Scanning-electron-microscopical study of the seminal vesicle, coagulating gland, ampullary gland and ventral prostate in the golden hamster

A study of the internal surfaces of the seminal vesicle, coagulating gland, ampullary gland and ventral prostate of the golden hamster was carried out by scanning electron microscopy. The internal surface of each of these glands was found to display characteristic features in topography and in arrangements of the microvilli. The features are useful in the identification of these glandular tissues in situ.     

Immunoelectron microscopic localization of aromatase in human placenta and ovary using microwave fixation

In this study we investigated the immunohistochemical localization of a unique aromatase, a single protein of 51,000 daltons, in the human placenta and ovary at light and electron microscopic levels. Microwave fixation was adopted for the immunoelectron microscopic study because it is an excellent method for preserving antigenicity and subcellular structures in frozen sections. Tissue samples from four immature human placentas, four full-term human placentas, and two human ovaries fixed in 10% formalin were examined by light microscopy. In addition, tissues from three full-term human placentas and one immature human placenta fixed in 4% paraformaldehyde were examined by electron microscopy. By light microscopy, immunoreactivity for this aromatase was located in the syncytiotrophoblast and a part of the cytotrophoblast of the placenta and in the lutein and granulosa cells of the ovary. Immunoelectron microscopy revealed that the aromatase antigen was localized on the surface of the microvilli, the lateral plasma membrane, and in the endoplasmic reticulum (ER) in the syncytiotrophoblast of the placenta. The positive immunoreactivity in the syncytiotrophoblast ER is consistent with previous results using antibodies for other types of aromatase, whereas the reactivity on the microvilli has not been previously described. The present report describes the fine localization of this unique aromatase in placental and ovarian tissues; its localization on the plasma membranes requires further physiological investigation.     

Ultrastructure of the tube-foot of an ophiuroid echinoderm, Hemipholis elongata

The morphology of the tube-foot of the brittlestar, Hemipholis elongata was examined by transmission and scanning electron microscopy. The entire surface of the tubefoot is covered by microvilli and a thick cuticle layer. At the tip of the tube-foot the cuticle layer is thinner and sensory-secretory complexes are seen. These are composed of two secretary cells and a central ciliated sensory cell. Scanning electron microscopy shows that the cilium which extends from the receptor cell ends flush with the surrounding microvilli. These studies suggest that the tube-feet in ophiuroids are important structures in sensory-reception, gasexchange as well as locomotion. The hemoglobin containing cells within the lumen of the tubefeet may serve in oxygen transport and storage.     

Filamentous structure of the external surface of abalone eggs revealed by quick-freeze deep-etch technique

The external surface of abalone eggs was examined by thin section and quick-freeze, deep-etch electron microscopy. In thin sections, networks of fine filaments were found interconnecting the adjacent microvilli on the surface of unfertilized eggs. Quick-freeze, deep-etch electron microscopy revealed the three-dimensional structure of these networks of filaments on the external surface of the egg. Mainly two networks of filaments were identified; one was composed of thicker (14–19 nm) filaments interconnecting with the neighboring microvilli nearly horizontally, and the other was composed of thinner (8–14 nm) branched filaments closely surrounding the microvilli surface as well as highly interconnecting neighboring microvilli in a polygonal pattern. The overall structure of the filamentous network on the egg surface showed no distinct alteration after fertilization. These networks of filaments observed on the egg surface may play a key role in sperm–egg interaction.     

Surface fine structure of the globiferous pedicellariae of the regular echinoid,Psammechinus miliaris gmelin

The globiferous pedicellariae of Psammechinus miliaris are described. Two fixation methods giving minimal distortion and rapid tissue hardening were adapted for soft tissue preparation for scanning electron microscopy. The pedicellarial valves are covered by a microvillous epithelium. The outer valve epithelial microvilli overlying red spherulocytes in the epidermis are characterized by a filament matrix radiating out from each microvillus. These microvilli may function in epidermal absorption of organic solutes. The inner valve microvilli are more densely packed and the filament matrix is absent. Ciliation is confined to the inner valve surface where the cilia are concentrated to form a distal sensory pad and sensory hillock. Behavioural evidence suggests a chemo- and mechanosensory role for the inner valve surface.     

Role of microvilli in surface changes of synchronized P815Y mastocytoma cells

The surface morphology of synchronized P815Y mastocytoma cells has been examined by scanning electron microscopy. Early G1 cells are comparatively smooth or light villated, whereas at later stages the surface becomes progressively more villated. In G1 cell most microvilli have a uniform diameter, whereas in S and G2 cells, many microvilli show branching and often originate from much larger surface protuberances. Small "blebs" are seen on the surface of many cells but these structures do not appear to be a characteristic feature of cells at any one stage of the cycle. The presence of microvilli increases the total surface of the cell to such an extent that the ratio of volume to surface area remains constant throughout the cell cycle. The mechanism of cytokinesis is thus a physical one, involving the unfolding of previously accumulated microvilli.     

