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At least 541 records · Page 30Linked to original sources
PubMed2001

5-azacytidine induces chromosomal breakage in the root tips of wheat carrying the cuckoo chromosome 4S(L) from Aegilops sharonensis.

The cuckoo chromosome 4S(L) from Aegilops sharonensis is preferentially transmitted when introduced by hybridization into common wheat, Triticum aestivum. Gametocidal (Gc) factors carried in 4S(L) induce chromosome breakage in meiospores not containing them, ensuring their transmission to the progeny. Chromosome breakage and break-fusion-bridge (BFB) cycles can also be observed during early embryo sac development of chromosome 4S(L) addition lines to wheat, often leading to the presence of dicentric chromosomes in the subsequent progeny. However, the process responsible for inducing the primary chromosomal breaks only appears to occur during the initial divisions of the embryo and endosperm. In the presence of chromosome 4S(L), treatment with the hypomethylating agent 5-azacytidine induces chromosome breakage in root tips. This suggests that the process of chromosome fragmentation, induced by the Gc factors during early seed development, is repressed at later stages by DNA methylation.

Anaphase↗
PubMed2006

The influence of chromosome flexibility on chromosome transport during anaphase A.

The role of protein flexibility in molecular motor function has previously been studied by considering a Brownian ratchet motor that is connected to its cargo by an elastic spring, with the result that the average velocity of the motor/cargo system is increased by reducing the stiffness of the linkage. Here, we extend this investigation to the case of chromosome transport during anaphase A, in which the relevant flexibility is not primarily in the motor/cargo linkage but rather in the cargo itself, i.e., in the chromosome. We model the motor mechanism as an imperfect Brownian ratchet with a built-in opposing load and the chromosome as a collection of discrete segments linked by an elastic energy function that discretizes the potential energy of an elastic rod. Thermal fluctuations are produced in the model by random forces, as in Brownian dynamics. All of the parameters that characterize the chromosome are known or can be estimated from experimental data, as can all but one of the motor parameters, which is adjusted to give the correct transport velocity of normal-length chromosomes. With the parameters so determined, we then reproduce the experimental finding of Nicklas [Nicklas, R. B. (1965) J. Cell Biol. 25, 119-135] that chromosome speed is essentially independent of chromosome length, even though our model contains no "velocity governor." We find instead that this effect is a consequence of chromosome flexibility, as it disappears when stiffer than normal chromosomes are considered.

Anaphase↗
PubMed1998

DNA-proportional distribution of radiation-induced chromosome aberrations analysed by fluorescence in situ hybridization painting of all chromosomes of a human female karyotype.

PURPOSE: This is the extension of a previous study, showing deviations from a DNA-proportional involvement of 12 single chromosomes (1-4, 6-10, 12, 14 and X) in radiation-induced translocations and dicentrics measured by FISH-painting and classified by standard cytogenetic scoring criteria. By adding data on chromosomes 2, 4, 5, 9, 11-13, 15-22 and X the analysis now comprises all chromosomes of a human female karyotype evaluated with three nomenclature systems (PAINT, S & S and a conventional method). MATERIAL AND METHODS: Metaphase spreads were prepared from lymphocytes irradiated with 3 Gy 220 kV X-rays. FISH painting was performed with single chromosome-specific probes in combination with a pancentromeric probe. RESULTS: Deviations from a DNA-proportional distribution became apparent for all aberration parameters analysed with the three nomenclature systems. Chromosomes 2, 3 and 6 were less frequently involved and chromosomes 16, 17 and 20 were more frequently involved in exchange aberrations. Generally, smaller chromosomes (15-22, with the exception of chromosome 19) were more frequently involved in aberration formation than expected. CONCLUSION: The assumption that the probability of a chromosome being involved in an exchange aberration is proportional to its DNA content is not supported by the present data.

Cell Count↗
PubMed1991

Chromosome motion during attachment to the vertebrate spindle: initial saltatory-like behavior of chromosomes and quantitative analysis of force production by nascent kinetochore fibers.

