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PubMed2003

Apicobasal polarization: epithelial form and function.

The structure and function of epithelial sheets generally depend on apicobasal polarization, which is achieved and maintained by linking asymmetrically distributed intercellular junctions to the cytoskeleton of individual cells. Recent studies in both Drosophila and vertebrate epithelia have yielded new insights into the conserved mechanisms by which apicobasal polarity is established and maintained during development. In mature polarized epithelia, apicobasal polarity is important for the establishment of adhesive junctions and the formation of a paracellular diffusion barrier that prevents the movement of solutes across the epithelium. Recent findings show that segregation of ligand and receptor with one on each side of this barrier can be a crucial regulator of cell-cell signaling events.

Animals↗

PubMed1981

Ultrastructure of myocardial widened Z bands and endocardial cells in two teleostean species.

Widened myocardial Z bands and endocardial cells are described in two teleostean species Cichlasoma meeki and Corydoras aeneus. Widened Z bands containing mainly amorphous and electron-dense material were seen in a number of myocardial cells. Further, similar material may occur in large amounts beneath the sarcolemma and at intercellular junctions. Occasionally, we observed continuity between the latter material and that in expanded Z bands. In C. meeki the ventricular endocardial layer consists of two structurally different cell types, whereas in C. aeneus only one cell type was seen. The functional aspects of widened Z bands are discussed.

Animals↗

PubMed1994

Cell cycle of transdifferentiating supporting cells in the basilar papilla.

Mitosis of supporting cells has been shown to contribute to the cellular repopulation of the basilar papilla after acoustic trauma. In the present work we report data obtained with light and transmission electron microscopy after acoustic trauma in chicks. We report changes that occur in cell shape, surface morphology, intercellular junctions, nuclear shape and location, and cytoplasmic organization of supporting cells after trauma. The findings strongly suggest that supporting cells transdifferentiate and that the proliferative pattern is similar to interkinetic nuclear migration, as previously shown in the developing neural tube and basilar papilla. S-phase nuclei were positioned adjacent to the basement membrane, suggesting that interaction with the extracellular matrix may occur during the cell cycle. Supporting cells divided with the long axis of the spindle parallel to the reticular lamina and displayed no signs of intercellular communication during mitosis. This suggested to us that the fate of the progeny cells is determined prior to mitosis and that the progeny may be of identical phenotypic fate. Dividing cells had a smooth apical surface. The smooth surface may provide a marker to help identify dividing cells with scanning electron microscope analysis.

Animals↗

PubMed1972

Permeability of intestinal capillaries. Pathway followed by dextrans and glycogens.

The pathway followed by macromolecules across the wall of visceral capillaries has been studied by using a set of tracers of graded sizes, ranging in diameter from 100 A (ferritin) to 300 A (glycogen). Polysaccharide particles, i.e. dextran 75 (mol wt approximately 75,000; diam approximately 125 A), dextran 250 (mol wt 250,000; diam approximately 225 A), shellfish glycogen (diam approximately 200 A) and rabbit liver glycogen (diam approximately 300 A), are well tolerated by Wistar-Furth rats and give no vascular reactions ascribable to histamine release. Good definition and high contrast of the tracer particles were obtained in a one-step fixation-in block staining of the tissues by a mixture containing aldehydes, OsO(4) and lead citrate in phosphate or arsenate buffer, pH 7.4, followed by lead staining of sections. The glycogens and dextrans used move out of the plasma through the fenestrae and channels of the endothelium relatively fast (3-7 min) and create in the pericapillary spaces transient (2-5 min) concentration gradients centered on the fenestrated sectors of the capillary walls. The tracers also gained access to the plasmalemmal vesicles, first on the blood front and subsequently on the tissue front of the endothelium. The particles are temporarily retained by the basement membrane. No probe moved through the intercellular junctions. It is concluded that, in visceral capillaries, the fenestrae, channels, and plasmalemmal vesicles, viewed as related parts in a system of dynamic structures, are the structural equivalent of the large pore system.

