Electron microscopy reviews最新文献

The present work attempts to demonstrate that cryofixation is a valuable method for the study of the nervous tissue. The use of the newly developed methods of cryofixation and freeze-etching without fixatives or cryoprotectants allows new exciting perspectives for the electron microscopical observation of cellular components, emphasizing their three-dimensional morphological structures. Significant contributions have been made on the fine structure of the cytoskeleton, cell membranes and cell organelles. The components of the cytoskeleton are distributed in different composition through the perikarya, dendrites and axon. The ubiquitous presence of the cytoskeleton suggests a crucial role in the functional activities of the neurons, especially in relation to the intracellular communication and to developmental and regeneration processes. Vitrified cellular membranes of myelin sheaths and rod outer segments have been observed in hydrated state by using cryofixation and cryotransfer techniques. These procedures allow new insights into the supramolecular structure and an approximation of morphological data to the present biophysical membrane model including a critical comparison with the current descriptions gained by conventional electron microscopy.

The collective term “immunoelectron microscopy” subsumes a number of techniques in which the biological material is decorated with specific antibodies, prior to being visualized in the electron microscope. In this article, we have reviewed literature on immunoelectron microscopy that focusses on the analysis of the molecular architecture of proteins, in particular of enzymes and of multienzyme complexes. Molecular immunoelectron microscopy has been remarkably successful with multi-subunit enzymes of complex quaternary structures, and in many cases the data have been the basis for the eventual development of detailed three-dimensional molecular models. The elucidation of subunit composition and juxtaposition of a given enzyme, an important accomplishment in itself, has in turn stimulated and guided discussions on the catalytic mechanism; illustrative examples include F₁ ATPase and citrate lyase, among others. Here we have chosen a variety of enzymes, multienzyme complexes, and non-enzymatic proteins to demonstrate the versatility of immunoelectron microscopy, to illustrate methodological prerequisites and limitations, and to discuss significance and implications of individual immunoelectron microscopy studies.

Bacterial lipopolysaccharides (LPS), which are important components of the cell wall of gram-negative bacteria, induce a number of host responses both beneficial and harmful. The present review elucidates the uptake, distribution and functions of LPS in mononuclear phagocytes in an attempt to gain an insight into the mechanisms which control the pathogenesis of LPS mediated septic shock. The unique feature of LPS bilayer structure, the tagged LPS and antibodies to LPS provide means for studying binding, uptake, fate and subcellular distribution of LPS in tissues and cells. LPS bind to monocytes and macrophages by specific interaction via receptors such as scavenger receptors, CD14 and CD18 and by non-specific interactions, and enter the cells via receptor-mediated endocytosis, absorptive pinocytosis, phagocytosis, and diffusion. The ingested LPS are localized in pinocytic vesicles, phagocytic vacuoles, cytoplasm, mitochondria, rough endoplasmic reticulum, Golgi apparatus, and nucleus. The interactions of LPS with monocytes and macrophages trigger a broad spectrum of cellular responses, including production of important bioactive factors or mediators, such as IL-1, TNF, interferons, prostaglandins, and macrophage-derived growth factor, which are implicated in the pathogenesis of septic shock and wound healing. However, There is no conclusive evidence indicating that production of the mediators can only be induced through specific interactions.

New results concerning the ultrastructure of human alpha 2-macroglobulin (α₂M) molecules are presented in connection and comparison with the historical, the current and our own most recent, even unpublished results on the structure and function of α₂M and related proteins.

The electron microscopic approach uses classical negative staining, combined with the new imaging mode “Electron Energy Loss Spectroscopy”, which provides unusual contrast, resolution and readability of the electron micrographs. Immuno- and cryoelectron microscopy, as well as image processing has provided new data necessary to the building of tentative 3D models of the molecule.

A model for the native tetrameric α₂M is described for the first time, and tries to explain and gather the various observations, sometimes contradictory, taken from different laboratories. A revised version for a model of the methylamine- and proteinase-transformed forms of α₂M is also shown. The probable positions of the bait regions and the thiol esters are given on both models. We confirm that α₂M is a twin trap capable of inactivating one or two proteinases by partial immobilization. Preliminary results on the production of crystals of α₂M-chy-motrypsin complexes are also presented. A critical analysis of our models is presented in comparisom with others. The technical limitations reached with some techniques and some possible extensions of future research in the field are also presented.

