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Query: UMLS:C0276640 (TEM)
 20,729 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Bundles of collagen fibrils, elastic fibres and fibroblasts are organized into a network that lies in the plane of a large portion of the bat wing. By ultrastructural (TEM and SEM) and biochemical analyses it was found that individual bundles of the net are similar to elastic ligaments. Although elastic fibres predominate, they are integrated and aligned in parallel with small bundles of collagen. A reticulum of fibroblasts, joined by focal junctions, forms a cellular framework throughout each bundle. Because of the unique features of the fibre bundles of the bat's wing, in particular their accessibility, and the parallel alignment of the collagen fibrils and elastic fibres in each easily isolatable fibre bundle, they should prove a most valuable model for connective tissue studies, particularly for the study of collagen-elastin interactions.
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PMID:A collagen and elastic network in the wing of the bat. 64

High molecular weight aggregates were extracted from human amnion using buffers containing 6 M guanidine hydrochloride. Rotary shadowed preparations and negatively stained samples examined by electron microscopy showed that each aggregate appeared to be a string of globular structures joined by fine filaments, giving the appearance of beads on a string. The periodicity of the beads was variable. A mouse monoclonal antibody directed against a previously characterized pepsin fragment of fibrillin was used with gold-conjugated secondary antibody and immunoelectron microscopy to show that the aggregates contained fibrillin. Similar structures were found in non-denaturing homogenates of skin, tongue, ligament, ciliary zonule, cartilage, and vitreous humor. When immunogold-labeled beaded structures were prepared for electron microscopy in the same manner as tissue, the beaded structures could no longer be seen. Instead, gold-labeled microfibrils were found which appeared to be the same as the fibrillin-containing matrix microfibrils observed in connective tissues and often associated with elastin. Thus, standard TEM protocols including fixation, dehydration, and embedding alter the ultrastructural appearance of microfibrils as compared with negative stain or rotary shadowing techniques. When skin was stretched and prepared for electron microscopy while still under tension, beaded filaments were seen in the tissue sections, but were not visible in non-stretched controls. In addition, when stretched ligament was immunolabeled with antibody directed against fibrillin while still under tension, the periodicity of antibodies along the microfibrils increased compared with non-stretched controls. We propose that microfibrils contain globular structures connected by fine filaments composed at lease in part of highly ordered, periodically distributed fibrillin molecules, whose periodicity is subject to change dependent on the tensional forces applied to the tissue in which they are contained.
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PMID:Extraction of extendable beaded structures and their identification as fibrillin-containing extracellular matrix microfibrils. 200 73

Light microscopy of the mandibular joint tissues from fetal mice show a distribution of fibrillar structures in the articular fibrous capsule covering the condylar head. Further SEM and TEM studies were conducted on autoclaved xiphoid and mandibular condylar processes of the fetuses for observation of the elastic system fibers in these cartilaginous tissues. SEM showed that non-collaginous fibers branched and united to form a complicated network in the cartilage. A fine structure study on diameter distribution of the fibers indicated elastogenesis in the differentiating cell layer and fiber maturation in the articular surfaces and calcification layer, thus suggesting a sequential development, growth, and degeneration of the cellular and fibrillar components in the cartilage, as well as bidirectional cell differentiation in the growing mandibular joint. A further TEM study on these autoclaved connective tissues showed the elastic system fibers in the network to be composed of fine microfibrils and amorphous elastin. The elastic fibers in the condylar cartilage were a loose network having many tortuous main and oblique elastic fibers, and coiling oxytalan fibers.
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PMID:Fine structure of cartilage elastic system fibers, in particular those of the mandibular condyle. 264 Sep 43

A combined transmission (TEM) and scanning (SEM) electron microscopic study was performed on aortae of deoxycorticosterone-salt (DOC-salt)-treated rats and spontaneously hypertensive rats (SHR) to compare the effects of hypertension as well as its reversal on the aortic intima. To best reproduce the in vivo state of the vasculature, rats were perfusion-fixed at pressures corrected for each individual animal (30 mm Hg below measured systolic pressure). The intimal alterations were focal and thus were best appreciated with the combined use of SEM and TEM. Qualitatively, both models of hypertension showed similar intimal changes, which consisted of subintimal thickening due to an accumulation of both extracellular material and cells. Subendothelial cells with a morphology indicating a blood-borne origin were present simultaneously with cells derived from the vessel wall. The increased subendothelial extracellular material included precipitated plasma proteins, reticulated basement membrane, collagen fibers, and fragments of elastin. Increase in the height of endothelial cells with distortion of nuclear shape was prominent. Withdrawal of DOC-salt combined with low-salt diet for 11 weeks did not result in a discernible regression of these intimal changes despite normalization of blood pressure. We conclude that vascular injury, once induced, may be difficult to reverse and suggest that areas of prior damage may serve as foci for later vascular complications.
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PMID:Effects of hypertension and its reversal on aortic intima lesions of the rat. 737 54

The maintenance of the mechanical properties of the vessels results from the correct arrangement of smooth muscle cells and extracellular fibrous proteins (elastin and collagen) in their wall. The morphology of extracellular matrix modifications, particularly of elastin, was investigated in inflammatory (IA) and non specific (NSA) abdominal aortic aneurysms by scanning (SEM), transmission (TEM) and immunoelectron microscopy. Both NSAs and IAs were significantly characterized by extensive extracellular matrix remodelling, including different patterns of elastin degradation. Elastic and collagen fibres distribution appeared to be extensively altered in IAs, while it conformed more to a normal pattern in NSAs. With respect to NSAs, the morphology of elastic fibres in IAs was modified to such an extent that their identification by TEM had a rely on immunocytochemical methods and by SEM on back-scattered electron analysis. The observed ultrastructural changes are indicative of the central role of extracellular matrix modifications in the pathogenesis of IAs and NSAs.
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PMID:The morphology of elastin in non-specific and inflammatory abdominal aortic aneurysms. A comparative transmission, scanning and immunoelectronmicroscopy study. 769 23

This research is designed to evaluate a number of biological markers to estimate harmful exposure on coal miners from different mining regions in France and to relate the outcome to differences in prevalence of coal worker pneumoconiosis (CWP) between these regions. Eight epidemiological groups of active and ex-miners (smokers and non-smokers) have been selected in the French collieries (North, Lorraine and Provence) according to their occupational and pneumoconiotic status. The following biomarkers have been evaluated: cellularity of sputum, elementary analysis of particles in TEM/EDAX, plasma neutral metalloendo-peptidase elastase type (NMEP), leucocyte elastase (HLE), fibronectin (FN) and elastin peptides. Pulmonary alveolitis, expressed by sputum cellularity, is different between active workers groups but not related to the general background of pneumoconiosis prevalence in the French collieries. In the plasma parameters, fibronectin, HLE and NMEP significantly increased in all groups of coal mine workers as compared to the control group, except for fibronectin parameter in Lorraine collierie. The degree of increase of these parameters allow us to discriminate the different groups and suggest that plasma FN, HLE and NMEP may be considered as biological markers of chronic inhalation of coal mine dust particles. The decrease of elastin peptides level in the Lorraine group alone suggests a specific alteration of elastin metabolism. These parameters were not related to the development of pneumoconiosis and its degree of severity.
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PMID:Biological markers as indicators of exposure and pneumoconiotic risk: prospective study. 840 28

Transmission of Pseudodiplorchis americanus is restricted to the brief period when its host, a desert toad, enters water to spawn. The parasite accumulates its entire annual reproductive output within an elongated uterus during the 10-11-month period of host hibernation. Embryos of P. americanus, at all stages of development, are retained within the uterus which eventually becomes packed with around 150 encapsulated infective larvae. Recently formed eggs, which comprise a fertilized ovum and 2-3 vitelline cells, are closely surrounded by a primary eggshell which stains positively for acidic proteins and keratin. Initially, during passage along the proximal uterus, the egg capsule is only 60 microns in diameter, but as it passes to the distal uterus it expands to 800 microns in diameter to accommodate the growing larva. Due to chemical alterations or complete replacement of the shell, the final (secondary) egg capsule is a large sac-like structure composed of elastin. The flexible nature of this shell maximizes the numbers of infective larvae which can be stored in utero. TEM studies have revealed this capsule to be composed of multi-laminate membranes with a specialized cytoplasmic lining involved in a unique mechanism for embryo nutrition. This is the first report of an elastin-type eggshell within the Monogenea.
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PMID:Histological analysis of the egg capsule of the ovoviviparous polystomatid monogenean, Pseudodiplorchis americanus. 936 90