Animals↗

PubMed1991

Concomitant changes in endothelial cell junctions and extracellular matrix components in the chick embryo aorta.

According to previous studies, a process of endothelial activation seems to be occurring in the chick embryo between days 7 and 18. Also, endothelial cells respond to collagen as a substratum between 12 and 18 days, and this response diminishes until it almost disappears after birth. In the present study, aortas from chick embryos (days 7 to 21), and from chicks (14 days posthatching) were used. The results obtained by the freeze-fracturing technique, showed that between days 12 and 14 the intramembranous particles were aggregated into linear or clustered arrays in the fracture P-face of endothelial cells. This could signify that some kind of gap junction-like coupling may occur between adjacent endothelial cells. Our results also indicate that in advanced stages (21-day-old chick embryos and 14-day-old chicks) the growth of small aggregates into larger aggregates or plaques could occur. In addition to gap junctions, the presence of macular and linear tight junctions, reported as focal tight junctions (day 14 of development) macular and linear tight junctions with free-ending strands oriented parallel to one another (21 days) and smooth contoured ridges (14 days post-hatching) were observed. This sequence of changes may represent a development from linear to macular, to a more occluding arrangement, and may also reflect an endothelial cell polarization. Histochemical study of proteoglycans was done by using cuprolinic blue according to the critical electrolyte concentration method. Cuprolinic blue-positive granular, elongated and microfibrillar materials were found in the subendothelial region, forming a meshwork that occupies the extracellular space. Qualitative and quantitative changes were observed both in proteoglycans and in other extracellular matrix components throughout development, suggesting an increase in extracellular matrix complexity. These results lead us to suggest that the assembly of a more complex extracellular matrix, concomitantly with the formation of intercellular junctions during development, might influence the polarization of endothelium in the aorta of the chick embryo.

Animals↗

PubMed1981

Freeze-fractured replica of Schlemm's canal and the trabecular meshwork in the primate.

Using a freeze-fracture technique, the fine structure of the Schlemm's canal and trabecular meshwork in the monkey was studied with special reference to intercellular junctions. Gap junctions were observed between the endothelial cells of Schlemm's canal and between the trabecular meshwork cells. Maculae occludentes were rarely observed between the endothelial cells of the inner wall of Schlemm's canal. The trabecular meshwork cells appeared to act in an electrotonic and metabolic syncytium.

Animals↗

PubMed1979

Microvascular permeability to macromolecules in thermal injury.

Thermal injury of the skin causes an inflammatory reaction with formation of edema, mainly due to vasodilatation, increased extravascular osmotic activity and increased microvascular permeability to macromolecules. These reactions are due to local and systemic effects . At the site of injury heat itself causes microvascular damage. Vascular changes may also be mediated by vasoactive compounds, e.g. liberation of histamine and increased synthesis of prostaglandins. Reflex mechanisms elicited via the nervous system must also be considered. Morphological studies revealed increased number of vacuoles, a large number of open endothelial intercellular junctions and changes of the interstitial tissue at the site of thermal injury. The vascular reactions described can be modified by drugs, especially indomethacin which inhibits the synthesis of prostaglandins and drugs which competitively antagonize the effects of histamine at H2-receptors.

Animals↗

PubMed1981

Fetal and neonatal rat intestinal capillaries: a TEM study of changes in the mural structure.

The development of intestinal mucosal capillaries was studied in Wistar rats from the fourteenth day of gestation through the second postnatal day with the transmission electron microscope. The microvessels develop first as continuous capillaries without a basal lamina and become fenestrated during later stages of gestation. In the thickened areas of the cytoplasm of endothelial cells at early stages, there is a paucity of pinocytotic vesicles; but some vesicles are observed which are larger than those in the adult. Later in gestation these larger vesicles can still be seen, but the frequency of their occurrence decreases with the maturation of the vessels. The intercellular junctions vary in length and shape, and the space between the outer leaflets of the apposed cell membranes is usually 20 nm. Surrounding the abluminal surface of the endothelium, the incipient basal lamina appears attenuated and incomplete until at least the second day of neonatal life.

