ISSN:1059-910X    

DOI:10.1002/jemt.1070280502

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe cytoskeleton of chondrocytes consists of microfilaments made of actin, microtubules made of tubulin, and intermediate filaments made of a variety of subunits. Actin filaments are not prominent in vivo but may form in vitro. In culture, changes in filament polymerisation are important in determining cell shape, initiating chondrogenesis, and maintaining the chondrogenic phenotype. Microtubules, besides their role in cell division, organise the distribution of organelles and are involved in secretory transport mechanisms in collagen and proteoglycan synthesis. A variety of intermediate filaments may be present, frequently forming large whorled aggregates. The filaments include vimentin, cytokeratins, and glial fibrillary acidic protein. These may occur at different depths in articular cartilage. Vimentin accumulates during development of some fibrocartilages with increased mechanical loading. Together with other elements of the cytoskeleton, intermediate filaments could form part of a mechanotransduction system by which cells respond to external forces and sense changes in their external environment. © 1994 Wiley‐Liss, I

ISSN:1059-910X    

DOI:10.1002/jemt.1070280503

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractCollagens are the major proteinaceous constituents of cartilage. Three collagen types participate in the formation of striated fibrils of cartilage, collagens II, IX, and XI. Collagen II and XI belong to the subgroup of fibrillar collagens and are structurally closely related, differing mainly in their N‐propeptides. Collagen IX has a very different structure but is nevertheless an essential constituent of the striated fibrils. Two other collagen types are also found in cartilage but form distinct structures. Collagen VI, found mainly in the periphery of the chondrocytes, forms beaded filaments. These filaments are probably formed by interaction of collagen VI with hyaluronan. Collagen X is expressed by hypertrophic chondrocytes. It has been shown to form in vitro hexagonal lattices and in vivo to be associated either with striated fibrils or with mats which may correspond to the lattices. The functional role of the collagen diversity in cartilage is discussed. © 1994 Wiley‐Liss,

ISSN:1059-910X    

DOI:10.1002/jemt.1070280504

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractHyaline cartilage contains five well‐characterized proteoglycans in its extracellular matrix, and it is likely that others exist. The largest in size and most abundant by weight is aggrecan, a proteoglycan that possesses over 100 chondroitin sulfate and keratan sulfate chains. Aggrecan is also characterized by its ability to interact with hyaluronic acid to form large proteoglycan aggregates. Both the high anionic charge on the individual aggrecan molecules endowed by the sulfated glycosaminoglycan chains and the localization within the matrix endowed by aggregate formation are essential for aggrecan function. The molecule provides cartilage with its osmotic properties, which give articular cartilage its ability to resist compressive loads. The other proteoglycans are characterized by their ability to interact with collagen. They are much smaller than aggrecan in size but may be present in similar molar amounts. Decorin, biglycan, and fibromodulin are closely related in protein structure but differ in glycosaminoglycan composition and function. Decorin and biglycan possess one and two dermatan sulfate chains, respectively, whereas fibromodulin bears several keratan sulfate chains. Decorin and fibromodulin both interact with the type II collagen fibrils in the matrix and may play a role in fibrillogenesis and interfibril interactions. Biglycan is preferentially localized in the pericellular matrix, where it may interact with type VI collagen. Finally, type IX collagen can also be considered as a proteoglycan, as its α2(IX) chain may bear a glycosaminoglycan chain. It may serve as a bridge between the collagen fibrils or with the interspersed aggrecan network. © 1994 Wiley‐Liss

ISSN:1059-910X    

DOI:10.1002/jemt.1070280505

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractBiochemical and biophysical studies have shown that the composition and sedimentation velocity of cartilage proteoglycans change with age, but these investigations cannot demonstrate the alterations in molecular structure responsible for these changes. Development of quantitative electron microscopic methods has made it possible to define the age‐related structural changes in aggregating proteoglycans and to correlate the alterations in their structure with changes in tissue composition and morphology. Electron microscopic measurement of human and animal hyaline cartilage proteoglycans has shown that with increasing age the length of the chondroitin sulfate–rich region of aggregating proteoglycan monomers (aggrecan molecules) decreases, the variability in aggrecan length increases, the density of aggrecan keratan sulfate chains increases, the number of monomers per aggregate decreases, and the proportion of monomers that aggregate declines. Proteoglycans from the nucleus pulposus of the intervertebral disc show similar but more dramatic age‐related alterations. At birth, nucleus pulposus aggrecan molecules are smaller and more variable in length than those found in articular cartilage. Within the first year of human life, the populations of aggregates and large aggrecan molecules analogous to those found in articular cartilage decline until few if any of these molecules remain in the central disc tissues of skeletally mature individuals. The mechanisms of the age‐related changes in cartilage proteoglycans have not been fully explained, but measurement of proteoglycans synthesized by chondrocytes of different ages suggests that alterations in synthesis produce at least some of the age‐related changes in aggrecan molecules. Degradation of aggrecan chondroitin sulfate–rich regions in the matrix probably also contributes to the structural changes seen by electron microscopy. Age‐related changes in proteoglycan aggregation may be due to alterations in link protein function or inhibition of aggregation of newly synthesized aggrecan molecules by accumulation of degraded aggrecan molecules. © 1994 W

