bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ultrastructure of Paneth cells in the intestine of various mammals
Authors: Satoh Yohichi , Yamano Miki , Matsuda Mitsuyoshi , Ono Kazuyuki 
Published: February 2005

AbstractPaneth cells in the following species were observed under an electron microscope: human, rhesus monkey, hare, guinea pig, rat, nude rat, mouse, golden hamster, and insect feeder bat. Secretory granules containing homogeneous electron‐dense materials were observed in the Paneth cells of humans, monkeys, hares, guinea pigs, and bats; mouse Paneth‐cell granules were bipartite (central core and peripheral halo), and the Paneth cells in rats and golden hamsters had secretory granules showing various electron densities. In humans, monkeys, and bats, immature granules near the Golgi apparatus sometimes showed bipartite substructure. The number and size of secretory granules were also diverse among various animal species. Some lysosome‐like bodies were commonly observed in peri‐ or supranuclear regions, though the size and shape of the bodies differed from cell to cell. In apical cytoplasm, small clear vesicles (100–200 nm diameter) were more‐or‐less observed in all species examined, and it was especially note that rat Paneth cells contained many clear vesicles. Small dense‐cored vesicles (150–200 nm diameter) were rare. It is unlikely that the various ultrastructural features of Paneth cells correlate with the phylogenetical classification.
A new method for phase identification for electron diffractionists
Authors: Mighell Alan D. , Himes Vicky L. 
Published: February 2005

AbstractAn accurate analytical procedure for phase identification for electron diffractionists has been developed. The method opens new frontiers in the identification of solid‐state materials, as crystalline samples in the size range 10 μm to 10 Å can be accurately characterized. Research with NIST CRYSTAL DATA (a large database with chemical, physical, and crystallographic data on solid‐state materials) has proved that a material can be uniquely characterized on the basis of its lattice and chemical composition. To characterize a material, it is sufficient to determine any primitive cell of the lattice and the element types present. Using a modern analytical electron microscope (AEM), the experimentalist can collect the required data on an unknown sample. The lattice information is obtained by rotation of the sample to obtain two or more planes of data. From these planes, a unit cell defining the lattice can be deduced. The chemical data are determined by energy‐dispersive spectroscopy (EDS). Once the experimental data are measured, the unknown is identified against the database of knowns using lattice/element‐type matching techniques. The basic strategy consists of three conceptual steps. First, the unknown lattice is searched against the database to find all lattices that are the same or related; the results are kept in set 1. Second, the unknown is searched against the database to find all materials with the same or similar element types; the results are kept in set 2. Finally, the results in sets 1 and 2 are combined to obtain the answer set. Experience has proved that the procedure is highly selective and reliable.
Transformation of the amphibian oocyte into the egg: Structural and biochemical events
Authors: Bement William M. , Capco David G. 
Published: February 2005

AbstractAmphibian oocytes, arrested in prophase I, are stimulated to progress to metaphase II by progesterone. This process is referred to as meiotic maturation and transforms the oocyte, which cannot support the early events of embryogenesis, into the egg, which can. Meiotic maturation entails global reorganization of cell ultrastructure: In the cell cortex, the plasma membrane flattens and the cortical granules undergo redistribution. In the cell periphery, the annulate lamellae disassemble and the mitochondria become dispersed. In the cell interior, the germinal vesicle becomes disassembled and the meiotic spindles form. Marked changes in the cytoskeleton and mRNA distribution also occur throughout the cell. All of these events are temporally correlated with intracellular signalling events: Fluctuations in cAMP levels, changes in pH, phosphorylation and dephosphorylation, and ion flux changes. Evidence suggests that specific intracellular signals are responsible for specific reorganizations of ultrastructure and mRNA distribution.
Modification of the Polaron sputter‐coater unit for glow‐discharge activation of carbon support films
Authors: Benada O. , Pokorný V. 
Published: February 2005

