Development Of Protrusions Research Articles

Cytoskeletal self-organization in neuromorphogenesis.

Self-organization of dynamic microtubules via interactions with associated motors plays a critical role in spindle formation. The microtubule-based mechanisms underlying other aspects of cellular morphogenesis, such as the formation and development of protrusions from neuronal cells is less well understood. In a recent study, we investigated the molecular mechanism that underlies the massive reorganization of microtubules induced in non-neuronal cells by expression of the neuronal microtubule stabilizer MAP2c. In that study we directly observed cortical dynein complexes and how they affect the dynamic behavior of motile microtubules in living cells. We found that stationary dynein complexes transiently associate with motile microtubules near the cell cortex and that their rapid turnover facilitates efficient microtubule transport. Here, we discuss our findings in the larger context of cellular morphogenesis with specific focus on self-organizing principles from which cellular shape patterns such as the thin protrusions of neurons can emerge.

A New Mechanism for Pillar Formation during Tumor-Induced Intussusceptive Angiogenesis: Inverse Sprouting

One of the hallmarks of intussusceptive angiogenesis is the development of intraluminal connective tissue pillars. The exact mechanism of pillar formation has not yet been elucidated. By using electron and confocal microscopy, we observed intraluminal nascent pillars that contain a collagen bundle covered by endothelial cells (ECs) in the vasculature of experimental tumors. We proposed a new mechanism for the development of these pillars. First, intraluminal endothelial bridges are formed. Second, localized dissolution of the basement membrane occurs and a bridging EC attaches to a collagen bundle in the underlying connective tissue. A pulling force is then exerted by the actin cytoskeleton of the ECs via specific attachment points, which contain vinculin, to the collagen bundle, resulting in suction and subsequent transport of the collagen bundle into and through the vessel lumen. Third, the pillar matures through the immigration of connective tissue cells and the deposition of new collagenous connective tissue. The proposed simple mechanism generates a connection between the processes of endothelial bridging and intussusceptive angiogenesis and identifies the source of the force behind pillar formation. Moreover, it ensures the rapid formation of pillars from pre-existing building blocks and the maintenance of EC polarity. To describe it, we coined the term inverse sprouting.

On the Microstructure of the Initial Oxide Grown by Controlled Annealing and Oxidation on a NiCoCrAlY Bond Coating

Different pre-annealing and pre-oxidation treatments were conducted on a dual phase γ+β Ni–21Co–18Cr–22Al–0.2Y (at.%) bond coating for 1 hr at 1373 K (i) with or without a native oxide upon heating, (ii) in two different atmospheres upon heating, and (iii) under various oxygen partial pressures (pO2) in the range of 0.1–105 Pa during oxidation. The chemical composition, structure, morphology and phase constitution of the resulting oxide layers were investigated using a range of analytical techniques. It is found that the exclusive formation of a continuous α-Al2O3 layer without the simultaneous formation of NiAl2O4 spinel was promoted for oxidation at low pO2. The formation of metastable θ-Al2O3 was suppressed for a low fraction of the β phase, coupled with a high fraction of segregated Y at the initial bond coat surface. Initial Y segregation and incorporation of Y2O3 and Y3Al5O12 within the developing oxide layer was promoted in the absence of a native oxide and for heating in an inert atmosphere. The development of protrusions (i.e. pegs) at the oxide/coating interface, as a result of the incorporation of internal Y2O3 precipitates by the inward growing oxide layer, was most pronounced upon heating in an inert atmosphere, followed by oxidation at an intermediate pO2.

Influence of the Adsorption of N Species on the Anodic Dissolution of Ni

The dissolution and passivation of Ni in nitrite-containing acid solutions are investigated by Auger spectroscopy, atomic force microscopy, and conventional electrochemical techniques. The dissolution/ passivation of the Ni surface is consistent with a competition between adsorbed OH- and nitrogen-containing species with a potential-dependent surface coverage. Nitrogen-containing species hinder the passivation of the Ni surface, shifting the formation of the complex nickel hydroxide/oxide film to more positive potential values. The dynamics of the dissolving interface, followed by atomic force microscopy, reflect first the competition of adsorbed species, leading to the development of protrusions and cavities, and finally the formation of the passive film that promotes surface smoothening by a preferential dissolution of the protrusion tips under ohmic control.

Interface dynamics for copper electrodeposition: the role of organic additives in the growth mode.

An atomistic model for Cu electrodeposition under nonequilibrium conditions is presented. Cu electrodeposition takes place with a height-dependent deposition rate that accounts for fluctuations in the local Cu2+ ions concentration at the interface, followed by surface diffusion. This model leads to an unstable interface with the development of protrusions and grooves. Subsequently the model is extended to account for the presence of organic additives, which compete with Cu2+ for adsorption at protrusions, leading to a stable interface with scaling exponents consistent with those of the Edwards-Wilkinson equation. The model reproduces the interface evolution experimentally observed for Cu electrodeposition in the absence and in the presence of organic additives.

Protrusive growth from giant liposomes driven by actin polymerization.

Development of protrusions in the cell is indispensable in the process of cell motility. Membrane protrusion has long been suggested to occur as a result of actin polymerization immediately beneath the cell membrane at the leading edge, but elucidation of the mechanism is insufficient because of the complexity of the cell. To study the mechanism, we prepared giant liposomes containing monomeric actin (100 or 200 microM) and introduced KCl into individual liposomes by an electroporation technique. On the electroporation, the giant liposomes deformed. Most importantly, protrusive structure grew from the liposomes containing 200 microM actin at rates (ranging from 0.3 to 0.7 micrometer/s) similar to those obtained in the cell. The deformation occurred in a time range (30 approximately 100 s) similar to that of actin polymerization monitored in a cuvette (ca. 50 s). Concomitant with deformation, Brownian motion of micron-sized particles entrapped in the liposomes almost ceased. From these observations, we conclude that actin polymerization in the liposomes caused the protrusive formation.

Etching behavior ofSi(001)−2×1studied with optical anisotropy

Etching of single-domain $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1$ by 800-eV ${\mathrm{Ar}}^{+}$ ions has been studied using surface-induced optical-anisotropy measurements in the temperature range from 293 to 870 K. At 293 K, the surface area which is distorted by one impinging ion is determined to be $3.9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}{\mathrm{cm}}^{2},$ and at this temperature no annealing was observed. With increasing temperatures the etch behavior gradually changes from mere roughening to a situation where ion-induced surface damage is restored. At 670 K and ${10}^{11}{\mathrm{ions}\mathrm{}\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}{\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ no ion-induced changes in the optical anisotropy could be observed, and hence ${D}_{B}$ step etching occurs. During ion bombardment at higher temperatures we observed the development of protrusions on the surface with facets in the ${11l}$ directions. Protrusions were also found during etching by ${\mathrm{O}}_{2}$ at 1020 K, and their development is attributed to pinning at residual contaminations. Formation of protrusions during sample cleaning may be responsible for the large scatter in reported optical-anisotropy data of clean single-domain $\mathrm{Si}(001)\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}1.$ This illustrates the importance of a well-controlled sample preparation procedure.

Histological changes in aging lumbar intervertebral discs. Their role in protrusions and prolapses.

To study the relationships between the changes due to aging in lumbar intervertebral discs and the development of protrusion or prolapse, we carried out histological studies on operative specimens of thirty-one discs, of which twenty-two had been protruded and nine, prolapsed. The specimens were obtained during twenty-nine operations for herniation of a lumbar intervertebral disc in patients who were sixty years old or older. Changes in the anulus fibrosus were more extensive in the nine prolapsed discs than in the twenty-two protruded discs. Of the nine prolapsed discs, myxomatous degeneration, fibrosis, and swollen anular fibers were found in all nine, and cysts were seen in five. Of the twenty-two protruded discs, only five showed myxomatous degeneration; ten, fibrosis; one, a cyst; and sixteen, swollen fibers. For comparison, we also studied specimens that had been obtained at operation from twenty-one other patients, twenty to fifty-nine years old, who had a prolapsed disc. The anulus showed myxomatous degeneration in all twenty-one specimens, cysts in eight, and fibrosis in ten. In addition, we examined 368 autopsy specimens from people who had been between twenty-five and eighty-five years old at the time of death. In many of the subjects who had died in the sixth decade of life or later, we found that the orientation of the inner fiber bundles of the anulus fibrosus was reversed, so that they bulged inward. The reversal appeared to be the result of myxomatous degeneration of the middle fibers of the anulus, atrophy of the nucleus, and narrowing of the disc space. These histological findings suggest explanations for the predominance of protrusions of the nucleus pulposus in patients who are less than sixty years old and of prolapse of the anulus fibrosus in the few patients who are more than sixty years old who have herniation of an intervertebral disc.

A study on budding protrusions of human seminiferous tubules.

In order to elucidate the morphogenesis of seminiferous tubular protrusions, histometric, microscopic and electron microscopic studies were performed on the testes of 202 Japanese men, including 117 sudden deaths, 75 hospital deaths and 10 prostatic cancer cases. Protrusions usually occurred at outer convexes of multi-bending tubular portions and were divided into dome, sessile, pedunculated and multi-branched types. Aggregated Sertoli cells were present in dome-type protrusions as a major component, and spermatogenesis associated with active mitoses of spermatogonia was induced with development of protrusions. Protruding walls consisted of inner compact and outer loose layers. Distribution of lipid droplets in Sertoli cell cytoplasm in protrusions was different from those in the original tubules. The incidence of protrusions peaked in the forties and sixties, respectively, in the case of hospital and sudden death cases with underlying tubular atrophy. The findings suggest that tubular protrusions take place as a compensatory reaction for declining spermatogenesis, and therefore, probably represent a regenerative phenomenon in hypospermatogenic testes.

The risk of acetabular protrusion following prosthetic replacement of the femoral head.

A total of 24 patients treated with hemiarthroplasty showed a crude frequency of acetabular protrusion of 26 per cent. Two factors were associated with the development of protrusion: the length of the follow-up period and previous hip operation. The frequency of protrusion was estimated using logistic regression techniques based on information concerning the age of the patients, the length of the follow-up period and any previous hip operation. The frequency ranged from 4.8 per cent for a patient of 75 years or under, with a follow-up period of less than 12 months and no previous hip operation, to 61 per cent for patients of over 75 years, with a follow-up period exceeding 12 months, and a previous hip operation. Patients of over 75 years were 1.7 times more likely to develop protrusion than younger patients, patients previously operated on were 2.3 times more likely to develop protrusion than those not operated on previously, and patients with a follow-up time period exceeding 12 months were 7.9 times more likely to develop protrusion than patients with a shorter follow-up time.

Affinity labels for membrane components involved in the uptake of bile acids and of phallotoxins by hepatocytes. Development of covalently binding derivatives of bile acids and of compounds related to cholecystographic agents.

A series of covalently binding derivatives of bile acids, fusidic acid and of compounds similar to cholecystographic agents were synthesized. Nearly all of them inhibited the development of protrusions on the surface of isolated hepatocytes regularly seen after treatment with phalloidin. The same compounds inhibited the uptake of demethylphalloin and of cholate in a concentration dependent manner. Two kinds of effects could be distinguished: The irreversible part of the inhibition depended on the incubation period and could not be removed by washing procedures. The reversible one was independent on the duration of the preincubation. Final results indicated that the tested derivatives inhibited either both transports, and the phalloidin response of liver cells to the same degree and in the same manner, or were found to be ineffective in all tests. The above parallelism supports the hypothesis that phallotoxins may be translocated by a carrier system normally responsible for the uptake of bile acids from the portal blood.

Acetabular protrusion following endoprosthetic hip surgery: a multifactorial study.

Acetabular protrusion was found in 56 out of 211 patients fitted with a hemiprosthesis. The indication for operation was acute femoral neck fracture or failure following a previous internal fixation. A number of radiological variables were analysed with respect to their possible association with preoperative, operative and follow-up variables. After a preliminary screening of variables a deeper analysis was performed by fitting log-linear models to the data. Our analysis showed that the development of protrusion has a significant association with follow-up time. A previous hip operation was also significantly associated with the development of protrusion. This may be an indication for total hip replacement in some patients who now receive a hemiprosthesis as a secondary operation. Acetabular protrusion was significantly associated with the development of postoperative pain, while the other clinical symptoms and signs lacked any direct association with protrusion. Although acetabular protrusion and loosening of the prosthetic stem showed a significant association the analysis indicated that pain was primarily due to protrusion.

Trypsin protection of hepatocytes against phalloidin.

The most typical effect of phalloidin in vitro is the development of protrusions on the surface of hepatocytes within 10–20 min. This mode of cell deformation corresponds to the invaginations of the plasma membrane with subsequent vacuolization, seen in whole livers during phalloidin poisoning. Low concentrations of trypsin delay or prevent this typical response of hepatocytes to phalloidin in a dose dependent manner. The protective effect of trypsin depends on the concentrations of the enzyme and of the toxin, but not markedly on the duration of the preincubation with the enzyme.

Avian viruses in adult cells in vitro A comparison of fowlpox, bronchitis, laryngotracheitis, and newcastle disease viruses in tissue cultures of embryonic and adult fowl cells

Tissue culture techniques have been used to compare the susceptibility of normal adult fowl fibroblasts and epithelial cells and embryonic fowl fibroblasts to three strains of Newcastle disease virus (NDV) (one virulent, two avirulent), fowlpox (FP) virus, infectious bronchitis (IB) virus, and infectious laryngotracheitis (ILT) virus. All strains of virus studied were able to multiply in adult epithelial cells; only IB and ILT viruses were not shown to multiply in adult fibroblasts. Embryonic fibroblasts supported the multiplication of all the viruses except IB, which could be recovered only from the first passage in vitro. A characteristic cytopathic effect (CPE) was seen in adult epithelial cells infected with each of the virus types studied (except IB virus). In the case of NDV this consisted in the formation of inclusion bodies in the cytoplasm and syncytia; with FP virus, rounding of cells, cytoplasmic eosinophilia, and development of protrusions on the cell were observed; and with ILT virus nuclear inclusion bodies were formed, with or without concomitant syncytia. In adult and embryonic fibroblasts similar cytopathic effects were observed, but they were not always so extensive. In infected organ cultures of embryonic fowl trachea the effects of virus action on the tissues resembled those seen in infected chorioallantoic membranes or in infected fowls in vivo. The effects on individual cells were of a similar kind to those found in monolayer cultures.