Electron-microscopic study of the excretory system of hungry females of the tick Hyalomma asiaticum P. Sch. et E. Schl. 2]

In H. asiaticum the cells of the Malpighian tubules and these of the rectal cas have the uniform structure: the apical surface is covered with microvilli, the basal plasmatic membrane forms relatively small invaginations. As to ultrastructural characters, there is no distinct division of the Malpighian tubule into departments. The distal ends of the tubules are not only somewhat enlarged and form the so-called ampulla cells of which are noticeably flattened. The microvilli and basal folds of the plasmatic membrane in this area of the tubule are indistinct. The cells of the ampulla and the neighbouring area of the tubule are characterized by the presence of inclusions with mucopolysaccharide secretion confined by the membrane. The microvilli are most developed on cells of the proximal ends of the Malpighian tubules. Well developed microvilli of the rectal sac form a striated border each containing a microtube inside. The basal invaginations are developed here better than in the cells of the Malpighian tubules.     

Scanning electron microscopic studies of virus-infected cells. I. Cytopathic effects and maturation of vesicular stomatitis virus in L2 cells.

L2 cells infected with vesicular stomatitis virus under single-cycle conditions have been studied by scanning electron microscopy after preparation by the critical point drying technique. Three dimensional images of intact cells show bullet-shaped vesicular stomatitis virus virions budding singly and in radiating clusters both from the plasma membrane between cellular microvilli and from the sides of microvilli. Virus-induced cytopathic effects observed by scanning electron microscopy include intermeshing of microvilli, loss of filipodia which attach cells to the substrate, and rounding up and detachment of infected cells from the substrate.     

A scanning electron microscopic study of SV40 infected cells.

The surface of the SV40-infected African green monkey kidney (AGMK) cells was studied morphologically by scanning electron microscopy. In 24 hr post infection (p.i.), the cell surface was covered with slightly elongated microvilli. The microvilli increased in number. In 96 hr.p.i. most of the cells showed SV40-specific cytopathic effects (CPE). Nuclear swellings and the elongation of microvilli were eminent. Microvilli were observed projecting with high densities especially on the nuclear portions of the cell surfaces. Features suggesting cytoplasmic vacuolization were also observed in some cells. Spherical particles viewed in some of the cells at the late stage of infection were considered SV40 virions. Their origin was also discussed.     

Carbohydrate cytochemistry of the intestinal epithelium of Ascaris suum. Nature of the microvilli glycocalyx and basal lamella.

Results of various cytochemical tests demonstrate large deposits of glycogen within the intestinal absorptive cells of Ascaris suum. Carbohydrate material is also associated with the microvilli surface and basal lamella. Staining produced by the periodate-thiocarbohydrazide-osmium procedure was abolished by analine or m-aminophenol. Diastase digestion did not alter the staining on the microvilli surface. Similar results were seen using the silver methenamine procedure. A positive reaction was noted on the microvilli surface, vesicles in both the apical and basal cytoplasm, Golgi apparatus, and basal lamella. Lanthanum nitrate stained the microvilli surface and intercellular spaces between absorptive cells. Alcian blue or cetylpyridinium chloride in combination with lanthanum enhanced the staining produced by lanthanum alone. These results suggest the presence of acidic glycans on both the microvilli surface and basal lamella.     

Morphology of rabbit collecting duct.

