Showing papers on "Metaphase published in 1981"
TL;DR: In situ hybridization to human metaphase chromosomes of the 3H-labeled cloned DNA resulted in highly significant labeling of band p36 of chromosome 1, such that 22% of all chromosome grains were located on this region.
Abstract: Recombinant lambda bacteriophage clone H3 containing a human DNA segment of 14.9 kb present in one or two copies per haploid genome was isolated. In situ hybridization in human metaphase chromosomes of the 3H-labeled cloned DNA resulted in highly significant labeling (53% of cells) of band p36 of chromosome 1, such that 22% of all chromosomal grains were located on this region. Hybridization was dependent upon the presence of dextran sulfate in the hybridization mixture and was not affected by repetitive DNA competitor. These results demonstrate localization of a single copy sequence on human metaphase chromosomes.
740 citations
TL;DR: The specificity of the staining of CREST scleroderma patient serum was investigated by immunofluorescence and immunoelectron microscopy, and it was concluded that the presumptive kinetochores duplicate in G2 of the cell cycle.
Abstract: The specificity of the staining of CREST scleroderma patient serum was investigated by immunofluorescence and immunoelectron microscopy. The serum was found to stain the centromere region of mitotic chromosomes in many mammalian cell types by immunofluorescence. It also localized discrete spots in interphase nuclei which we have termed "presumptive kinetochores." The number of presumptive kinetochores per cell corresponds to the chromosome number in the cell lines observed. Use of the immunoperoxidase technique to localize the antisera on PtK2 cells at the electron microscopic level revealed the specificity of the sera for the trilaminar kinetochore disks on metaphase and anaphase chromosomes. Presumptive kinetochores in the interphase nuclei were also visible in the electron microscope as randomly arranged, darkly stained spheres averaging 0.22 micrometers in diameter. Preabsorption of the antisera was attended using microtubule protein, purified tubulin, actin, and microtubule-associated proteins. None of these proteins diminished the immunofluorescence staining of the sera, indicating that the antibody-specific antigen(s) is a previously unrecognized component of the kinetochore region. In some interphase cells observed by both immunofluorescence and immunoelectron microscopy, the presumptive kinetochores appeared as double rather than single spots. Analysis of results obtained using a microspectrophotometer to quantify DNA in individual cells double stained with scleroderma serum and the DNA fluorescent dye, propidium iodide, led to the conclusion that the presumptive kinetochores duplicate in G2 of the cell cycle.
295 citations
TL;DR: Friend leukemia cells resistant to cadmium toxicity were selected and revealed that the resistant cells are nearly tetraploid and contain, on the average, three very small chromosomes that are absent from non-resistant Friend cells.
Abstract: Friend leukemia cells resistant to cadmium toxicity were selected. More than 70% of total cysteine incorporation in these cells was into the metal-binding protein, metallothionein. We used cDNA and genomic DNA clones containing the metallothionein-I gene to measure the concentration of its mRNA, the rate of gene transcription, and the number of genes. On a per cell basis, optimally induced, cadmium-resistant cells have a 14-fold more metallothionein-I mRNA, a 6-fold higher rate of metallothionein-I gene transcription, and 6-fold more metallothionein-I genes than do nonresistant cells. Metaphase spreads revealed that the resistant cells are nearly tetraploid and contain, on the average, three very small chromosomes that are absent from non-resistant Friend cells.
274 citations
TL;DR: It can be inferred from this and other data that a substantial number of MTs run uninterrupted between the kinetochore and the polar region in untreated metaphase PtK1 cells.
Abstract: When metaphase PtK1 cells are cooled to 6–8 ° C for 4–6 h the free, polar, and astral spindle microtubules (MTs) disassemble while the MTs of each kinetochore fiber cluster together and persist as bundles of cold-stable MTs. These cold-stable kinetochore fibers are similar to untreated kinetochore fibers in both their length (i.e., 5–6 μm) and in the number of kinetochore-associated MTs (i.e., 20–45) of which they are comprised. Quantitative information concerning the lengths of MTs within these fibers was obtained by tracking individual MTs between serial transverse sections. Approximately 1/2 of the kinetochore MTs in each fiber were found to run uninterrupted into the polar region of the spindle. It can be inferred from this and other data that a substantial number of MTs run uninterrupted between the kinetochore and the polar region in untreated metaphase PtK1 cells.