AbstractWe describe a modification of the Polaron sputter‐coater unit series 11 HD enabling activation of carbon support films for electron microscopy of macromolecules and macromolecular assemblies. The modification is simple and the device can be used in two modes, for sputter‐coating of SEM samples and for glow‐discharge activation of carbon support films. Examples of protein‐free spreading of DNA and negative staining of bacteriophage particles on activated carbon support films are presented.
Ultrastructural correlates of meiotic maturation in mammalian oocytes
Authors: McGaughey Robert W. , Racowsky Catherine , Rider Virginia , Baldwin Kendall , DeMarais Alyce A. , Webster Scott D. 
Published: February 2005

AbstractImmature mammalian oocytes reside in ovarian follicles with junctionally coupled granulosa cells. When released from a currently undefined meiotic arresting influence, these oocytes resume meiosis to progress from late diplotene (germinal vesicle stage) through the first meiotic division to metaphase II. Oocytes remain at metaphase II until fertilization activates them to complete meiosis. This review summarizes ultrastructural events that occur during meiotic maturation in mammals. Developmental correlates that promise a clearer understanding of regulatory mechanisms operating to control maturation are emphasized. By use of TEM of thin sections, freeze‐fracture analysis, and replicated oocyte cortical patches, we demonstrate stage‐specific changes in the oocyte nucleus, reorganization of cytoplasmic organelles, correlations between oocyte maturational commitment and the junctional integrity of associated granulosa cells, and definition of the components comprising the oocyte cortical cytoplasm.
Morphology of mammalian sperm membranes during differentiation, maturation, and capacitation
Authors: Bearer Elaine L. , Friend Daniel S. 
Published: February 2005

AbstractThe mammalian spermatozoon is a highly polarized cell whose surface membrane can be divided into five functionally, structurally, and biochemically distinct domains. These domains are formed during spermatogenesis, continue to be modified during passage through the epididymis, and are further refined in the female reproductive tract. The integrity of these domains appears to be necessary for the sperm to perform its function—fusion with the egg and subsequent fertilization. The domains can be identified morphologically by their surface contours and texture, the content, distribution, and organization of intramembranous particles after freeze‐fracture, and by the density of surface and cytoplasmic electron‐dense coatings in thin sections. By using a variety of labels that stain carbohydrates (lectins), lipids (filipin and polymyxin B), and monoclonal antibodies to specific membrane constituents, the biochemical composition of these contiguous membrane regions has also been partly elucidated. We review here what is known about the structure, composition, and behavior of each membrane domain in the mature sperm and include some information regarding domain formation during spermatogenesis. The sperm is an excellent model system to study the creation and maintenance of cell polarity, granule exocytosis, and fertilization. Hopefully this review will provide impetus for future studies aimed more directly at addressing the relationship of its morphology to its functions.
Three‐dimensional organization of the golgi complex observed by scanning electron microscopy
Authors: Tanaka Keiichi , Fukudome Hatsuko 
Published: February 2005

AbstractWith the development of new specimen preparation techniques and improvements in instrumental resolution, scanning electron microscopy (SEM) became an effective means of studying the three‐dimensional organization of the Golgi complex. When specimens prepared by the osmium‐DMSO‐osmium method are observed with high‐resolution SEMs, cis‐most cisternae of Golgi stacks appear as sieve‐like plates with many small perforations. In some cell types, larger fenestrations are also present. The trans‐most cisternae showed a fenestrated or retucular pattern. At the trans‐side of Golgi stacks, distinctive structures, such as a well‐developed tubular plexus or a single widely extended cisterna, are observed in some types of cells. In lacrimal gland cells, Golgi stacks are linked by an irregular network of anastomosing branches extending throughout the cytoplasm. In these cells, the piled cisternae seemed to be connected to each other either directly within the stack or via cisternae of other stacks. Connections between Golgi stack and rough endoplasmic reticulum (ER) were often found in our SEM observations. In nerve cells, interconnecting tubules arise from rough ER and most often fuse with the rim of the cis‐cisternae of Golgi stacks.
Trans‐Golgi reticulum
Authors: Geuze Hans J. , Morré D. James 
Published: February 2005