Recently the assumed structural and functional homogeneity of the collecting duct (CD) has been questioned. The objective of this study was to determine if heterogeneity occurs in luminal surface membrane structure or in cytoplasmic configuration of cells in the collecting duct or both. Straight segments of cortical and medullary CD were examined in perfusion-fixed rabbit kidneys with scanning electron microscopy (SEM), light (LM) and transmission electron microscopy (TEM). Principal cells were the most abundant cells in all CD regions; intercalated cells comprised 37% of the cell population on the cortex, 18% in the outer medulla, and less than 1% in the inner medulla. SEM revealed two surface patterns among the ciliated principal cells: 1, located in the cortex and outer medulla, with few surface microvilli, and 2, located in the inner medulla, with abundant microvilli. Intercalated cells exhibited four distinctive luminal surface configurations: I, numerous short microvilli; II, both short and elongate microvilli; III, microplicae alone; and IV, both microvilli and microplicae. Intercalated cells with patterns I and II were predominant in the cortex, while cells with patterns III and IV were most common at the corticomedullary junction. TEM confirmed that marked variation existed in cytoplasmic structures of both principal and intercalated cells. These findings may either indicate the presence of several specific types of principal and intercalated cells or reflect different functional states of the principal and intercalated cells. Regardless of their significance, their presence must be considered in studies seeking to establish precise structural-functional relationships in this region of the rabbit renal tubule.     

The hydrosmotic effect of vasopressin: a scanning electrom-microscope study.

Scanning electron-microscopy (SEM) was used to investigate the hydrosmotic effect of vasopressin on the apical surface of urinary bladders of toads Bufo marinus. Bladders were mounted on glass chambers and water fluxes were monitored with an optical method. Tissues were fixed in 2% glutaraldehyde and processed for SEM. Three types of cells were seen on the surface of control bladders:large polygonal (granular) cells, with blunt microvilli; smaller (mitochondria-rich) cells, with longer microvilli; goblet cells. Neither exposure of the bladders to a large osmotic gradient nor exposure to vasopressin in the absence of a gradient altered appreciably the epithelial surface. In contrast, the combination of vasopressin and an osmotic gradient resulted ina conspicuous diminution of the blunt microvilli. However, the small cells with longer microvilli remained unchanged. Identical results were seen with cAMP or theophylline in the presence of an osmotic gradient. These findings suggest that the hydrosmotic effect of vasopressin is mainly exerted on the granular cells of toad bladder and confirm observations made by others with the electron-microscope.     

Characteristics of the upper cell surface in cultures of normal and SV-40 virus-transformed epithelium of mouse kidney. Study with the aid of scanning electron microscopy]

Central cells of the normal epithelial sheet are sparsely covered by microvilli. Numerous microvilli were seen in the regions of intercellular contacts. Marginal cells of sheets had a finely developed lamellar cytoplasm (lameloplasm) with smooth upper surface at their free margins. A transformed cell line (MPTR) resembled normal parent cells by its ability to form monolayered sheets in cultures. More microvilli of increased length appeared on the upper surface of central MPTR cells. The normal structure of lamelloplasm was changed at the free edge of the MPTR sheets. It is suggested that abnormal cell attachment to the substratum may be responsible for the altered cell surface morphology (increased length of microvilli, defective, structure of lamelloplasm) in the MPTR cultures.     

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.     

High-resolution scanning electron microscopic study of the mouse submandibular salivary gland.

The submandibular gland of the mouse was studied by high-resolution scanning electron microscopy, using the osmium-dimethylsulfoxide-osmium method. The three-dimensional structures of the intracellular membranous organelles of acinar cells were clearly revealed. The luminal surface of cisterns of the granular endoplasmic reticulum and Golgi apparatus exhibited particles of 8-15 nm in diameter. The secretory canaliculi presented short microvilli which were irregularly arranged. The striated duct cells were characterized by rich mitochondria arranged vertically in the basal portion. The lamellar mitochondrial cristae were noted in three-dimensional images. The luminal surface extended short microvilli, while that of the excretory duct cell presented complicated microplicae. The capillary endotheliocytes showed a few short microvilli, and their fenestrated areas were bordered by cytoplasmic crests. Fenestrae were 50-80 nm in diameter and showed a plug in their center. The basement membranes of the acini and capillaries showed a spongy structure with various strands and meshes. Collagenous fibrils crisscrossed on their surface.     

A quantitative and morphological study of ectodermal microvilli in ten areas in the control and experimental prenatal rat.

