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At least 1,369 records · Page 76Linked to original sources
PubMed2003

Adhesion dynamics and cytoskeletal structure of gliding human fibrosarcoma cells: a hypothetical model of cell migration.

During motility of fibroblast type cells on planar surfaces, adhesions are formed at the anterior of the protruding lamella, which remain stationary relative to the substrate and undergo a maturation process as the cell passes over them. Through these adhesions force is exerted, the orientation of which is parallel to the direction of the movement. Here we show that, during gliding-type motility of human tumor cells, characterized by a semicircular shape, adhesions were found at the outer rim of the cells, along the semicircle. Time-lapse microscopy of GFP-vinculin-expressing cells showed that these adhesions were constantly renewed at the cell edge and followed a curved trajectory according to the graded radial extension model. Eventually, the adhesions reached the long axis of the cell where they were retracted into the cell body. Actin cables formed arcs, with the concave face at the anterior of the lamella found to be oriented in the direction of movement. Since adhesions moved backward with respect to the cell, actin cables connected to these adhesions must continuously grow, reaching maximal size at the long axis of the cell. Contraction of the arcs is responsible for the forward movement of the cell body.

Cell Adhesion↗
PubMed1985

Rous sarcoma virus-transformed fibroblasts adhere primarily at discrete protrusions of the ventral membrane called podosomes.

Rous sarcoma virus-transformed BHK cells (RSV/B4-BHK) adhere to a fibronectin-coated substratum primarily at specific dot-shaped sites. Such sites contain actin and vinculin and represent close contacts with the substratum as revealed by interference reflection microscopy. Only a few adhesion plaques and actin filament bundles can be detected in these cells as compared to untransformed parental fibroblasts. In thin sections examined with transmission electron microscopy (TEM) these adhesion sites correspond to short protrusions of the ventral cell surface that contact the substratum at their apical portion. These structures, which may represent cellular feet, are therefore called podosomes. By screening a number of different transformed fibroblasts plated on a fibronectin-coated substratum we find that podosomes are common to mammalian and avian cell lines transformed either by Rous sarcoma virus (RSV) or by Fujinami avian sarcoma virus (FSV), whose oncogenes encode specific tyrosine kinases. Using antibodies reacting with phosphotyrosine in immunofluorescence experiments, we show that phosphotyrosine-containing molecules are concentrated in podosomes. Podosomes are not detected in fibroblasts transformed by other retroviruses (Snyder-Theilen sarcoma virus, Abelson leukemia virus and Kirsten sarcoma virus) or by DNA tumor viruses (polyoma, SV40), indicating that podosome-mediated adhesion in transformed fibroblasts is related to the peculiar properties of some oncoproteins and possibly to their tropism for adhesion systems. Podosomes and adhesion plaques, although similar in cytoskeletal protein composition, have different mechanisms and kinetics of formation. Assembly of podosomes, in fact (i) does not require fetal calf serum (FCS) in the adhesion medium, that is necessary for the organization of adhesion plaques; (ii) does not require protein synthesis; and (iii) is insensitive to the ionophore monensin, that prevents adhesion plaque formation. Moreover, during attachment to fibronectin-coated dishes, podosomes appear in the initial phase (60 min) of attachment, while adhesion plaques require a minimum of 180 min. In conclusion podosomes of RSV- and FSV-transformed fibroblasts represent a phenotypic variant of adhesion structures.

Actins↗
PubMed2003

Noninvasive measurement of viscosity from damping of capillary waves.

Capillary waves are surface waves on fluids with wavelengths in the millimeter range. The determination of viscosity from the damping of capillary waves is of great practical importance as it affords the possibility of measuring the viscosity of fluids noninvasively. In this paper a noncontact method for generation and detection of capillary waves on fluid is described. A miniature laser interferometer is employed to measure noninvasively the wave amplitude and its attenuation with a resolution of about 10 nm. As a test case, the attenuation data for capillary waves on pure water are used to obtain the kinematic viscosity of water as a function of temperature. The results compare favorably with the most reliable published data on the subject.

Capillary Action↗
PubMed2001

The life cycle of Trypanosoma cruzi revisited.

The basic features of the life cycle of Trypanosoma cruzi have been known for nearly a century. Various aspects of the life cycle, however, have been elucidated only recently, whilst others remain either controversial or unstudied. Here, we present a revised life cycle influenced by recent findings and specific questions that remain unresolved.

Animals↗
PubMed2001

Complete development and long-term maintenance of Cryptosporidium parvum human and cattle genotypes in cell culture.

This study describes the complete development (from sporozoites to sporulated oocysts) of Cryptosporidium parvum (human and cattle genotypes) in the HCT-8 cell line. Furthermore, for the first time the complete life cycle was perpetuated in vitro for up to 25 days by subculturing. The long-term maintenance of the developmental cycle of the parasite in vitro appeared to be due to the initiation of the auto-reinfection cycle of C. parvum. This auto-reinfection is characterised by the production and excystation of new invasive sporozoites from thin-walled oocysts, with subsequent maintenance of the complete life cycle in vitro. In addition, thin-walled oocysts of the cattle genotype were infective for ARC/Swiss mice but similar oocysts of the human genotype were not. This culture system will provide a model for propagation of the complete life cycle of C. parvum in vitro.

Animals↗
PubMed2003

Elasticity of alveolar bone near dental implant-bone interfaces after one month's healing.

