Showing papers on "Metaphase published in 1967"

Cell motility by labile association of molecules. The nature of mitotic spindle fibers and their role in chromosome movement.

Abstract: This article summarizes our current views on the dynamic structure of the mitotic spindle and its relation to mitotic chromosome movements. The following statements are based on measurements of birefringence of spindle fibers in living cells, normally developing or experimentally modified by various physical and chemical agents, including high and low temperatures, antimitotic drugs, heavy water, and ultraviolet microbeam irradiation. Data were also obtained concomitantly with electron microscopy employing a new fixative and through measurements of isolated spindle protein. Spindle fibers in living cells are labile dynamic structures whose constituent filaments (microtubules) undergo cyclic breakdown and reformation. The dynamic state is maintained by an equilibrium between a pool of protein molecules and their linearly aggregated polymers, which constitute the microtubules or filaments. In living cells under physiological conditions, the association of the molecules into polymers is very weak (absolute value of Δ F 25°C S 25°C ≃ 100 eu) or by the addition of heavy water. The spindle proteins tend to polymerize with orienting centers as their geometrical foci. The centrioles, kinetochores, and cell plate act as orienting centers successively during mitosis. Filaments are more concentrated adjacent to an orienting center and yield higher birefringence. Astral rays, continuous fibers, chromosomal fibers, and phragmoplast fibers are thus formed by successive reorganization of the same protein molecules. During late prophase and metaphase, polymerization takes place predominantly at the kinetochores; in metaphase and anaphase, depolymerization is prevalent near the spindle poles. When the concentration of spindle protein is high, fusiform bundles of polymer are precipitated out even in the absence of obvious orienting centers. The shift of equilibrium from free protein molecules to polymer increases the length and number of the spindle microtubules or filaments. Slow depolymerization of the polymers, which can be brought about by low concentrations of colchicine or by gradual cooling, allows the filaments to shorten and perform work. The dynamic equilibrium controlled by orienting centers and other factors provides a plasusible mechanism by which chromosomes and other organelles, as well as the cell surface, are deformed or moved by temporarily organized arrays of microtubules or filaments.

Meiosis in Coprinus lagopus: a comparative study with light and electron microscopy.

Abstract: Meiosis within fruiting bodies of Coprinus lagopus Fr. is closely synchronized. This conveniently facilitates joint light- and electron-microscope observations. Before nuclear fusion the chromatin appears diffuse in the light microscope; after nuclear fusion individual chromosomes can be recognized. In the electron micrographs the chromatin of pre-fusion and early fusion nuclei cannot be recognized as defined structures with the fixation and staining procedures employed. At the time of synapsis the lateral components of the synaptinemal complexes can be seen in the micrographs. The pairing process of the two chromosomes of the homologous pairs is believed to involve two steps: (1) two homologous chromosomes become aligned in parallel, and (2) pairing occurs by formation of the synaptinemal complex including the central synaptic component. The term synaptic centre is coined for the central component, which is believed to be the zone where crossing-over occurs. The formation of this structure in relation to homologous pairing, and the structural organization of the synaptinemal complexes are discussed. At meiotic metaphase, the chromosomes congregate around the central spindle microtubules. They are contracted and contain densely packed chromatin fibrils. Two types of spindle microtubules are demonstrated: (1) the chromosomal microtubules directly connecting the chromosomes to the centrosomes, and (2) the central spindle microtubules connecting the two centrosomes. The centrosomes are round, fibril-containing bodies approximately 0.3 µ in diameter. They have been observed outside the nuclear envelope at pachytene, but do not show the characteristic structure normally found in animal cells.

The structure and behavior of the nucleolus organizer in mammalian cells.