Animals↗

PubMed2005

p38gamma regulates the localisation of SAP97 in the cytoskeleton by modulating its interaction with GKAP.

Activation of the p38 MAP kinase pathways is crucial for the adaptation of mammalian cells to changes in the osmolarity of the environment. Here we identify SAP97/hDlg, the mammalian homologue of the Drosophila tumour suppressor Dlg, as a physiological substrate for the p38gamma MAP kinase (SAPK3/p38gamma) isoform. SAP97/hDlg is a scaffold protein that forms multiprotein complexes with a variety of proteins and is targeted to the cytoskeleton by its association with the protein guanylate kinase-associated protein (GKAP). The SAPK3/p38gamma-catalysed phosphorylation of SAP97/hDlg triggers its dissociation from GKAP and therefore releases it from the cytoskeleton. This is likely to regulate the integrity of intercellular-junctional complexes, and cell shape and volume in response to osmotic stress.

Adaptor Proteins, Signal Transducing↗

PubMedDate not supplied

The vasculature of the rat embryo: an electron microscope study.

The ultrastructure of portions of the arterial and venous systems of the 11.5 day old Wistar rat embryos has been studied by scanning and transmission electron microscopy. The vessels at this stage of development are in the form of capillaries, and the arterial and venous types can be distinguished by the morphology of the endothelial cells by SEM. The endothelial cells of the arterial vessels gave prominent nuclear bulges and numerous microvilli apart from their spindle shape, whilst those of the veins appear flattened, are polygonal in shape, and have few microvilli. Transmission electron microscopy shows that the endothelial cells of the arteries and veins are identical in structure. The ultrastructure of these cells resembles that of endothelial cells at later stages of development including the adult type in that mature forms of cytoplasmic organelles are obtained. In studies on the intercellular junctions and fenestrations with lanthanum nitrate, the impression is formed that the vessels at this stage are impermeable to small molecular size particles, compared with adult capillaries. This suggests that cytoplasmic vesicles must play a major role in the transport of macromolecules in the 11.5 day embryonic vessels.

Animals↗

PubMed1980

Morphogenetic movements during the early development of the chick eye. An ultrastructural and spatial reconstructive study. B. Invagination of the optic vesicle and fusion of its walls.

Cell death as occurring in the developing optic cup of two to three-day-old chick embryos was investigated with the transmission electron microscope. Two circumscribed areas of cell death were found: The first appears during phase 1 (18 somites, stage 13-) in the middle of the invaginating optic vesicle wall; the second appears during phase 3 (24-28 somites, stages 15 and 16) in the optic stalk where it is connected with the diencephalon. Ultrastructural observations of dead cells with clumped nuclei are phagocytosed by neighbouring neuroepithelial cells. No invasion of macrophages from the mesenchyme was observed. Necrotic cells were occasionally found in the optocoel. After the invagination of the optic vesicle has been completed (at the end of the third day incubation) the layers of the optic cup meet, but there is no real cytoplasmic fusion. Some intercellular junctions are suggested to be precursors of gap junctions occurring in later stages. The role of changing cellular connections between lateral cell surfaces during invagination of the optic vesicle is discussed. Such a process could be responsible for the lengthening of the non-invaginating optic vesicle wall, i.e. the outer layer of the optic cup.

Animals↗

PubMed2001

Heterogeneity of endothelial junctions is reflected by differential expression and specific subcellular localization of the three JAM family members.