AbstractThe trans‐Golgi apparatus reticulum is that portion of the Golgi apparatus located in the trans‐most aspect of the stack exhibiting certain characteristic morphological and functional characteristics. The membranes of the trans‐Golgi reticulum are reticular in form, thickened with plasma membrane‐like characteristics and with a considerable portion of their surface covered by clathrin coats. The enzymes thiamine pyrophosphatase and sialyl‐ and galactosyl transferases are functional markers. Correlative studies show the trans‐Golgi apparatus reticulum to be involved in glycoprotein, enzyme and receptor processing and sorting along multiple pathways. Sorting and transfer of constituents to lysosomes, to secretory granules, or to the plasma membrane emerge as dominant functions.
Analysis of protein transport through the golgi in a reconstituted cell‐free system
Authors: Wattenberg Binks W. 
Published: February 2005

AbstractThe processes which transport membrane proteins between compartments of the Golgi apparatus have been reconstituted in vitro using isolated Golgi fractions. This cell‐free system allows a detailed analysis of protein transport not possible in intact cells. Transport of the membrane glycoprotein (G protein) of vesicular stomatitis virus (VSV) is measured from a “donor” to an “acceptor” Golgi fraction. The donor Golgi fraction is prepared from VSV‐infected Chinese hamster ovary (CHO) mutant cells deficient in the glycosylation enzyme N‐acetylglucosamine transferase I. “Acceptor” is prepared from uninfected wild‐type CHO cells. Transport is measured by the addition of N‐acetylglucosamine to G protein, which can occur only upon movement of G protein from donor to acceptor. Transport requires physiological pH and osmolarity, is dependent on nucleotide triphosphates, and is mediated by proteins both from cytosol and on the Golgi membranes. Protein movement is inhibited by the non‐hydrolyzable GTP analogue, GTPγS. The process of transport proceeds through the budding, pinching off, targeting, and fusion of transport vesicles. In this system these vesicles are initially coated with a non‐clathrin coat and are targeted with this coat intact. Several of the proteins which mediate transport have been characterized, and isolated to homogeneity. The successful development of this assay has led to the formulation of cell free assays for protein transport between other compartments. Comparison of these systems indicates that some common mechanisms of vesicular movement are used in transport between a variety of membrane compartments.
High‐Angle annular dark‐field imaging on a tem/stem system
Authors: Otten Max T. 
Published: February 2005

AbstractThe technique of high‐angle annular dark‐field (HAADF) imaging, which is highly sensitive to atomic‐number contrast, can be performed on TEM/STEM systems using the standard annular dark‐field detector. For optimum HAADF imaging, the TEM/STEM must have a high maximum diffraction angle, small minimum camera length, and a descanning facility. The sensitivity of the technique is demonstrated to be about 105 to 106 times higher than energy‐dispersive X‐ray spectroscopy. Examples are shown from semiconductor, catalysis, ceramics, and particle analysis applications.
Gamete interactions and the fate of sperm organelles in fertilized echinoderm eggs
Authors: Longo Frank J. 
Published: February 2005

AbstractInvestigations of gamete fusion, sperm entry and the fate of the sperm nucleus, plasma membrane, mitochondrion, and axonemal complex in fertilized echinoderm eggs are reviewed. The timing of gamete fusion with respect to the onset of electrical activity characteristic of the activated egg and the affects of fixation conditions on the stability of fusing membranes are discussed. Observations from investigations using cationized ferritin labeled gametes and immunogold cytochemistry to demonstrate the mixing of sperm plasma membrane components within the egg plasma membrane, in particular along the surface of the fertilization cone, are compared with results from studies in somatic cells. Transformations of the sperm nucleus into a male pronucleus, consisting of sperm nuclear envelope breakdown, chromatin dispersion, and formation of a pronuclear envelope, are correlated with recent biochemical observation of similar processes in other cellular systems. Fates of the sperm mitochondrion and axonemal complex are examined.
Multiple intracellular signals coordinate structural dynamics in the sea urchin egg cortex at fertilization
Authors: Chandler Douglas E. 
Published: February 2005