Abstract: The regularly occurring secondary constrictions on metaphase chromosomes of mammalian cells prove to be nucleolus organizers as expected The expression of nucleolus organizers as secondary constrictions, however, varies from cell to cell and from tissue to tissue, including cultivation in vitro Electron micrographs of the organizer region show that the nucleolus organizer at metaphase is not a constriction The width of the organizer area is the same as the condensed chromosomal arms; but the filaments, which are the major components of this region, show a diameter of 50–70 A The condensed chromosome arms consist of filaments 150–200 A in diameter In some mammalian species, structures similar to the nucleolus organizer are located at the end of chromosomes These may be terminal nucleolus organizers

Chromosome-exchange Aberrations in Human Lymphocytes

Abstract: SummaryThe probability of finding a given chromosome in a dicentric is directly proportional to the length of that chromosome at interphase, but not to the length of the early replicating portion of the interphase chromosome or to its length at metaphase. The number of dicentric chromosomes and centric rings per cell is limited primarily by the number of centromeres. These results are consistent with the assumption that every chromosome break is a site for chromosome-exchange.

Fine structure of division in ciliate protozoa. I. Micronuclear mitosis in Blepharisma.

Abstract: The mitotic, micronuclear division of the heterotrichous genus Blepharisma has been studied by electron microscopy. Dividing ciliates were selected from clone-derived mass cultures and fixed for electron microscopy by exposure to the vapor of 2% osmium tetroxide; individual Blepharisma were encapsulated and sectioned. Distinctive features of the mitosis are the presence of an intact nuclear envelope during the entire process and the absence of centrioles at the polar ends of the micronuclear figures. Spindle microtubules (SMT) first appear in advance of chromosome alignment, become more numerous and precisely aligned by metaphase, lengthen greatly in anaphase, and persist through telophase. Distinct chromosomal and continuous SMT are present. At telophase, daughter nuclei are separated by a spindle elongation of more than 40 µ, and a new nuclear envelope is formed in close apposition to the chromatin mass of each daughter nucleus and excludes the great amount of spindle material formed during division. The original nuclear envelope which has remained structurally intact then becomes discontinuous and releases the newly formed nucleus into the cytoplasm. The micronuclear envelope seems to lack the conspicuous pores that are typical of nuclear envelopes. The morphology, size, formation, and function of SMT and the nature of micronuclear division are discussed.

Structure of and homology between pachytene and somatic metaphase chromosomes of the tomato

Abstract: The pachytene and somatic metaphase chromosomes of tomato are structurally differentiated into proximal chromatic and distal achromatic parts. The pachytene chromosomes have very clear and characteristic chromosome markers, with the help of which all 12 bivalents can be clearly identified. Based on the size, the arm ratio, the ratio of chromatic parts and the presence and size of achromatic parts, all 12 pairs of somatic chromosomes can also be identified, and each pair be homologised with the corresponding pachytene bivalent. A comparison of the lengths of chromatic and achromatic parts of pachytene chromosomes with the chromatic and achromatic parts of the corresponding somatic chromosomes indicate, that, on an average, the chromatic parts are contracted by a factor of 4 to 5, whereas the achromatic parts are contracted by a factor of 30. The heteropycnosis near the centromere in tomato chromosomes therefore is not a special characteristic of meiotic chromosomes, but present in somatic metaphase chromosomes also.

The time of synthesis and the conservation of mitosis-related proteins in cultured human amnion cells

Abstract: p-Fluorophenylalanine (PFPA), an analogue of phenylalanine which may be incorporated into proteins, increases the duration of mitosis. In the present experiments, based upon quantitative analyses of time-lapse cinemicrographic films, brief treatments of cells with PFPA are shown to affect the duration of metaphase in only those cells which enter division during or shortly after treatment. The offspring of cells with prolonged metaphases also tend to have prolonged metaphases. Analyses of the kinetics of the appearance of prolonged metaphases indicate that some protein specifically associated with mitosis is synthesized primarily during a period which corresponds closely to G2. The manner in which the defect is passed on to daughter cells indicates that the protein involved is conserved and reutilized by daughter cells for their subsequent divisions. Comparable experiments performed with low concentrations of puromycin indicate that the major effect of PFPA is due to its incorporation into protein rather than its ability to inhibit protein synthesis. The fact that puromycin-induced effects can also be passed on to daughter cells is interpreted to mean that cells make only specific amounts of some mitosis-associated proteins and that if a cell "inherits" a deficiency in such protein it is not able to compensate for the deficiency.