This review illustrates the use of experimental approaches combined with microscopy to study the biology of monogenean parasites. Studies of feeding, development, reproduction, and systematics have been based on gyrodactylids, flatworms infecting teleost fishes. In a contrasting system involving an amphibian host in a desert environment, analysis of adaptations to extreme conditions has focused on Pseudodiplorchis americanus. The unusual reproductive strategies, particularly the interactions between mother and offspring, are highlighted for both monogeneans. Species of Gyrodactylus are viviparous, maintaining up to three generations of embryos simultaneously in utero, and many of their reproductive specializations are related to progenesis. Embryo nutrition takes place via a metabolically-active syncytial uterine lining that has close association with the parental gut. Microscopy has also proved an essential adjunct to molecular studies of speciation and host specificity. P. americanus is ovoviviparous and the adaptations for embryo maintenance are unique. The primary keratin-type eggshell is replaced by a flexible secondary elastin capsule produced by the uterus; parental nutrients are transferred through cytoplasmic connections to the developing embryo. TEM has demonstrated unique adaptations of P. americanus to its micro-environments, including secretion of tegumental vesicles that provide protection from digestive enzymes during migration through the host gut. This paper highlights the potential of monogeneans for studies of fundamental biological principles.
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PMID:Life history specializations of monogenean flatworms: a review of experimental and microscopical studies. 976 19

Sturgeons are bony fish that retain structural traits typical of the more primitive Chondrostei. From an evolutionary viewpoint, sturgeons are considered relic fish. However, they show remarkable ecological plasticity and are well adapted to contemporary environmental conditions. Although development of the cardiovascular system is critical for all organs and systems, and is affected by evolutionary changes, the structure of the sturgeon heart has been mostly overlooked. This is also true for the conus arteriosus, which, as in Chondrostei, is endowed with several rows of valves and a layer of contractile myocardium. This work reports on the structure of the valves, the endocardium, and the subendocardium of the conus arteriosus of the sturgeon (Acipenser naccarii) heart. It is part of a broader study that aims to cover the entire structure of the sturgeon heart. The conus arteriosus of 15 A. naccarii hearts, ranging in age from juveniles to sexually-differentiated adults, has been studied by conventional light, transmission (TEM), and scanning electron microscopy (SEM). In addition, maceration of the soft tissues with NaOH, and actin localization by fluorescent phalloidin has been used. The conus is a tubular chamber that arises from the right ventricular side and presents two constrictions at the conus-ventricle and conus-aorta junctions. The conus is endowed with three rows of valves: one distal and two proximal. The segment of the conus located between the distal and the two proximal rows is devoid of valvular structures. The distal row has four leaflets, while the two proximal rows show the greatest variation in leaflet number, size, and shape. All leaflets have collagenous chordae tendineae arising from the free border and from the parietal side of the leaflets. The endocardium is a flat endothelium which shows a thick, irregular basement membrane. The leaflet body is formed by a loose connective tissue which blends with the subendocardium. The subendocardium is a connective tissue consisting of myofibroblasts, collagen, and elastin. It is divided into two distinct areas: one proximal, which shows little elastin and poorly organized collagen; and one distal, which is rich in elastin, with cells and extracellular fibers organized into layers that are oriented in alternative circumferential and longitudinal directions. The present report is the first systematic analysis of the structure of the sturgeon conus. Descriptions of the conus valves should recognize the existence of three valve rows only. The variability in valve morphology, and the loose structure of the leaflet tissue make it unlikely that the valves play an effective role in preventing blood backflow. In this regard, the ventricle-conus constriction may act as a sphincter. The subendocardium is an elastic coat capable of actively sustaining the tissue deformation that accompanies the heart contractile cycle. Further comparative studies are needed to provide deeper insight into the structural changes that accompany phyletic diversification.
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PMID:Structure of the conus arteriosus of the sturgeon (Acipenser naccarii) heart. I: the conus valves and the subendocardium. 1198 88

The elastic properties of elastin have essentially been discussed in terms of dominant entropic components, with questions still remaining about whether the basic mechanism is compatible with the classical theory of rubber elasticity. A better understanding of the structure-function relationships in terms of the protein's elastic properties remains an important goal in elastin science. Recently, we succeeded in the exon-by-exon synthesis of all polypeptide sequences encoded by the so-called hydrophobic exons and almost all of the cross-linking exons of human tropoelastin. Among these, the peptide encoded by exon 5 (PGGLAGAGLGA) has been extensively studied by classical spectroscopic methods, such as CD and NMR spectroscopy, and by molecular dynamics simulations. The results obtained clearly evidenced a large flexibility of the polypeptide chain, which oscillates between rather extended conformations, such as PPII, and folded ones, such as beta turns. At the supramolecular level, we obtained evidence by TEM that shows that the peptide encoded by exon 5 is able to self-assemble in fibrillar structures, a result indicating that the "information" for self-assembly is also contained within a small domain of tropoelastin.
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PMID:Dissection of human tropoelastin: solution structure, dynamics and self-assembly of the exon 5 peptide. 1522 25


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