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N Paweletz

Publications and source records attributed to N Paweletz.

At least 55 records · Page 3Linked to original sources
PubMed1991

Lack of detectable kinetochores on some chromosomes in mouse x human hybrids.

When treated with an anti-kinetochore antibody present in the sera of scleroderma (var. CREST) patients, most chromosomes exhibit kinetochore dots at the position of the centromere. In this paper we report that some chromosomes in the mouse x human somatic cell hybrid fail to show these dots. In the early passages in a hybrid, HYG-1, the frequency of such chromosomes was higher (0.85%) than in later passages (0.45%) studied after five months of continuous culturing. In parallel, the mean number of human chromosomes in the hybrid also dropped. The somewhat hypodiploid parental cell lines, when similarly treated, showed only a rare chromosome without kinetochore dots. Immunoblots of the proteins showed that the sera used for kinetochore detection recognized all major centromere proteins (CENPs). Electron microscopy of some offlying metaphase chromosomes in another hybrid, HR61, exhibited a lack of trilamellar kinetochores. This study suggests that akinetochoric chromosomes might provide a novel mechanism responsible for chromosome loss and genesis of aneuploidy. In early passages, some cells in the hybrid showed detached kinetochores. These autonomous kinetochores could be seen in clusters and involved some mouse chromosomes also. Potential significance of these autonomous kinetochores in generating compound centromeres is discussed.

Animals↗
PubMed1990

Centromere separation. Early replication of repetitive DNA associated with inactive centromeres.

Four types of stable dicentric and one octacentric chromosomes from mouse brain tumor cells and L-929 cells were analyzed for the timing of replication of repetitive deoxyribonucleic acid (DNA) located in the centric and pericentric regions associated with active versus inactive centromeres. The repetitive DNA present in the heterochromatin blocks of inactive centromeres replicates much earlier than similar DNA associated with the active centromeres. The former appears to replicate during early to mid S when several euchromatic segments are still replicating. There seems to be little or no overlap in the timing of replication of the repetitive DNA present in the vicinity of prematurely separating centromeres (which are accessory and nonfunctional) and those that separate at meta-anaphase junction (which are the functional centromeres). In the absence of any information about the mechanism(s) controlling initiation and completion of DNA synthesis in the two types of heterochromatic blocks, the differential timing of replication of the DNA with similar base composition remains an enigma.

Animals↗
PubMed1990

The nucleolar chromatin and the secondary constriction.

We have traced the nucleolar chromatin from early prophase to the metaphase stage. In prophase this chromatin begins to condense and in metaphase it is fully condensed. In mitotic chromosomes, this chromatin remains surrounded by achromatic materials resembling the fibrillar centre. As such this region of the chromosomes appears as a gap or constriction at the light microscope level. The possible role of this achromatic material in relation to nucleologenesis and satellite association has been discussed.

Animals↗
PubMed1990

Mitosis arrested by deuterium oxide. Light microscopic, immunofluorescence and ultrastructural characterization.

Dynamics and correctness of mitotic division of PtK1 cells grown in vitro in the presence of deuterium oxide were assessed by morphological criteria. Incubation of PtK1 monolayers for 2 h in media supplemented with 25% to 75% D2O retarded in a dose-dependent manner the interphase/prophase transition, thus substantially decreasing the fraction of prophase cells. The progression of mitosis was also arrested at the metaphase/anaphase transition resulting in an accumulation of prometaphase and metaphase cells. After a prolonged incubation (12-24 h) in 75% D2O, prophase cells reappeared, often displaying a peculiar, "overmatured" pattern of chromosome condensation. In the presence of D2O an "overmatured" prophase cell is able to transform into a prometaphase cell and then directly into a multinucleate/micronucleate cell. Arrested prometaphase and metaphase cells developed restitution nuclei when incubated up to 24 h in the media containing 25% to 75% of heavy water. Immunofluorescence and electron microscopic studies revealed that the treatment with deuterium oxide profoundly disturbed development of the mitotic spindle. On the basis of these observations, a possible mechanism of the antimitotic action of deuterium oxide is discussed. We postulate that centrosomally controlled transformation of the microtubular cytoskeleton into the mitotic spindle is impaired by D2O. This delays the progression of prophase and disturbs congression of chromosomes into a regular metaphase plate.

Animals↗
PubMed1989

Evolution of compound centromeres. A new phenomenon.

A new type of centromere aberration in a transformed cell line of rat cerebral endothelial origin is described. These cells exhibit normal monocentric, dicentric, and multicentric chromosomes. The centromeres in dicentrics and multicentrics express variable locations along the chromosome. The centromeres in some of the multicentrics are located next to each other, with small intervening noncentromeric chromatin. In others, the centromeres appear to be in the immediate vicinity of each other with no evidence of intervening chromatin. This organization of the centromeres results in what appears to be a compound centromere composed of some multiples of single centromeres. All centromeres deposit kinetochore proteins that respond to kinetochore antibody. This evidence and that obtained from electron microscopy permits the conclusion that various centromeres/kinetochores in the compound structure are functional. The study presented here points to the existence of compound large centromeres--a novel phenomenon in cytogenetics--that may be prevalent in cancer cells. In the present cell line these regions appear as long, neck-like structures in some chromosomes and may be similar to some in vivo situations such as the X in Indian muntjac.