Mitotic Delay and Chromosomal Aberrations Induced by X Rays in Synchronized Chinese Hamster Cells In Vitro

Abstract: Synchronized Chinese hamster cell populations in vitro were X-irradiated at different stages of the cell cycle and examined at the next metaphase. Mitotic delay varied according to the stage of the cell cycle at the time of irradiation. It was greatest for cells irradiated in middle to late S, moderate for cells irradiated in G2, and least for cells irradiated in G1. It increased approximately linearly with dose (0.7 hr./100 rad for S cells and 0.3 hr./100 rad for G1 cells). Chromosomal aberration rates also depended on the stage of the cell cycle at which the cells were irradiated. Chromatid aberrations were induced mostly during G2 and S (more in early S than late S), while chromosome aberrations were induced mainly in G1. Total breaks after 500 or 750 R showed a minimum frequency in late S and a maximum frequency in G2. This form of response correlates, but only in a general qualitative way, with the dependence of survival on cell cycle stage previously reported. Mitotic delay has a dependence on cell cycle stage quite different from either chromosomal aberrations or survival.

A new marker for chromosome studies in the mouse.

Abstract: THE mouse is one of the best mammals for genetic and cytogenetic investigations. Unfortunately, its value for cytogenetic research is restricted because all forty chromosomes are acrocentric. Their sizes range in the ratio of 5 : 2 (longest to shortest) with relatively little difference other than length to help in identification. At the first metaphase stage of meiosis, twenty bivalents are normally formed and this pairing is commonly used to correlate abnormal configurations with specific chromosome changes. It is obvious, however, that cellular markers (cells with a visible different karyotype from the normal) would be useful for transplantation experiments and work on carcinogenesis or radiation chimeras. Some translocations induced in mice by X-irradiation have been used as such cellular markers1,2.

Changes in surface charge of HeLa cells during the cell cycle.

Abstract: A METHOD of obtaining large numbers of fixed cells in metaphase arrested by colchicine, from a population of cells growing on a glass surface, by a method dependent on the attenuated adhesion of the cells to the surface has been described1. A modification of this method was suggested to obtain a viable population of synchronous cells. This was demonstrated2 and a method for obtaining large numbers of HeLa cells of which 80 per cent to 95 per cent showed mitotic figures has been described3. The decrease in attachment of the mitotic cells was ascribed to a decrease in the area over which the adhesion occurred1. It is, however, possible that there is a change in the intrinsic strength of the cell-glass adhesions arising from an alteration in the physical properties of the surface of the cells which round up during mitosis. One of the most easily determined of these properties is the ξ-potential arising from the cell surface charge, and accordingly we have made determinations of the electrophoretic mobility of parasynchronous populations of HeLa cells at various stages in the cell cycle.

Age and the cell cycle of the mouse colonic epithelium

Abstract: The colonic progenitor population has been investigated in four age groups of male Swiss albino mice utilizing tritium thymidine and autoradiography. The duration of the progenitor cell cycle and its component phases as well as the DNA synthetic index were determined for each age group following sequential sacrifice of the experimental animals. Analysis of the kinetics of metaphase labeling revealed that the mean duration of the cell cycle lengthens with age, whereas S (about 7.8 hours), G2 and M remain relatively constant. Estimates of the cell cycle from the ratio of the S-phase duration to the DNA synthetic index also demonstrate an increase with age, although the values derived from this method do not agree with those based on metaphase labeling. Determination of the DNA synthetic index disclosed a decrease in the percentage of labeled cells with increasing age. Thus, the prolongation of the mean duration of the cell cycle apparently results from an increase in the G1-phase.

An analysis of heterochromatin in maize root tips

Abstract: The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with B chromosomes; (b) the proportion of DNA to histone is identical with that of nuclei containing only normal chromosomes; (c) the amount of nonhistone protein in proportion to DNA in interphase is less in nuclei with B chromosomes than in normal nuclei. In condensed B chromosomes the ratio of nonhistone protein to DNA is similar to that in other condensed chromatin, such as metaphase chromosomes and degenerating nuclei. The B chromosomes appear to have no effect on nucleolar RNA and protein. Replication of B chromosomes is precisely controlled and is comparable to that of the ordinary chromosomes not only in synthesis for mitosis but also in formation of polyploid nuclei of root cap and protoxylem cells.