Before forming a monopolar attachment to the closest spindle pole, chromosomes attaching in newt (Taricha granulosa) pneumocytes generally reside in an optically clear region of cytoplasm that is largely devoid of cytoskeletal components, organelles, and other chromosomes. We have previously demonstrated that chromosome attachment in these cells occurs when an astral microtubule contacts one of the kinetochores (Hayden, J., S. S. Bowser, and C. L. Rieder. 1990. J. Cell Biol. 111:1039-1045), and that once this association is established the chromosome can be transported poleward along the surface of the microtubule (Rieder, C. L., and S. P. Alexander. 1990. J. Cell Biol. 110:81-95). In the study reported here we used video enhanced differential interference contrast light microscopy and digital image processing to compare, at high spatial and temporal resolution (0.1 microns and 0.93 s, respectively), the microtubule-mediated poleward movement of attaching chromosomes and poleward moving particles on the spindle. The results of this analysis demonstrate obvious similarities between minus end-directed particle motion on the newt pneumocyte spindle and the motion of attaching chromosomes. This is consistent with the hypothesis that both are driven by a similar force-generating mechanism. We then used the Brownian displacements of particles in the vicinity of attaching chromosomes to calculate the apparent viscosity of cytoplasm through which the chromosomes were moving. From these data, and that from our kinetic analyses and previous work, we calculate the force-producing potential of nascent kinetochore fibers in newt pneumocytes to be approximately 0.1-7.4 x 10(-6) dyn/microtubule) This is essentially equivalent to that calculated by Nicklas (Nicklas, R.B. 1988. Annu. Rev. Biophys. Biophys. Chem. 17:431-449) for prometaphase (4 x 10(-6) dyn/microtubule) and anaphase (5 x 10(-6) dyn/microtubule) chromosomes in Melanoplus. Thus, within the limits of experimental error, there appears to be a remarkable consistency in force production per microtubule throughout the various stages of mitosis and between groups of diverse taxonomic affinities.

Animals↗
PubMed1996

The force for poleward chromosome motion in Haemanthus cells acts along the length of the chromosome during metaphase but only at the kinetochore during anaphase.

The force for poleward chromosome motion during mitosis is thought to act, in all higher organisms, exclusively through the kinetochore. We have used time-lapse. video-enhanced, differential interference contrast light microscopy to determine the behavior of kinetochore-free "acentric" chromosome fragments and "monocentric" chromosomes containing one kinetochore, created at various stages of mitosis in living higher plant (Haemanthus) cells by laser microsurgery. Acentric fragments and monocentric chromosomes generated during spindle formation and metaphase both moved towards the closest spindle pole at a rate (approximately 1.0 microm/min) similar to the poleward motion of anaphase chromosomes. This poleward transport of chromosome fragments ceased near the onset of anaphase and was replaced. near midanaphase, by another force that now transported the fragments to the spindle equator at 1.5-2.0 microm/min. These fragments then remained near the spindle midzone until phragmoplast development, at which time they were again transported randomly poleward but now at approximately 3 microm/min. This behavior of acentric chromosome fragments on anastral plant spindles differs from that reported for the astral spindles of vertebrate cells, and demonstrates that in forming plant spindles, a force for poleward chromosome motion is generated independent of the kinetochore. The data further suggest that the three stages of non-kinetochore chromosome transport we observed are all mediated by the spindle microtubules. Finally, our findings reveal that there are fundamental differences between the transport properties of forming mitotic spindles in plants and vertebrates.

Anaphase↗
PubMed2000

A kinase-anchoring protein (AKAP)95 recruits human chromosome-associated protein (hCAP)-D2/Eg7 for chromosome condensation in mitotic extract.

