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PubMed1983

Fine structures of sponge cell membranes: comparative study with freeze-fracture and conventional thin section methods.

Freeze-fracture replicas of sponge cell membranes revealed in general a low density of intramembranous particles, with the exceptions of the membrane (silicalemma) surrounding the siliceous spicules in Ephydatia and the membranes of spherulous cells in Chondrosia. In addition, several types of particle arrangements were observed. A classical necklace is present at the base of the choanocyte flagellum. Rosettes of particles are particularly obvious in the apical membranes of choanocytes, where they are associated with the fuzzy coat covering these cells. Parallel ridges of particles were observed along the microvilli of the choanocyte collar, at sites of insertion of connecting filaments. Rows of particles were observed in the plasma membrane of pinacocytes in Ephydatia where they are located on areas deformed by protruding fibrillar inclusions. Pinacocyte plasma membranes in this species also can contain accumulations of particles which are likely related to desmosomes. Single rows of aligned particles and double rows of staggered particles (sometimes organized in large plates) in addition to rhombic particle arrays were encountered on replicas of marine sponge cell membranes. No classical arrangements corresponding to gap junctions, tight junctions or septate desmosomes were observed. The significance of these data is analysed.

Animals↗
PubMed1988

Roles of cell junctions in gametogenesis and in early embryonic development.

Recent reviews of the role of cell junctions in development have focused primarily upon functions related to the relatively subtle physiological modulation of their subunits in relation to fundamental developmental processes in a wide variety of organisms. There is, however, considerable support from numerous laboratories that the more radical modulation of the presence and number of junctional subunits in many diverse tissues may play a pivotal role in a wide spectrum of developmental phenomena ranging from gametogenesis to organogenesis. Since a great deal of recent interest in this latter subject has concentrated upon vertebrate systems including mammals, this review will examine the functional significance of the modulation of gap junctions, tight junctions and desmosomes in a developing idealized mammalian system from gamete formation to tissue and organ differentiation during embryo-genesis.

Animals↗
PubMed2002

Recent progress on the molecular organization of myelinated axons.

The structure of myelinated axons was well described 100 years ago by Ramón y Cajal, and now their molecular organization is being revealed. The basal lamina of myelinating Schwann cells contains laminin-2, and their abaxonal/outer membrane contains two laminin-2 receptors, alpha6beta4 integrin and dystroglycan. Dystroglycan binds utrophin, a short dystrophin isoform (Dp116), and dystroglycan-related protein 2 (DRP2), all of which are part of a macromolecular complex. Utrophin is linked to the actin cytoskeleton, and DRP2 binds to periaxin, a PDZ domain protein associated with the cell membrane. Non-compact myelin--found at incisures and paranodes--contains adherens junctions, tight junctions, and gap junctions. Nodal microvilli contain F-actin, ERM proteins, and cell adhesion molecules that may govern the clustering of voltage-gated Na+ channels in the nodal axolemma. Na(v)1.6 is the predominant voltage-gated Na+ channel in mature nerves, and is linked to the spectrin cytoskeleton by ankyrinG. The paranodal glial loops contain neurofascin 155, which likely interacts with heterodimers composed of contactin and Caspr/paranodin to form septate-like junctions. The juxtaparanodal axonal membrane contains the potassium channels Kv1.1 and Kv1.2, their associated beta2 subunit, as well as Caspr2. Kv1.1, Kv1.2, and Caspr2 all have PDZ binding sites and likely interact with the same PDZ binding protein. Like Caspr, Caspr2 has a band 4.1 binding domain, and both Caspr and Caspr2 probably bind to the band 4.1 B isoform that is specifically found associated with the paranodal and juxtaparanodal axolemma. When the paranode is disrupted by mutations (in cgt-, contactin-, and Caspr-null mice), the localization of these paranodal and juxtaparanodal proteins is altered: Kv1.1, Kv1.2, and Caspr2 are juxtaposed to the nodal axolemma, and this reorganization is associated with altered conduction of myelinated fibers. Understanding how axon-Schwann interactions create the molecular architecture of myelinated axons is fundamental and almost certainly involved in the pathogenesis of peripheral neuropathies.

Animals↗
PubMed2005

GEF-H1 is involved in agonist-induced human pulmonary endothelial barrier dysfunction.

