Electron microscopy reviews最新文献

In this review, the literature on ultrastructural morphometry of each of the main types of human blood leucocytes has been considered, together with the technical and numerical procedures essential for valid analysis. Quantitative data have been reported for these cell types in health and comparisons have been made with those in disease states. In monocytes, and in macrophages developing from them, subtle ultrastructural differences have been detected and quantitated in malignant lymphoma; as the mononuclear phagocytes were not themselves neoplastic, the changes may have related to defects in host defence. Change in the ultrastructural characteristics of leukaemic monoblasts have also been reported. Lymphocytes and malignant lymphoid cells have been extensively investigated: differences between different types and subsets have been shown to be present in both normal lymphocytes and their malignant counterparts in leukaemias and lymphomas. Particular attention has been paid to morphometric assessment of nuclear shape and size in these disorders and to its possible value as a diagnostic tool. Granulocytes have so far been the subject of few morphometric studies, although in hypereosinophilic syndrome, cellular changes have been defined and have thrown light on the abnormal pattern of degranulation. There have also been scattered reports on the cells of acute myelogenous leukaemia. The use of computers and sophisticated statistical packages has greatly facilitated the application of multiple comparison procedures and has permitted discriminant analysis to be carried out where appropriate.

This review shows that ultrastructural morphometry of leucocytes will have an increasing application in clinical pathology.

Nucleoli are the morphological expression of the activity of a defined set of chromosomal segments bearing rRNA genes. The topological distribution and composition of the intranucleolar chromatin as well as the definition of nucleolar structures in which enzymes of the rDNA transcription machinery reside have been investigated in mammalian cells by various immunogold labelling approaches at the ultrastructural level. The precise intranucleolar location of rRNA genes has been further specified by electron microscopic in situ hybridization with a non-autoradiographic procedure.

Our results indicate that the fibrillar centers are the sole nucleolar structures where rDNA, core histones, RNA polymerase I and DNA topoisomerase I are located together.

Taking into account the potential value and limitations of immunoelectron microscopic techniques, we propose that transcription of the rRNA genes takes place within the confines of the fibrillar centers, probably close to the boundary regions to the surrounding dense fibrillar component.

We have used the electron microscope to examine ultrastructurally several events occuring during the biogenesis of two very abundant chorion (eggshell) mRNA molecules in the follicle cells of Drosophila melanogaster—namely, selective gene amplification, transcription initiation and termination, and RNA rocessing. We find that the highly transcribed s36 and s38 genes are positioned in the central region of large, multi-forked amplified DNA structures. Transcript morphology is consistent with the known presence of a small intron at the 5' end of each gene. mature transcripts are associated with spliceosomes, demonstrating that splice site selection occurs co-transcriptionally but that splicing is completed after transcript release from the template. We have also mapped the termination sites for the genes. The two genes exhibit efficient termination very near their poly(A) sites—within a 210 bp region for s36 and a 360 bp region for s38.

We compared the fine structure and electron microscopic cytochemical findings of basophils and mast cells from humans, guinea pigs, rabbits, mice and rats. The particulate structure was the most frequently observed and most typical structure of human and rabbit basophil granules and of guinea pig mast cell granules. The most prominent feature of guinea pig basophils and murine mast cells was that the fine structure of the granules was homogeneous. The fine structure of the granules in guinea pig basophils resembled that in murine mast cells, while the fine structure of the granules of guinea pig mast cells resembled those in human and rabbit mast cells. In mouse mast cells in culture, the majority of the granules contained small vesicles, which were also observed in human basophils in culture and in mouse basophils in vivo. The degrees of cytochemical reactivity of acid mucopolysaccharides among the species were different. Peroxidase activity was positive in most basophils and in human mast cells.

Among mammals, the granules of basophils and mast cells present heterogeneous fine structure. It is of interest that the basophil granules of some species resemble the mast cell granules rather than the basophil granules of other species.

In this review, the ultrastructure of the normal human chorionic villus is examined and illustrated. The outer covering of trophoblast, comprising the generative cytotrophoblast and the multinucleated syncytiotrophoblast which is derived from it, is described, including such features as the microvillous surface, vesicles and vacuoles, endoplasmic reticulum and secretory droplets. The structure, composition, development and inclusions of the trophoblastic basement membrane are discussed, and the ultrastructure of the various components of the stroma, including reticulum cells, fibroblasts, Hofbauer cells, capillaries and the non-cellular matrix are illustrated and described, with special reference to their inter-relationships and function.