Association of the condensin multiprotein complex with chromatin is required for chromosome condensation at mitosis. What regulates condensin targeting to chromatin is largely unknown. We previously showed that the nuclear A kinase-anchoring protein, AKAP95, is implicated in chromosome condensation. We demonstrate here that AKAP95 acts as a targeting protein for human chromosome-associated protein (hCAP)-D2/Eg7, a component of the human condensin complex, to chromosomes. In HeLa cell mitotic extract, AKAP95 redistributes from the nuclear matrix to chromatin. When association of AKAP95 with chromatin is prevented, the chromatin does not condense. Condensation is rescued by a recombinant AKAP95 peptide containing the 306 COOH-terminal amino acids of AKAP95. Recombinant AKAP95 binds chromatin and elicits recruitment of Eg7 to chromosomes in a concentration-dependent manner. Amount of Eg7 recruited correlates with extent of chromosome condensation: resolution into distinct chromosomes is obtained only when near-endogenous levels of Eg7 are recruited. Eg7 and AKAP95 immunofluorescently colocalize to the central region of methanol-fixed metaphase chromosomes. GST pull-down data also suggest that AKAP95 recruits several condensin subunits. The results implicate AKAP95 as a receptor that assists condensin targeting to chromosomes.

Amino Acid Sequence↗
PubMed2004

Chromosome instabilities and programmed cell death in tapetal cells of maize with B chromosomes and effects on pollen viability.

B chromosomes (B's), knobbed chromosomes, and chromosome 6 (NOR) of maize undergo nondisjunction and micronucleus formation in binucleate tapetal cells. These chromosome instabilities are regular events in the program of tapetal cell death, but the B's strongly increase A chromosome instability. We studied 1B and 0B plants belonging to selected lines for high or low B transmission rate and their F1 hybrids. These lines are characterized by meiotic conservation or loss of B chromosomes, respectively. The female B transmission (fBtl) allele(s) for low B transmission is dominant, inducing micronucleus formation and B nondisjunction. We hypothesize that the fBtl allele(s) induces knob instability. This instability would be sufficient to produce B loss in both meiocytes and binucleate tapetal cells. B instability could, in turn, produce instabilities in all chromosomes of maize complement. To establish whether the chromosomal instabilities are related to the tapetal programmed cell death (PCD) process, we applied the TUNEL technique. PCD, estimated as the frequency of binucleate tapetal cells with TUNEL label, was significantly correlated with the formation of micronuclei and the frequency of pollen abortion. It can be concluded that the observed chromosome instabilities are important to the PCD process and to the development of microspores to form viable pollen grains.

Apoptosis↗
PubMed1997

Effect of rye A and B chromosomes on meiotic association of Hordeum marinum ssp. gussoneanum (4x) chromosomes in intergeneric hybrids.

Chromosome association at metaphase I was studied in PMCs of eight H. marinum ssp. gussoneanum (4x) x rye hybrids. Differences in the levels of association separated six hybrids with 2n = 23 including 14 Hordeum, 7 rye A and 2 rye B chromosomes into two groups of three plants each, a "low association" group with means of 0.03III + 4.43II (1.55 rings + 2.88 rods) + 5.10I and 6.03 chiasmata/cell, and a "high association" group with means of 0.01IV + 0.03III + 6.40II (3.55 rings + 2.85 rods) + 1.13I and 10.04 chiasmata/cell. The low number of plants studied prevents a safe estimate of the number of genes involved, but the significant difference between groups suggests the presence in the rye genome of two major genes, or two genotypes, for control of meiotic chromosome association. In two additional hybrids with 2n = 25, one of each above-mentioned group, the presence of two extra rye B chromosomes raised chiasma frequencies by ca 1.5, indicating a promoting effect on chromosome association. The level of Hordeum chromosome association in the "high association" group and the observation of up to 7 Hordeum ring bivalents in some cells agree with an autoploid origin of H. marinum ssp. gussoneanum (4x). Hordeum and rye chromosomes formed a few heterogenomic bi- and trivalents. Most rye A chromosomes formed univalents, but 2.7% were included in associations. Rye B chromosomes generally formed rod bivalents. The use of genome analysis in its traditional sense is discussed.

