Cellular Skeleton Research Articles

The effect of gravity on microtubule self-organisation

The molecular processes by which gravity biological systems are effected by gravity are not understood. Theoreticians have proposed this might arise through the bifurcation properties of certain types of non-linear chemical reactions that self-organise by reaction and diffusion. We have found that in-vitro preparations of microtubules, an important element of the cellular skeleton, show this type of behaviour. The solutions self-organise and the morphology that arises depend upon the sample orientation, with respect to gravity, at a critical moment at an early stage in the development of the self-organised state. As predicted by theories of this type, no self-organisation occurs when the microtubules are assembled under low gravity conditions. At a molecular level this behaviour results from an interaction of gravity with macroscopic concentration and density fluctuations arising from processes of microtubule contraction and elongation. Numerical simulations of reaction and diffusion in a population of microtubules, leads to macroscopic self-organisation when a small effect somehow creates an asymmetry in the direction of microtubule growth. This can arise either by a force that slightly favours some microtubule orientations or by an asymmetry in molecular transport and diffusion such as may arise in the presence of gravity.

Apoptosis in liver disease

A variety of biological functions are regulated through extracellular signals. Amongst the best studied examples is growth control, which is achieved by the regulatory function of growth factors. In recent years it has become apparent that cell death (apoptosis) is controlled in a similar fashion.Apoptosis, firstly a morphologically defined process, is a highly controlled type of cell death that plays a critical role in embryonic development, deletion of autoreactive T-cells and adult tissue homoeostasis. There is increasing evidence that derangement of the apoptotic program is the underlying cause of a series of diseases including liver diseases. The deadly program can be initiated by ligand binding to membrane bound receptors such as CD95 (Fas), which is the most prominent cell death inducing member of the TNF receptor superfamily. The core of the subsequently activated intracellular machinery is formed by a set of proteases, namely caspases. Once activated, they orchestrate the complete destruction of the cellular skeleton leading to the typical apoptotic morphology. This review focuses on the underlying mechanism leading to derangement of the usually highly controlled apoptotic program in different liver diseases.

Characterizing “Blue Blobs”

To investigate the nature and origin of "blue blobs" (Bbs) in atrophic Pap smears in postmenopausal women and to study their clinical significance. A retrospective study of 412 atrophic Pap smears from postmenopausal women was done to detect the presence of Bbs. The smears from 24 cases showing Bbs were further studied to evaluate the nature of the Bbs with special stains, immunohistochemistry and electron microscopy. Bbs showed a heterogeneous morphology, with variable numbers and staining intensity. The diameter of Bbs was approximately equivalent to that of a parabasal/intermediate squamous cell. Special stains showed Bbs to be positive for periodic acid-Schiff and methyl green pyronin and negative for mucicarmine and calcium. Immunohistochemistry revealed Bbs to be positive for cytokeratin, epithelial membrane antigen and carcinoembryonic antigen and negative for vimentin and muscle-specific actin. Some Bbs had residual ghost nuclear shadows. Electron microscopy revealed cellular skeletons with residual tonofilaments enmeshed within a loose cytoskeleton matrix and nuclei with variable degrees of degeneration. Special stains, immunohistochemistry and electron microscopy indicated that Bbs represent parabasal/intermediate squamous cells exhibiting various degree of degeneration. In general, Bbs appear to be of no clinical significance except as a source of potential diagnostic error.

Effects of Melamine Particle Size on Flexible Polyurethane Foam Properties

The purpose of this paper is to elucidate the relationships between the size of the melamine particles dispersed and the foam properties such as hardness, tensile strength, resiliency, and flammability in the formulation of the flame retarded polyurethane high resilient molded foam. Fine melamine particles, ca. 5 Im in average, were compared with the generally-used large ones, ca. 60 ym in average, for their effects on the properties of the resultant foam. Conventionally-used ACTCOL MF-34M, a polyether-polyol dispersing large melamine particles, and specially-developed ACTOOL MF-34N, a polyether-polyol dispersing fine melamine particles, were employed in this study. The foam with the fine particles showed higher hardness, better tensile properties, and less flammability than that with the larger ones. The resiliency of the foam, however, was slightly low in the fine particle system compares to that in the large particle system. By optical microscopy, we found that the fine particles dispersed everywhere in the foam skeleton and that the large particles were located only in the strut joints because the particles are larger than the strut thickness. With an increase in melamine content, the cellular structure was unchanged in the fine particle system, but in the large particle system the struts became thin and the melamine-embedded joints became thick. The deforming ways of the cellular skeletons were also monitored by optical microscopy during the compression and the stretching of the foams. When the foam was compressed, every part of the skeleton deformed in the fine particle system, and the struts mainly deformed in the large particle system. When the foam was stretched, the struts oriented to the longitudinal direction in the fine particle system, and the melamine-embedded rigid joints inhibited the orientation of the struts in the large particle system. The differences in mechanical properties of the foams obtained were thought to depend on the ways the melamine particles disperse in the cell skeleton. As for the difference in the flammability, the location and the surface area of the particles would be the important factors. The results in this paper indicate that a flame retarded foam with better physical properties can be manufactured by a polyol including melamine particles smaller than the strut thickness of the resultant foam.