Endothelial cells are linked to each other through intercellular junctional complexes that regulate the barrier and fence function of the vascular wall. The nature of these intercellular contacts varies with the need for permeability: For example, in brain the impervious blood-brain barrier is maintained by "tight" contacts between endothelial cells. By contrast, in high endothelial venules (HEVs), where lymphocytes continuously exit the bloodstream, the contacts are generally leaky. The precise molecular components that define the type of junction remain to be characterized. An immunoglobulin superfamily molecule named JAM-2, specifically expressed in lymphatic endothelial cells and HEVs, was recently identified. JAM-3 was cloned and characterized in the current study, and JAM-1, -2, and -3 were shown to form a novel protein family belonging to the larger cortical thymocyte Xenopus (CTX) molecular family. Using antibodies specific for each of the 3 family members, their specific participation in different types of cell-cell contact in vivo and their specific and differential localization in lateral contacts or tight junctions were demonstrated. Furthermore, it was shown that JAM-1 and JAM-2 differentially regulate paracellular permeability, suggesting that the presence of JAM-1, -2, or -3 in vascular junctions may play a role in regulating vascular function in vivo.

Amino Acid Sequence↗

PubMed2006

Hepatocyte nuclear factor 4alpha orchestrates expression of cell adhesion proteins during the epithelial transformation of the developing liver.

Epithelial formation is a central facet of organogenesis that relies on intercellular junction assembly to create functionally distinct apical and basal cell surfaces. How this process is regulated during embryonic development remains obscure. Previous studies using conditional knockout mice have shown that loss of hepatocyte nuclear factor 4alpha (HNF4alpha) blocks the epithelial transformation of the fetal liver, suggesting that HNF4alpha is a central regulator of epithelial morphogenesis. Although HNF4alpha-null hepatocytes do not express E-cadherin (also called CDH1), we show here that E-cadherin is dispensable for liver development, implying that HNF4alpha regulates additional aspects of epithelial formation. Microarray and molecular analyses reveal that HNF4alpha regulates the developmental expression of a myriad of proteins required for cell junction assembly and adhesion. Our findings define a fundamental mechanism through which generation of tissue epithelia during development is coordinated with the onset of organ function.

Animals↗

PubMed2006

Understanding ERM proteins--the awesome power of genetics finally brought to bear.

In epithelial cells, the Ezrin, Radixin and Moesin (ERM) proteins are involved in many cellular functions, including regulation of actin cytoskeleton, control of cell shape, adhesion and motility, and modulation of signaling pathways. However, discerning the specific cellular roles of ERMs has been complicated by redundancy between these proteins. Recent genetic studies in model organisms have identified unique roles for ERM proteins. These include the regulation of morphogenesis and maintenance of integrity of epithelial cells, stabilization of intercellular junctions, and regulation of the Rho small GTPase. These studies also suggest that ERMs have roles in actomyosin contractility and vesicular trafficking in the apical domain of epithelial cells. Thus, genetic analysis has enhanced our understanding of these widely expressed membrane-associated proteins.

Actomyosin↗

PubMed1999

Characterization of human vascular endothelial cadherin glycans.

The glycosylation pattern of human vascular endothelial cadherin (VE-cadherin), purified from cultured human umbilical cord vein endothelial cells, was analyzed. VE-cadherin was metabolically radiolabeled with d-[6-(3)H]glucosamine, isolated by immunoprecipitation, purified by SDS-PAGE and in-gel digested with endoproteinase Asp N. Oligosaccharides were sequentially released from resulting glycopeptides and analyzed by chromatographic profiling. The results revealed that VE-cadherin carries predominantly sialylated diantennary and hybrid-type glycans in addition to some triantennary and high mannose-type species. Highly branched, tetraantennary oligosaccharides were found in trace amounts only. Immunohistochemical labeling of VE-cadherin and sialic acids displayed a codistribution along the intercellular junctions in endothelial cells of human umbilical arteries, veins, and cultured endothelial monolayers. Ca(2+)-depletion, performed on cultured endothelial cells, resulted in a reversible complete disappearance of VE-cadherin and of almost all sialic acid staining from the junctions. Sialidase treatment of whole cells caused a change of VE-cadherin immunofluorescence from a continuous and netlike superstructural organization to a scattered inconsistent one. Hence, cell surface sialic acids might play a role in VE-cadherin organization.