231 citations
TL;DR: In animal chromatin, a fraction of the histone 2A's and 2B's is covalently attached to the protein ubiquitin through an isopeptide linkage, and all ubiquitinated histones, including the four H2A variants and the H2B's are absent from isolated metaphase chromosomes.
186 citations
TL;DR: It has been shown that this method, which involves detergent lysis of metaphase cells and polyamines to stabilize the DNA, yields lower coefficients of variation and background levels in the DNA histograms than is currently obtained by hexylene glycol based methods.
Abstract: A new method for the preparation of metaphase chromosomes for flow analysis has been evaluated. It has been shown that this method, which involves detergent lysis of metaphase cells and polyamines to stabilize the DNA, yields lower coefficients of variation and background levels in the DNA histograms than is currently obtained by hexylene glycol based methods. A conventional flow cytometer (FACS-II) has been used to resolve the human karyotype into about 14 peaks after ethidium bromide staining and excitation with a relatively low level of illumination (0.4 W at 488 nm). Flow karyotypes have also been obtained from suspension cell lines, in particular from the mouse cell line, Friend 707/B10. The only disadvantage of this method is that the chromosomes are highly condensed and therefore banding studies on sorted chromosomes may not be possible.
170 citations
TL;DR: It is inferred that extranuclear forces, presumably involving astral microtubules, pull on the incipient daughter nuclei and that the central spindle limits the separation rate.
Abstract: The anaphase-telophase spindle usually elongates, and it has been assumed that the spindle pushes the incipient daughter nuclei apart. To test this assumption, we used a laser microbeam to sever the central spindle of the fungus, Fusarium solani, and measured the rate of separation of incipient daughter nuclei. When the microbeam was aimed beside the spindle separation occurred at a rate (8.6 micrometer/min) that did not differ significantly from the rate (7.6 micrometer/m) in unirradiated cells. But when the spindle was irradiated, it broke, and the separation was much faster (22.4 micrometer/min). Irradiation of cytoplasm lateral to one spindle pole resulted in a 1.5 micrometer/min reduction in the rate (6.1 micrometer/min) of separation. From these and other data, we infer that extranuclear forces, presumably involving astral microtubules, pull on the incipient daughter nuclei and that the central spindle limits the separation rate. Astral microtubules are associated with the plasma membrane or, sometimes, with the rough endoplasmic reticulum. Most of the spindle microtubules that are present at metaphase are depolymerized during anaphase and early telophase.
159 citations
TL;DR: Human erythrocyte ankyrin immunoreactivity was localized by indirect immunofluorescence in a colchicine- and detergent-sensitive cytoplasmic meshwork in interphase cells and this binding was displaced by brain MAPs.
Abstract: Human erythrocyte ankyrin, the membrane attachment protein for spectrin, has been detected by radioimmunoassay in a variety of cells and tissues. This report identifies polypeptides crossreacting with ankyrin in brain and HeLa cells and demonstrates that one function of these ankyrin analogues involves association with microtubules. Ankyrin immunoreactivity was localized by indirect immunofluorescence in a colchicine- and detergent-sensitive cytoplasmic meshwork in interphase cells. There also was specific nuclear staining, localized in a bright spots, which was displaced entirely by ankyrin or by high molecular weight microtubule-associated proteins (MAPs) from brain. In dividing cells, the punctate nuclear staining and the meshwork disappeared. Fluorescence was localized at the spindle pole during metaphase and was redistributed to the cleavage furrow in later stages of mitosis. An immunoreactive Mr 370,000 polypeptide comigrating with MAP1 was identified in brain extracts and copolymerized with microtubules through repeated cycles of polymerization and depolymerization. Finally, erythrocyte ankyrin associated with microtubules prepared from pure tubulin, and this binding was displaced by brain MAPs.
