Showing papers on "Metaphase published in 1971"
TL;DR: The shape and fine structure of ventricular (primitive ependymal) cells during their generation cycle was studied and it was found that microfilaments are present in telophase cells before outgrowth of external processes and in growing tips of internal processes.
Abstract: The shape and fine structure of ventricular (primitive ependymal) cells during their generation cycle was studied. Interphase cells are radially oriented bipolar elements with processes spanning the thickness of the brain wall. Zonular junctional complexes joining internal processes at the ventricle consist of gap junctions and wider intermediate junctions. The external limiting layer consists of expanded end-feet in simple apposition; they resemble axonal growth cones and contain a feltwork of 60 A microfilaments, elements of smooth endoplasmic reticulum but no microtubules. During prophase, nuclei of ventricular cells move to a juxtaventricular position, while their external processes remain fully extended. The internal processes of such cells contain numerous longitudinally arranged microtubules and microfilaments. Subsequent to nuclear migration, in prometaphase or metaphase, the cell withdraws or pinches off its external process and becomes nearly spherical. During telophase an asymmetrical furrow formation results in a thin connector (midbody) between daughter cells which is adjacent to the ventricle and attached there by the junctional complex. Either before or after complete separation, an external process starts regrowing towards the external limiting layer, eventually resulting in a bipolar interphase cell again. Microfilaments are present in telophase cells before outgrowth of external processes and in growing tips of external processes.
222 citations
TL;DR: Data support the hypothesis that spindle elongation occurs by growth of prepositioned microtubules which "push" the poles apart, and indicates that not all interpolar microtubule extended from pole to pole.
Abstract: The mitotic spindle of many mammalian cells undergoes an abrupt elongation at anaphase. In both cultured rat kangaroo (strain PtK1) and Chinese hamster (strain Don-C) fibroblasts, the distance from pole to pole at metaphase doubles during anaphase and telophase. In order to determine the organization and distribution of spindle microtubules during the elongation process, cells were fixed and flat embedded in Epon 812. Selected cells were photographed with the phase-contrast microscope and then serially sectioned perpendicular to the major spindle axis. Microtubule profiles were counted in selected sections, and the number was plotted with respect to position along the spindle axis. Interpretation of the distribution profiles indicated that not all interpolar microtubules extended from pole to pole. It is estimated that 55–70% of the interpolar microtubules are overlapped at the cell equator while 30–45% extend across the equator into both half spindles. This arrangement appeared to persist from early anaphase (before elongation) until telophase after the elongation process. Although sliding or shearing of microtubules may occur in the spindle, such appears not to be the mechanism by which the spindle elongates in anaphase. Instead, our data support the hypothesis that spindle elongation occurs by growth of prepositioned microtubules which "push" the poles apart.
174 citations
TL;DR: Using the Giemsa stain, it was observed that these areas stained more darkly than the remainder of the chromosome material on denaturation and reassociation in situ, indicating that, even in these conditions, there is re-association of the satellite DNA strands and that there may be a simpler technique in which no satellite DNA need be added.
Abstract: A SIMPLE technique is described here which locates regions of satellite or highly repetitive DNA within mammalian metaphase chromosomes and helps the study of relationships between these regions and those which are heterochromatic and late replicating. The technique arose from attempts to hybridize radioactively labelled satellite DNA from mouse1, guineapig2 and calf3 in situ with complementary regions in metaphase chromosomes, as described by Jones4 and Pardue and Gall5. The areas of hybrids formed in this manner were always located around the centromere. Using the Giemsa stain we also observed that these areas stained more darkly than the remainder of the chromosome material on denaturation and reassociation in situ, without the addition of satellite DNA. This indicated that, even in these conditions, there is re-association of the satellite DNA strands and that there may be a simpler technique in which no satellite DNA need be added. Ideally, a clear picture of the satellite DNA would be obtained in metaphase chromosomes by denaturing the DNA strands and allowing them to reassociate for varying times in an adequate buffer. In this manner, with increasing time of reassociation there would be within the chromosomes a progression of darkly staining regions of satellite DNA which would contrast sharply with lightly staining regions of the remaining DNA.
159 citations
TL;DR: Gross details of the reproductive cycle and the cytology of oogenesis were studied in 155 egg clutches produced by 69 captive individuals of the triploid parthenogenetic lizard Cnemidophorus uniparens.
Abstract: Gross details of the reproductive cycle and the cytology of oogenesis were studied in 155 egg clutches produced by 69 captive individuals of the triploid parthenogenetic lizard Cnemidophorus uniparens. The mean clutch cycle lasted 23 days. The mean number of ova per clutch was 3.3, and the mean number of oocytes per right and left ovaries was 1.65 and 1.70, respectively. Comparison of the size of the oocytes at ovulation (9–10 mm) with the estimated mean duration of vitellogenesis (8.8 days) gave an average of approximately 1 mm yolk deposition per day. The mean time for the retention of eggs in the oviducts was 9.3 days. The germinal disc of the oocyte consists of a series of layers formed by the arrangement of various cytoplasmic and yolk particles in the polar region. In a mature oocyte the germinal vesicle is located immediately below the vitelline membrane and lies at the center of the germinal disc. The germinal vesicle is characterized by a dense disc-like cluster of diplotene chromosomes. Diplonema extends until near ovulation when the oocytes have attained a size of about 9 mm. Diakinesis and metaphase I occur rapidly and immediately prior to ovulation. Counts of approximately as many bivalents as there are somatic chromosomes were obtained from oocytes at diakinesis and metaphase I.
The second division occurs almost immediately before or at the precise moment of ovulation. The chromosomes of the first polar body consist of dyads, of which there are as many as the triploid number of 69. A metaphase II plate obtained in polar view also revealed dyad chromosomes, of which there were approximately as many as the triploid somatic number. The second telophase is normal as evidenced by formation of the second polar body. Chromosomes from the opposing telophase plates show a monad structure. The presence of as many bivalents in the first division as the triploid somatic number of 69 indicates that the 3N condition of C. uniparens was doubled prior to meiosis. This is further supported by the occurrence of two maturation divisions each giving rise to a polar body, by the dyad structure of the chromosomes in the first polar body and the second metaphase, and by the presence of monochromosomes at telophase II. Thus, parthenogenesis in these lizards is of the meiotic type. The somatic number of chromosomes is doubled early in oogenesis presumably by a premeiotic endoduplication, and the 3N level is restored by two subsequent maturation divisions.
153 citations
TL;DR: On the basis of staining reaction, late replicating heterochromatic regions fall into five categories, the relationships and functional significance of these categories is discussed.
Abstract: Cultured human peripheral blood lymphocytes were labelled with 3H-thymidine in the early or late S phase prior to mitosis. Quinacrine fluorescence patterns in metaphase chromosomes were then recorded photographically and the slides reprocessed for autoradiography so that the same metaphase cells were examined with the two techniques. The intensity and distribution of 3H-thymidine labelling was compared with the intensity and distribution of Q fluorescence with particular reference to chromosomes 1, 13, 14, 15, 17, 18, 19, 20, 21 and 22. It was found that chromosome regions showing bright fluorescence were also late replicating and that, in general, patterns of late replications reflected the patterns of fluorescence. Exceptions to this generalisation included the late labelling X chromosome in cells of female origin and areas near the centromeres on chromosomes 1, 9, 16 and 22. These centromeric regions show a dull fluorescence but, with exception of chromosome 9, are strongly Giemsa-positive in the ASG staining technique. On the basis of staining reaction, late replicating heterochromatic regions fall into five categories, the relationships and functional significance of these categories is discussed.
130 citations
TL;DR: The development of procedures for the isolation of unfixed metaphase chromosomes has made feasible a direct analysis of their morphology, and a model of chromosome architecture was developed to accommodate evidence from studies using both light and electron microscopy.
Abstract: The development of procedures for the isolation of unfixed metaphase chromosomes has made feasible a direct analysis of their morphology. Wholemount stereo electron microscopy was used to examine intact and partially disrupted chromosomes produced by physical shearing and extraction with salt and urea solutions. A model of chromosome architecture was developed to accommodate evidence from studies using both light and electron microscopy. In the proposed model the chromatid (anaphase chromosome) consists of two half-chromatids; each half-chromatid contains two deoxyribonucleoprotein ribbons wound into a single fiber (termed the core), with many loops of chromatin (termed epichromatin) attached along its length. The core ribbons are each about 50 A thick by 4000 A wide and are composed of many parallel deoxyribonucleoprotein strands. The epichromatin loops appear to be 250 A supercoiled fibers containing about 75 per cent of the chromosomal DNA. The epichromatin can be selectively removed from the core fibers by extraction with 2.0 M NaCl or 6.0 M urea solutions.
129 citations
TL;DR: It is suggested that the shape of the metaphase spindle cannot be maintained if there is tension in the component microtubules and could be due to some other component pulling the chromosomes over the rigid microtubular framework.
Abstract: I PREVIOUSLY suggested that the shape of the metaphase spindle cannot be maintained if there is tension in the component microtubules1. Spindle tension has been detected2,3 and could be due to some other component pulling the chromosomes over the rigid microtubular framework.
91 citations
TL;DR: Nucleolar RNA synthesis and processing resume within 90 minutes of release from metaphase arrest, and this resumption is not dependent on the synthesis of new proteins.
91 citations
TL;DR: The kinetics of the translocation inductions show that some observations fit very well with a two-event process but that others seem to be in better agreement with the postulate that translocation induction is mainly the result of a one-track process.
Abstract: The translocations considered in the present review are only the reciprocal translocations that involve exchange of terminal segments between non-homologous chromosomes and therefore require two breaks and rejoins During many years this type of translocation has been ascertained by analyzing the F1 progeny of treated and control animals for heritable semi-sterility, but at present the translocations induced in spermatogonia are studied by cytological techniques in the derived spermatocytes because at diakinesis-first metaphase stage of meiosis the homologous chromosome segments of the rearranged and interchanged chromosomes will pair to form characteristic translocation configurations The kinetics of the translocation inductions show that some observations fit very well with a two-event process but that others seem to be in better agreement with the postulate that translocation induction is mainly the result of a one-track process No statistical difference between the strains of mice is observed with respect to the rate of affected cells Some decrease in the yield of spermatocytes with translocation configurations is found for long intervals of time between irradiation and observation The analysis of the F1 progeny derived from irradiated spermatogonia shows that the frequency of translocated offspring is always much lower than expected from the rate of translocated spermatocytes in the irradiated animals
70 citations
TL;DR: The location of erythroblasts in the cell cycle was determined by combining Feulgen cytophotometry with thymidine radioautography and the distribution of Hb values for metaphase cells suggests that there are six Hb classes corresponding to the number of cell cycles in the proliferative phase.
Abstract: Primitive erythroblasts in the circulating blood of the chick embryo continue to divide while synthesizing hemoglobin (Hb). Hb measurements on successive generations of erythroblasts show that there is a progressive increase in the Hb content of both interphase and metaphase cells. Furthermore, for any given embryo the Hb content of metaphase cells is always significantly greater than that of interphase cells. The distribution of Hb values for metaphase cells suggests that there are six Hb classes corresponding to the number of cell cycles in the proliferative phase. The location of erythroblasts in the cell cycle was determined by combining Feulgen cytophotometry with thymidine radioautography on the same cells. Measurements of the Hb content for erythroblasts in different compartments of the cell cycle (G1, S, G2, and M) show a progressive increase through the cycle. Thus, the amount of Hb per cell is a function of the number of cell divisions since the initiation of Hb synthesis and, to a lesser degree, the stage of the cell cycle. Earlier generations of erythroblasts synthesize Hb at a faster rate than the terminal generation. Several models have been proposed to explain these findings.
69 citations
TL;DR: Ostergren's hypothesis, which postulated a centrifugal force, γ, moving the chromosomes to the periphery of the metaphase plate, failed to account for several important features of mitotic and meiotic spindles, including γ.
Abstract: OSTERGREN1 suggested that, before and during metaphase, the mitotic and meiotic chromosomes are subjected to pole-directed forces α, which orient the chromosomes at the equator of the spindle and separate them at anaphase. He also postulated a centrifugal force, γ, moving the chromosomes to the periphery of the metaphase plate; but he could suggest no physical explanation for γ. McIntosh et al.2 developed Ostergren's hypothesis, but failed to account for several important features of mitotic and meiotic spindles, including γ.
