Blast-like cell compartment in carcinogen-induced proliferating bile ductules.

Small non-epithelial cells with morphological features of blast-like cells are found within a proliferating intrahepatic biliary system after institution in rats of a diethylnitrosamine, 2-acetylaminofluorene, partial hepatectomy carcinogenesis protocol. Two to three days after the partial hepatectomy step of the carcinogen protocol, the small blast-like cells are evident beneath a layer of bile ductule epithelial cells that line the walls of the bile ductules. The basally located small cells are not exposed to the bile ductule lumen or to the surrounding basal lamina. They ranged in size from 3.0 to 5.0 microns, exhibit an undifferentiated phenotype, including a high nucleus-to-cytoplasm ratio and no to minimal differentiated cytoplasmic and surface structures. Mitosis of blast-like cells are evident, and their nuclei express proliferating nuclear cell antigen. The ductal blast-like cells do not express cytokeratin 19, oval cell antigen 270.38, or actin immunoreactivity, in contrast to bile ductule epithelial cells. The basal cells, as well as bile ductule epithelial cells, are negative for a panel of T and B lymphocyte surface markers in contrast to lymphocytes present in the connective tissue stroma surrounding the bile ductules and throughout the hepatic parenchyma. Within some segments of the biliary system, some of the ductal blast-like cells increased in size to approximately 10 microns and showed increased amounts of cytoplasmic organelles and plasma membrane filapodia but did not develop the polarized phenotype of bile ductule epithelial cells (ie, apical microvilli, desmosomes, connections to bile ductule cells, and exposure to duct lumen); however, their nuclear morphology was essentially similar to the smaller basal cells. We also found bile ductules to contain two types of polarized epithelial cells, one with the characteristic oval nucleus of the oval/bile ductule epithelial cells and the other, transitional epithelial cells with a rounder nucleus and prominent nucleoli. The transitional cells exhibit a similar apical-basal polarity and antigenic phenotype as the oval/bile ductule epithelial cells. However, transitional cells are larger and have an overall less dense cytoplasm than the bile ductule epithelial/oval cells, and some show apical microvilli changes and small catalase-positive peroxisomes. These observations indicate that a greater diversity of cell types exist within intrahepatic bile ductules of rats treated with carcinogens. Furthermore, the nonpolarized ductal blast-like cells undergo proliferation and are significantly different in phenotype from other hepatic cells previously reported as candidates for liver progenitor cells.     

Expression of vimentin in proliferating and damaged bile ductules and interlobular bile ducts in nonneoplastic hepatobiliary diseases.

Biliary epithelial cells express characteristically cytokeratin in their cytoplasm in normal and diseased livers. The present study disclosed that vimentin was frequently expressed in the cytoplasm of proliferating and damaged bile ductules and interlobular bile ducts, while their normal counterparts were negative for vimentin. Although this expression itself seemed nonspecific to any of the hepatobiliary diseases examined, bile ductules and interlobular bile ducts were frequently positive in chronic cholestatic and necroinflammatory liver diseases. In biliary epithelial cells, vimentin was localized around the nucleus or in the subnuclear regions, when present. Immunoelectron microscopically, reaction products for vimentin and for cytokeratin were found on bundles of intermediate filaments in the cytoplasm of biliary epithelial cells. The former was found mostly in the paranuclear and subnuclear regions, while the latter detected around the desmosomes, in addition to the paranuclear cytoplasm. Vimentin and cytokeratin were also seen together under immunoelectron microscopy on the same intermediate filaments. It seems likely that aberrant expression of vimentin in bile ductules and interlobular bile ducts and heterogeneous antigenic expression of intermediate filaments in the same biliary epithelial cells may be related to proliferation of, reorganization of, or damage to the ductular and ductal biliary cells in a variety of hepatobiliary diseases.     

Scanning electron microscopy

The technology of scanning electron microscopy (SEM) is described in brief. Its application to the study of cell and tissue structure is demonstrated and the evolution of the concept of 'topographical histology' is discussed. Some current literature on the applications of SEM is reviewed under the headings of experimental pathology and human pathology. While SEM has become an indispensable technique for the experimental morphologist, its application to diagnostic pathology and cytology is still at an early exploratory stage.     

Scanning electron microscopy of body fluids.

Scanning Electron Microscopic (SEM) examination of body fluid specimens submitted for cytopathological diagnosis is technically easy and can be accomplished within hours. Specimens refrigerated for as long as 72 hr show no significant structural alterations that would interfere with recognition of diagnostically significant cells. SEM is particularly well suited for these specimens because the cells are free floating, and even cells in clusters have "natural" surfaces. Clinical uses of SEM on body fluids include the identification of ambiguous cells, distinction of reactive (benign) mesothelial cells from metastatic adenocarcinoma, and distinction of lymphoid cells from small cell carcinoma of the lung. In addition, SEM of these fluids assists cytologists to better understand the cellular features and associations seen in the light microscope. Ultrastructural analysis can be an important component of the Quality Assurance Plan for those cytodiagnostic laboratories that have access to an electron microscopy facility.     

