Nuclear Bridges Research Articles

The development of the central cell of Brassica campestris prior to fertilization

The development of the central cell of Brassica campestris cv. Candle (canola-rapeseed) was examined using techniques of light and electron microscopy and cytochemistry. The mature central cell is devoid of the large central vacuole characteristic of the early cellular stage of megagametophyte development. Prior to anthesis, cell wall projections, of the transfer cell type, develop on the lateral wall of the central cell. These central cell wall projections extend from the midregion of the megagametophyte to the egg apparatus and are immediately adjacent to the starch-containing region of the inner and outer integuments. The cell wall projections are periodic acid – thiocarbohydrazide – silver proteinate positive as are the contents of dictyosome vesicles that appear to contribute to their formation. Mitochondria are associated with the wall projections as is a network of central cell endoplasmic reticulum that extends from the wall projections to the egg apparatus. Microtubules are associated with the migrating chalazal polar nucleus. The two polar nuclei partially fuse prior to double fertilization, united by nuclear bridges and endoplasmic reticulum interconnections. Proplastids are a characteristic feature of the immature cellular megagametophyte. By anthesis, the proplastids of the mature central cell develop into chloroplasts with stacked thylakoids and starch deposits. Microbodies are frequently found associated with lipid bodies, and polysomes with the endoplasmic reticulum of the mature central cell. Key words: Brassica, central cell, megagametophyte, ovule, transfer cell.

Nuclear Λ-transitions and electronic bridges

Nuclear γ-transitions via an electronic-bridge (EB) mechanism are considered theoretically. The relative probabilities for the elastic and inelastic EB deexcitation effect are calculated in the framework of Dirac-Hartree-Slater (DHS) model of atom. The probability of O+−O+ γ-transitions due to EB mechanism are discussed. The results of calculations are compared with experimental data.

Ultrastructure of Fanconi anemia fibroblasts.

Employing indirect immunofluorescence and conventional electron microscopy, gross nuclear aberrations were observed in cultured interphase fibroblasts derived from a patient suffering from Fanconi's anemia (FA). Such aberrations were predominantly expressed in cells at high passages between 28 and 34. The structure of the nuclei appeared compound in nature, often consisting of two to three nuclear fragments connected to each other by thin nuclear bridges containing chromatin and nuclear lamin material. In other cases, the nuclei appeared lobed or budded but the cells did not contain distinct nuclear fragments. Chromatin was conspicuously absent from some nuclear lobes, revealing empty, cage-like structures comprising nuclear lamin material. Micronuclei were often abundant in the perinuclear cytoplasm but in some instances they appeared to be composed of chromatin lacking a delineating nuclear lamin matrix. Residual cytoskeletons examined by whole-mount electron microscopy revealed a network of intermediate filaments (IFs) within FA fibroblasts forming a bridge between the plasma membrane and the nucleus or its major fragments. In addition, there were thinner, 3-4 nm filaments connecting individual IFs with the surface of the nucleus. Micronuclei that were not connected to the main nuclear body, but which were delineated by a distinct lamina and possessed nuclear pores, did not appear to be anchored to the IF network. Multinuclearity, nuclear fragmentation, irregular chromatin distribution and inter-nuclear chromatin/lamin bridges might result from a failure in the redistribution of chromatin to sister nuclei, incomplete cytokinesis and proliferation of nuclear envelope material. These phenomena point to precocious aging of FA fibroblasts and may occur as a consequence of spontaneous damage to the sister chromatids or through the action of DNA-toxic agents.

Nuclear bridges within multinucleated giant cells in subacute encephalitis of acquired immune deficiency syndrome (AIDS).

Six cases of subacute encephalitis in AIDS were examined with special reference to the nuclear morphology of multinucleated giant cells (MGC's). Although rare in some, all cases showed nuclear bridges which were thin strands connecting individual nuclei. Even more frequently observed were nuclear processes which were probably parts of nuclear bridges or disconnected ends of nuclear bridges. Nuclear bridges and processes were not features of mitosis but were composed of nucleoplasm. They appear to be a feature of MGC's in AIDS but may not be limited to this condition.

NUCLEAR BRIDGES IN MULTINUCLEATED GIANT CELLS ASSOCIATED WITH PRIMARY LYMPHOMA OF THE BRAIN IN AN AIDS PATIENT.

NUCLEAR BRIDGES IN MULTINUCLEATED GIANT CELLS ASSOCIATED WITH PRIMARY LYMPHOMA OF THE BRAIN IN AN AIDS PATIENT.