ISSN:1059-910X    

DOI:10.1002/jemt.1070280506

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe epiphyseal growth plate and articular cartilage matrices were preserved by slam freezing and freeze substitution to optimally retain the native organization for both cellular and matrix components. These specimens were stained and examined using conventional electron microscopic methods. The highly integrated, proteoglycan‐rich matrices were examined by computer image analysis using such parameters as distribution, connectivity, orientation, and a variety of morphometric analyses. Also, different aspects of electron tomography and 3D rendering of matrix vesicles and their associated mineral deposits from epiphyseal growth plates and turkey leg tendons are presented. © 1994 Wiley‐Liss,

ISSN:1059-910X    

DOI:10.1002/jemt.1070280507

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractTechniques are described for the extraction onto carbon replicas of precipitates and inclusions from Mg and Al‐based alloys for analytical transmission electron microscopy. EDX analysis of Mn precipitates from a MG‐Mn alloy illustrates the problems that can arise from spurious X‐rays, caused by the use of a 3mm disc specimen. Published 1994 Wiley‐Li

ISSN:1059-910X    

DOI:10.1002/jemt.1070280508

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractHigh‐angle annular dark‐field or Z‐contrast microscopy was used to demonstrate that well dispersed metal supported catalysts consist of nanometer sized clusters. Depending upon the impregnated metal, different cluster sizes were observed. Grouping of Pd clusters could also be confirmed by analytical electron microscopy. © 1994 Wiley‐L

ISSN:1059-910X    

DOI:10.1002/jemt.1070280509

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe ultrastructural features of AA‐2 cells infected with either of two strains of simian immunodeficiency virus (SIVMne‐E11Sor SIVSMM‐PBj) were examined by scanning electron microscopy (SEM). Transformed CD4+ human B lymphocytes (AA‐2) were inoculated with SIV and observed at 2, 4, and 7 days post‐inoculation (dPI). Infected AA‐2 cells were distinguished by the progressive loss of microvilli, and variable numbers of free or protruding spherical particles measuring 90–120nm in diameter along the cell surface. Syncytial cell formation (complexes of fused cells) and necrotic cells were evident at each time point with the most numerous observations at 7 dPI. While the distribution and severity of the viral induced changes increased with time and affected virtually all cells by 7 dPI, the alterations were detected sooner and were more pronounced in SIVSMM‐PBjinfected cells. This finding is consistent with the in vivo data from primate studies using the same strains of SIV. Syncytial cells exhibited slight to moderate indentations which appeared to coincide with the boundaries of individual cells forming the complex. The plasma membrane of syncytial cells was relatively smooth and lacked microvilli. Spherical particles and buds protruding from the plasma membrane were predominate features of syncytial cell surfaces. By the employment of antisera generated against whole SIVMne‐E11S,both transmission and scanning immunoelectron microscopy confirmed the identity of the spherical structures as free and budding SIV virions. © 19

ISSN:1059-910X    

DOI:10.1002/jemt.1070280510

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA fully automated image analyzing system was developed for the quantitative study of cells in culture. It was able to count cells, to classify cells according to their morphological characteristics and to follow cell culture development. A specific procedure was designed to process Hoffman modulation contrast images. It detects local gray level differences while using conditional dilation techniques. We were able to successfully detect aggregated unstained cells, presently a technical limit in image segmentation. Living cells can be studied in a noninvasive and nondestructive way with this system. An improved automatic focusing algorithm was developed which ensured an accurate prediction of the optimal focus position. A strictly defined sampling procedure was applied to estimate unbiasedly cell density and obtain precisely cell contours. The evaluation of the system was carried out on Chinese hamster ovary (CHO‐NTR) cell cultures treated with a newly developed neurotensin agonist JMV449. Chinese hamster ovary cell division was found to be retarded 20 hours after the JMV449 treatment, while the morphology of CHO‐NTR cells has already undergone significant changes 12 hours after the treatment. This image analyzing system provides the possibility to follow cell culture development (e.g., cell density evolution, cell morphological changes) under various experimental conditions. © 1994 Wiley‐Lis

ISSN:1059-910X    

DOI:10.1002/jemt.1070280511

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY