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B K Vig

Publications and source records attributed to B K Vig.

At least 55 records · Page 3Linked to original sources
PubMed1988

Sequence of centromere separation: generation of unstable multicentric chromosomes in a rat cell line.

A transformed cell line, B1, of cerebral endothelial origin from the Wistar-Kyoto male rat has chromatid and chromosome type bridges in virtually every cell. It exhibits various dicentric and polycentric chromosomes. Most dicentrics are symmetric isochromosomes. Certain isodicentrics are present in a fair segment of the cell population; however, almost all cells have some newly arising isodicentrics. The live cells show a lengthened prometaphase. Anaphase is also retarded possibly due to the occurrence of bridges. At anaphase some multicentrics split at only one centromere. When pulled to the two poles the unsplit centromeres and the distal chromosome segment form a side arm bridge. Another mechanism appears to be a total lack of separation of daughter centromeres at meta-anaphase ('meiotic-like' behavior of mitotic chromosomes). This is realized by the pulling of each of the two unsplit centromeres to opposite poles and results in bridges with both sister chromatids running parallel to each other. A break at corresponding weak points in the two sister chromatids followed by rejoining can form a dicentric isochromosome. A third mechanism, the breakage-fusion-bridge cycle, is also operative but would not produce isodicentrics. In the case of the first two mechanisms some or all centromeres apparently split between telophase and onset of the following DNA synthesis rather than at the usual time at late metaphase. These observations may suggest some previously unknown behavior of multicentric chromosomes during mitosis.

Anaphase↗
PubMed1988

Sequence of centromere separation: differential replication of pericentric heterochromatin in multicentric chromosomes.

The dicentric and multicentric chromosomes in L cells and a brain tumor cell line of mouse display only one site of kinetochore formation associated with the 'active' centromere. The accessory or 'inactive' centromeres show premature separation. These cell lines were treated with 10(-6) M 5-bromodeoxyuridine (BrdUrd) followed by anti-BrdUrd antibody to study the pattern of replication of pericentric heterochromatin flanking the active vs inactive centromeres. Regardless of its quantity, heterochromatin around the inactive centromere replicates earlier than that associated with the active centromere. There appears to be a relationship between the timing of separation of a centromere and the timing of replication of pericentric heterochromatin. The premature replication of heterochromatin associated with an inactive centromere may be responsible for its premature separation and, hence, inactivity.

Animals↗
PubMed1987

Sequence of centromere separation: a possible role for repetitive DNA.

The centromeres of a mitotic cell at the meta-anaphase junction separate in a non-random, genetically controlled sequence before anaphase migration ensues. In several, but not all, of the organisms studied so far it appears that the timing of separation of a centromere into two visible units depends upon the quantity of pericentric heterochromatin. A critical analysis of this parameter of cell cycle suggests that the sequence of centromere separation is influenced by repetitive DNA present in the pericentric region. In those cases with qualitatively uniform repetitive DNA in centromeric regions, the chromosomes carrying lesser quantities separate earlier than those with greater amounts. However, the overall pattern of separation may be determined by interactions between both quantitative and qualitative parameters of the repetitive DNA. It has been suggested that repetitive DNA has no transcriptional properties. It is probably only a structural component which acts as a site for the accumulation of protein molecules synthesized by some locus not present in the centromeric region. These proteins accumulate to saturate the centromeric repetitive DNA resulting in a (trilaminar) structure called the kinetochore. The longer the stretch to be saturated, the larger would be the kinetochore-like structure. Once saturated, the centromere splits into two subunits. Premature separation results in a lack of saturation and formation of an 'immature' kinetochore. This may lead to chromosome malsegregation. Thus, indirectly, one property of repetitive DNA in the centromeric region appears to be the maintenance of diploidy.

Anaphase↗
PubMed1986

Characterization of kinetochores in multicentric chromosomes.