Actins↗

PubMed1975

Culture of arterial endothelial cells: characterization and growth of bovine aortic cells.

Arterial endothelial cells were obtained from bovine aortae by mild treatment with collagenase and medium perfusion. These cells were cultured in RPMI-1640 medium containing 15mM Hepes buffer and 35% fetal calf serum at pH 7.35. Essentially all (90-95%) the effluent cells were viable and 80% of these cells attached to the substratum within 1 hour. Small patches of attached cells coalesced to form confluent monolayers in 3-5 days. Confluent monolayers of endothelial cells consisted of a homogeneous population of tightly packed, polygonal cells. Selected cultures were serially subcultured (trypsin-EDTA) for 12-14 months (30-35 passages) without any apparent change in morphology or loss of growth characteristics. Primary and three-month old (15 passages) cultures had population doubling times of 32-34 hours and 29-31 hours, respectively. These cells (primary and subcultures) did not require a minimum cell number to become established in culture. Bovine endothelial cells (primary, first, fifth and thirteenth passages) were characterized ultrastructurally by the presence of Weibel-Palade bodies, pinocytotic vesicles and microfilaments and immunologically by the presence of thrombosthenin-like contractile proteins and Factor VIII antigen. The intercellular junctions of post-confluenct cultures stained specifically with silver nitrate. From these data, we concluded that identifiable endothelial cells could be obtained from bovine aortae and cultured and maintained for prolonged periods of time.

Animals↗

PubMed1997

Structural and ultrastructural study of the myocardium after 24-hour preservation in University of Wisconsin solution.

This study deals with myocardial preservation after 24 hours of continuous perfusion with University of Wisconsin (UW) solution, focusing on the morphological changes produced by preservation and reperfusion, and their possible relationship to the composition of the solution and the immediate hemodynamic findings after orthotopic heart transplantation in dogs. Following preservation, the histological images of the myocardium were normal in almost every case. After revascularization, although 50% of the hearts recovered preoperative functional levels, there were relevant histological changes in all of them. These changes consisted of interstitial edema, damage to at least 50% of the mitochondria, presence of contraction bands, loss of intercellular junction structure and vasoconstriction. According to these results, the association of continuous perfusion and UW solution appears to be effective during the ischemic period of prolonged myocardial preservation, but not during reperfusion. Perhaps the proportion of viable hearts could be increased by preventing vasoconstriction.

Animals↗

PubMedDate not supplied

Ultrastructure of pleural mesothelioma and pulmonary adenocarcinoma in malignant effusions as compared with reactive mesothelial cells.

OBJECTIVE: To determine the ultrastructural features of diffuse malignant pleural mesothelioma cells in cytologic specimens from pleural effusions. STUDY DESIGN: We retrospectively studied 35 pleural effusions: 12 diffuse malignant pleural mesotheliomas (8 epithelial type, 4 biphasic type), 12 pulmonary adenocarcinomas and 11 cases of reactive mesothelial cells. RESULTS: In the cytoplasm, reactive and malignant mesothelial cells had more-abundant intermediate filaments (P < .05, P < .01) and fewer free ribosomes (P < .001, P < .001) than adenocarcinoma cells. Reactive mesothelial cells had fewer mitochondria than mesothelioma cells (P < .05). Mesothelioma cells had longer, thinner microvilli on the cell surfaces (P < .001); length/diameter ratios of microvilli were 19.1 +/- 7.0 (mesothelioma) vs. 9.1 +/- 2.2 (adenocarcinoma) and 9.2 +/- 2.4 (mesothelial cells). Giant intercellular junctions (desmosomes or desmosomelike structures > 1 micron in length) were found in eight cases of mesothelioma. Core filaments or rootlets in microvilli were present in two cases of adenocarcinoma. CONCLUSION: Because cytologic specimens from pleural effusions were easy to obtain, we think ultrastructural cytology is useful in distinguishing mesothelioma from adenocarcinoma and benign effusions.

Adenocarcinoma↗