This study provides a baseline of mainly quantitative morphologic information in relation to the ectodermal microvilli in ten areas in the control and experimental prenatal rat with special reference to the period of neural tube closure. Embryos from six litters were used and ten areas were examined mainly with the scanning electron microscope. Statistical analysis showed no significant difference between litters nor between the ten areas examined. In the 376 hr (day 15.6) fetus only the ectodermal cells of the nostril region demonstrated a rich population of microvilli, a fact possibly associated with late maturation of that region. Some evidence is provided to show that there is an increase in the population of microvilli in the 276 hr (day 11.5) embryo following experimentally induced zinc deficiency and introduction of nicotine in the culture medium. The possible mechanisms underlying the increase in ectodermal microvilli are i) an attempt by ectodermal cells to absorb nutrients, ii) a reflection of cells under stress, iii) failure of early embryonic ectodermal cells to shed microvilli normally associated with developmental changes, and iv) a generalized developmental delay rather than some cellular response to a trace element nutritional deficiency and a teratogen.     

Regeneration of proximal tubules of the rat kidney following sublimate necrosis. A scanning electron microscopic study

Necrosis of the proximal tubules of the rat kidney was induced by low (1.5 mg/kg) doses of sublimate. Epithelial necrosis and regeneration were followed by scanning electron microscopy for 10 days. Regressive and regenerative processes were observed simultaneously. The naked basement membrane is first invaded by flat epithelial cells lacking microvilli. Within a few hours microvilli appear followed by the formation of regular brush-border and interdigitations cells. After 7--10 days the newly formed epithelium cannot be distinguished from the intact one.     

Colloidal iron hydroxide-binding to the surfaces of chick embryo fibroblasts transformed by wild-type and a temperature-sensitive mutant of Rous sarcoma virus.

The densities of colloidal iron hydroxide (CIH) particles binding to the surfaces of chick embryo fibroblasts were determined before and after transformation with wild type Rous sarcoma virus and a temperature sensitive (ts) mutant of this virus. On the basis of in vitro behavior, cells transformed by the ts virus manifest a malignant phenotype at 36 degrees C (permissive temperature) and appear normal at 41 degrees C (non-permissive temperature). At the permissive temperatures there is a significant increase in CIH particle-binding to spaces of cell surface between microvilli on the wild type and ts transformed cells. At the non-permissive temperature this significant increase in binding is only observed on the wild type transformant, while the density found on the ts transformant is not significantly different from the untransformed state. Therefore, in vitro characteristics of normalcy and malignancy are reflected in changes in the CIH binding properties of the cell surface spaces between microvilli. The CIH densities observed on the microvilli are significantly different from the density on the spaces between them for each of the classes of cells studied at either temperature. The microvilli are found to bind a lower density of particles in five of the six cases. No correlations between microvilli particle density and transformation to in vitro malignant characteristics were observed.     

The role of microvilli in the agglutination of cells by concanavalin A

Morphological correlates of lectin agglutinability were examined in eight cell lines of varying sensitivity to agglutination by concanavalin A (ConA). The number of microvilli on the surface of cells growing in monolayers was positively correlated with agglutinability. However, when cells were brought into suspension, they all developed numerous microvilli which persisted when the cells were treated with ConA regardless of whether or not they were agglutinated by the lectin. Treatment of cells with dibutyryl cyclic AMP (db-cAMP) and theophylline caused a parallel decrease in agglutinability and numbers of microvilli in monolayer cultures, but suspended cells from control and treated cultures were identical in appearance in the absence or presence of ConA. The surface morphology of cells agglutinated by ConA was very similar to that of cells that spontaneously agglutinated in the absence of the lectin, and surface bound ConA was rapidly withdrawn from microvilli on all cell types. Neither the morphology of cells nor the surface distribution of ConA can explain observed differences in agglutinability.     