Can Risk-Benefit Analysis Provide Consistent Policy Evaluations of Projects Involving Loss of Life?

Many public projects such as the construction of nuclear reactors, roads and bridges involve risks to life. Risk-benefit analysis assesses the costs and benefits of these projects by an extension of the well-known willingness-to-pay (compensating variation) criterion to these situations (see Mishan (i982) or Jones-Lee (I976)). The approach taken is an ex ante one, looking at people's expected ,utility (or a substitute) before deaths occur rather than a measure of actual (ex post) welfare losses and gains. A good case can be made against these ex ante decision rules (see Broome (I978), Hammond (I983) or Ulph (I982)) but we do not consider it in this paper. Even in the ex ante setting, however, the willingness-to-pay measures used in risk-benefit analysis may not be consistent with individual welfare. These difficulties are surveyed by Arrow (I983). Experimental evidence shows that individuals do not update their subjective probabilities in a way that is consistent with Bayes' theorem -'preference reversal' (willingness to pay is opposite to stated preferences) occurs, and choices depend on the way in which alternatives are described ('framing'). As serious as these problems are, we address, in this paper, the question of the consistency of risk-benefit tests even when individuals are rational and perfectly informed (subjective and objective probabilities coincide) and compensating (or equivalent) variations are summed across individuals to provide a social riskbenefit test. We investigate the conditions under which these tests provide orderings of all the social alternatives, thus avoiding inconsistent social preferences (for example, alternative x preferred to alternative y and y to x, or x preferred to y, y preferred to z, and z preferred to x). We require individual preferences to be consistent in the sense of Hicks and Allais (utility depends on the probability of being alive and on consumption enjoyed while alive) and consider as well the special case of the expected utility hypothesis. We show that, in a simple one-good model (Section I), both compensating and equivalent variations are exact indexes of individual welfare gain or loss. Accepting a project if and only if the sum of compensating variations is positive is equivalent (in this model only) to the (ex ante) potential Pareto improvement criterion for project acceptance. Lemma i argues that the compensating variation (or equivalent variation)

Observations of Radio Galaxies and QSR with Ratan-600

We shall tell you briefly about the main observational program connected with radio galaxies. Different theories of radio galaxies predict different types of spectral index variations across the main body of the source. One would expect that the best solution of the problem is the construction of two-dimensional maps at a number of frequencies. However, we suggest that in some cases (i.e., for standard well-aligned structures) one-dimensional images with filled aperture may be much more accurate in determination of the variations of the spectral index along the major axes of radio galaxies. We now have 47 one-dimensional multifrequency images of all sources brighter than 1 Jy at centimeter wavelengths in the declination range −43° −+53° resolvable with our beam. Up to 7 frequencies were used (1.35, 2.08, 3.9, 6.5, 8.2, 13, and 31 cm). Cyg A is the best example showing structures of different scale: nuclear sources, bridges, main bubbles, and hot spots.

Cytogenetic effects of styrene and styrene oxide on human lymphocytes and Allium cepa.

Styrene and styrene oxide induce cytogenetic effects already at very low concentrations (0.01% v/v or even less); the effects are similar in both in vitro human lymphocytes and in vivo onion root tip cells (Allium cepa L.). It is characteristic that styrene treatment is more potent in causing chromosome breakage in both systems. In Allium styrene induced inhibition of mitotic spindle action as revealed by a strong c-mitotic effect. Also the number of micronuclei and nuclear bridges increased in both test systems, especially after styrene oxide treatment. Furthermore, the metaphase chromosome morphology in the cells treated with styrene oxide was strongly affected. In both systems, chromosome destruction was observed, or else the chromosome material was decondensed and resulted in a characteristic fuzzy appearance of Allium chromosomes or a banded appearance of human lymphocyte chromosomes. A specific effect of styrene oxide on the chromosomal proteins is thus suggested. The data obtained from the autoradiographic studies with Allium support the idea that [7--3H] styrene oxide binds irreversibly to the cytoplasmic and nuclear macromolecules.

Prefabricated Systems: A Suggested Course Outline

The rapid development of the prefabricated systems industry has created a need for college educated professionals. Prefabrication has developed to the point that today it is applied in the design and construction of such complex structures as nuclear power plants, airports, bridges, and many others. This paper contains a broad outline for an educational program that could be applied to many specialized institutions of higher education. Among those institutions, technology today occupies a very important role as it bridges the gap between the technician and the engineer.

Electron-microscope observations of mitosis and cytokinesis in multinucleate protoplasts of soybean.