Morphologic Differences between Latent Membrane Protein-1 (LMP-1)-Positive and Negative Tumour Cells in Epstein-Barr Virus (EBV)-Related Childhood Hodgkin's Disease: A Morphometric Study

The values of five cellular morphometric parameters (longest and shortest cytoplasmic axis, cellular circumference, area and roundness coefficient) were compared between 20 Latent Membrane Protein 1 (LMP-1)-positive and an equal number of LMP-1-negative Reed-Sternberg and Hodgkin (HRS) cells for each of 13 cases of Hodgkin's disease (HD) occurring in children (aged 3-15 years); the presence of Epstein-Barr virus (EBV) encoded EBER mRNAs had previously been detected in all cases using RNA in situ hybridisation (RISH), while the presence of LMP-1 was immunohistochemically detected using the alkaline phosphatase-antialkaline phosphatase (APAAP) method. The longest and shortest axis, circumference and area were larger in LMP-1-positive than in LMP-1 negative HRS cells, while the roundness coefficient of LMP-positive HRS cells was smaller than that of LMP-1 negative cells. All differences were statistically highly significant when univariate (paired comparisons) t-test were used. Multivariate analysis (Hotelling's T2 test) showed all differences (except the roundness coefficient) to be significant both at the 5% and 1% level of significance. These results provide a numerical basis for the alteration brought by the expression of LMP-1 in the cellular skeleton of tumour (HRS) cells in EBV-related childhood HD cases.

Interaction of aggregated native and mutant IgE receptors with the cellular skeleton.

When aggregated, cell surface proteins become resistant to solubilization by detergents, presumably because of aggregation-induced or -stabilized interactions between the membrane protein and the cytoskeleton or plasma membrane skeleton. We genetically engineered variants of the tetrameric high-affinity receptor for IgE (Fc epsilon RI) to identify a site on its alpha, beta, or gamma chains that mediates such putative interactions. Using flow cytofluorometry, we studied rat basophilic leukemia cells, transiently transfected COS cells, and stably transfected P815 cells bearing wild-type and mutated receptors. We observed that (i) solubilization was markedly dependent on the degree of aggregation, the extent varying somewhat with the cell type and, particularly at lower levels of aggregation, with the time after addition of detergent; (ii) truncation of no single cytoplasmic domain of the alpha, beta, or gamma chains ablated the insolubilization effect; and (iii) incomplete receptors were also efficiently insolubilized by aggregation. Thus receptors consisting only of alpha and gamma chains, a "receptor" consisting of only the ectodomain of the alpha chain attached to the plasma membrane by a glycosyl-phosphatidyl inositol anchor, and "receptors" consisting only of minimally modified gamma chains were resistant to solubilization after aggregation. We conclude that no unique subunit or domain of Fc epsilon RI mediates the insolubilization phenomenon. Our results support a model in which the bridging of membrane proteins leads to their becoming nonspecifically enmeshed in a network of membrane skeletal proteins on either the outside and/or the inside of the membrane so that dissolution of the lipid bilayer becomes irrelevant.

The glial framework of central white matter tracts: Segmented rows of contiguous interfascicular oligodendrocytes and solitary astrocytes give rise to a continuous meshwork of transverse and longitudinal processes in the adult rat fimbria

The cellular skeleton of the adult rat fimbria consists of regularly spaced interfascicular glial rows of considerable length, running in the longitudinal (axonal) axis of the tract. Each row consists of a series of repeated segments made up of a stretch of interfascicular oligodendrocytes lying in direct contact with each other, and separated from the adjacent segments by usually solitary interfascicular astrocytes. A typical segment would be around 60 microns long, and have an axial core of about eight contiguous oligodendrocytes surrounded by a shell of about 1,200 axons, 70% of which are myelinated. In the transverse plane of the tract, adjacent segments are stacked together with a core-to-core distance of around 15 microns. The interfascicular oligodendrocytes have radial stem processes (in a plane transverse to the axonal axis) which give rise to the longitudinal myelinating (internodal) processes. Both transverse and longitudinal oligodendrocytic processes are longer than the dimensions of the segment (in which their cell bodies lie) and its axonal shell. They thus cooperate in myelinating axons of adjacent segments in both planes. The interfascicular astrocytes have three distinct types of processes: radial, longitudinal, and vascular (bearing end feet). The radial astrocytic processes are thick and tapering, and the processes of individual astrocytes extend transversely (in the plane of the original embryonic radial glial processes) for a total of at least 100 microns. The considerably more numerous longitudinal astrocytic processes arise from all parts of the cell bodies and radial processes. They are up to at least 30 microns long, thin, untapering, and largely unbranched, and are interdigitated among the fimbrial axons. In the radial plane, the astrocytic radial processes spread out through a wide swathe of adjacent segments, so that the integrated meshwork of interpenetrating longitudinal processes arising from overlapping radial processes of astrocytes from many different interfascicular rows provides a continuous longitudinal substrate for the fimbrial axons.

Cytoskeletal Protein Distributions in the Leading Edge of a Cell as an Indicator of Cell Contact Inhibition of Motility

The movement of cells is very important to many functions in the body. Cell motility is important to many vital functions of the body such as the repair of wounds, the development of the embryo during pregnancy, and the countering of diseases. When cell motility is uncontrolled it can contribute to the metastasis of tumor cells. Within the body of cells there are structural components that support and organize cell elements much like the skeleton supports the body. This cellular skeleton, or cytoskeleton, is made up of proteins that assemble into filamentous chains called microfilaments and microtubules. These filaments move and directionalize the cell mass. When two cells run into each other they stop all motile functions temporarily as a result of signalling between them. Then the cells change direction and move away from the contact site. This series of reactions is known as contact inhibition of motility. It is thought that cytoskeletal filaments are involved in this series of actions. To better comprehend the phenomenon of contact inhibition, cellular reactions were studied using cultured, fluorescence-tagged fibroblast cells. Cultures of these cells were observed using a high-powered microscope and time-lapse video recording.

Distribution of Cytoplasmic Microtubules in Migrating Corneal Epithelial Cells An Immunofluorescence Study

Microtubules constitute one of the three components of the cellular skeleton (cytoskeleton) and have been implicated in the control of cell polarity, shape, intracellular transport, directional cell motility, and mitosis. With specific antibodies against tubulin, the principal microtubular protein, the cytoplasmic distribution of microtubules was demonstrated in tissue-cultured rat corneal epithelium. This was compared with the distribution of actin, another component of the cytoskeleton. Microtubules are essential for the late phase of corneal epithelial wound healing, characterized mainly by cell mitosis. As yet, little is known about their function in the nonmitotic early phase of healing, but possibilities include the maintenance of cell shape and intracellular transport.

Effect of Heat Shock on the Intracellular Distribution of Proteins

Exposure of cells to heat induces thermotolerance, a transient resistance to subsequent heat challenges. It has been shown that thermotolerance is correlated in time with the enhanced synthesis of heat shock proteins. In this study, the association of induced heat shock proteins with various cellular fractions was investigated and the heat-induced changes in skeletal protein composition in thermotolerant and control cells was compared. All three major heat shock proteins induced in Chinese hamster fibroblasts after a 46 degrees C, 4-min heat treatment (70, 87, and 110 kDa) were purified with the cytoplasmic fraction, whereas only the 70-kDa protein was also found in other cell fractions, including that containing the cellular skeleton. Immediately after a second heat treatment at 45 degrees C for 45 min, the 110-kDa protein from thermotolerant cells also purified extensively with the cellular skeletal fraction. In this regard, the 110-kDa protein behaved similarly to many other cellular proteins, since we observed an overall temperature-dependent increase in the total labeled protein content of the high-salt-resistant cellular skeletal fraction after heat shock. Pulse-chase studies demonstrated that this increased protein content gradually returned to normal levels after a 3-hr incubation at 37 degrees C. The alteration or recovery kinetics of the total labeled protein content of the cellular skeletal fraction after heat shock did not correlate with the dramatic increase in survival observed in thermotolerant cells. The relationship between heat shock proteins and thermotolerance, therefore, does not correlate directly with changes in the heat-induced cellular alterations leading to differences in protein fractionation.

Preparation of nuclear matrices from cultured cells: subfractionation of nuclei in situ.

Analyses of the different structural systems of the nucleus and the proteins associated with them pose many problems. Because these systems are largely overlapping, in situ localization studies that preserve the in vivo location of proteins and cellular structures often are not satisfactory. In contrast, biochemical cell fractionation may provide artifactual results due to cross-contamination of extracts and structures. To overcome these problems, we have developed a method that combines biochemical cell fractionation and in situ localization and leads to the preparation of a residual cellular skeleton (nuclear matrix and cytoskeletal elements) from cultured cells. This method's main feature is that cell fractionation is performed in situ. Therefore, structures not solubilized in a particular extraction step remain attached to the substrate and retain their morphology. Before and after each extraction step they can be analyzed for the presence and location of the protein under study by using immunological or cytochemical techniques. Thereby the in vivo origin of a protein solubilized in a particular extraction step is determined. The solubilized protein then may be further characterized biochemically. In addition, to allow analyses of proteins associated with the residual cellular skeleton, we have developed conditions for its solubilization that do not interfere with enzymatic and immunological studies.