132 citations
TL;DR: A single kinetochore moves twice the normal mass of chromatin (two chromatids) at the same velocity with which it moves a single chromatid, showing that the velocity withWhich a kinetchore moves is independent, within limits, of the mass associated with it.
Abstract: The role of the kinetochore in chromosome movement was studied by 532-nm wavelength laser microirradiation of mitotic PtK2 cells. When the kinetochore of a single chromatid is irradiated at mitotic prometaphase or metaphase, the whole chromosome moves towards the pole to which the unirradiated kinetochore is oriented, while the remaining chromosomes congregate on the metaphase plate. The chromatids of the irradiated chromosome remain attached to one another until anaphase, at which time they separate by a distance of 1 or 2 micrometers and remain parallel to each other, not undergoing any poleward separation. Electron microscopy shows that irradiated chromatids exhibit either no recognizable kinetochore structure or a typical inactive kinetochore in which the tri-layer structure is present but has no microtubules associated with it. Graphical analysis of the movement of the irradiated chromosome shows that the chromosome moves to the pole rapidly with a velocity of approximately 3 micrometers/min. If the chromosome is close to one pole at irradiation, and the kinetochore oriented towards that pole is irradiated, the chromosome moves across the spindle to the opposite pole. The chromosome is slowed down as it traverses the equatorial region, but the velocity in both half-spindles is approximately the same as the anaphase velocity of a single chromatid. Thus a single kinetochore moves twice the normal mass of chromatin (two chromatids) at the same velocity with which it moves a single chromatid, showing that the velocity with which a kinetochore moves is independent, within limits, of the mass associated with it.
127 citations
TL;DR: Significant and reproducible differences between normal individuals have been detected and have been correlated with differences in the centric heterochromatin of certain chromosomes as revealed in their C-banded karyotypes.
Abstract: A method for high-resolution analysis of the human karyotype by flow cytometry has been developed. Metaphase chromosomes are prepared from short-term peripheral blood cultures, stained with ethidium bromide, and analyzed on a standard fluorescence-activated cell sorter (FACS-II). Flow karyotypes with up to 20 peaks can be obtained with coefficients of variation in the range 1-2%. At this level of resolution the contribution of many of the human chromosomes can be evaluated separately. Significant and reproducible differences between normal individuals have been detected and have been correlated with differences in the centric heterochromatin of certain chromosomes as revealed in their C-banded karyotypes.
108 citations
TL;DR: The meiotic pollen mother cells of Tradescantia (spiderwort) are highly synchronized in their prophase I and tetrad stages and Chromosomes of this stage are sensitive to physical or chemical mut...
Abstract: The meiotic pollen mother cells (PMC) of Tradescantia (spiderwort) are highly synchronized in their prophase I and tetrad stages. Chromosomes of this stage are sensitive to physical or chemical mutagens. Thus high frequency of acentric fragments or sticky chromosomes can be induced with very low level of mutagens. These induced chromosome aberrations become micronuclei (MCN) in the synchronized tetrads and they can be easily identified and scored. Based upon these features, the Tradescantia micronucleus bioassay was established. This bioassay involves the exposure of PMC in the young inflorescences of the plant cuttings to gaseous agents through diffusion, to liquid agent through absorption and dialysis from the stem to flower buds, or to radiation. The exposed samples are fixed in aceto-alcohol (1:3) and prepared into microslides by using the aceto-carmine squash method. Frequencies of MCN in a large population of synchronized tetrads are the indications of genetic damage caused by the agents. Mature pollen grains of Tradescantia are free cells which can be cultured in lactose-agar medium. The generative cells in the cultured pollen tubes can carry out mitosis similar to the in vivo condition. The G2 interphase chromosomes of pollen mitosis are highly sensitive to gaseous or liquid chemicals and radiation. Treatments can be applied to these mitotic generative cells of the mature pollen or the mitotic generative nuclei of the developing pollen tube. The mitotic chromosomes of the generative cells are allowed to proceed through mitosis in the culture medium and slides are prepared for metaphase figures. Frequencies of various types of chromatid aberrations can be scored and used as the indices of genetic damage.