AbstractFertilization of the sea urchin egg is accompanied by a sequence of structural changes in the egg cortex that include exocytosis, endocytosis, and microvillar growth. This architectural reorganization is coordinated by two intracellular signals: a rapid, transient rise in cyto‐solic free calcium and a slower, longer lasting increase in cytoplasmic pH. In this report we provide ultrastructural views of these events in quick‐frozen eggs and discuss their relationship to the calcium and pH signals.
Fertilization of the mouse oocyte
Authors: Calarco Patricia G. 
Published: February 2005

AbstractThis paper presents morphological data on mouse oocyte maturation and fertilization, reviews evidence supporting the existence of a sperm receptor, and suggests future directions for this line of research. We used scanning electron microscopy to examine oocytes under a variety of conditions. The surfaces of mature mouse oocytes are seen to be similar whether maturation occurs in vivo or in vitro. Capacitated sperm (both acrosome‐intact and acrosome‐reacted) are observed to interact with the microvilli of the oocyte surface.Little is known about oocyte surface proteins that mediate fertilization in mammals. Data of ours and others show that enzyme treatment of live unfertilized eggs interferes with sperm binding. Enzyme treatment (trypsin, chymotrypsin treatment, or pronase) reduces the number of bound sperm, suggesting removal of a surface protein involved in fertilization. Trypsin treatment also causes some lengthening of surface microvilli in a belt surrounding the metaphase II region. After metabolic labeling, proteins of zona‐free unfertilized eggs can be identified by SDS‐PAGE and autoradiography. Comparison of 1‐D gels from untreated and enzyme‐treated eggs show the nearly complete disappearance of proteins of 263, 170, 137, 97, and 87 kD after digestion; an increase in a 66 kD protein after trypsin or chymotrypsin; and a major new band of 20 kD after chymotrypsin treatment. Fertilized eggs show the loss of a 255–265 kD band among other changes. Proteins of 97 kD and 87 kD were seen previously by surface labeling (Johnson and Calarco, 1980b), and our 97 kD and 66 kD bands are similar in molecular weight to those identified by Boldt et al. (1989). Taken together, these data identify a few candidate proteins for the role of sperm receptor on the egg surface.Future work should focus on identification of the surface protein(s) which functions physiologically in fertilization by developing fertilization‐blocking antibodies. Relatedness to other mammalian sperm receptors and identification of the genes involved would provide valuable information to our understanding of fertilization and to the problems of infertility and contraception.
The three‐dimensional architecture of the mitotic spindle, analyzed by confocal fluorescence and electron microscopy
Authors: Merdes Andreas , Stelzer Ernst H. K. , De Mey Jan 
Published: February 2005

AbstractFluorescence microscopy techniques have become important tools in mitosis research. The well‐known disadvantages of fluorescence microscopy, rapid bleaching, phototoxicity and out‐of‐focus contributions blurring the in‐focus image are obstacles which still need to be overcome. Confocal fluorescence microscopy has the potential to improve our capabilities of analyzing cells, because of its excellent depth‐discrimination and image processing power. We have been using a confocal fluorescence microscope for the study of the mechanism of poleward chromosome movement, and report here (1) a cell preparation technique, which allows labeling of fixation sensitive spindle antigens with acceptable microtubule preservation; (2) the use of image processing methods to represent the spatial distribution of various labeled elements in pseudocolour; (3) a novel immunoelectron microscopic labeling method for microtubules, which allows the visualization of their distribution in semithin sections at low magnification; and (4) a first attempt to study microtubule dynamics with a confocal fluorescence microscope in living cells, microinjected with rhodamine labeled tubulin.Our experience indicates that confocal fluorescence microscopy provides real advantages for the study of spatial colocalization of antigens in the mitotic spindle. It does not, however, overcome the basic limits of resolution of the light microscope. Therefore, it has been necessary to use an electron microscopic method. Our preliminary results with living cells show that it is possible to visualize the entire microtubule network in stereo, but that the sensitivity of the instrument is still too low to perform dynamic time studies. It will be worthwhile to further develop this new type of optical instrumentation and explore its usefulness on both fixed and living cells.
Ultrastructural cryoimmunocytochemistry is a convenient tool for the study of DNA replication in cultured cells
Authors: Raska Ivan , Michel Laurée Salamin , Jarnik Michal , Dundr Miroslav , Fakan Stanislav , Gasser Susan , Gassmann Max , Hübscher Ulrich , Izaurralde Eliza , Martinez Ernest , Richter Arndt , Dubochet Jacques 
Published: February 2005