Long-term cultures of certain rat and mouse cell lines carry several dicentric and some multicentric chromosomes. Using antikinetochore antibodies obtainable from serum of scleroderma (var. CREST) patients we studied the number of kinetochores formed along the length of these chromosomes. The rat cells displayed as many kinetochores as there were centromeres. However, mouse cells showed the synthesis of only one kinetochore in dicentric and multicentric chromosomes which had been in the culture for a period of 1 year or more. When translocations were induced by bleomycin in mouse L cells, the newly formed dicentric chromosomes showed the formation of two kinetochores. It is not known when the accessory centromeres lose their capacity to assemble kinetochore proteins. Possibly, in the rat the 'latent' kinetochore lack a specific component which renders them ineffective for microtubule binding. The reason for the formation of only one kinetochore in mouse multicentric chromosomes is not clear. It may be due to the accumulation of mutations, modification of the kinetochore protein so that it lacks the antibody binding component, or a more effective regulatory gene than in the rat.

Animals↗
PubMed1986

Sequence of centromere separation: a mechanism for orderly separation of dicentrics.

Stable dicentric chromosomes from three mouse cell lines (viz., SEWA Rec4, brain tumor, and L-cells), as well as a human t(9;11) line were analyzed for the sequence in which the two centromeres separate. At prometaphase, as well as in many cells at midmetaphase, the dicentrics express the two centromeres in the form of two primary constrictions. As the cell advances to late metaphase, one of the constrictions loosens the two chromatids so that eventually there is no connection between them. The other centromere stays intact during this period and separates into two units at the metaanaphase junction along with the rest of the genome. The centromere that separates prematurely (out-of-phase) usually is the same in a given dicentric. It is proposed that such a prematurely separating centromere does not function as active element during chromatid migration. Apparently, in dicentrics some sort of control is exerted to eliminate the functioning of one centromere. The nature of such control is not understood at this time. The mouse dicentrics "synthesize" only one kinetochore as definable by antikinetochore antibody studies.

Animals↗
PubMed1986

Sequence of centromere separation: kinetochore formation in induced laggards and micronuclei.

Mouse L-cells were treated with bis-benzimidazole derivative (Hoechst 33258), caffeine and bleomycin in order to study genesis of laggards and micronuclei and formation of kinetochores as revealed by antikinetochore antibody staining. Apparently, the Hoechst 33258-induced decondensation experienced by the A:T-rich pericentric heterochromatin does not extend into the centromeric region and does not affect formation, physical appearance or function of kinetochores. The laggards induced by Hoechst 33258 are generally whole chromosome laggards which have antikinetochore antibody binding sites. These kinetochore-carrying laggards were seen to lie outside the spindle region in cells untreated with spindle inhibitors or hypotonic and stained differentially for spindle and chromosomes. Some micronuclei did not show kinetochore dots indicating their origin in acentric chromosome fragments. When cells were treated with caffeine or bleomycin, both types of micronuclei, namely those carrying kinetochores and those generated by acentric fragments, were seen. These results are interesting in that caffeine prevents the rejoining of chromosome breaks and one would expect only kinetochore-less micronuclei in caffeine-treated cells. It may mean that caffeine also induces aneuploidy. The L-cells carry minichromosomes which are no more than a pair of kinetochore dots. Such chromosomes, though detectable by antikinetochore antibody staining, may be missed in routine, acid-fixed, Giemsa-stained preparations.

Aneuploidy↗
PubMed1985

Aneuploidy induced by agricultural pesticides: where do we stand?

Even though aneuploidy is one of the worst afflictions of man, efforts to develop a mammalian test system for the study of induced nondisjunction have largely failed. A few scattered successes usually deal with Drosophila, fungi, plants, and mammalian cell cultures. The present paper discusses possible avenues to be explored for developing reliable test systems. These include: (i) epidemiological studies, (ii) analysis of fluorescent Y bodies, (iii) direct visualization of sperm chromosomes, (iv) analysis of out-of-phase centromere separation sequences, and (v) the soybean spot test. Currently there is no satisfactory explanation for a lack of mutagen-induced nondisjunction, the repeated occurrence of births of trisomic children to some couples, the astounding success of selection of a rare disomic sperm for fertilizing an egg in the presence of millions of normal ones, and having twice as many errors occurring in meiosis I as in meiosis II. An hypothesis is presented which suggests that out-of-phase separation of a centromere during early embryogenesis results in formation of mosaic individuals. Such mosaicism for a given chromosome in the gametic tissue would account for all the dilemmas mentioned above. Some supporting evidence for this concept is presented. It requires a new look at the mechanism of the origin and potential of transmission of aneusomic gametes.