TL;DR: During progesterone-induced meiotic maturation of Xenopus oocytes in vitro, 7 morphological stages were defined and a lamellar microtubule organizing center (MTOC) was present.
Abstract: During progesterone-induced meiotic maturation of Xenopus oocytes in vitro, 7 morphological stages were defined. Using cytological analysis, nuclear breakdown was divided into three stages. Stage 1 corresponded to basal germinal vesicle breakdown. Stage 2 was characterized by the advent and development of a fibrillar network formed by microtubules at the basal part of the nucleus. Below, a lamellar microtubule organizing center (MTOC) was present. Numerous vesicles of smooth endoplasmic reticulum were proximal to both of these structures. During its formation and modification (stages 2 and 3), the fibrillar network migrated towards the animal pole. A prometaphase 1 stage was observed before the formation of the metaphase 1 spindle.
Journal Article•
TL;DR: In both unpretreated root tip metaphases and pretreated mitoses of Hordeum vulgare L. cv.
Abstract: In both unpretreated root tip metaphases and pretreated mitoses of Hordeum vulgare L. cv. Sultan x Secale africanum Stapf F1 hybrids, Hordeum chromosomes tended to be nearer the centre of the mitosis than Secale chromosomes. This was clear in 4 serially sectioned cells examined in the electron microscope. In Feulgen squashes of 38 of 40 cells studied in the light microscope, the mean distances in each cell from the mean centromere position for the cell was less for Hordeum centromeres than for Scale centromeres. Such spatial separation of parent genomes might prevent pairing of homoeologues in hybrids.
TL;DR: Proteins resistant to sarcosyl-Cs2SO4 treatment are associated exclusively with skeleton-attached DNA both in interphase nuclei and metaphase chromosomes and a group of tightly bound low molecular weight polypeptides seem to be randomly distributed throughout the whole DNA loop.
TL;DR: The results indicate that differentiation of Z and W chromosomes in the gonochoristic trematodes resulted from: partial constitutive heterochromatinization of the W chromosome and translocation of part of one sex chromosome onto another (Schistosomatium douthitti and Heterobilharzia americana, American schistosomes).
Abstract: The morphology of C-banded metaphase chromosomes has been studied in two hermaphroditic and ten gonochoristic digenetic trematodes (schistosomes). Comparison of numbers and morphology of chromosomes indicates that the karyotype of primitive trematodes probably was composed of 10 (or 11) pairs of telocentric or subtelocentrie chromosomes, and reduction of chromosome numbers in advanced species resulted from centromeric fusion rather than elimination of chromosomes. Observation of heteromorphic chromosomes in a hermaphroditic trematode (Spirorchis) suggested a differentiation of “pre-sex” chromosomes in species ancestral to dioecious trematodes which possess distinctly differentiated sex chromosomes. Our results indicate that differentiation of Z and W chromosomes in the gonochoristic trematodes resulted from: (a) partial constitutive heterochromatinization of the W chromosome (Schistosoma mansoni and S. haematobium complexes, African schistosomes), (b) deletion of part of the W (S. japonicum and S. mekongi, Asian schistosomes), and (c) translocation of part of one sex chromosome onto another (Schistosomatium douthitti and Heterobilharzia americana, American schistosomes) with subsequent heterochromatinization of the W in H. americana.
TL;DR: The described isolation and purification method yielded relatively pure chromosome suspension and the uptake of the isolated plant chromosomes into recipient wheat, parsley, and maize protoplasts was induced by polyethylene-glycol treatment.
Abstract: For mass isolation of plant metaphase chromosomes, cultured cells of wheat (Triticum monococcum) and parsley (Petroselinum hortense) were synchronized by hydroxyurea and colchicine treatment. This synchronization procedure resulted in high mitotic synchrony, especially in suspension cultures of parsley in which 80% of the cells were found to be at the metaphase stage. Mitotic protoplasts isolated from these synchronized cell cultures served as a source for isolation of chromosomes. The described isolation and purification method yielded relatively pure chromosome suspension. The uptake of the isolated plant chromosomes into recipient wheat, parsley, and maize protoplasts was induced by polyethylene-glycol treatment. Cytological studies provided evidences for uptake of plant chromosomes into plant protoplasts.
