugose mosaic. Counts in two years showed that aphid populations were highest on the earlier planted potatoes, and were increased by dung, sulphate of ammonia and superphosphate, but were reduced by muriate of potash.     

Studies in the Diagnosis of Mineral Deficiency

Material from four fertilizer trials on barley in Hampshire was analysed with the principal purpose of comparing the extent to which the potassium content of different plant organs was diagnostic of potassium deficiency. Samples of older leaf blades and sheaths, young leaves, stems and ears were gathered at the time of ear emergence from each of the 108 plots, and analysed spectrographically for calcium, iron, magnesium, manganese, potassium and sodium.
Differences in composition between plants from the different sites were proportionately greater in the older leaf blades than in the other organs for calcium, the young leaves for manganese and sodium, and the older leaf blades and sheaths for potassium. Differences in sodium and manganese content at the different sites appeared to be related to the differences in potassium status.
Applications of muriate of potash increased the potassium content of all organs except the ears, and decreased the content of magnesium, manganese and sodium, and of iron at one site. The effect of potassium supply on manganese and sodium content was most marked in the young leaves. The proportional increases observed in potassium content as a result of application of muriate of potash were similar at all four sites, in spite of the fact that responses in growth and yield differed greatly.
As between the four sites, the responses to muriate of potash observed in the yields of grain are significantly correlated with the potassium content of the older leaf blades and the stems, and the following tentative limiting values are put forward, above which no increase in grain yield as a result of potassic manuring may be expected:
(a) in the older leaf blades at the time of ear emergence 0.92% potassium in dry matter, (b) in the stems at the time of ear emergence 1–01 % potassium in dry matter.     

Distribution of spontaneous chromosome breaks in human chromosomes

Summary Localization of chromosome breaks in human chromosomes was analyzed in 264 peripheral lymphocyte cultures. Three hundred and sixty-nine chromosome breaks could be exactly localized to a chromosome band or region of the Paris Conference nomenclature. The distribution of breaks in the chromosome regions was found to be nonrandom. Chromosome 3 alone had 23% of the breaks and region 3p2 had 13% of the total breaks. Some other chromosome regions, such as 5p1, 9q1, 14q2, and 16q2 also displayed clustering of breaks. Sex chromosomes had less breaks than expected. Spontaneous chromosome breaks were almost exclusively located in the lightly stained G bands.Supported by grants from the Foundation for Pediatric Research and Research Foundation of Orion Corporation Ltd.     

Localization of translocation breakpoints in somatic metaphase chromosomes of barley

Karyotype analyses based on staining by acetocarmine followed by Giemsa N-banding of somatic metaphase chromosomes of Hordeum vulgare L. were carried out on 61 reciprocal translocations induced by X-irradiation. By means of computer-based karyotype analyses all of the 122 breakpoints could be localized to defined sites or segments distributed over the seven barley chromosomes. The pre-definition of translocations with respect to their rearranged chromosome arms from other studies rendered it possible to define the break positions even in translocations having exchanged segments equal in size and the breakpoints located distally to any Giemsa band or other cytological marker. The breakpoints were found to be non-randomly spaced along the chromosomes and their arms. All breaks but one occurred in interband regions of the chromosomes, and none of the breaks was located directly within a centromere. However, short and long chromosome arms recombined at random. An improved tester set of translocations depicting the known break positions of most distal location is presented.     

The occurrence of G-bands in the mitotic chromosomes of the amphibian Xenopus muelleri

The mitotic chromosomes from cultured cells of Xenopus muelleri were G-banded with trypsin and/or with trypsin/urea. These amphibian chromosomes were not found to be more highly contracted at metaphase than those of mammals or reptiles and trypsin G-banding was more easily induced than in the case of most reptilian chromosomes. The organization of vertebrate chromosomes into distinct early replicating (R-bands) and late replicating (G-bands) replicon clusters may be characteristic of eucaryotes in general.     