Euglena is an organism that every student of biology has observed; its morphology has been a subject of interest since the early microscopic literature for its enigmatic role of “plant-like” or “animal-like” organism. Therefore, this review has no pretensions to absolute novelty, but, like a journey to the centre of the earth, will attempt to arouse the reader's curiosity by taking him inside the cell Euglena, through the canal opening into the reservoir chamber. In light of the most recent knowledge, though much remains to be clarified, the aim is to provide information from ultramicroscopical studies on the apical zone of Euglena and possible functional meanings of the structures present therein. The survey of these structures is carried on as a study in correlation: TEM of cells after various treatments is correlated with SEM of cells fixed by means of different techniques. Notes on locomotion and other features of cytological and biological interest are added to assist with the comprehension of this microorganism.

In this review, the structure and biological formation of hard α-keratins are drawn together.

The hard keratins comprising wool, hairs, quills, hooves, horns, nails and baleen contain partly α-helical polypeptides which show homology with epidermal polypeptides only in the helical regions. These polypeptides (about 32 chains) are organized into intermediate filaments (IFs) of 7.5 nm diameter which are embedded in variable amounts of a matrix of non-helical cystine-rich proteins and glycine-tyrosine-rich proteins. The total number of proteins may exceed 100. In addition keratins contain a variety of lipid components.

Wool and hair are produced in follicles in a multistep procedure. In the lower levels of the follicle, IFs without associated matrix are found. Subsequently matrix proteins are laid down between the IFs and further synthesis takes place concurrently. Finally the proteins are insolubilized by the oxidative formation of disulphide bonds.

Keratinized fibres shows considerable complexity and diversity in the structural arrangement of IFs and matrix within cortical cells. Typically the IFs show hexagonal packing or give a whorl-like appearance in cross-section.

Osteoclasts are multinucleated giant cells showing specialized membrane structures, clear zones and ruffled borders, which are responsible for the process of bone resorption. These cells arrive at the resorption site via the bloodstream as mononuclear cells, derived from haemopoietic precursors in the spleen or bone marrow, which fuse prior to resorption. The osteoclast may share an early progenitor cell, the granulocyte macrophage colony-forming unit (GM-CFU) with monocytes, macrophages and granulocytes, implying that osteoclasts share the pluripotent haemopoietic stem cell with all other haemopoietic cells.

In the past, elucidation of the structure of these cells relied upon traditional ultrastructural techniques. Transmission electron microscopic studies revealed details of the unique ultrastructure of these cells and, in combination with stereological techniques, showed the response of cells to various hormonal stimuli. Scanning electron microscopy not only demonstrated the surface appearance of osteoclasts, and their predilection for spreading on various substratum components, but has also been used as an adjunct in resorption assays in which areas of resorption lacunae are measured as indicators of cell activity. Recent advances in fields such as immunocytochemistry and freeze fracture techniques have contributed towards a more detailed delineation of antigenic profile, cytoskeletal structure and localization of enzymatic pathways.

The osteoclast is subject to extensive regulatory mechanisms and it has been established that the osteoblast plays a major roˆle in mediating the effects of osteotropic hormones and local mediators on these cells. Hence, research aimed at elucidating the coupling mechanisms between these two cells may result in new therapies for bone disease.

Experimental evidence is presented showing that the plant mitochondrial and chloroplast genomes are multipartite and, that besides a large circular genomic DNA, they contain subgenomic minicircular and plasmid-like molecules. It is demonstrated that plant mitochondrial and chloroplast DNAs are packaged into deoxynucleoprotein fibrils comprising nucleosome-like and nucleomere-like globules; the fibrils form loops and rosette-like structures with central proteinaceous components. A similar structure is characteristic of the subgenomic DNAs. The basic proteins involved in the formation of nucleosome-like globules are quite different from the nuclear histones, indeed the basic proteins from plant mitochondria and chloroplasts are also distinct. Some of the basic proteins share common antigens with the E. coli HU protein. The genetic code for the mitochondrial and chloroplast genes is universal. The only codon now thought to be different from the universal in the mitochondrial genome is corrected during post-transcriptional mRNA editing. There are two hexanucleotides in the promoters of the chloroplast genes homologous to the sequences in −10 and −35 regions of the prokaryotic genes promoters requisite for transcription. Promoter sequences of the plant mitochondria genes responsible for transcription regulation were not identified. Immunoelectronmicroscopic evidence suggest that mitochondrial and chloroplast RNA polymerases have antigens in common with the β-subunit of E. coli RNA polymerase. It is shown that the mitochondrial genes are intensely transcribed in the dark and repressed by illumination. Electron microscopy demonstrated that about 70% of plant mitochondria contain numerous RNA polymerase molecules in the dark, but this percentage falls to 10–15% after light exposure.