AbstractIn the present study, we have optimized an immunocytochemical ultrastructural approach for in situ localization of newly synthesized DNA in unsynchronized as well as in synchronized human HeLa cells and in exponentially growing mouse P815 cells, which had incorporated bromodeoxyuridine (BrdU) during short pulses varying from 1 to 20 minues. The incorporated BrdU was detected in hydrolyzed ultrathin cryosections or Lowicryl sections by means of a monoclonal antibody, revealed by secondary colloidal gold‐labeled probes. The results demonstrate our ability to study, with high resolution and reproducibility, DNA replication during consecutive periods of the S‐phase, which is monitored by the incorporation of tritiated thymidine. In addition, this approach allows one to perform a concomitant mapping of replicated DNA and various enzymes of the replisome.
Effects of substrate texture and curvature on the morphology of cultured cells
Authors: Hogan Margaret E. , Degaetano Douglas H. , Klomparens Karen L. 
Published: February 2005

AbstractThe ultrastructural characteristics of several growth matrices were examined using two cell types chosen for their distinct growth habits. Chinese hamster ovary cells and Balb‐c 3T3 mouse fibroblasts were grown on flat substrates (glass, tissue culture plastic, Millipore filters) as well as spherical (glass, tissue culture plastic, cross‐linked dextran) substrates. Cells were plated maintaining equal densities and growth surface area. Once the majority of the cells reached confluency, the cell's morphology on each matrix was examined using scanning electron microscopy. Digital analysis was performed on cell attachment area to compare the effect of each matrix on cell spreading.Variation in cell shape was dramatic between matrices, being most noticeable between a textured surface (filter, dextran bead) and that of a smooth (glass) surface. Even within smooth surfaces, some variation was observed. There was also an effect of matrix curvature on cell attachment area, the greatest being in the 3T3‐c Balb cells, causing an overall decrease in the area of attachment between cell and matrix. The changes seen could also be related to the particular cell type used. Hamster ovary cells tended to be cylindrical and showed little effect between matrices, whereas the mouse fibroblasts, which are more flattened, showed the matrix effect to a greater degree.This study demonstrates the necessity of being aware of substrate‐induced cell changes in tissue culture, where some variation in cell shape may be due to the surface on which the cells are grown as opposed to the experimental procedure.
Electron crystallography at atomic resolution: The structure of the odd‐chain paraffin n‐tritriacontane
Authors: Dorset Douglas L. , Zhang Weiping 
Published: February 2005

AbstractThe crystal structure of the odd‐chain paraffin, n‐tritriacontane, nC33H68, is determined directly by using low‐dose electron microscope images and electron diffraction intensity data from epitaxially grown microcrystals. Phases of the most intense “polyethylene” reflections are determined from triplet structure‐invariant relationships often used in X‐ray crystallography. Low‐dose electron microscopic images provide phases of the low‐angle “lamellar” reflections and these can be used with one‐dimensional structure‐invariant relationships to determine other phases on the 00ℓ reciprocal row. The phase set is sufficient to calculate an electrostatic potential map which is directly interpretable as a structure image at atomic resolution.
The effect of aluminium coating on elemental standards in X‐ray microanalysis
Authors: Hopkins Diane M. , Jackson Alan D. , Oates Kenneth 
Published: February 2005

AbstractThe standardisation of frozen hydrated bulk biological specimens using gelatin standards is described. The relationship between corrected elemental X‐ray counts and ionic concentration was found to be linear, and minimum detectable limits for each element are stated. Variations in uncorrected standard curves were found to be due to changes in aluminium coating thickness. There was an inverse relationship between coating thickness and elemental X‐ray counts. The factors causing this are discussed. To avoid errors arising from inconsistent aluminium thickness, experimental material should only be compared with standards of similar aluminium net counts. This can be achieved most easily by mounting and analysing specimen and standard together.