TL;DR: DNA extracted from HeLa cell metaphase chromosomes fractionated on the basis of sedimentation velocity in glycerol-sucrose gradients has been tested for the capacity to hybridize with highly purified tRNA and 5 s RNA and results obtained indicate that the sites for these two RNA classes are distributed among chromosomes of all size ranges.
TL;DR: The continued synthesis of both 5S and 4S RNA in metaphase-arrested HeLa cells is demonstrated, and the ratio of uridine incorporation to RNA methylation is used to correct for the alteration in the specific activity of the pyrimidine pool during metaphase arrest.
Abstract: The continued synthesis of both 5S and 4S RNA in metaphase-arrested HeLa cells is demonstrated; 5S RNA is apparently synthesized at approximately 74 percent of the interphase rate, while 4S RNA is synthesized at approximately one-third the rate. The ratio of uridine incorporation to RNA methylation is used to correct for the alteration in the specific activity of the pyrimidine pool during metaphase arrest.
TL;DR: Human and mouse chromosomes can be distinguished on the basis of different amounts of centric heterochromatin and different patterns of fluorescent banding.
Abstract: Human and mouse chromosomes can be distinguished on the basis of different amounts of centric heterochromatin and different patterns of fluorescent banding.
TL;DR: With the application of fluorescent technique, it is now possible to recognize characteristic banding patterns in human chromosomes and a simple nomenclature for the bands is suggested according to their visual identification.
Abstract: With the application of fluorescent technique, it is now possible to recognize characteristic banding patterns in human chromosomes. A simple nomenclature for the bands is suggested according to their visual identification.
TL;DR: Metaphase spreads from male and female mice of various inbred and random-bred types were stained with the DNA-binding fluorochrome quinacrine mustard and this treatment caused the chromosomes to display.
Abstract: Metaphase spreads from male and female mice of various inbred and random-bred types were stained with the DNA-binding fluorochrome quinacrine mustard. This treatment caused the chromosomes to display
TL;DR: A hypothesis is advanced in which a balance between the activities of a chromosome pulverization factor and a nuclear envelope formation factor, the former in metaphase cells and the latter in interphase cells, is decisive as to the nature of morphologic events observed in virus-induced fused cells.
Abstract: The process of cellular fusion induced by Sendai virus in Chinese hamster cells (Don line) afforded us the opportunity to study nuclear envelope formation around metaphase sets in the presence of interphase nuclei, when chromosome pulverization failed to occur in such multinucleate cells. Morphologically, the enveloped metaphase chromosomes resembled a normal telophase nucleus, though minor differences prompted us to call it telophase-like. Electron microscopic observations demonstrated that the membranes enveloping the chromosomes appeared to be identical with a normal nuclear envelope. The longer the cells were incubated with Colcemid before fusion, the higher was the number of cells with telophase-like nuclei and the lower the percentage of cells with pulverizations. Furthermore, the number of pulverizations bore a somewhat direct relationship to the ratio of metaphase to interphase nuclei in multinucleate cells, and the number of telophase-like nuclei was inversely proportional to this ratio. A hypothesis is advanced in which a balance between the activities of a chromosome pulverization factor and a nuclear envelope formation factor, the former in metaphase cells and the latter in interphase cells, is decisive as to the nature of morphologic events observed in virus-induced fused cells.
TL;DR: The data indicate that caution should be exercised in the use of colchicine for determining cell cycle duration and/or the effects of physical and chemical agents on the cycle.