Acute lymphoblastic leukemia: a study of 25 cases by scanning electron microscopy.

Cells from 25 cases of acute lymphoblastic leukemia (ALL) were studied under the scanning electron microscope (SEM). In 24 of the cases, the vast majority of circulating leukaemic cells had few microvilli. Villous cells were rarely encountered and prominent ridge-like profiles and ruffled membranes were not seen. Only six cases were studied by immunological techniques and four of the cases were of the null type while in two the cells bore detectable T-markers. It seems that ALL is almost always associated with the presence of cells with few microvilli in the peripheral circulation, differing in this respect from most cases of CLL. Although circulating leukaemic lymphocytes with few microvilli are sometimes seen in CLL, the most frequent cell type encountered is a more villous lymphocyte. Differences between leukaemic cells from patients with ALL, CLL and non-lymphoblastic leukaemias are discussed. It appears that SEM may help to distinguish lymphoblastic and nonlymphoblastic leukaemic cells in many instances and can be used as a useful adjunct to other modes of microscopy in the diagnosis of acute leukaemia.     

Lipid-cell interactions. Induction of microvilli on the cell surface by liposomes

Treatment of cells with sonicated egg lecithin (EL) liposomes induced microvilli on the surface of mouse embryo fibroblasts and cells of an epithelioid MPTR strain. Unsonicated liposomes and sonicated dipalmitoyllecithin (DPL) liposomes do not induce microvilli on the surface of these cells. It is supposed that microvilli induction is caused by modification of the cell surface composition by small liquid-crystalline liposomes (e.g. by fusion with plasma membrane or transfer of some components from the cell surface to liposomes and vice versa). Microvilli induction by lipsomes provides a system for investigation of their role in cell life.     

Diminution of L cell microvilli following exposure to 25-hydroxycholesterol.

The effect of sterol depletion on the topology of mouse L cells was studied by scanning electron microscopy. Treatment of cells with 25-hydroxycholesterol inhibited the synthesis of cellular sterol and diminished the number of microvilli on the cell surface. Simultaneous addition of mevalonic acid or cholesterol to cells during treatment with the inhibitor prevented the loss of microvilli. These results demonstrate that cholesterol is important in maintaining the ultrastructure of the surface membrane of nucleated mammalian cells.     

A scanning electron microscopic study of the luteo-follicular complex. II. Events leading to ovulation.

Morphological changes on the ovarian surface of different mammals both before and during ovulation have been examined by scanning electron microscopy. Preovulatory follicles were blisterlike structures that protruded markedly from the ovarian surface. Basal areas of preovulatory follicles were covered with polyhedral cells containing numerous microvilli, whereas on the lateral surfaces, superficial cells were elongated and possessed few microvilli. At the apex of the follicle, cells were very flattened and possessed few microvilli, which were present only in regions of intercellular contact. In some apical areas, cells appeared to be degenerating, whereas in other regions, groups of cells had "sloughed off." In addition, a fluidlike material was observed to exude from intercellular spaces of the superficial epithelium and to cover some apical cells. By transmission electron microscopy, the same fluidlike material was observed to (1) infiltrate the connective tissue of the tunica albuginea, (2) accumulate under the basal lamina, and (3) distend intercellular spaces of the superficial epithelium. Just prior to ovulation, large, irregular areas of the apex were ruptured and the oocyte, covered with a large amount of fluid, appeared to emerge from the follicle. At ovulation, the oocyte was not completely covered with follicle cells and the zona pellucida was clearly evident. The surface of the zona was quite irregular and contained numerous infoldings, channels and crypts. Follicle cells had polyhedral or star shapes and possessed large cytoplasmic evaginations that obliquely penetrated the zona. Both the zona pellucida and corona cells were covered with a fine layer of granular material. The SEM results and parallel TEM observations suggest that a local increase of fluids (edema) may be an important factor in the final decomposition of the distended and weakened apex of the preovulatory follicle. In addition, the participation of follicle cells, smooth muscle cells and the oviduct in the escape of the oocyte from the ruptured follicle is discussed.     