Transmission electron microscopy has emerged as an ideal tool for the study and diagnosis of various disorders that involve collagen, since the information obtained by this technique is at the ultrastructural level. Structural alterations of collagen fibrils brought about by these disorders are discussed. The positive staining pattern of such fibrils is also investigated. In addition, this review describes how quantitative studies of electron-optical images from abnormal collagen fibrils can lead to information about the changes produced by collagen defects which relate to molecular or fibril architecture.

Taken altogether, the EM evidence we have obtained indicates that the induced (both viral and PEG) and spontaneous (entrance of a splenocyte into a cell) fusion of mammalian somatic cells are associated with alterations in the structure of fusing cells. For example there are alterations in the structure of not only the surfaces of fusing cells but also in the nucleus envelopes and cytoplasmic organelles after PEG treatment. Also, there is long retention of cellular plasma membrane remnants in virally-induced heterokaryons. In short, for each case the alterations were unquestionably specific, in response to the imposed challenge. These specific features not only determine the efficiency and rate of fusion, but also the mode by which the hybrid nucleus is formed. This mode directly determines the fate of the synkaryon and the stability of the so formed hybrid genome. It might be thought that an increase in the inner nuclear envelope observed in some hybrids would counteract the consequences of the disproportions arising between the increase in cell volume and nuclear surface. The finger-like invaginations of the hybrid nuclei nuclear envelope, surrounded by replicatively and transcriptionally active chromatin, appear to be EM demonstrations of such counteracting mechanisms. These invaginations, by augmenting the available inner layer, most likely increase the anchorage sites for chromatin. It is noteworthy that the invaginations occur mainly in multichromosomal hybrids with little chromosome loss. It appears possible that some of the hybrids may contain particular chromosomes from the more differentiated parent cell.

We describe here the basic structure of the aorta, the changes with aging and ultrastructural appearance of atherosclerosis of human and animal models. The architecture of the aortic wall is highly organized, for adaptation to changes of blood pressure. The main cells composing the vessel are endothelial cells and smooth muscle cells. They maintain the integrity and homeostasis of the aorta along with the extracellular matrix of collagen fibrils, elastic fibers and glycosaminoglycans. The structural changes with aging and atherogenesis are a compensative or degenerative phenomenon caused by many factors. Three major cells are the endothelial cell, smooth muscle cell and monocyte-derived macrophages (as well as platelets) all of which are involved in atherogenesis. Foam cells in atheromatous lesions are derived from macrophages and smooth muscle cells. Recently, the molecular biological nature and function of these cells and their derived-factors have been thoroughly investigated in cell culture and in experimental animal models caused by a mechanical injury of the endothelium or by a dietary induced hypercholesterolemia. However, the mechanism of the endothelial injury in vivo as well as formation of atheromatous cores of human atherosclerosis is not exactly understood. Some structural and functional changes inherent to the arterial wall during aging may play an important role in initiation or progression of human atherosclerosis.

The purpose of this review is to provide information of the role played by electron microscopy in respect of bacteriophage structure. This 40 years' “love story” between phages and microscopy was a valuable contribution to the progress of scientific knowledge in molecular biology. In spite of the rather drastic treatment required for electron microscopical analysis, it was possible to reveal the molecular organization and morphogenic pathway of many of the bacteriophages cited in this paper.

The biological importance of iron for most living cells has been under increasing attention during recent years. In addition to iron deficiency, iron overload has been recognized as a significant metabolic abnormality with potentially damaging consequences. The iron-storing compounds ferritin and hemosiderin have the unique quality of being ultrastructurally recognizable because of the electron-density of the iron concentrated within their particles. In this review, the electron microscopic features of iron overload are discussed, as found in various subcellular compartments and different types of cells and tissues. Defensive mechanisms against iron overload are exhibited by most cell lines and include: (1) the capacity of synthesis of the protein apoferritin by most cells whenever the concentration of ambient iron increases, (2) the capacity to bind toxic inorganic iron within the hollow shell of apoferritin; the transfer of the assembled iron-rich ferritin molecules into siderosomes and (3) the capability of further iron segregation within siderosomes by degradation of ferritin to hemosiderin. The study provides examples of cytosiderosis in different types of cells and tissues, as well as iron-related ultrastructural pathological changes.