Information is scarce about Young's modulus of healing bone surrounding an implant. The purpose of this preliminary study is to quantify elastic properties of pig alveolar bone that has healed for 1 month around titanium threaded dental implants, using the nanoindentation method. Two 2-year-old Sinclair miniswine were used for the study. Nanoindentation tests perpendicular to the bucco-lingual cross section were performed on harvested implant-bone blocks using the Hysitron TriboScope III. Nomarski differential interference contrast microscopy was used to identify pyramidal indentation measurements that were from bone. Reduced moduli, averaged for all anatomical regions, were found to start low (6.17 GPa) at the interface and gradually increase (slope=0.014) to a distance of 150 microm (7.89 GPa) from the implant surface, and then flatten to a slope of 0.001 from 150 to 1500 microm (10.13 GPa). Mean reduced modulus and its relationship to distance did not differ significantly by anatomic location (e.g., coronal, middle, and apical third; P>/=0.28 for all relevant tests) at 1 month after implantation.

Alveolar Bone Loss↗
PubMed1998

Development and validation of a nanometer manipulation and measurement system for biomechanical testing of single macro-molecules.

A biomechanical testing system for single macro-molecules has been developed using optical tweezers. To achieve nanometer manipulation and measurement, a piezo-stage and an interferometer were adopted. A systematic calibration was then performed on the displacement resolution. The piezo-stage has a noise level around 1 nm standard deviation, and the interferometer has a noise level of less than 5 nm standard deviation. The results revealed that the system has a nanometer resolution which is sufficient for the measurement of deformation and stiffness of single macro-molecules.

Biomechanical Phenomena↗
PubMed2003

A simple method for enriching populations of transfected CHO cells for cells of higher specific productivity.

To establish a simple and rapid method for the screening of stable recombinant Chinese hamster ovary (CHO) cell lines, we have developed a cell surface labeling technique using fluorescently tagged antibodies that bind to secreted target proteins at low temperature. Using fluorescence intensity as the sole criterion for selection of cells, we are able to enrich populations of highly productive cells using preparative flow cytometry sorting. Reiterative sorting based on selection of cells having the highest fluorescence intensity of cell surface labeled protein results in dramatic increases in specific cellular productivity. Using lymphotoxin-beta receptor IgG fusion protein as a model system, we have demonstrated a greater than 20-fold increase in specific productivity (0.49-11.5 pg cell(-1) day(-1)) (pcd) without the use of methotrexate (MTX)-mediated selection or amplification. In addition, the flow cytometry used to enrich for and clone high producer cell lines has reduced development time by more than 50% and the number of screening assays by more than 10-fold. When a transfected population of CHO cells expressing a humanized version of the murine monoclonal antibody (mAb) AQC2 directed against human alpha 1 beta 1 integrin was subjected to the same treatment, a 25-fold improvement in specific productivity (0.3-8.0 pcd) was observed. Furthermore, similar application of this technique to MTX-amplified clones resulted in up to 120-fold overall improvement in specific productivity (up to 42 pcd). Greater than 20 examples are also presented to demonstrate the robustness and performance of this technique.

Animals↗
PubMed1998

Morphological and electrical characteristics of postnatal hippocampal neurons in culture: the presence of bicuculline- and strychnine-sensitive IPSPs.

A modified method was developed for tissue-culturing postnatal hippocampal neurons using simple mechanical trituration for cell isolation and not including any hydrolysing enzymes, nerve growth factors or antiproliferating agents. The morphological properties of such neurons were characterized with light and interference polarizing microscopy, which revealed the appearance of growth cones from peripheral neurons and the presence of different types of neurons, including bipolar, stellate and pyramidal-like cells (i.e., pyramidal and dentate gyrus granule cells), which could be related to their putative counterparts in intact brain. The whole-cell configuration of the patch-clamp method was used for electrophysiological recordings of inhibitory synapses between these dissociated cultured neurons from the early postnatal rat hippocampus. This study indicated the presence of tetrodotoxin (TTX)-sensitive and TTX-resistant inhibitory postsynaptic potential (IPSPs) and inhibitory postsynaptic currents (IPSCs) in current-clamp and voltage clamp modes respectively. The coincident reversal potentials for IPSCs and for GABAA and glycine-evoked currents, and the sensitivity of the IPSCs to bicuculline or strychnine, indicated that these IPSCs were Cl-(-)dependent and mediated by either GABAA or glycine receptors. Inhibitory postsynaptic currents recorded under voltage-clamp conditions decayed with a time course that could be fitted by a single exponential with a value of 26 ms. An average quantal content of 2.5 was responsible for a typical GABA and glycine-activated IPSC and a single quantum for GABAergic input was inferred to activate about 160, and for glycinergic, about 200 Cl-, channels.

Action Potentials↗
PubMed2000

Analysis of programmed cell death in the nematode Caenorhabditis elegans.

The nematode Caenorhabditis elegans has been shown to be an excellent model organism with which to study the mechanisms of programmed cell death because of its powerful genetics and the ability to study cell death with single-cell resolution. In this chapter, we describe methods that are commonly used to examine various aspects of programmed cell death in C. elegans. These methods, in combination with genetic analyses, have helped identify and characterize many components of the C. elegans cell death pathway, illuminating the mechanisms by which these components affect programmed cell death.

Animals↗