Streptonigrin: Effect on the First Meiotic Metaphase of the Mouse Egg

Abstract: Streptonigrin, an antibiotic and antitumor agent, alters the chromosomes of the mouse ovum during meiosis. Agglutination of bivalents or achromatic gaps and breaks occurred in the larger pairs both in vitro and in vivo. This newly detected cytogenetic effect suggests that such agents can gain access to developing mammalian ova and destroy the normal progress of meiosis.

The stage of chromosome duplication in the cell cycle as revealed by x-ray breakage and 3H-thymidine labeling.

Abstract: By means of combined experiments of X-irradiation and 3H-thymidine labeling of the chromosomes which are in the phase of synthesis, and the subsequent analysis at metaphase on the autoradiographs of the chromosomal damage induced during interphase, it was shown that in somatic cells from a quasi-diploid Chinese hamster line cultured in vitro the chromosomes change their response to radiation from single (chromosome type aberrations) to double (chromatid type aberrations) in late G1. These results are interpreted to indicate that the chromosome splits into two chromatids in G1, before DNA replication. — By extending the observations at the second metaphase after irradiation, it was also seen that cells irradiated while in G2 or late S when they reach the second post-irradiation mitosis still exhibit, beside chromosome type aberrations, many chromatid exchanges, some of which are labeled. Two hypotheses are suggested to account for this unexpected reappearance of chromatid aberrations at the second post-irradiation division. The first hypothesis is that they arise from half-chromatid aberrations. The second hypothesis, which derives from a new interpretation of the mechanisms of production of chromosome aberrations recently forwarded by Evans, is that they arise from gaps or achromatic lesions which undergo, as the cells go through the next cycle, a two-step repair process culminating in the production of aberrations.

Induction of chromosome- and chromatid-type aberrations by phleomycin.

Abstract: When lateral roots of Vicia faba are treated with tritiated thymidine and phleomycin, it is found that all aberrations induced by the chemical before total mitotic inhibition are in unlabeled (G 2 ) cells. After recovery from mitotic inhibition, numerous chromosome-type aberrations are seen in metaphase cells. Treatment for 24 h results in differential erosion of some nuclei, with dense accumulations of Feulgen-positive material around the nucleoli.

Real chromatid deletions versus gaps.

Abstract: The validity of previous scoring of radiation-induced chromatid deletions detected at metaphase has been brought into serious question by Revell in recent years. He finds in Vicia that only 1 20 to 1 100 of the apparent chromatid deletions are real, the remaining large fraction are achromatic lesions or “gaps”. Here, this problem was studied in Tradescantia microspores, γ-irradiated in late interphase (S or perhaps G2), by analysis of the chromatid types of aberrations at metaphase and at anaphase. A real chromatid deletion will release its fragment at anaphase, the gap will not. The scoring validity of metaphase-detected chromatid deletions was established by observation, at the same dose, of an equal frequency of free fragments at anaphase. Metaphase scoring of all other aberration types was similarly confirmed, and yield per rad agreed with previous metaphase scoring. The frequency of gaps was at the most but a third that of the confirmed real chromatid deletions, actually probably less. (Radiation was delivered at low intensity (50 rad/h), which, on Revell's hypothesis, should have maximized the ratio of gap to chromatid deletion production.) Reasons for the 60- to 300-fold disagreement ( 1 3 versus 20 1 to 100 1 ) in scoring of gaps in Vicia and in Tradescantia are considered. Differences in microscopic detection, staining methods, and stages irradiated are unlikelily as major contributors to the discrepancy; intrinsic species or possibly cell type differences are left as the most likely, though unexplained, reasons.