Multinucleate soybean protoplasts produced by spontaneous fusion during enzyme digestion of the cell wall initiated cell division after approximately 40 h in culture. The structure of these protoplasts during mitosis and cytokinesis was studied with both light and electron microscopes. Most nuclei did not fuse but divided synchronously. Interphase nuclei was commonly connected by short narrow nuclear bridges. At prophase and metaphase the nuclei appeared typical of those in most higher plants; technical difficulties prevented an adequate examination of protoplasts at anaphase. Telophase was characterized by cytokinesis involving phragmoplast and cell plate formation; however, complete partitioning of the cytoplasm by cell plants was not observed. Numerous coated vesicles were present near to or continuous with the cell plate and plasmalemma. The presence of a few dividing protoplasts with at least double the normal chromosome number suggests that some nuclear fusion occurred prior to mitosis. Very little cell wall material was detected at the margin of the dividing protoplasts.

Number of nuclei in isolated myocardial cells of pigs.

The heart muscle cells of eight pigs 18 days, 30 days, 6 months, and 8 months old were isolated by potash lye. Most cells contain 2, 4, 8, or 16 nuclei of equal or unequal size. The part of cells with 4, 8, or 16 nuclei increases between the age of 18 days and 6 months. Most nuclei are diploid but larger ones are polyploid with a DNA content up to 32C. There are topographical differences between the parts of the heart with the highest proportion of multinuclear cells at the base of the left ventricle and the lowest in the right heart. Hints at the mitotic origin of the nuclear rows are micronuclei and nuclear bridges. The isolation procedure permits cytophotometric DNA measurements after Feulgen stain. Furthermore the percentage of nuclear rows not corresponding to a total DNA of 4, 8, 16, or 32 diploid nuclei makes it possible to estimate the frequency of fragmentations during the isolation procedure. It comes up to approximately 5% of the cells.

Study on the fibrillar formation surrounding the nuclear bridge in some types of leukaemic cells.

Rieder cells which had a characteristically lobulated nucleus with a deep cleft were studied by both conventional and ultra‐high voltage electron microscopes in one case of acute granulocytic leukaemia and two cases of acute promyelocytic leukaemia. Light microscopically a few leukaemic cells in these cases possessed two nuclei. It was demonstrated that a bundle of microfilaments tightly surrounded the nuclear bridge of the Rieder cell. This finding seemed to be strikingly similar to that of the amphibian amitotic cell division observed by Pehlemann although origination of a bundle of microfilaments from the centriole and a process of cell division following the amitotic nuclear division could not be confirmed. Considering the possible contractile property of the microfilaments described hitherto in other types of cells, it is postulated that the Rieder cell in these types of leukaemia was produced by a process of abortive amitosis caused by the contraction of the microfilaments.

Induction of Nuclear Bridges in Vicia faba Root Meristematic Cells by m-Nitrobenzhydrazide

Induction of Nuclear Bridges in Vicia faba Root Meristematic Cells by m-Nitrobenzhydrazide

Ultrastructural studies in a particular case of congenital dyserythropoietic anemia (CDA).

A case of CDA was investigated electron microscopically which clinically and serologically has been classified as type II. However, we have found the ultrastructural criteria both of CDA type I (open interconnections between heterochromatin of interphase nucleus and cytoplasm as well as alterations of the heterochromatin and nuclear envelope) and of type II (characteristic marginal spaces and sequestrations in the cytoplasm and nuclear protrusions). Only nuclear bridges — light microscopical characteristics of the CDA type I — were not observed. It was impossible to classify our case of CDA into type I or II from ultrastructural aspects. Two hypothetical explanations of these phenomena are discussed.

Ultrastructural studies on monocytic leukaemia.

Summary. Bone marrdw specimens from four cases of pure monocytic leukaemia. (Schilling type) and three cases of myelo‐monocytic leukaemia (Naegeli type) were examined by electron microscopy. The hallmark of the monoblasts and more mature monocytoid forms was the extreme nuclear irregularity with frequent nuclear bridges and blebs. Abundant cytoplasm with a serrated margin, dense granules, numerous pinocytic vesicles and vacuoles, frequent peri‐nuclear fibrillar bands and a well‐developed Golgi zone served as additional criteria for identifying monoblasts. Various stages in the maturation of monoblasts were observed. Stem cells possessed a large round nucleus which became extremely folded with increasing maturity. The graduai appearance of condensed chromatin paralleled this nuclear polymorphism. The fine structure of these monoblasts was compared with that of myeloblasts to point out distinguishing features. It is felt that ultrastructural analysis can be of value in separating pure monocytic leukaemia from myelo‐monocytic leukaemia.