Retention of lens specificity in long-term cultures of diploid rabbit lens epithelial cells

The ventral surface of the deep layer of gastrulating quail and chick embryos was examined using scanning electron microscopy. On the basis of cell protrusions, three or four different cell types were recognized. Cells covered with microplicae were found in the caudal region of the germ and as a narrow band extending along the lateral and anterior borders of the area pellucida. Cells covered with microvilli were found in a horseshoe-shaped zone in the anterior part of the germ. Beneath the rostral end of the primitive streak, the flattened deep-layer cells exhibited intercellular ridges and few microvilli. This area was surrounded by cells that usually had extended microvilli. The pattern of these cell types is discussed in relation to the formation of the different tissues that compose the deep layer in gastrulating embryos.     

Surface configuration of mesothelial cells in effusions. A comparative light microscopic and scanning electron microscopic study.

Surface configuration of mesothelial cells identified by light microscopy (LM) has been studied by scanning electron microscopy (SEM). It has been shown that mesothelial cells may have a variable SEM appearance. The surfaces of a small proportion of mesothelial cells are covered by regular microvilli (MV) and show openings of the pinocytotic vesicles. The surfaces of the majority of these cells are covered by vesicles or blebs. An intermediate population of mesothelial cells, i.e., cells displaying side-by-side blebs and MV, has also been observed. The latter cells no longer display pinocytotic vesicles. Occasional mesothelial cells have smooth surfaces. It has been shown by LM and transmission electron microscopy that cells with blebs are viable and capable of mitotic activity. It is concluded that mesothelial cells, detached from their epithelial setting, lose microvilli and pinocytotic vesicles and acquire surface blebs. The possible relationship between mesothelial cells and macrophages based on surface features has been discussed.     

Tissue culture and scanning electron microscopy of breast carcinoma 'cell line MCF-7' from pleural effusion

The surface ultrastructure of tissue-cultured cells derived from the pleural effusion of metastatic scirrhous breast carcinoma in the human MDF-7 cell line was studied by scanning electron microscopy. It was found to form monolayers of various colonies or collections of cells which were either separate or intimately adherent. The surface ultrastructure of the cells was found to be exclusively formed of microvilli. Data suggesting a diagnostic significance of microvilli in cancer cells were discussed. Observations were made which point to the existence of a compensatory absorptive functional activity exerted by the microvilli.     

CONCOMITANT EFFECTS OF INSULIN ON SURFACE MEMBRANE CONFORMATION AND POLYSOME PROFILES OF SERUM-STARVED BALB/C 3T3 FIBROBLASTS

By scanning and transmission electron microscopy we have shown that insulin rapidly reversed changes in surface membrane conformation and polysome profile induced by the transfer of actively growing Balb/c 3T3 fibroblasts from a serum-containing to a serum-free medium. Morphometric analysis of polysome profiles revealed a 94% aggregation of total f ribosomes during logarithmic growth. This figure fell to 78% after 18 h of serum starvation. The number of f ribosomes per unit area of cytoplasm also fell. 1 h of insulin treatment restored aggregation to 92% and increased the number of f ribosomes per unit area of cytoplasm by 22%. Scanning electron microscopy of logarithmically growing cells revealed an abundance of surface microvilli, whereas serum starvation promoted a smooth surface with few microvilli. After 1 h of insulin treatment, microvilli reappeared with a distribution and subcellular organization characteristic of exponential growth. This study shows the combined and rapid effect of insulin on the regulation of polysome formation and the promotion of a specific surface membrane conformation in cultured cells. The observations are consistent with the knowledge that insulin, acting on the surface membrane, can influence such parameters as membrane transport, and the rates of protein and RNA synthesis.     

Changes in cell surface and cortical cytoplasmic organization during early embryogenesis in the preimplantation mouse embryo

Membrane topography and organization of cortical cytoskeletal elements and organelles during early embryogenesis of the mouse have been studied by transmission and scanning electron microscopy with improved cellular preservation. At the four- and early eight-cell stages, blastomeres are round, and scanning electron microscopy shows a uniform distribution of microvilli over the cell surface. At the onset of morphogenesis, a reorganization of the blastomere surface is observed in which microvilli becomes restricted to an apical region and the basal zone of intercellular contact. As the blastomeres spread on each other during compaction, many microvilli remain in the basal region of imminent cell-cell contacts, but few are present where the cells have completed spreading on each other. Microvilli on the surface of these embryos contain linear arrays of microfilaments with lateral cross bridges. Microtubules and mitochondria become localized beneath the apposed cell membranes during compaction. Arrays of cortical microtubules are aligned parallel to regions of apposed membranes. During cytokinesis, microtubules become redistributed in the region of the mitotic spindle, and fewer microvilli are present on most of the cell surface. The cell surface and cortical changes initiated during compaction are the first manifestations of cell polarity in embryogenesis. These and previous findings are interpreted as evidence that cell surface changes associated with trophoblast development appear as early as the eight-cell stage. Our observations suggest that morphogenesis involves the activation of a developmental program which coordinately controls cortical cytoplasmic and cell surface organization.     

The surface topography of the NIH 3T3 line in proliferating and resting states

The surface topography of resting (serum-deprived) and proliferating (serum-stimulated) NIH 3T3 monolayer cell cultures has been examined by scanning electron microscopy. During G1 and S periods of the cell cycle the cells exhibited well pronounced surface microvilli localized mainly in the perinuclear zone, whereas serum deprivation led to a relatively smooth surface with few microvilli. The observed differences are not likely to be associated with the degree of cell spreading over the substrate, rather reflecting metabolic peculiarities of proliferating and resting cells.     

Surface characteristics of isopod digestive gland epithelium studied by SEM

The structure of the digestive gland epithelium of a terrestrial isopod Porcellio scaber has been investigated by conventional scanning electron microscopy (SEM), focused ion beam–scanning electron microscopy (FIB/SEM), and light microscopy in order to provide evidence on morphology of the gland epithelial surface in animals from a stock culture. We investigated the shape of cells, extrusion of lipid droplets, shape and distribution of microvilli, and the presence of bacteria on the cell surface. A total of 22 animals were investigated and we found some variability in the appearance of the gland epithelial surface. Seventeen of the animals had dome-shaped digestive gland “normal” epithelial cells, which were densely and homogeneously covered by microvilli and varying proportions of which extruded lipid droplets. On the surface of microvilli we routinely observed sparsely distributed bacteria of different shapes. Five of the 22 animals had “abnormal” epithelial cells with a significantly altered shape. In three of these animals, the cells were much smaller, partly or completely flat or sometimes pyramid-like. A thick layer of bacteria was detected on the microvillous border, and in places, the shape and size of microvilli were altered. In two animals, hypertrophic cells containing large vacuoles were observed indicating a characteristic intracellular infection. The potential of SEM in morphological investigations of epithelial surfaces is discussed.     

A scanning electron microscope study of the extraembryonic endoderm of the 8th-day mouse embryo

Abstract. Late primitive streak embryos were dissected to reveal the junction between the visceral (VE) and parietal (PE) extraembryonic endoderm. Scanning electron microscopy showed that the two cell types differ markedly in their surface morphology and intercellular organization: the VE cells have numerous apical microvilli and form part of a continuous epithelial layer, while the smoother PE cells are scattered individually over the surface of Reichert's membrane. One interpretation of the morphology of the junction between the two tissues is that visceral endoderm cells in this region are detaching from the epithelial layer, migrating on to Reichert's membrane and differentiating into parietal endoderm. Preparatory to this, the visceral endoderm cells in the junctional zone may undergo extensive reorganization of their surface membranes.     

Scanning Electron microscopic Study on the Early Development of Silkworm Eggs (Bombyx mori L.)

Morphological changes of the surface of eggs of the silkworm Bombyx mori L. were studied during early developmental stages by scanning electron microscopy. The egg surface was covered with numerous microvilli at least until 4 h after oviposition. At 6 h the microvilli were replaced by ruffle-like microprojections. This suggests that developmental changes of the surface structure may occur without direct influence of cleavage nuclei. Immediately before blastoderm cell formation, microvilli reappeared in the presumptive groove area. The ruffles seen on the apical portion of newly-formed blastoderm cells gradually became flattened, while microvilli developed on the lateral side of the cells. The mode of blastoderm cell formation is different from the typical one seen in most species of insects.     

Electron microscopic observation of the invasion process of Cryptosporidium parvum in severe combined immunodeficiency mice

Cryptosporidium parvum mainly invades the intestinal epithelium and causes watery diarrhea in humans and calves. However, the invasion process has not yet been clarified. In the present study, the invasion process of C. parvum in severe combined immunodeficiency (SCID) mice was examined. Infected mice were necropsied; the ilea were double-fixed routinely and observed by scanning and transmission electron microscopy. In addition, the microvillus membrane was observed by ruthenium red staining. Scanning electron micrographs showed elongation of the microvilli at the periphery of the parasite. The microvilli were shown to be along the surface of the parasite in higher magnification. Transmission electron microscopy confirmed that the invading parasites were located among microvilli. Parasites existed in the parasitophorous vacuole formed by the microvillus membrane. The parasite pellicle attached to the host cell membrane at the bottom of the parasite, and then the pellicle and host cell membrane became unclear. Subsequently, the pellicle became complicated and formed a feeder organelle. In addition, invasion of the parasite was not observed in either a microvillus or the cytoplasm of the host cell. Therefore, C. parvum invades among microvilli, is covered with membranes derived from numerous microvilli, and develops within the host cell.     