Effect of some fertilizers on hatching of cereal cysts nematode,Heterodera avenae

Experiments were conducted in laboratory and pot conditions to determine the effects of urea, di-ammonium phosphate (DAP), single super phosphate (SSP), muriate of potash (MOP) and zinc sulphate (ZnSO₄) on hatching of Heterodera avenae. Two concentrations of each fertilizer were tested in lab for which 10 cysts and 5 ml of each concentration were taken in 5 cm diameter Petri plates. Observations were recorded at weekly intervals up to six weeks. Urea, DAP, SSP and MOP inhibited hatching and ZnSO₄ increased it. After six weeks, hatching was least (5.45%) in higher dose of urea and greatest (46.9%) in higher dose of ZnSO₄. In pot experiment, two doses of urea and single dose of SSP, MOP, and ZnSO₄ were applied in H. avenae-infested soil and WH-1105 wheat was sown. Observations on nematodes in roots, soil and remaining cyst contents were recorded 40 days after sowing. Among all the fertilizers, least nematodes in soil and roots were found at higher dose of urea and greatest number in ZnSO₄.     

Application of mFISH for the analysis of chemically-induced chromosomal aberrations: a model for the formation of triradial chromosomes

Using a human lymphoblastoid cell line WTK-1, we applied multicolor fluorescence in situ hybridization (mFISH) technique to analyze mitomycin C (MMC)-induced chromatid exchanges, focusing especially on the triradial chromosomes. It was found that the triradial chromosomes were formed with a specific rearrangement, "recipient and donor" relationship. The exchange sites of the recipient chromosomes were on single chromatid breaks and distributed randomly throughout the interstitial, pericentromeric, and terminal regions. In counterpart, donor chromosomes exchanged on isochromatid breaks of their telomeric and/or subtelomeric regions with the single chromatid breaks of recipient chromosomes. More than 80% of the scored triradial chromosomes were formed with such rearrangements, and few acentric chromosome fragments derived from the donor chromosomes could be detected in the metaphases observed. We therefore suggest that biological mechanisms of breakages between the recipient and donor chromosomes are different: the former due to direct DNA-damage by MMC, but the latter due to indirect DNA-damage depending on telomeric specific structure/function.     

Distribution of Mitomycin C-induced damage in human chromosomes with special reference to regions of repetitive DNA

The distribution of gaps, breaks, exchanges and other effects induced by Mitomycin C on human chromosomes was analysed to examine the possibility of a correlation between chromosome lesions and regions of repetitive DNA. Homologous and non-homologous exchanges between chromosomes Nos. 1, 9 and 16, and also between and with the acrocentric chromosomes were more frequent than expected, but breaks and gaps appeared to be located randomly with regard to chromosome light and dark bands.     

Localization of breaks induced by vinyl chloride in the human chromosomes of lymphocytes

A group of 67 workers occupationally exposed to VCM was examined for the presence and distribution of breaks along the chromosomal length. Breaks induced by VCM are not randomly distributed as had been expected in a normal population. According to our results there exist highly sensitive and highly resistant locations along the chromosomes to the actions of VCM. The link between the highly sensitive segments of chromosomes, fragile sites and the activation of oncogenes is discussed.     

Effect of mitomycin C on the structure of human chromosomes observed in metaphase after labelling by moderate thermal denaturation]

Mitomycin C induced chromosome rearrangements were analysed in cultured human leukocytes by reverse banding technique. Breaks and chromosomal exchanges involved preferentialy the entromeric region of some chromosomes (1, 5, 9, 16, and 20). Associations between acrocentric chromosomes was not found to be increased. But acrocentric associations with centromeric regions were frequently present. The differences between the mechanism of exchanges and breaks are discussed. The part of heterochromatin in post replication DNA repair is considered.     