TL;DR: The XY bivalent is characterized by the presence of unique material located between the two half-bivalents at the site of synapsis, which may represent a morphological manifestation of the hypothetical cohesive elements (collochores) which are thought to function in conjunction of the X and Y chromosomes.
Abstract: Individual bivalents or chromosomes have been identified in Drosophila melanogaster spermatocytes at metaphase I, anaphase I, metaphase II and anaphase II in electron micrographs of serial sections. Identification was based on a combination of chromosome volume analysis, bivalent topology, and kinetochore position. — Kinetochore microtubule numbers have been obtained for the identified chromosomes at all four meiotic stages. Average numbers in D. melanogaster are relatively low compared to reported numbers of other higher eukaryotes. There are no differences in kinetochore microtubule numbers within a stage despite a large (approximately tenfold) difference in chromosome volume between the largest and the smallest chromosome. A comparison between the two meiotic metaphases (metaphase I and metaphase II) reveals that metaphase I kinetochores possess twice as many microtubules as metaphase II kinetochores. — Other microtubules in addition to those that end on or penetrate the kinetochore are found in the vicinity of the kinetochore. These microtubules penetrate the chromosome rather than the kinetochore proper and are more numerous at metaphase I than at the other division stages.
TL;DR: Evidence is presented to suggest that the formation of the desmotubule of a plasmodesma is by the squeezing of a strand of endoplasmic reticulum between the vesicles of the cell plate.
Abstract: The structure and distribution of cytoplasmic membranes during mitosis and cytokinesis in maize root tip meristematic cells was investigated by low and high voltage electron microscopy. The electron opacity of the nuclear envelope and endoplasmic reticulum (ER) was enhanced by staining the tissue in a mixture of zinc iodide and osmium tetroxide. Thin sections show the nuclear envelope to disassemble at prophase and become indistinguishable from the surrounding ER and polar aggregations of ER. In thick sections under the high voltage electron microscope the spindle is seen to be surrounded by a mass of tubular (TER) and cisternal (CER) endoplasmic reticulum derived from both the nuclear envelope and ER, which persists through metaphase and anaphase. At anaphase strands of TER traverse the spindle between the arms of the chromosomes. The octagonal nuclear pore complexes disappear by metaphase, but irregular-shaped pores persist in the membranes during mitosis. It is suggested that these form a template for pore-complex reformation during telophase. Phragmoplast formation is preceded by an aggregation of TER across the spindle at anaphase. Evidence is presented to suggest that the formation of the desmotubule of a plasmodesma is by the squeezing of a strand of endoplasmic reticulum between the vesicles of the cell plate.
TL;DR: Mitotic chromosomes from human peripheral lymphocytes studied at the junction of metaphase and anaphase show that the centromeres of various chromosomes separate in a nonrandom, apparently genetically controlled sequence.
Abstract: Mitotic chromosomes from human peripheral lymphocytes studied at the junction of metaphase and anaphase show that the centromeres of various chromosomes separate in a nonrandom, apparently genetically controlled sequence. It does not depend upon the position of the centromere in the chromosome, the length of the chromosome or total amount of detectable C-chromatin. In man, several chromosomes e.g. 18, 17, 2, separate very early. Such “early” cells do not include nos. 1, 13, 14, 15, and Y and very rarely nos. 21 and 22. The last separating chromosomes are those from group D, G, no. 1, 16, and Y. The possible implication of these findings in evolution, non-disjunction and the control of centromere separation sequences is discussed.
TL;DR: The results indicate that the pole-to-chromosome region of the metaphase spindle contains G actin but little if any conventional F actin, which supports the hypothesis that F act in is involved in force generation for cell cleavage and is not inconsistent with the possibility that actin outside the spindle may be involved in chromosomal movement.
Abstract: The distribution and polymerization state of actin in metaphase rat kangaroo cells was studied by fluorescence microscopy. Formaldehyde-fixed, acetone-extracted cells were labeled with either of two types of actin probes. The first, 7-nitrobenz-2-oxa-1,3-diazole-phallacidin, has high affinity for F actin and does not bind monomeric G actin. The second was a conjugate of DNase I labeled with either tetramethylrhodamine or fluorescein. DNase binds with high affinity to G actin and with lesser affinity to F actin. The polymerization state of actin was deduced by comparing the fluorescence distribution of the phallacidin derivative with that of the fluorescent DNase. The results indicate that the pole-to-chromosome region of the metaphase spindle contains G actin but little if any conventional F actin. F actin is found concentrated in a diffuse distribution outside the spindle region in metaphase cells and returns to the interzone area between the chromosomes by early telophase. These results exclude spindle models for chromosomal movement that require more than about five F actin filaments per chromosome, support the hypothesis that F actin is involved in force generation for cell cleavage, and are not inconsistent with the possibility that actin outside the spindle may be involved in chromosomal movement.
TL;DR: It is concluded that extensive DNA rearrangement has taken place during amplification in methotrexate-resistant mouse lymphoma EL4 cells and mouse melanoma PG19 cells.
TL;DR: It is indicated that CB and H 2 CB lead to formation of binucleated cells by causing aberrant cleavage furrowing and inhibition of contractile ring microfilaments.
TL;DR: It is concluded that the ER participates in controlling the Mt system, perhaps via calcium ions (membrane-bound calcium ions have been visualized by staining with chlorotetracycline) but that, on the other hand, the Mount system also influences the distribution of the ER.
Abstract: The interphase nucleus in theFunaria caulonema tip cells is associated with many non-cortical microtubules (Mts). In prophase, the cortical Mts disappear in the nuclear region; in contrast to moss leaflets, a preprophase band of Mts is not formed in the caulonema. The Mts of the early spindle are associated with the fragments of the nuclear envelope. Remnants of the nucleolus remain in the form of granular bodies till interphase. The metaphase chromosomes have distinct kinetochores; the kinetochore Mts are intermingled with non-kinetochore Mts running closely along the chromatin. Each kinetochore is associated with an ER cisterna. ER cisternae also accompany the spindle fibers in metaphase and anaphase. In telophase, Golgi vesicles accumulate in the periphery of the developing cell plate where no Mts are found. The reorientation of the cell plate into an oblique position can be inhibited by colchicine. It is concluded that the ER participates in controlling the Mt system, perhaps via calcium ions (membrane-bound calcium ions have been visualized by staining with chlorotetracycline) but that, on the other hand, the Mt system also influences the distribution of the ER. The occurrence and function of the preprophase band of Mts is discussed.
TL;DR: Two procedures for the isolation from short-term lymphocyte cultures of metaphase chromosomes that are morphologically intact, suitable for flow cytometric analysis and purification, and have DNA of high molecular weight are described.
Abstract: Flow cytometry is uniquely suited for distinguishing between isolated mammalian chromosomes differing in DNA content1,2 or DNA-base composition3,4. Using this technique, the 24 types of human chromosomes can be resolved into 15 groups when stained with Hoechst 33258 (refs 3, 5). When Hoechst 33258 (HO) and chromomycin A3 (CA3) are used, 20 groups of human chromosomes can be distinguished by dual-beam flow cytometry3,6, and the relative frequency of chromosomes in each group estimated. Flow measurements provide a precise description of the average chromosome complement of the cell population (a flow karyotype7) that is sensitive to chromosomal rearrangements2,8 and frequency changes; and also enable individual chromosomes to be purified, for example, for gene mapping9. Until now, chromosomes have been isolated for flow cytometry only from established fibroblast cultures. However, the maintenance of such cultures is time-consuming and expensive, and there is the risk that chromosomal rearrangements may occur during extended fibroblast culture. Here we describe two procedures for the isolation from short-term lymphocyte cultures of metaphase chromosomes that are morphologically intact, suitable for flow cytometric analysis and purification, and have DNA of high molecular weight.
TL;DR: Using this PCC-SCD system on synchronous and asynchronous Chinese hamster ovary cells, it is demonstrated that the replication patterns of the CHO cells can be categorized into G1/S, early, early-mid, mid-late, and late S phase patterns according to the amount of replicated chromosomes.
Abstract: Sister chromatids of metaphase chromosomes can be differentially stained if the cells have replicated their DNA semiconservatively for two cell cycles in a medium containing 5-bromodeoxyuridine (BrdU). When prematurely condensed chromosomes (PCC) are induced in cells during the second S phase after BrdU is added to the medium, the replicated chromosome segments show sister chromatid differential (SCD) staining. Employing this PCC-SCD system on synchronous and asynchronous Chinese hamster ovary (CHO) cells, we have demonstrated that the replication patterns of the CHO cells can be categorized into G1/S, early, early-mid, mid-late, and late S phase patterns according to the amount of replicated chromosomes. During the first 4 h of the S phase, the replication patterns show SCD staining in chains of small chromosome segments. The amount of replicated chromosomes increase during the mid-late and late S categories (last 4 h). Significantly, small SCD segments are also present during these late intervals of the S phase. Measurements of these replicated segments indicate the presence of characteristic chromosome fragment sizes between 0.2 to 1.2 μm in all S phase cells except those at G1/S which contain no SCD fragments. These small segments are operationally defined as chromosome replicating units or chromosomal replicons. They are interpreted to be composed of clusters of molecular DNA replicons. The larger SCD segments in the late S cells may arise by the joining of adjacent chromosomal replicons. Further application of this PCC-SCD method to study the chromosome replication process of two other rodents, Peromyscus eremicus and Microtus agrestis, with peculiar chromosomal locations of heterochromatin has demonstrated an ordered sequence of chromosome replication. The euchromatin and heterochromatin of the two species undergo two separate sequences of decondensation, replication, and condensation during the early-mid and mid-late intervals respectively of the S phase. Similar-sized chromosomal replicons are present in both types of chromatin. These data suggest that mammalian chromosomes are replicated in groups of replicating units, or chromosomal replicons, along their lengths. The organization and structure of these chromosomal replicons with respect to those of the interphase nucleus and metaphase chromosomes are discussed.
TL;DR: Measurements of centromere distances between all possible pairs of chromosomes as well as on the relative position of chromosomes in circular spreads revealed no evidence for homologous somatic association during interphase and metaphase or any other suprachromosomal ordering principle.
Abstract: Premature chromosome condensation (PCC) was induced in order to study the arrangement of muntjac chromosomes in the interphase nuclei of proliferating and resting cells with respect to their polarity and the spatial relationship between them. The data were compared with the situation in in situ fixed and colcemid blocked metaphases. It appears that in rapidly dividing cells almost all G1- and G2 interphase chromosomes exhibit the Rabl type polarized orientation. This pattern still predominates in G0 lymphocytes which may have been arrested at this stage for some months or even years. — The location of the small chromosome Y2 was found to be “central” in normal metaphases but “peripheral” in colcemid blocked mitoses. The behavior in the premature condensed chromosome preparations was intermediate. Measurements of centromere distances between all possible pairs of chromosomes as well as on the relative position of chromosomes in circular spreads revealed no evidence for homologous somatic association during interphase and metaphase or any other suprachromosomal ordering principle. Interphase chromosome orientation seems to be solely the result of chromosome arrangement of the foregoing anaphase. Association between heterochromatic regions or the nucleolus organizers did not substantially influence this pattern. There is no support for speculations that in mammalian cells close proximity of homologoues sites is instrumental in functional cooperation.
TL;DR: Chromatin organization during male meiosis in Bombyx mori has been investigated utilizing the Miller spreading procedure, suggesting that the loop conformation of prophase is maintained throughout meiosis.
Abstract: Chromatin organization during male meiosis in Bombyx mori has been investigated utilizing the Miller spreading procedure. During meiotic prophase, the linear 200–300 A chromatin fibers evident at interphase are folded into tandem arrays of approximately 7,000 loops per haploid genome. Adjacent loops visualized during early prophase are separated by 0.15–0.2 nm of nucleosomal DNA. Meiotic metaphase chromosomes display numerous loops which project radially from the central region of the chromosome suggesting that the loop conformation of prophase is maintained throughout meiosis. Spread preparations of spermatogenic stages through pachytene allow the visualization of actively transcribed ribosomal DNA. Throughout this period, these transcription units appear to be organized into loops in such a way that one active transcription unit exists on a single loop. Furthermore, there are various levels of transcription on different ribosomal loops, although the number of loops displaying active transcription remains constant throughout this period.