Scanning electron microscopy of mouse intrahepatic structures.

Livers of normal mice were prepared for scanning electron microscopic (SEM) study by fracturing or slicing lobes fixed in situ by perfusion with paraformaldehyde. Fracturing fixed liver exposes surfaces of hepatocytes and sinusoidal endothelial cells, whereas slicing the tissue reveals the internal structures of portal tracts. Earlier studies have delineated the major surface characteristics of hepatocytes and sinusoidal endothelial cells of rats. Surfaces of hepatocytes in the mouse differ from those in the rat by having larger and more numerous peg and hole complexes on the flat intercellular surface and less dense populations of perisinusoidal microvilli. Sinusoidal endothelial cells in the mouse have fewer large fenestrations than do similar cells in the rat; clusters of small fenestrations appear similarly distributed in both species. The surfaces of capsular mesothelial cells, Kupffer cells, bile duct epithelial cells, and endothelial cells of major vessels are similar in rat and mouse.The methods described for preparing liver for SEM examination are simple, rapid, and reproducible. The SEM is a useful tool with which to study intrahepatic surface structures, and its use may allow further correlations to be made between hepatic structure and function in both health and disease.     

Scanning electron microscopy of synaptonemal complexes

The novel application of scanning electron microscopy to study whole-mount surface-spread synaptonemal complex complements of rye (Secale cereale) and rat (Rattus norvegicus) is described. Scanning electron microscopy is able to resolve the third dimension in such preparations and improve the tracing of the continuity of lateral elements without losing information that could be obtained by conventional transmission electron microscopy. This improvement is likely to benefit detailed studies of chromosome synapsis and karyology, and may provide a means of circumventing technical obstacles inhibiting the use of surface-spreads as substrates forin situ hybridization under the electron microscope.     

Scanning electron microscopy in oral cytology

Sixty-three cell smears from oral mucosa were studied by scanning electron microscopy. Among them, smears from ten healthy controls showed three kinds of cells: flat (superficial) cells with linear anastomosing microridges and microvilli; polygonal (intermediate) cells with well-defined crests between their faces and numerous microvilli; and round (parabasal) cells entirely covered by microvilli. Twenty-five smears from patients with untreated squamous-cell carcinoma showed enlarged polymorphous cells (round, globular, and elongated); microvilli, variable in their dimensions, were irregularly distributed on their surfaces. Eighteen smears from patients with severe epithelial dysplasia showed polymorphous cells with discontinuous but obvious edges separating their faces and with irregular microvilli and ridges. Nine smears were also performed in patients with various other mucosal lesions (lichen planus, leukoplakia, white sponge naevus, pemphigus vulgaris, and herpes). All of these smears were studied comparatively between examination of smears and biopsies by light microscopy. The smears were truly reliable, particularly for distinguishing between dysplastic and tumoral cells.     

Morphogenesis of chordae tendineae. I: Scanning electron microscopy

The formation of the chordae tendineae of the left atrioventricular valve in the chick embryo is described using scanning electron microscopy. These supportive structures for the valve cusps develop between days 6 and 13 of incubation. Elevations which represent the primitive papillary muscles form on the ventricular wall. These elevations bifurcate into thin, weblike folds which are attached to the primitive valve cusps. The folds are the primordia of the chordae tendineae. Linear ridges develop on the web between the cusp and papillary muscle. These ridges alternate with depressions. The depressions become perforate to create the individual chorda from the linear ridges. Multiple perforations form initially but they typically consolidate to create one large aperture between two chordae. Some interchordal connections of tissue do persist throughout the period studied. During the period of perforation, prominent rounded cells are typical of the endocardium between the chordae. These cells are similar at the scanning electron microscope level to those present in the formation of the foramina secunda of the atrial septum. Primary, secondary, and tertiary chordae tendineae appear to develop in the same manner. First order chordae (those attached at the free margin of a cusp) are not found in the chick embryo. The majority of the chordae are second order, which insert into the ventricular surface of the cusp a short distance from the free edge. These chordae typically have a horizontal banding or grooving along their length. Third order chordae which extend from the papillary muscle to the ventricular wall are also present. It is suggested that chordal development is a programmed cellular and hemodynamic event.     

Scanning electron microscopy of Blastocystis hominis cysts

Scanning electron microscopy of Blastocystishominis cysts reveals that some cysts have an outer coat, whereas others are naked. If intact, the outer coat forms a fan-like structure around the cyst and its surface is granular. The fragmented outer coat adheres to other cysts and bacteria, forming irregular clumps. Received: 15 September 1997 / Accepted: 2 December 1997