Regulation of surface topography of mouse peritoneal cells. Formation of microvilli and vesiculated pits on omental mesothelial cells by serum and other proteins

The mesothelial cells of the mouse omentum provide an in vivo model for the study of the mobilization of labile microvilli on the cell surface. These mesothelial cells are sparsely covered with microvilli and large pits 150--400 nm in diameter, termed vesiculated pits. On the unstimulated cell, the microvilli average 44/100 microns2 and pits, 30/100 microns 2 of surface and they are rapidly induced to increase in number by the intraperitoneal injection of isologous mouse serum. After 2 min, microvilli increase threefold, continue to sevenfold at 30 min, and decrease to fourfold at 90 min. Vesiculated pits increased with similar kinetics. Bovine serum albumin and gamma globulin also stimulate the microvilli and pits to form, but the response is a slow, gradual rise to five- or sixfold the normal value at 90 min. Evidence indicates that multiple factors, possibly including insulin and immunoglobulins, are involved in the effect of serum. The close physical and temporal relationship between microvilli and pits suggests that a correlation exists in their mobilization by the cell and it is hypothesized that microvilli function in the regulation of the cortical microfilament network in effecting this mobilization.     

Morphometric analysis of epithelial cells of frog urinary bladder, II. Effect of ADH, calcium ionophore (A23187) and verapamil on isolated dissociated cells

Isolated frog urinary bladder epithelial cells, upon dissociation lose their polarity and develop microridges and occasional microvilli in a global fashion. These cells, when exposed only to isotonic Ringer's solution manifest a membrane conformation with smooth discontinuous microridges, a cytoplasm with numerous free ribosomes, rough ER, thin Golgi cisternae, mitochondria, small vacuoles, electron-dense granules, few microtubules, and numerous microfilaments and intermediate filaments with an apparent random distribution, the dissociated cells, when treated with ADH or calcium ionophore (A23187), have the appearance of numerous elongated microvilli over the entire cell surface. The cytoplasm, under these conditions, is occupied by large vacuoles with a distribution of long profiles of aggrephores and associated vesicles. The peripheral cytoplasm as well as the cavities of the elongated microvilli of these cells contain large concentrations of microfilaments often showing a strong axial orientation to the long axis of the microvilli. Many of these filamentous elements appear in contact with the apical membrane of these microvilli with an alignment with the external glycocalyx. There is an indication that these morphocytological changes as revealed by SEM and TEM studies, correlated with a redistribution and realignment of microfilaments and possibly microtubules as detected by fluorescent microscopy using immunofluorescent antibody labeling for actin and tubulin. Cells treated with verapamil, a calcium antagonist, presented dwarf and stout microvilli with little detectable alterations in the cytoplasmic compositions from that of non-hormonal treated cells. Verapamil prevented ADH induction of microvilli, with the membrane, under these conditions, appearing as compact microridges. The results indicate that calcium ionophore, like ADH, produces intense formation of microvilli in dissociated cells, mobilization and realignment of microfilaments, microtubules, increase in the density of vesicles, aggrephores and possibly secretory granules, whereas the calcium antagonist, verapamil, opposes these actions. The results suggests a prominent role of calcium in the morphological changes induced by ADH.     

A scanning electron microscope study of mouse peritoneal mesothelium.

As seen in the scanning electron microscope, peritoneal mesothelial cells of the mouse diaphragm, anterior abdominal wall and intestinal serosa carry numerous microvilli. These microvilli are absent over certain areas of the cell surface and are sometimes, interlocked in meshwork patterns or coronal formation. The apical cell membranes of the mesothelium at the base of the microvilli, are invaginated by many plasmalemmal vesicles and vacuoles and carry a number of protruding spherical structures. Deep circular craters, giving the impression of stomata, are also visible.