TL;DR: The results show that the distribution of MTs and the total amount of polymerized tubulin (MTs) in the spindle change during mitosis, suggesting the assembly and disassembly ofMTs as well as the dislocation of MTS during mitotes.
Abstract: Birefringence of the mitotic apparatus (MA) and its change during mitosis in sea urchin eggs were quantitatively determined using the birefringence detection apparatus reported in the preceding paper (Hiramoto el al., 1981, J. Cell Biol. 89:115-120). The birefringence and the form of the MA are represented by five parameters: peak retardation (delta p), through retardation (delta t), interpolar distance (D1), the distance (D2) between chromosome groups moving toward poles, and the distance (D3) between two retardation peaks. Distributions of birefringence retardation and the coefficient of birefringence in the spindle were quantitatively determined in MAs isolated during metaphase and anaphase. The distribution of microtubules (MTs) contained in the spindle is attributable to the form birefringence caused by regularly arranged MTs. The distribution coincided fairly well with the distribution of MTs in isolated MAs determined by electron microscopy. Under the same assumption, the distribution of MTS in the spindle in living cells during mitosis was determined. The results show that the distribution of MTs and the total amount of polymerized tubulin (MTs) in the spindle change during mitosis, suggesting the assembly and disassembly of MTs as well as the dislocation of MTs during mitosis.
TL;DR: Nonrandom segregation in Neocurtilla hexadactyla involves a unique modification at the kinetochores of particular chromosomes, which presumably affects the manner in which these chromosomes are integrated within the spindle.
Abstract: During meiosis I in males of the mole cricket Neocurtilla (Gryllotalpa) hexadactyla, the univalent X1 chromosome and the heteromorphic X2Y chromosome pair segregate nonrandomly; the X1 and X2 chromosomes move to the same pole in anaphase. By means of ultrastructural analysis of serial sections of cells in several stages of meiosis I, metaphase of meiosis II, and mitosis, we found that the kinetochore region of two of the three nonrandomly segregating chromosomes differ from autosomal kinetochores only during meiosis I. The distinction is most pronounced at metaphase I when massive aggregates of electron-dense substance mark the kinetochores of X1 and Y chromosomes. The lateral position of the kinetochores of X1 and Y chromosomes and the association of these chromosomes with microtubules running toward both poles are also characteristic of meiosis I and further distinguish X1 and Y from the autosomes. Nonrandomly segregating chromosomes are typically positioned within the spindle so that the kinetochoric sides of the X2Y pair and the X1 chromosome are both turned toward the same interpolar spindle axis. This spatial relationship may be a result of a linkage of X1 and Y chromosomes lying in opposite half spindles via a small bundle of microtubules that runs between their unusual kinetochores. Thus, nonrandom segregation in Neocurtilla hexadactyla involves a unique modification at the kinetochores of particular chromosomes, which presumably affects the manner in which these chromosomes are integrated within the spindle.
TL;DR: Continuous exposure of Chinese hamster ovary cells and human colon cancer cells to colcemid to block cycling cells in metaphase, suppressing re‐entry into G1 allowed rapid quantitation of cycle traverse rates.
Abstract: To provide a rapid method for examining cell cycle dynamics, we utilized continuous exposure of Chinese hamster ovary cells and human colon cancer cells to colcemid to block cycling cells in metaphase, suppressing re-entry into G1. Changes in cell cycle compartment distribution were monitored by DNA flow cytometry. Analysis of the rate of G2 + M compartment accumulation after addition of colcemid permitted calculation of all cycle transit parameters. These compared favorably with data in the same cell lines determined by the fraction of labeled mitoses technique. Serial assessment of DNA flow cytometry after addition of colcemid permits rapid quantitation of cycle traverse rates.