Aneuploidy↗
PubMed1984

Chromosome studies in human subjects chronically exposed to arsenic in drinking water.

A two-year study was carried out on human subjects of various ages and backgrounds who had been drinking water containing more than 0.05 mg/liter (0.05 ppm) arsenic for a period of at least five years. The main aim was to correlate the frequency of chromosome aberrations and sister chromatid exchanges in the lymphocytes with the amount of arsenic in the water. In addition, we explored the incidence of skin cancer, fetal wastage, and genetic or developmental abnormalities. Several other variables--eg, coffee, wine, and cigarette consumption; sex; residence (rural vs urban); and exposure to chemicals, smelters, or pesticides--were also taken into consideration. The data on chromosome aberrations (104 exposed and 86 control individuals) and on sister chromatid exchanges (98 exposed and 83 control individuals) did not show that arsenic at concentrations used by our population (greater than 0.05 mg/liter) has any effect on these parameters. Similarly, no other health effects of arsenic at these concentrations were found.

Arsenic↗
PubMed1984

Sequence of centromere separation another mechanism for the origin of nondisjunction.

The most commonly accepted view about the origin of aneuploidy is that it is due to errors in meiotic division. However, its rare occurrence makes it difficult to explain recurrent births of trisomic children to some parents. This problem causes more serious concern when one accepts that an abnormal (n + 1 or n - 1) sperm would enter fertilization by overriding thousands, or even millions, of normal haploid sperms. Also, the failure of aneuploidy to be induced in the offspring of mammals treated with mutagens raises questions about the effectiveness of the accepted mode of origin of errors. Current concepts also do not explain why one observes more errors of meiotic I, than of meiotic II, origin. It is known that most chromosomes separating at meta-anaphase junction in mitosis follow a nonrandom, genetically controlled sequence of separation. The present proposal makes use of out-of-phase separation of a rare chromosome, like premature separation in mitosis of the X in elderly humans or of an 18 in parents of trisomy 18 children. The suggestion is made that such out-of-phase separation results in aneuploid cell lines by total failure of the centromere to separate or by it separating too early, before the spindle is formed. The prematurely separating centromeres, it appears, do not attach to spindle fibers and hence cause nondisjunction. Such nondisjunction in embryonic stages will produce apparently normal individuals with mosaicism in somatic and/or gametic tissue. An individual carrying mosaicism in gonadal tissue will produce a large number of abnormal gametes, one of which may have a reasonable chance of entering fertilization. This mode of origin of aneuploidy takes care of all questions raised above and finds support in the data available in the literature. Several of the suggestions made in the hypothesis are easily testable.

Adult↗
PubMed1984

Sequence of centromere separation: orderly separation of multicentric chromosomes in mouse L cells.

Mouse L cells have many dicentric chromosomes and one with eight centromeres. All eight centromeres behave similarly until midmetaphase when most centromeres split into two units each in apparently quick succession but out-of-phase. This premature separation leaves one or perhaps two closely located centromeres intact, which separate at late metaphase-anaphase, drawing the two chromatids to opposite poles. Such dominance of one centromere over all others, though unexplained, ensures the lack of any mitotic abnormality such as bridges or fragments. These observations show that all the centromeres are retained as functional primary constrictions except for a change in functional regulation when more than one centromere are located on a chromosome.

Animals↗
PubMed1984

Evolution of an octacentric isochromosome in mouse L-cells.