Animals↗
PubMed1989

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

The B1 cell line of rat cerebral endothelium origin exhibits several dicentric and multicentric chromosomes. These chromosomes, unlike multicentrics in mouse (Vig and Zinkowski 1986) do not show premature centromere separation. All centromeres deposit kinetochore proteins and appear to be functional. Even the centromeres which fail to migrate to the poles during anaphase and make side arm bridges bind to spindle microtubules. Some multicentric chromosomes show kinetochores spaced apart with intervening stretches of euchromatin while others are located adjacent to each other thus exhibiting tandem repeats and forming a "compound" kinetochore (Brinkeley et al. 1984). Also, unlike mouse multicentric chromosomes in which different pericentric regions and the centromeres replicate at different times, the rat chromosomes appear to replicate all pericentric and centric regions in a given multicentric simultaneously. The present studies indicate that centromeres in rat and mouse replicate during the last part of the S-phase and in continuation with the pericentric heterochromatin.

Animals↗
PubMed1989

Centromere structure and function in neoplasia.

The mammalian centromere plays an essential role in maintenance of diploidy in the cell. It is therefore imperative that we understand the structure and function of the mammalian centromere in order to plan strategy to control the incidence of aneuploidy and resultant malformations of the nonneoplastic as well as neoplastic tissues. Even though considerable information is available about the structure and some functional aspects of centromeres of lower eukaryotes such as yeast, the structure of the mammalian centromere is still a matter of conjecture limited to an understanding of the base composition of the alphoid sequences putatively located in the centromeric DNA of higher apes. We do, however, have a better understanding of the structure and role of the kinetochore. In all eukaryotes analyzed so far, the centromeres in a given genome separate in a sequential manner dependent upon the time of replication of pericentric and centromeric DNA. Some chromosomes, generally found in neoplastic cells, that carry more than one centromere show premature separation of the accessory centromeres. These centromeres and the associated pericentric regions replicate their DNA in an earlier part of the S phase than those that show kinetochore activity; both, however, carry DNA of the same composition. The active centromeres in these chromosomes show kinetochore protein binding as detected by antikinetochore antibody; the inactive centromeres are usually devoid of these proteins. The double minutes in neoplastic cells also lack kinetochore proteins, perhaps due to a lack of any centromere. Some dicentric and multicentric chromosomes in cancer cells and transformed cell lines do not display premature centromere separation. In these chromosomes, all centromeric sites show kinetochore proteins and all centromeric regions replicate their DNA simultaneously. These chromosomes also exhibited meiotic-like behavior of some centromeres and show postanaphase separation of some centromeres, resulting in bridges. These bridges, upon breakage and rejoining of sister chromatids, generate new multicentric chromosomes. The resulting chromosomes also exhibit formation of compound kinetochores. Some of these phenomena are novel descriptions of the centromere behavior in cancer cells. This review also discusses the role of aberrant centromere separation in human biology, providing correlates between errors of centromere separation and neoplasia.

Animals↗
PubMed1989

Sequence of centromere separation: kinetochore formation and DNA replication in dicentric chromosomes showing premature centromere separation in rat cerebral cells.

A subpopulation of rat cerebral endothelial cells, designated B1, exhibits an array of multicentric chromosomes. Because of the formation of bridges at anaphase, this cell population produced new types of multicentrics at every cell division. These chromosomes showed kinetochore proteins at every centromeric site and all centromeric regions replicated their DNA at the end of the S phase, more or less simultaneously. A new subpopulation of cells, designated B2, obtained from the original sample frozen at Wayne State University displayed several dicentrics. In contrast to B1 these chromosomes exhibit premature centromere separation as reported for mouse and human cell lines. These B2 dicentrics show only one site of kinetochore protein deposition. The timing of DNA replication around the centric region of prematurely separating centromere is also changed similar to the earlier reported premature DNA synthesis for mouse dicentrics. These observations suggest a universality of relationship between premature centromere separation, a lack of kinetochore formation, and early replication of the centric/pericentric DNA associated with these centromeres. The cause of sudden change from activity to inactivity of these chromosomes, though interesting, is not clear.

Animals↗
PubMed1989

Tumor-related angiogenesis.

In recent years, tumor-related angiogenesis has become an important field of research in oncology. It could be stated that growth of solid tumors is completely dependent on neovascularization to provide the tumor with all required nutrients. Special compounds (tumor angiogenesis factor[s]) are released by tumor cells into the environment to stimulate different types of normal cells to become active for the tumor. In particular, endothelial cells of neighboring capillaries are induced to react. They disintegrate their own basal lamina, detach from their neighbors, enter the extracellular matrix, and migrate toward the tumor mass. Cell divisions occur within such sprouts, thereby increasing the number of migrating endothelial cells. Strands of such cells are formed, and inter- and intracellular lumina develop. Loops of these hollow strands anastomose to form a network of new vessels which become connected with the blood circulation. The tumor mass thus becomes vascularized and can continue to grow. The prevention of neoangiogenesis has an enormous impact on cancer treatment by inhibiting the growth of the tumor. In this review, all important aspects of tumor-related angiogenesis are presented.