Chromosomes↗
PubMed1991

Physical and genetic mapping of Candida albicans: several genes previously assigned to chromosome 1 map to chromosome R, the rDNA-containing linkage group.

Analysis of the karyotypes of multiple Candida albicans isolates by pulsed-field electrophoresis confirms the observation by Lasker et al. of eight chromosomes. The genes previously assigned to chromosome 1 in fact fall into two groups, one (including ADE1, SOR9, and CDC10) is linked to the ribosomal DNA genes on a chromosome called R, whereas the others are found on chromosome 1. Chromosome R varies in electrophoretic mobility among strains, usually running equal to or faster than chromosome 1 but in rare cases running slower than chromosome 1. In strain 1012A, the decreased mobility of one homolog is associated with the very large majority of the rDNA genes being on that homolog; the second homolog, with only a few copies, migrates with chromosome 2. Linkage analysis by using spheroplast fusion confirms the gene assignments made by hybridization to blots of the electrophoretic karyotype. A newly cloned gene, LYS2, hybridizes to chromosome 1.

Blotting, Southern↗
PubMed1992

A non-isotopic in situ hybridisation study of the chromosomal origin of 15 supernumerary marker chromosomes in man.

Fifteen patients presenting with mosaic or non-mosaic karyotypes containing a distamycin-DAPI negative de novo or familial supernumerary marker chromosome were studied with non-isotopic in situ hybridisation using a library of alphoid centromere specific and satellite II/III probes. The in situ hybridisation studies showed that seven markers were derived from satellited autosomes (three chromosome 13/21, two chromosome 14, two chromosome 22), six from non-satellited autosomes (two chromosome 4, one chromosome 12, one chromosome 16, two chromosome 19), and one from the Y chromosome. One non-mosaic marker was negative for all the alphoid and satellite II/III probes used.

Abnormalities, Multiple↗
PubMed2003

The paternal sex ratio chromosome in the parasitic wasp Trichogramma kaykai condenses the paternal chromosomes into a dense chromatin mass.

A recently discovered B chromosome in the parasitoid wasp Trichogramma kaykai was found to be transmitted through males only. Shortly after fertilization, this chromosome eliminates the paternal chromosome set leaving the maternal chromosomes and itself intact. Consequently, the sex ratio in these wasps is changed in favour of males by modifying fertilized diploid eggs into male haploid offspring. In this study, we show that in fertilized eggs at the first mitosis the paternal sex ratio (PSR) chromosome condenses the paternal chromosomes into a so-called paternal chromatin mass (PCM). During this process, the PSR chromosome is morphologically unaffected and is incorporated into the nucleus containing the maternal chromosomes. In the first five mitotic divisions, 67% of the PCMs are associated with one of the nuclei in the embryo. Furthermore, in embryos with an unassociated PCM, all nuclei are at the same mitotic stage, whereas 68% of the PCM-associated nuclei are at a different mitotic phase than the other nuclei in the embryo. Our observations reveal an obvious similarity of the mode of action of the PSR chromosome in T. kaykai with that of the PSR-induced paternal genome loss in the unrelated wasp Nasonia vitripennis.

Animals↗
PubMed1980

Patterns of replication of human chromosomes in human x mouse hybrids with different chromosomal compositions.

The order of termination of DNA replication of ten human chromosomes remaining in a hybrid between normal human skin fibroblasts and mouse RAG calls has been analyzed. The human chromosomes were Nos. 2, 3, 4, 5, 6, 7, 10, 16, 17 and the Y. The order of replication of these chromosomes was essentially the same as that of the corresponding chromosomes in normal fibroblasts. This hybrid contained four human chromosomes, 6, 16, 17, and the Y, which were not present in a related hybrid (RRP5-4) which had been studied previously. Several chromosomes in RRP5-4, including 4, 5, and 7, had been shown to replicate at different times than the same chromosomes in the normal parental fibroblasts. These results suggest that there may be specific genes which are important for the control of the precise order of replication of human fibroblast chromosomes. These genes could be located on chromosomes which were retained in the hybrid analyzed here but which were missing from RRP5-4.