Locomotion and the phylogeny of the Metazoa

Abstract Among the lower Metazoa, the basic structure of the animals sets limits to the locomotory techniques available to them and to the habitats they can occupy. Small but critical structural changes overcome these limitations and once achieved they have resulted in major phyletic radiations. Small organisms up to 1–2 mm in length can, by ciliary action, swim, creep on the substratum or creep in it as a meiofauna. Once this size is much exceeded only creeping on the substratum is possible. The largest of the earliest Metazoa exceeded this limit and formed the basis of an important radiation of surface creeping forms including Turbellaria, Nemertea and Mollusca, the larger members of which supplement or replace ciliary locomotion by muscular activity. A cellular hydrostatic skeleton permits reversible changes of shape produced by contraction of the body-wall muscles in small organisms, but with increasing size, particularly as structural elements are developed to conserve the shape of the animal, such a...

Cellular Skeletons and RNA Messages

This chapter presents the experimental results that suggest an interrelation between cellular topology and nucleic acid metabolism. Gentle lysis of HeLa cells with a nonionic detergent reveals an elaborate remnant structure that retains much of the cellular morphology. Electron micrographs and biochemical studies show that a majority of the protein synthetic apparatus remains affixed to this “cytoskeleton.” It discusses that the skeleton structure possibly plays an important role in cytoplasmic RNA metabolism. Two of the small RNA species found in mammalian cells, ScK and ScL, are intimately associated with the cytoskeleton, and ScL is, in part, associated with membranes. The function of these molecules is unknown, but there is the possibility that they serve a structural role and may help determine the architecture of the cytoskeleton. If so, then RNA metabolism could play a direct role in determining cellular topology. The nucleus also has a “skeletal” structure, although much less can be visualized in this case. Many of the small RNA species are found localized in this nuclear skeleton, suggesting that they also may play a role in either structure or function determination. The chapter reviews that the experiments indicates an aspect of the metazoan cell with no obvious counterpart in bacteria—that is, an interrelation between spatial organization and RNA metabolism.

Colchicine-Sensitive Microtubules

Publisher Summary Colchicine and several other compounds are fine tools for analyzing the assembly of a microtubule protein into tubules. Microtubules underlie the development of asymmetric cell shapes. Slow morphogenetic movements involving microtubule polymerization tend to be colchicine sensitive. Microtubules may be considered cellular skeletons, especially with respect to the development of a new form, but they may also be intimately involved in other complex functions of eukaryotic cells. The assembly of a microtubule protein into mitotic spindle microtubules may account directly for the generation of force in mitosis. In addition, conformational changes in microtubule protein may account for the chemosensitivity of the nervous system of higher animals. The interactions of tubulin proteins with small molecules explain the processes of touch, hearing, olfaction, chemotaxis, and generation of action potentials.

A Permian Hydrozoan Mound, Yukon Territory

A carbonate mound built by the hydrozoan Palaeoaplysina has been found in a poorly-exposed sequence of Lower Permian rocks in the northern Richardson Mountains of the Yukon Territory. Similar hydrozoan mounds have been described from Russia and northwestern United States. The Yukon mound is 12 ft (3.7 m) thick and at least 70 ft (21 m) long. It is underlain by marine siltstones and sandstones, and probably shale. The main mound rock is composed of curved hydrozoan plates enclosed in a bioclastic wackestone matrix, and is overlain successively by tubular–foram packstone and oolitic grainstone. Palaeoaplysina is characterized by a plate-like, laterally-expanding growth form, an internal canal system, a cellular calcareous skeleton, and 'mamelons' on the upper surface of well-preserved plates; 'mamelons' are the principal criterion for placing Palaeoaplysina in the Class Hydrozoa of the coelenterates.The Yukon mound is part of a thick sequence of Lower Permian terrigenous clastic and carbonate rocks deposited on the northern shelf of the ancestral Aklavik Arch. The repetition of similar rock types in the sequence indicates cyclicity, a thesis supported by similarities between the Yukon mound sequence and the Virgilian mound cycles in New Mexico.Lower Permian hydrozoan mounds and associated facies in the Pre-urals of Russia are known oil producers. The possibility exists that hydrozoan mounds, perhaps in multiple cyclic build-ups, may occur in upper Paleozoic rocks in the subsurface of the Yukon Territory. With suitable porosity development and source rocks, these predicted subsurface mounds could become hydrocarbon reservoirs and thus targets for oil exploration.