The chromosome variability of the Indian muntjac in somatic cell hybrids]

Hybrids were produced between the Indian muntjak fibroblasts and rat Jensen sarcoma cell line (JF1) auxotrophic for asparagine. They were selected without cloning under conditions providing survival of parental Indian muntjak and hybrid cells. This allowed to compare the Indian muntjak chromosome variability in the parental cells and hybrids under identical culture conditions. The frequency of muntjak chromosome aberrations proved to de higher in the hybrids (up to 47%) than in the parental cells (6.5%). Predominant are chromosomal breaks and dicentrics. The latter are mainly formed by fusion of chromosomes 1 and 2. The most fragile are 1 and X-chromosomes. Chromosomal breaks are evenly distributed along chromosome 1, and "hot" points are observed in X-chromosome. Possible mechanisms of the Indian muntjak chromosome rearrangements induced by somatic cell hybridization are discussed.     

Studies in the diagnosis of mineral deficiency; the composition of weed leaves in relation to potassium deficiency in barley

Leaves of five weed species (Brassica sinapis, Cirsium arvense, Polygonum aviculare, P. convolvulus and Potentilla reptans) from fertilizer trials on barley at four sites in Hampshire were analysed with a view to using their composition in forecasting the response of barley to fertilizers. The samples were gathered from as many of the 108 plots as possible, and were analysed spectrographically for calcium, iron, magnesium, manganese, potassium and sodium.
Marked differences in composition between the five species were recorded, the most noteworthy being the high sodium content of Brassica sinapis and Cirsium arvense and the high manganese content of Potentilla reptans. There were also marked differences between the four sites, but these were not uniform as between the different species, and often failed to agree with those observed for barley.
Superphosphate applications decreased the manganese content of the weeds in many cases, and increased their calcium content. Muriate of potash increased their potassium content, but tended to decrease that of magnesium and sodium. The only general effect of sulphate of ammonia on the composition of the weeds was a decrease in iron content.
Except in Cirsium arvense , the potassium content of weed leaves was correlated with that of barley on the same plot if differences within a site only were considered. Differences between sites were not correlated in this way. The correlation between potassium content of weed leaves and the response of barley to muriate of potash application was worthy of note only in Polygonum convolvulus , and even in this case the correlation of site differences did not reach significance. It is tentatively suggested that increases in the grain yield of barley as a result of muriate of potash application are likely to occur only where the leaves of P. convolvulus contain less than 1.83% potassium.     

Increased chromosomal instability in lymphocytes from elderly humans

Lymphocytes from young and old donors were incubated with PHA for 96 h and exposed to [3H]Tdr during the last 24 h of culture. Comparable amounts of [3H]Tdr were incorporated into chromosomes of old and young lymphocytes as measured by autoradiography of metaphase chromosomes. However, chromosomal damage and cell-cycle arrest were far greater in lymphocytes from old as compared to young humans. The frequency of chromosome breaks, fragments, exchange figures and dicentric chromosomes induced by [3H]Tdr was greater in cultures from old than in cultures from young humans. Lymphocytes from old donors exposed to 20 microM BrdU during the last 24 h of culture showed significantly more sister-chromatid exchanges than did lymphocytes from young donors. These data suggest that chromosomes in lymphocytes from old donors express more damage after exposure to [3H]Tdr or BrdU than do chromosomes in lymphocytes from young donors.     

The relation between chemically induced sister-chromatid exchanges and chromatid breakage.

Studies of classical chromosome aberrations and sister-chromatid exchanges (SCES) suggest independent mechanisms for the two events despite some common features. Examination of chromosome breakage caused by X-rays, visible light, and viruses has shown that few chromatid breaks are accompanied by SCEs at the sites of breaks. No similar observations were available for chemically induced breaks, but it has been reported that rat chromosomes exposed to dimethylbenzanthracene (DMBA) contained a preponderance of both aberrations and SCEs in certain specific regions, implicating a common process in their formation. These conclusions were drawn from a comparison of breaks induced in vivo with SCEs induced in vitro. However, we used 7 chemical mutagens to induce both chromatid breaks and SCEs in "harlequin" chromosomes of cultured rat and Chinese hamster ovary (CHO) cells and found that 25% of the 914 breaks scored were associated with SCEs. The proportion of breaks accompanied by SCEs is related to the overall SCE frequency and falls into the range predicted on the basis that breaks and SCEs occur independently. The reported association between sites for SCEs and aberrations also reflects secondary factors, such as induction of SCEs and aberrations during DNA synthesis in late replicating regions of the chromosomes.     