Angiogenesis Inducing Agents↗
PubMed1989

Disorganization of mitosis in HeLa cells by deuterium oxide.

We assessed, by light and electron microscopy, the influence of deuterium oxide on the dynamics of mitosis and on the morphology of the mitotic apparatus in HeLa cells grown in vitro. A 2-h incubation of HeLa monolayers with low concentrations of D2O (1%-25%) in the medium increased the frequency of multipolar divisions up to 20 times the control level. Substitution of 10% and 25% D2O for H2O induced changes in the proportions of mitotic phases. These changes could be fully reversed to the control pattern after 1 h of recovery in non-deuterated medium. Fifty % D2O strongly inhibited, and 75% D2O blocked the cell cycle before prophase and at (pro-)metaphase. In cells treated with 50% D2O conspicuous morphological changes of the interphase chromatin as well as ultrastructural abnormalities of all mitotic phases were regularly observed. Overall, these results confirmed the antimitotic activity of deuterium oxide and revealed that it could also influence the cell cycle before mitosis. It is suggested that interference with diverse cellular constituents rather than a specific influence on microtubule turnover could be responsible for the disorganization of the cell cycle in HeLa cells by D2O.

Chromatin↗
PubMed1989

Centromere separation and aneuploidy: a lesson from multicentric chromosomes.

Premature centromere separation somehow nullifies the deposition of kinetochore proteins in multicentric chromosomes, is associated with early DNA replication of the centromere and the pericentric region and results in a lack of functionality of the centromere. It is conceivable that monocentric chromosomes which show premature separation, like the X chromosome as found in elderly human females (Fitzgerald et al, 1975), may have similar properties which result in a failure of centromere function and, hence, aneuploidy. This may be one of the general mechanisms by which chromosomes malsegregate.

Aneuploidy↗
PubMed1989

The behavior of centrosomes in multinucleate cells formed after colcemid treatment.

Multinucleate PtK1 cells were generated by treating the cells with colcemid for up to 60 h. Cells with scattered chromosomes reconstructed nuclear envelopes around these chromosomes. After recovery of up to 36 h these multinucleate cells went into mitosis. In such cells mainly two types of spindles are found: a bipolar spindle with some "accessory" half-spindles and multipolar mitotic apparatus with several equally-sized half-spindles ordered in an irregular way. Ultrastructural studies revealed centrosomes within such spindles which had not developed a microtubular connection to chromosomes and obviously could not act as mitotic pole. This result is interpreted in the way that centrosomes undergo a maturation cycle. Immature centrosomes cannot form mitotic poles. The asynchrony of the cycles of the multiple centrosomes seems to be generated by an uneven distribution of special factor(s).

Animals↗
PubMed1989

Post-metaphase mitotic events in cells treated with dinitrophenol.

The sequence of post-metaphase mitotic events, such as anaphase movement A and B, chromosome decondensation, nuclear envelope reformation and cytokinesis, has been studied in 2,4-initrophenol (DNP)-treated HeLa cells. The effects of DNP were found to be dose dependent and at concentrations higher than 3 mM, both anaphase A and B movements were totally and nearly instantaneously arrested. It could be shown that cytokinesis did not depend on the completion of anaphase movements. This was also true for nuclear envelope reformation which could take place even around condensed chromosomes arrested in anaphase. The post-metaphase mitotic events do not follow a strict causal sequence, but they can be dissociated from each other in anaphase-arrested cells.

2,4-Dinitrophenol↗
PubMed1988

Microtubule rearrangements during mitosis in multinucleate cells.

The peroxidase-antiperoxidase (PAP) method for the detection of polymerized tubulin has been used to study the microtubule rearrangements during mitosis in PtK1 and HeLa multinucleate cells obtained by polyethyleneglycol (PEG)-mediated fusion. We demonstrate here that the transition of the microtubular cytoskeleton from interphase to mitosis is an inducible event and independent of the factor(s) responsible for chromatin condensation and nuclear envelope breakdown. However, for the induction of the microtubule rearrangements nuclear envelope breakdown is required. At midprophase, cytoskeletal microtubule rearrangements start for multinucleate PtK1 cells, whereas in HeLa cells such changes are delayed, and a more abrupt transition is observed here. After complete nuclear envelope breakdown (prometaphase) mitotic asters and spindles but no cytoplasmic (interphase) microtubuli can be observed in both systems. Metaphase is characterized by an interaction between the different mitotic poles which show the form of bipolar spindles, but individual separated mitotic poles far removed from the chromatin can also be seen.

Animals↗
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↗