Adult↗
PubMed1994

B-chromosome systems in the greater glider, Petauroides volans (Marsupialia: Pseudocheiridae). II. Investigation of B-chromosome DNA sequences isolated by micromanipulation and PCR.

B chromosomes, despite their common occurrence throughout the animal and plant kingdoms, have not been investigated extensively at the molecular level. While the majority of B chromosomes occurring in animals have been described as heterochromatic, only a few researchers have examined the DNA of these chromosomes beyond this gross cytological level. This is the case in the largest of the gliding marsupial possums, the greater glider, Petauroides volans. To examine the molecular composition and localization of B-chromosome DNA sequences in P. volans, a combination of micromanipulation and the polymerase chain reaction was used in this study to isolate and then amplify the DNA of the B chromosomes. Localization of the isolated B-chromosome sequences to metaphase chromosomes was investigated using fluorescence in situ hybridization. The B chromosomes in this species are shown to be composed of a heterogeneous mixture of sequences, some of which are unique to the B chromosomes, while others exhibit homology to the centromeric regions of the autosomal complement.

Animals↗
PubMed1994

Assignment of TK1 encoding thymidine kinase to Syrian hamster chromosome 9 by microcell-mediated chromosome transfer.

We report here the assignment of TK1, the gene for thymidine kinase to Syrian hamster (Mesocricetus auratus) chromosome 9 (MAU9) by complementation mapping. Syrian hamster chromosomes derived from a wild type (TK+) subline of BHK cells were introduced via microcell-mediated chromosome transfer into B82 mouse cells deficient in thymidine kinase (TK-), a defect that prevents their growth in HAT culture media. Hybrid clones were selected in HAT media. Chromosome analyses of the microcell hybrids showed that the thymidine kinase deficiency of B82 cells was corrected by MAU9. Therefore, we assigned TK1 to MAU9. Previously, TK1 was assigned to mouse chromosome 11 (MMU11), rat chromosome 10 (RNO10), Chinese hamster chromosome 7 (CGR7), and human chromosome 17 (HSA17). The striking banding homology of MAU9 with RNO10, MMU11, CGR7 and HSA17 provides additional support for the assignment of TK1 to MAU9. To our knowledge, this is the first report of gene assignment to a specific Syrian hamster chromosome using the somatic cell hybridization technique.

Animals↗
PubMed1997

Identification of individual barley chromosomes based on repetitive sequences: conservative distribution of Afa-family repetitive sequences on the chromosomes of barley and wheat.

The Afa-family repetitive sequences were isolated from barley (Hordeum vulgare, 2n = 14) and cloned as pHvA14. This sequence distinguished each barely chromosome by in situ hybridization. Double color fluorescence in situ hybridization using pHvA14 and 5S rDNA or HvRT-family sequence (subtelomeric sequence of barley) allocated individual barley chromosomes showing a specific pattern of pHvA14 to chromosome 1H to 7H. As the case of the D genome chromosomes of Aegilops squarrosa and common wheat (Triticum aestivum) hybridized by its Afa-family sequences, the signals of pHvA14 in barley chromosomes tended to appear in the distal regions that do not carry many chromosome band markers. In the telomeric regions these signals always placed in more proximal portions than those of HvRT-family. Based on the distribution patterns of Afa-family sequences in the chromosomes of barley and D genome chromosomes of wheat, we discuss a possible mechanism of amplification of the repetitive sequences during the evolution of Triticeae. In addition, we show here that HvRT-family also could be used to distinguish individual barley chromosomes from the patterns of in situ hybridization.

Biological Evolution↗
PubMed2001

Barley chromosome addition lines of wheat for screening of AFLP markers on barley chromosomes.