Abstract: The effects of four concentrations of colchicine (2.5 x 10(-7), x 10(-5), x 10(-3), and x 10(-2)M) on the cell cycle of grasshopper neuroblasts have been determined by direct observations on living cells. The lowest concentration, 2.5 x 10(-7)M, does not completely disorganize the spindle but does retard its action. The three higher concentrations disorganize the spindle, so that all cells reaching metaphase are blocked in a c-mitotic condition throughout the period of observations (308 min at 38 degrees C, the minimum duration of the cell cycle in untreated neuroblasts). Continuous treatment with all concentrations reduces the rate at which neuroblasts enter metaphase, the extent of the reduction being a function of increasing concentration and time of exposure. After a short exposure to 2.5 x 10(-5)M colchicine, the neuroblasts recover from the inhibiting effects on progression through the cycle to metaphase, but they show no recovery from the inhibiting effects on spindle formation for more than 3 hr. Apparent stimulation of progression rate occurs early in exposure to all concentrations and during recovery from a short exposure to 2.5 x 10(-5)M. Morphological alterations in the chromatin of telophase, interphase, and prophase cells are induced by the higher concentrations of colchicine. The data indicate that caution should be exercised in the use of colchicine for determining cell cycle duration and/or the effects of physical and chemical agents on the cycle.
TL;DR: Irregularly folded, 250 Å thick fibers, which is the basic substructure of inactive chromatin and mitotic chromosomes, were found to be firmly attached to the annuli of the inner nuclear membrane at metaphase.
Abstract: Whole-mount preparations and thin sections of human interphase cells and metaphase chromosomes were examined by electron microscopy. Irregularly folded, 250 A thick fibers, which is the basic substructure of inactive chromatin and mitotic chromosomes, were found to be firmly attached to the annuli of the inner nuclear membrane. At metaphase, fragments of the nuclear membrane were seen to adhere to the chromatids. Single fibers stretching out from the telomeres were observed connecting chromatids of nonhomologous chromosomes. A possible model of DNA replication at the nuclear pore complex is presented.
TL;DR: Throughout mitosis the nuclear membrane remains intact and centrioles are not associated with the dividing nucleus, and the micronucleus has a peripheral layer of microtubules, a fibrous zone, and a core of condensed chromatin.
Abstract: Ultrastructural details of micronuclear mitosis in the ciliate P aurelia are described Throughout mitosis the nuclear membrane remains intact and centrioles are not associated with the dividing nucleus At late interphase the micronucleus has a peripheral layer of microtubules, a fibrous zone, and a core of condensed chromatin This core fragments at prophase, the peripheral microtubules disappear, and microtubules extend from the fibrous zone At metaphase, over 100 chromosomes could be seen, each attached to a bundle of microtubules though kinetochores were indistinct
TL;DR: A new Giemsa staining technique for the investigation of human metaphase chromosomes can be used to characterise the G group and Y chromosomes in patients with Down's syndrome.
TL;DR: The degree of synchrony in the course of the interphase periods G1, S and G2 and in the initiation of mitosis in the several nuclei of each cell of a polynucleate population induced by treatment with 0.1% caffeine is analysed.
Abstract: The degree of synchrony in the course of the interphase periods G1, S and G2 and in the initiation of mitosis in the several nuclei of each cell of a polynucleate population induced by treatment with 0.1% caffeine, in root meristems of Allium cepa, through inhibition of cytokinesis in two successive cell divisions is analysed by means of labelling with 3H-thymidine.—The S period is initiated simultaneously in all the nuclei of each polynucleate cell, which supports the hypothesis of a factor present in the cytoplasm that is responsible for inducing DNA synthesis.—However, all the nuclei in a polynucleate cell do not pass from the S period to the G2 period simultaneously, those surrounded by the greatest amount of cytoplasm, generally the outer nuclei, being the first to complete the S period (“early nuclei”) and beginning the prophase before their fellow-nuclei in the same cell (“late nuclei”).—From the metaphase onwards, however, all the nuclei in a polynucleate cell continue to develop synchronously. The synchronizing mechanism has a twofold aspect: the shortening of the G2 period in the “late nuclei” and the lengthening of it in the “early ones” and, on the other hand, an arrest of prophase in the “early nuclei” until the “late ones” have caught up, which suggests the existence of an inhibiting factor produced by the “late nuclei” capable of acting upon the early ones through the cytoplasm.
TL;DR: It became clear that the spindle tubules do not penetrate through the kinetochore, and the contraction of chromosomal tubules is believed to exert the force for the initial movement of anaphase chromosomes.
