Rabl's model of the interphase chromosome arrangement tested in Chinise hamster cells by premature chromosome condensation and laser-UV-microbeam experiments

In 1885 Carl Rabl published his theory on the internal structure of the interphase nucleus. We have tested two predictions of this theory in fibroblasts grown in vitro from a female Chinese hamster, namely (1) the Rabl-orientation of interphase chromosomes and (2) the stability of the chromosome arrangement established in telophase throughout the subsequent interphase. Tests were carried out by premature chromosome condensation (PCC) and laser-UV-microirradiation of the interphase nucleus. Rabl-orientation of chromosomes was observed in G1 PCCs and G2 PCCs. The cell nucleus was microirradiated in G1 at one or two sites and pulse-labelled with 3H-thymidine for 2h. Cells were processed for autoradiography either immediately thereafter or after an additional growth period of 10 to 60h. Autoradiographs show unscheduled DNA synthesis (UDS) in the microirradiated nuclear part(s). The distribution of labelled chromatin was evaluated in autoradiographs from 1035 cells after microirradiation of a single nuclear site and from 253 cells after microirradiation of two sites. After 30 to 60h postincubation the labelled regions still appeared coherent although the average size of the labelled nuclear area fr increased from 14.2% (0h) to 26.5% (60h). The relative distance dr, i.e. the distance between two microirradiated sites divided by the diameter of the whole nucleus, showed a slight decrease with increasing incubation time. Nine metaphase figures were evaluated for UDS-label after microirradiation of the nuclear edge in G1. An average of 4.3 chromosomes per cell were labelled. Several chromosomes showed joint labelling of both distal chromosome arms including the telomeres, while the centromeric region was free from label. This label pattern is interpreted as the result of a V-shaped orientation of these particular chromosomes in the interphase nucleus with their telomeric regions close to each other at the nuclear edge. Our data support the tested predictions of the Rabl-model. Small time-dependent changes of the nuclear space occupied by single chromosomes and of their relative positions in the interphase nucleus seem possible, while the territorial organization of interphase chromosomes and their arrangement in general is maintained during interphase. The present limitations of the methods used for this study are discussed

Formation of viable cell fragments by treatment with colchicine

Time-lapse cinematography of human fibroblasts revealed that mitotic cells separated into numerous cell fragments containing varying amounts of chromatin and cytoplasm when treated with colchicine. As cell fragments were very loosely attached to the surface of the culture vessel during their formation, they could be easily detached like mitotic cells by gently shaking the vessel and thus separated from normal interphase cells. Fragments obtained by this procedure were able to exclude trypan blue indicating, therefore, an intact cell membrane. When placed into Petri dishes many of them attached to and even spread out on the surface. Five hours later the majority of the attached fragments incorporated [3H]leucine. Time-lapse films showed that fragments were able to extend and retract pseudopodia at least for several hours after their formation. Although the fragments degenerated within a few days, in the present experiments the possibility was not excluded that fragments which had lost only a very small amount of chromatin and cytoplasm survived for longer periods of time. The observations clearly indicate viability of many newly formed fragments

Turbulent flow in pulsed extraction columns with internals of discs and rings:Turbulent kinetic energy and its dissipation rate during the pulsation

Turbulent energy parameters of single-phase pulsed flow in an extraction column with internals of immobile discs and rings (doughnuts) are studied. Simulation results are obtained by resolution of Reynolds equations coupled with k–ɛ model of turbulence. As far as pulsed flow is concerned, the evolution of space distribution of turbulent kinetic energy k and its dissipation rate ɛ during the pulsation is thoroughly studied. It is observed that the energy distribution on a contact stage changes periodically from rather homogeneous to highly inhomogeneous depending on instantaneous flow velocity. Significant difference between maximal and mean energy parameters is observed. It is supposed that the discrepancy between simulation and experimental results for the size of drops formed in the turbulent field might be attributed to mean energy presentation that smoothes the peak effects of a pulsed flow. Spatial zones and time intervals of high-turbulent kinetic energy are delimited presuming their dominant role for accurate foreseeing of size of drops in this type of equipment. It is shown that an “effective” energy level should be determined by selection over the high-energy time periods and zones in order to compensate the smoothing effect of mean energy level.The results obtained are useful for the calculation of drop size based on energy level at the stage, which is necessary for the determination of parameters of practical interest such as drop residence time and interphase mass transfer surface

The dynamics of replication licensing in live Caenorhabditis elegans embryos

Accurate DNA replication requires proper regulation of replication licensing, which entails loading MCM-2-7 onto replication origins. In this paper, we provide the first comprehensive view of replication licensing in vivo, using video microscopy of Caenorhabditis elegans embryos. As expected, MCM-2-7 loading in late M phase depended on the prereplicative complex (pre-RC) proteins: origin recognition complex (ORC), CDC-6, and CDT-1. However, many features we observed have not been described before: GFP-ORC-1 bound chromatin independently of ORC-2-5, and CDC-6 bound chromatin independently of ORC, whereas CDT-1 and MCM-2-7 DNA binding was interdependent. MCM-3 chromatin loading was irreversible, but CDC-6 and ORC turned over rapidly, consistent with ORC/CDC-6 loading multiple MCM-2-7 complexes. MCM-2-7 chromatin loading further reduced ORC and CDC-6 DNA binding. This dynamic behavior creates a feedback loop allowing ORC/CDC-6 to repeatedly load MCM-2-7 and distribute licensed origins along chromosomal DNA. During S phase, ORC and CDC-6 were excluded from nuclei, and DNA was overreplicated in export-defective cells. Thus, nucleocytoplasmic compartmentalization of licensing factors ensures that DNA replication occurs only once

Epoxy–amine/metal interphases: Influences from sharp needle-like crystal formation

When epoxy–amine liquid mixtures are applied onto metallic oxide layer, concomitant amine chemical sorption and metallic surface dissolution appear leading to the organo-metallic complex formation. We studied the interphase formation and used two different amines as hardener (isophoronediamine (IPDA) and diethylenetriamine (DETA)). If the complex concentration within the liquid amine or epoxy–amine prepolymer is higher than its solubility limit, complexes crystallize. Sharp needle-like crystals are observed only with modified IPDA. For Al-IPDA crystals, the melting point is about 78°C, but as the network is formed at this temperature, crystals remain present at the end of the polymerization cycle

Exposure of Tradescantia Microspores to Periodic Vibrations of 40-100 Hertz

Spherical chromosomal fragments determined in exposure of Tradescantia microspores to periodic vibration

The distribution of cytoplasmic microtubules throughout the cell cycle of the centric diatom Stephanopyxis turris: their role in nuclear migration and positioning the mitotic spindle during cytokinesis.

The cell cycle of the marine centric diatom Stephanopyxis turris consists of a series of spatially and temporally well-ordered events. We have used immunofluorescence microscopy to examine the role of cytoplasmic microtubules in these events. At interphase, microtubules radiate out from the microtubule-organizing center, forming a network around the nucleus and extending much of the length and breadth of the cell. As the cell enters mitosis, this network breaks down and a highly ordered mitotic spindle is formed. Peripheral microtubule bundles radiate out from each spindle pole and swing out and away from the central spindle during anaphase. Treatment of synchronized cells with 2.5 X 10(-8) M Nocodazole reversibly inhibited nuclear migration concurrent with the disappearance of the extensive cytoplasmic microtubule arrays associated with migrating nuclei. Microtubule arrays and mitotic spindles that reformed after the drug was washed out appeared normal. In contrast, cells treated with 5.0 X 10(-8) M Nocodazole were not able to complete nuclear migration after the drug was washed out and the mitotic spindles that formed were multipolar. Normal and multipolar spindles that were displaced toward one end of the cell by the drug treatment had no effect on the plane of division during cytokinesis. The cleavage furrow always bisected the cell regardless of the position of the mitotic spindle, resulting in binucleate/anucleate daughter cells. This suggests that in S. turris, unlike animal cells, the location of the plane of division is cortically determined before mitosis

Modelling the spatial organization of cell proliferation in the developing central nervous system

How far is neuroepithelial cell proliferation in the developing central nervous system a deterministic process? Or, to put it in a more precise way, how accurately can it be described by a deterministic mathematical model? To provide tracks to answer this question, a deterministic system of transport and diffusion partial differential equations, both physiologically and spatially structured, is introduced as a model to describe the spatially organized process of cell proliferation during the development of the central nervous system. As an initial step towards dealing with the three-dimensional case, a unidimensional version of the model is presented. Numerical analysis and numerical tests are performed. In this work we also achieve a first experimental validation of the proposed model, by using cell proliferation data recorded from histological sections obtained during the development of the optic tectum in the chick embryo