We conducted AFLP (Amplified Fragment Length Polymorphism) analysis with the six wheat-barley chromosome addition lines of common wheat cultivar Chinese Spring. We analyzed the AFLP fingerprints generated by 36 combinations of selective-amplification primers to find 103 markers specific to the barley chromosomes (2.9 markers per combination on average). The numbers of AFLP markers mapped to the barley chromosomes varied (one to 16) depending of the primer combinations. Each barley chromosome had 10 to 27 AFLP markers (17.2 markers on average). We identified the chromosome arms in which these markers are located using the barley telocentric addition lines (one to 20 markers per chromosome arm). The AFLP markers were not distributed evenly among chromosomes and chromosome arms. We could not determine the chromosome-arm locations for some of the barley-specific markers, either because such markers were found in both the short- and long-arm telocentric lines, or in neither line.

Chromosomes↗
PubMed1999

[Structure of chromatin and chromosomes in preparations of interphase nucleus derivatives, prepared by removal of the nucleuar envelopes. II. Structure of chromatin and associations of chromosomes in stretched amembranous nuclei and mitotic figures].

Preparations of surface stretched amembranous nuclei and mitotic figures were used for revealing the high order nuclear and chromosomal structures. The preparations were obtained by dropping amembraneous nuclei and mitotic figures suspension in methanol-glacial acetic acid mixture (3:1) on wetted superclean slides. Amembraneous nuclei and mitotic figures were isolated from intact murine and human cells (lines L1210, SK-UT-1B, PHA-stimulated lymphocytes) by means of their 1-5 min prefixational capillary pipetting with freshly prepared 0.018-0.06% Triton X-100 solution in the conditional cultural medium. Stretched amembraneous nuclei and mitotic figures had no features of induced chromatin dispersion and compaction. Stretched interphase amembraneous nuclei showed spatially separated individual structures (thin chromatin fibres, nucleoli, intranuclear bodies), polymorphous pattern of perinucleolar chromatin aggregation and episodically expressed beaded thick chromatin fibres and a chromocenter. The chromomeric pattern of the spread chromosomes of mitotic figures was quite similar but hardly identical with that of G-banding. The stretched prometaphase mitotic figures in all tested cell types always contained loose "residual" nucleoli looking like typical prophase nucleoli as concerns their shape and number per cell (mitotic figure). The majority of chromosomes of stretched mitotic figures and of prophase amembraneous nuclei were attached to the nucleolar material. All tested cell lines showed almost the same variation in number of nucleolus-attached chromosomes, per both prophase amembraneous nucleus and prometaphase mitotic figure. Some chromosomes of stretched mitotic figures were colocated with "residual" nucleoli and looked shortened and strongly condensed. Other chromosomes, locally associated with "residual" nucleoli, were straight and oriented radially to these. Mutual chromosomal arrangements in mitotic cells on smears and in stretched mitotic figures were analogous. Equatorial plates from PBS-washed SK-UT-1B cells displayed a better stretching capacity than those from untreated cells. In the former case metaphase chromosomes were seen more uniformly stretched and well identified after GTG-banding procedure. The number of interchromosomal (mainly telomere-telomeric and telomere-centromeric) connections per stretched mitotic figure (or per stretched prophase amembraneous nucleus) was minimum in late prometaphase, maximum in prophase and early prometaphase, and intermediate in metaphase. The obtained data are discussed in terms of topology and longitudinal heterogeneity of mitotic chromosomes.

Animals↗
PubMed2001

Microdissection and chromosome painting of plant B chromosomes.

Plant chromosome microdissection techniques together with different isolation and amplification methods of microisolated DNA are described. Such isolated DNA was used to 'chromosome paint' B chromosomes of the dicot Brachycome dichromosomatica and the monocot Secale cereale. It is demonstrated that the specific painting of the described chromosomes was possible because of enrichment for chromosome-specific repetitive sequences, rather than the chromosome specific low- and single-copy sequences which are responsible for the painting of mammalian chromosomes. The feasibility of 'chromosome painting' of standard chromosomes in plant species with relatively small or large genomes is discussed.

Asteraceae↗