Scanning and transmission electron microscopic studies of jejunal microvilli of the rat, hamster and dog

Scanning and transmission electron microscopy were used to investigate the surface area and number per unit area of microvilli from jejunal villus epithelial cells in the rat, hamster and dog. The calculated mean microvillus surface area was 0.419 μ², 0.573 μ², 0.751 μ² for the rat, hamster and dog respectively. The largest number of microvilli per square micron freeze dried villus surface was measured in the rat with a mean value of 65. Hamster and dog freeze dried specimens had lower mean values of 54 and 34 microvilli respectively. The total microvilli surface area in square micron per square micron villus surface was more closely related for the three species with values of 27.23 for the rat, 30.94 for the hamster and 25.53 for the dog. These data indicate an inverse relationship between the mean microvillus surface area and population density in the species studied. However, the total microvilli surface area per unit villus surface is relatively similar for the three species. The observed number of microvilli per unit villus surface was shown to vary depending upon the dehydration technique employed for preparation of scanning electron microscopic specimens. This variation probably reflects shrinkage artifact and should be considered in soft tissue studies involving the scanning electron microscope.     

Studies on corneal endothelial growth and repair. IV. Changes in the surface during cell division as revealed by scanning electron microscopy

Changes in the surface morphology of regenerating rabbit, rat and frog corneal endothelial cells in vivo have been investigated by scanning electron microscopy. In adult tissue these cells do not normally divide unless given a stimulus, such as injury. Surfaces of quiescent rabbit and rat cells are devoid of microvilli but display globular projections and surface pits up to 300 nm in diameter. However, regenerating endothelia are characterized by the appearance of microvilli which attain their greatest length when the cells are rounded. At this stage, cells also possess filopodia and broad processes. In cytokinesis, the microvilli have shortened and blebs and ruffles appear for the first time. In contrast to rabbits and rats, frog endothelial cells of noninjured tissue are covered by microvilli and smaller surface pits of 60-70 nm diameters. During regeneration, these cells have reduced numbers of microvilli and extensive foldings of the membrane. Neither blebs nor filopodia occur during the mitotic cycle and ruffles are not detected until cytokinesis.     

The collicular recess organ: Evidence for structural and secretory specialization of the ventricular lining in the collicular recess

Summary The collicular recess organ and adjacent portions of the collicular recess were studied by light microscopy, scanning electron microscopy and transmission electron microscopy. In the collicular recess, the ventricular wall contains folds and is well vascularized. The adluminal ependymal cells generally bear kinocilia and microvilli on their ventricular surface. Among the cilia, many secretory droplets, some axons, and few supraependymal cells are seen. Various stages of apocrine ependymosecretion are observed. In addition to tanycytes, coelocytes are found scattered throughout the ependymal lining of the collicular recess. Coelocytes, characterized by lumina containing cilia and a few microvilli, are accumulated in ependymal and hypependymal positions of the collicular recess organ at the roof of the collicular recess.Supported by PHS grants NS 09914 and T32 CA09156. We thank Dean Wyrick and John McNeill, Jr., for their technical assistanceNRSA Postdoctoral Trainee     

Placentation in garter snakes: scanning EM of the placental membranes of Thamnophis ordinoides and T. sirtalis

Surface topography and cross-sections of the placental membranes were examined by scanning electron microscopy in two species of Thamnophis. The chorionic epithelium of the chorioallantoic placenta consists of broad, squamous cells that lack surface specializations. The apposed uterine epithelium contains ciliated cells and larger, nonciliated cells. Neither the epithelium of the chorion nor that of the uterus is eroded; thus, underlying capillaries are not exposed to the luminal surface. In both the omphaloplacenta and the omphalallantoic placenta, epithelium of the omphalopleure consists of brush-border cells bearing prominent microvilli, interspersed with cells bearing minuscule microvilli. These surface epithelial cells are joined at their apices and their lateral surfaces are extensively sculpted by intercellular channels, presenting the appearance of an epithelium specialized for absorption. Deep to the epithelium lie the yolk spheres of the isolated yolk mass, interspersed with endodermal cells. Surface topography of the uterine epithelia of the omphaloplacenta and omphalallantoic placenta is relatively unspecialized. The acellular shell membrane separates maternal and fetal tissues in each of the three placental types. Marked differences in surface features of the chorioallantois and omphalopleure probably reflect different roles of these membranes in gas exchange and transfer of water and nutrients.