A sub-line of mouse L-cells exhibits a rather long biarmed chromosome which shows eight C-bands. Incorporation of BrdU for less than one cell cycle results in lateral asymmetry in the pericentromeric region as well as in the two arms. These regions of asymmetry correspond to four C-banding regions in each arm. Before it is fully condensed at metaphase, and particularly upon treatment with Hoechst, this chromosome expresses eight primary constrictions. Hence it is an octacentric. Presumably, it originated from tandem rejoinings between the short arms and the long arms of four chromosomes followed by the formation of an isochromosome. Since it is present in almost 100% cells, this octacentric chromosome must divide equationally at every cell division.

Animals↗
PubMed1983

Sequence of centromere separation: occurrence, possible significance, and control.

This review describes the existence of a phenomenon, sequential separation of centromeres, in mitotic cells of various species including both animals and plants. Critical observations at metaanaphase show that the centromeres of chromosomes in a given genome do not separate into two sister units randomly, but that there is a genetically controlled, nonrandom, species-specific sequence which is independent of the length of the chromosome or the position of the centromere. A stricter control appears to exist for late-separating than for early-separating chromosomes. At early stages of metaanaphase several chromosomes initiate onset of separation simultaneously or in rapid succession, but late-separating chromosomes are better defined in their sequential position. The effect of Colcemid on the sequence of separation is minimal. It is proposed that aneuploidy in humans and other organisms may result from out-of-phase separation of a given chromosome. With the exception of chromosome No. 16, it appears that very early- or very late-separating centromeres are involved in human trisomies more often than those in between. Perhaps one function of centromeric heterochromatin is the control of centromere separation. The amount of such chromatin shows a positive correlation with the timing of separation of the centromeres. Superimposed upon this quantitative influence is the qualitative aspect, as discussed for various genomes. This suggestion explains a lack of extremely large quantities of heterochromatin near the centromere. Its existence in the form of homogeneously staining regions distal to the centromere, as in some cancer cells or in sex chromosomes, seemingly has no influence on the separation of centromeres. A brief discussion of centromere separation errors in human disease is provided, and suggestions for further studies are made.

Aneuploidy↗
PubMed1983

Sequence of centromere separation: lack of Colcemid effect on the Chinese hamster genome.

This study describes the sequence of centromere separation in the Chinese hamster genome and the lack of any effect of Colcemid on this sequence. Analysis of bone marrow cells using sequential Giemsa staining and Q-banding established the sequence of centromere separation in cells derived from four Colcemid-treated and three untreated animals. Treatment of the data by use of the ANOVA test showed that the sequences established in the Colcemid-treated group did not differ from those in the untreated animals. The sequence of centromere separation in the Chinese hamster, as expressed by the pooled data from all seven animals, is chromosomes 1 and 2, followed by 3, 4, X, Y, 8, 9, 10, 5, 6, and 7.

Animals↗
PubMed1982

Soybean (Glycine max [L.] merrill) as a short-term assay for study of environmental mutagens. A report of the U.S. Environmental Protection Agency Gene-Tox Program.

The soybean (Glycine max [L.] Merrill) spot test is suggested as a preliminary screening test for environmental mutagens. This system makes use of various types of spots that originate from the treatment of seeds or seedlings with mutagens. The homozygous dominant y11y11 dark green leaves may show light green and very dark green spots; the heterozygous y11y11 light green leaves may show dark green, yellow or twin spots; and the homozygous recessive y11y11 yellow leaves show light green receptors. The interpretation is that twin spots on the y11y11 leaves originate from somatic crossing-over, and the singles originate primarily from losses or gains of the segments or chromosome carrying the gene y11 or y11. The yellow plants (y11y11) can produce light green sectors if y11 mutates to y11. Studies carried out with a host of chemical and physical agents lend support to the idea that the soybean system can distinguish between several genetic mechanisms underlying the formation of spots. Spots are detected against their native genetic and phenotype background, thus minimizing the effects due to physiological changes. The system is rapid (4-5 weeks per chemical), inexpensive, and involves an eukaryotic organism. It has the advantage of being adaptable for liquid solutions of chemicals, solid wastes, emulsions of chemicals (e.g., in lanolin), and gaseous products.

Crossing Over, Genetic↗