Abstract: Mitosis of the rat anterior pituitary cells was studied with the electron microscope. Most mitotic cells found in the anterior pituitary contained a number of secretory granules, and a somatotrophic cell in metaphase contained a Golgi apparatus with newly formed secretory granules. Hypertrophied thyrotrophic cells after thyroidectomy underwent mitosis. Some prolactin-producing cells in mitosis contained a great number of vacuolated cisterns of rough endoplasmic reticulum, which were the characteristic results of long term administration of estrogen to female rats. Hypertrophy of the anterior pituitary glands after removal of a target organ or the administration of estrogen may be brought about by the proliferation of cells of a specific type corresponding to the experiment. This proliferation carried out by mitotic cell division of fully differentiated adenohypophyseal cells. The theory that highly differentiated cells producing specific hormone cannot synthesize DNA and divide by mitosis was shown to be erroneous.The outer layer of a kinetochore was bent by the pulling force of chromosomal spindle tubules. As the inner layer was not bent in this case, it became clear that the spindle tubules do not penetrate through the kinetochore, and the contraction of chromosomal tubules is believed to exert the force for the initial movement of anaphase chromosomes.
TL;DR: A method for releasing chromosomes from metaphase human embryonic lung cells has been developed and seven HeLa cell lines have been established from individual mitotic cells isolated and cloned after manipulation.
Abstract: Chromosomes of HeLa, ERK, and human embryonic lung cells have been manipulated at different mitotic stages. A method for releasing chromosomes from metaphase human embryonic lung cells has been developed and seven HeLa cell lines have been established from individual mitotic cells isolated and cloned after manipulation.
TL;DR: The results strongly suggest that constitutive heterochromatin is localized in the same chromosomes throughout development and represents a specific entity.
Abstract: In the vole, Microtus agrestis, the constitutive heterochromatin is largely restricted to the giant sex chromosomes but varies in its degree of condensation in various cell types. In the cleavage embryos and fibroblasts it formed one or two long and extended heterochromatic fibers, in hepatocytes it formed two large and diffuse masses and in neurons, spermatogonia and oogonia it formed two large and compact masses. The basic patterns of all differentiated cells were essentially unchanged throughout development.—At all stages of development and in cells of all types, mitotic nuclei displayed two large heteropycnotic chromosomes in prophase and persistent condensation in telophase. Apposition and delayed separation of chromatids of the giant chromosomes was also observed in metaphase and anaphase, respectively. During the first meiotic prophase of spermatocytes and oocytes, the giant chromosomes were also heteropycnotic.—The results strongly suggest that constitutive heterochromatin is localized in the same chromosomes throughout development and represents a specific entity.
TL;DR: The mitotic delay appears to be specific for the parotid and submaxillary glands and continues to undergo DNA synthesis during the period of secretion following the drug.
TL;DR: Metaphase chromosomes of mice carrying Cattanach's translocation, which is the deletion of material from a medium-sized autosome and its insertion into an X chromosome, were stained with quinacrine mustard to identify the autosome involved in the translocation and localization of the transposed material within the X chromosome.
Abstract: Metaphase chromosomes of mice carrying Cattanach's translocation, which is the deletion of material from a medium-sized autosome and its insertion into an X chromosome, were stained with quinacrine mustard. Comparison of the fluorescence patterns of these chromosomes with those of the chromosomes of normal mice has allowed the identification of the autosome involved in the translocation and localization of the transposed material within the X chromosome. Since the material inserted into the X chromosome in Cattanach's translocation is known to carry part of linkage group I, we are now able to assign linkage group I to a specific chromosome pair of the normal fluorescent karyotype of the mouse.
TL;DR: The release of mitogenically-active kinins is proposed as the means by which kallikrein enhances cell proliferation in vivo.
Abstract: : A single intraperitoneal injection of a commercial preparation of kallikrein (3 or 5 units/100 gm) stimulated the mitotic actvity of cells in the thymus gland and the bone marrow of rats. This effect was observed three to six hours after injection as an increase in the mitotic index and the accumulation of cells in the metaphase stage of mitosis by the mitotic blocking agent, colcemid. Kallidrein did not affect the mitotic activity of isolated thymic lymphocytes. The release of mitogenically-active kinins is proposed as the means by which kallikrein enhances cell proliferation in vivo. (Author)