Analysis of restriction enzyme-induced DNA double-strand breaks in Chinese hamster ovary cells by pulsed-field gel electrophoresis: implications for chromosome damage.

Restriction enzymes can be electroporated into mammalian cells, and the induced DNA double-strand breaks can lead to aberrations in metaphase chromosomes. Chinese hamster ovary cells were electroporated with PstI, which generates 3' cohesive-end breaks, PvuII, which generates blunt-end breaks, or XbaI, which generates 5' cohesive-end breaks. Although all three restriction enzymes induced similar numbers of aberrant metaphase cells, PvuII was dramatically more effective at inducing both exchange-type and deletion-type chromosome aberrations. Our cytogenetic studies also indicated that enzymes are active within cells for only a short time. We used pulsed-field gel electrophoresis to investigate (i) how long it takes for enzymes to cleave DNA after electroporation into cells, (ii) how long enzymes are active in the cells, and (iii) how the DNA double-strand breaks induced are related to the aberrations observed in metaphase chromosomes. At the same concentrations used in the cytogenetic studies, all enzymes were active within 10 min of electroporation. PstI and PvuII showed a distinct peak in break formation at 20 min, whereas XbaI showed a gradual increase in break frequency over time. Another increase in the number of breaks observed with all three enzymes at 2 and 3 h after electroporation was probably due to nonspecific DNA degradation in a subpopulation of enzyme-damaged cells that lysed after enzyme exposure. Break frequency and chromosome aberration frequency were inversely related: The blunt-end cutter PvuII gave rise to the most aberrations but the fewest breaks, suggesting that it is the type of break rather than the break frequency that is important for chromosome aberration formation.     

The action of N-methyl-N-nitrosourea on non-established human cell lines in vitro. II. Non-random distribution of chromatid aberrations in diploid and Down's cells.

Chromatid gaps, breaks and aberrations involved in interchanges induced by N-methyl-N-nitrosourea (MNU) were found non-randomly distributed on individual chromosomes and chromosome segments (G bands) both in human diploid fibroblasts with trisomy 21 cultured in vitro. Aberration events were located exclusively in pale G bands. Considering cells in the first post-treatment mitosis, the pattern of aberration distribution, as revealed by the position of hot spots, varied with recovery time and was different in diploid and Down's cells. In comparison with diploid cells, the X chromosomes of Down's cells were not involved in aberrations. Despite the higher aberration frequencies of Down's cells, the number of hot spots and the proportion of aberrations located in hot spots were not increased in this cell type. Therefore, the increased chromosomal sensitivity to MNU of Down's cells does not reflect an increased sensitivity of special chromosomes or chromosome sites.     

Inter- und intrachromosomale Verteilung von Chromatidtranslokationen nach Einwirkung von Trenimon auf menschliche Leukocyten in vitro

250 chromatid interchanges induced by Trenimon were analyzed relative to their configuration, the participation of certain chromosomes or chromosome groups and the localization of the exchange points. Cis- and trans-configuration (=asymmetrical and symmetrical interchanges) have been observed in identical frequency. The same was seen relative to complete and incomplete reunion of the breaks. The interchromosomal as well as the intrachromosomal distribution of the exchange points was non-random. Homologous chromosomes participated in interchanges at a higher level of frequency than expected from their relative length. Chromosomes No. 6–12 and X as well as 16 and 21+22 took part in interchanges more frequently and chromosomes No. 2, 3, 4 and 5 more rarely than expected. The exchange points were frequently observed in the proximal regions of the chromosomes (incl. centromere) as well as in the short arms of chromosomes No. 13–15 and 21+22.