A phase contrast cinemicrographic analysis of elevated oxygen tension effects on cell dynamics in strain L cells

Phase contrast cinemicrographic methods and fixed preparations were used to ascertain the effect of prolonged exposure of strain L cells to Eagle MEM that was gassed with a mixture of 95% O 2 − 5% CO 2. The results of this study showed that division in synchronous strain L cells is inhibited by exposure to hyper-oxygenated medium when the cells are in early G1. The effect of elevated levels of oxygen delayed the separation of sister cells following mitosis by 4 to 12 h. Nucleolar morphology suggested that oxygen-treated cells may proceed slowly through S phase where they are partially arrested. Some synchronous cells were observed to round up after 3 h exposure to hyper-oxygenated medium. Some cells lysed after rounding up. Asynchronous strain L cells exposed to hyper-oxygenated medium exhibited cytological anomalies such as nuclear blistering, extrusion of nuclear material, multinuclear giant cell formation, and nuclear bridge formation following nuclear division.

The Production of Multinucleated Lymphocytes by Cytochalasin B. An Electron Microscopic Study

The cytochalasins are newly derived from moulds and are useful in studying nuclear division. Multinucleated fibroblasts were produced by CARTER [Nature 213: 261, 1967] and lymphocytes by us [Nature 216: 1134, 1967]. Lymphocytes with up to eight nuclei were seen. Progressive nuclear addition [1, 2, 3 etc.) was found instead of a doubling of the nuclei (1, 2, 4, etc.). The term ‘pseidomitosis’ was proposed for the process of synchronous mitosis, but which results in the division of only one nuclei.Our observations, using the light microscope shows the nuclei of binucleated cells to be similar in size and shape; however, in cells with more than two nuclei there is marked vaiation in size and shape of each nucleus. What might have appeared, in many instances, as separate nuclei are seen by electron microsopy to be lobes of a rather large and irregular nucleus. In other instances, small nuclear bridges connected what might appear as separate nuclei. Variation exists in nuclear size from rather large nuclei to very small micronuclei. Serial sectioning of cell nuclei verified the morphological variability seen in single sections. Spindle fibers and kinetochore attachment to the chromosomes revealed no unusual features. Electron microscopy showed synchronous division of nuclei. Golgi apparatus remained as a single large unit. There was a doubling of centrioles in binucleated cells. What appears as separate nuclei under the light microscope were connected by nuclear bridges. The finding suggests that as nuclei accumulate that the spindle bridge is unable to accurately divide the large numbers of chromosomes present.

THE DEVELOPMENT OF DNA CONTAINING NUCLEAR BRIDGES IN HUMAN CELLS

Nuclear bridges were observed in human cells of malignant origin and a small proportion of PHA-stimulated normal human lymphocytes (3.8%). Such structures were not seen in benign tissue or lymphocytes cultured without PHA. Classification of such bridges on the basis of morphologic development suggests a process leading to an abnormal nuclear division yielding hypodiploid micro-nuclei. H3-thymidine incorporation studies indicate that these bridges contain DNA.

Fine structure of extremely slender nuclear bridges in segmented cell nuclei

Fine structure of extremely slender nuclear bridges in segmented cell nuclei

The mitotic behavior of chromosomes in echinoderm eggs following incorporation of bromodeoxyuridine

1. 1. When eggs of the sand-dollar Dendraster excentricus are cultured in concentrations of bromodeoxyuridine (BUDR) above 1 × 10 − M, cleavage produces a disordered mass of cells, but a blastula is not formed. The effect is completely antagonized by an adequate concentration of thymidine. 2. 2. The developmental abnormality is attributed to a disturbance of the separation of sister chromosomes at anaphase. Chromosome bridges are formed, which persist as the cleavage furrow divides the cytoplasm. As the interphase nucleus is organized from the two bridged groups of chromosomes, it takes the apparent form of a single nucleus extending through the furrow as a nuclear bridge. At the next prophase, the chromosomes in the bridges recondense in extended form in which they came out of the previous division. The original bridges are broken at this next division, as new bridges form through the new furrows. The developmental abnormalities are attributed to the abnormalities of the distribution of chromosomes. 3. 3. In eggs of several species of sea urchins, the nuclear bridges are not formed as a rule, and early development to the blastula stage is normal. 4. 4. Hypotheses relating the chromosome separation to the properties of DNA which has incorporated BUDR are considered.