Chromosome Contraction by o-Isopropyl-N-Phenylcarbamate (IPC)

Abstract: A selective herbicide IPC (o-isopropyl-N-phenlycarbamate) causes contraction of chromosomes in the prophase, metaphase, and anaphase stages of mitosis in cells of treated root tips Effective concentrations in aqueous solution lie between 25 and 50 ppm, and effective times between 1 and 4 hr, depending upon the species of plant A suggested starting combination is 10 ppm for 2 hr This compound is effective in causing contraction of chromosomes in a wide range of plant species, as well as enhancing separation in acetocarmine and aceto-orcein squashes in many cases Possibly, it may produce similar results in species which have been found to be unaffected by colchicine, 8-hydroxyquinoline, p-dichlorobenzene, and other commonly used chemicals

Duration of the Mitotic Cycle in Cell Cultures of Haplopappus gracilis

Abstract: The duration of the cell cycle and its component phases in cell cultures of Haplopappus gracilis was estimated by means of pulse labelling with tritiated thymidine and subsequent autoradiographic techniques. The total duration of the mitotic cycle was found to be 22.0 hours. The average durations of the following component phases were: the synthetic period (S) 6.4 hours, the postsynthetic period (G2) 4.86 hours, prophase (P) 0.64 hours, metaphase (M) 0.40 hours, anaphase + early telophase (AT) 0.36 hours, the presynthetic period (G1) 9.34 hours. The results indicate that G1 and G2 are the phases, which are most prolonged in populations of cultivated cells when compared to the same phases in root lip cells from the same species.

A terminal association of two pericentric inversions in first metaphase cells of the australian grasshopper Austroicetes interioris (Acrididae)

Abstract: Austroicetes interioris is polymorphic for pericentric inversions. The three autosomal polymorphisms are considered to be heterotic. In each case the chromosome with the inversion differs from its standard counterpart in the amount of heterochromatin present. Consequently the various karyotypes have appreciable diversity in heterochromatin content. Two of the inversion chromosomes form a terminal association considered to be chiasmate in nature. The resulting quadrivalents favour one particular first metaphase orientation and this causes segregation distortion. The terminal associations and the heterochromatin disparity between the members of each polymorphism are considered to be due to translocations with break points situated in regions of little genetic activity near chromosome tips and causing interchange of telomeres but not of euchromatic segments. Evolutionary implications of such rearrangements are discussed.

Action spectra for mitotic spindle destruction and anaphase delay following irradiation of the cytoplasm with an ultraviolet microbeam

Abstract: — Previous workers have reported that, in a variety of cells, ultraviolet microbeam irradiation of cytoplasm adjacent to the mitotic spindle causes the spindle to diminish or disappear and have postulated that this effect is mediated by a spindle “poison” produced photochemically from a cytoplasmic precursor. In the present work, a microbeam action spectrum for this effect has been obtained to aid in the identification of this mediator material. A small portion of the cytoplasm of Ambystoma(salamander) tissue-culture cells was irradiated in early metaphase with ultraviolet microbeams of various wavelengths and intensities but of the same diameter (8 μ). Spindle destruction was scored by observing diminution of its image as seen with a polarization microscope. In addition, the time of anaphase was recorded so that an action spectrum for anaphase delay was also obtained. These two action spectra are quite similar and are nearly parallel to the absorption spectrum of a tyrosine-containing protein. A few proteins are discussed which might mediate this effect.

Oogenesis in the parthenogenetic stick insect Sipyloidea sipylus Westwood (Orthoptera, Phasmidae).

Abstract: Oogenesis in the parthenogenetic stick insectSipyloidea sipylus Westwood is described. The female has 80±2 chromosomes and is presumably tetraploid. Meiosis consists of two equational divisions and parthenogenesis is thus apomictic. In the end chamber meiosis proceeds as far as pachytene. After pachytene the chromosomes despiralize while the germinal vesicle of the growing oocyte develops. Endomeiosis occurs since, very likely, only univalents enter in the diffuse stage of the germinal vesicle. The vitellarium contains 10–12 growing oocytes, only the oldest of which shows yolk accumulation. Meiosis goes on in the cortical cytoplasm ventrally in the egg about 11 days before oviposition when the first prometaphase is observed. First metaphase lasts from about 6 days before oviposition until about 4 hours after oviposition. Meiosis ends about 9 to 20 hours after oviposition. The first metaphase chromosomes are tetrapartite through an extra chromosome doubling which requires that meiosis consists of two divisions instead of one. These divisions are normal. The first polar body also forms chromosomes and may divide abnormally before degenerating. The second polar body degenerates immediately. The pronucleus divides mitotically in the environment of the polar bodies during its migration to the micropylar area.