Endothelial cell (EC) permeability is precisely controlled by cytoskeletal elements [actin filaments, microtubules (MT), intermediate filaments] and cell contact protein complexes (focal adhesions, adherens junctions, tight junctions). We have recently shown that the edemagenic agonist thrombin caused partial MT disassembly, which was linked to activation of small GTPase Rho, Rho-mediated actin remodeling, cell contraction, and dysfunction of lung EC barrier. GEF-H1 is an MT-associated Rho-specific guanosine nucleotide (GDP/GTP) exchange factor, which in MT-unbound state stimulates Rho activity. In this study we tested hypothesis that GEF-H1 may be a key molecule involved in Rho activation, myosin light chain phosphorylation, actin remodeling, and EC barrier dysfunction associated with partial MT disassembly. Our results show that depletion of GEF-H1 or expression of dominant negative GEF-H1 mutant significantly attenuated permeability increase, actin stress fiber formation, and increased MLC and MYPT1 phosphorylation induced by thrombin or MT-depolymerizing agent nocodazole. In contrast, expression of wild-type or activated GEF-H1 mutants dramatically enhanced thrombin and nocodazole effects on stress fiber formation and cell retraction. These results show a critical role for the GEF-H1 in the Rho activation caused by MT disassembly and suggest GEF-H1 as a key molecule involved in cross talk between MT and actin cytoskeleton in agonist-induced Rho-dependent EC barrier regulation.

Actin Cytoskeleton↗
PubMed2001

Pericytes: cell biology and pathology.

Pericytes are perivascular cells with multifunctional activities which are now being elucidated. The functional interaction of pericytes with endothelial cells (EC) is now being established, using current molecular and cytochemical techniques. The detailed morphology of the pericyte has been well described. Pericytes extend long cytoplasmic processes over the surface of the EC, the two cells making interdigitating contacts. At points of contact, communicating gap junctions, tight junctions and adhesion plaques are present. Pericytes appear to show both structural and functional heterogeneity. The coverage of EC by pericytes varies considerably between different microvessel types and the location of pericytes on the microvessel is not random but appears to be functionally determined. Interaction between pericytes and EC is important for the maturation, remodelling and maintenance of the vascular system via the secretion of growth factors or modulation of the extracellular matrix. There is also evidence that pericytes are involved in the transport across the blood-brain barrier and the regulation of vascular permeability. The long-standing view that pericytes are the microvessel equivalent of larger vessel smooth muscle cells and are contractile is being reassessed using current methods. An important role for pericytes in pathology, and neuropathology in particular, has been indicated in hypertension, diabetic retinopathy, Alzheimer's disease, multiple sclerosis and CNS tumour formation.

Animals↗
PubMed1990

Myoendothelial junctions in human saphenous veins.

The frequency and morphology of myoendothelial junctions occurring in human saphenous veins have been investigated. The junctions are mostly established via slender membrane projections. The junction slit is filled with a electron-dense material, sometimes forming shark-tooth-like configurations. The morphology of these heterocellular junctions is not compatible in all cases with gap junctions, tight junctions or desmosomes. The frequency of heterocellular junctions in endothelial cells of saphenous veins is estimated to be approximately 10 per cell, but their significance is not finally determined.

Endothelium, Vascular↗
PubMed1979

Regional differences in the fine structure of the ciliary epithelium related to accommodation.

The ciliary bodies of five monkey eyes and one human eye were subdivided into five zones. The ciliary epithelium with its bordering stroma was investigated electron microscopically. The number of cell organelles of the nonpigmented (NPE) and pigmented (PE) epithelium (mitochondria, rough endoplasmic reticulum, Golgi complexes); intercellular junctions between NPE and NPE, PE and PE, and NPE and PE (desmosomes, puncta adhaerentia, gap junctions, tight junctions); and fenestrations of the capillary endothelium were quantitatively evaluated. All these types of cell organelles, fenestrations of the capillary endothelium, and gap junctions in the NPE were found in greater numbers at the crests of the ciliary processes than in the valleys between processes. On the other hand, the number of puncta adhaerentia is significantly higher in the valleys than at the crests. In the valleys, the internal limiting membrane performs an elaborate network of electron-dense strands in which many fine zonular fibers terminate. These fibers are believed to belong to the "tension fiber system." Their firm attachment to the ciliary epithelium and the great number of intercellular junctions known as mechanical structures lend further support to our concept that these structures function as a fulcrum in the process of accommodation.

Accommodation, Ocular↗
PubMed1991

Junctional systems in the pineal gland of the Wistar rat (Ratus ratus). A freeze-fracture and thin section study.

Intercellular junctions between neighbouring pinealocytes, glial cells, glial cells and pinealocytes as well as between nerve endings and parenchymal cells of the pineal gland of Wistar rats were investigated on freeze-fracture replicas and thin sections by transmission electron microscopy. Gap junctions, tight junctions and the annular gap junctions have been revealed. In addition, chemical synapses between nerve endings and pinealocytes have been observed.

Animals↗
PubMed1989

[Kaposi's sarcoma--ultrastructural study of 7 cases].

The ultrastructure of 7 cases of Kaposi's sarcoma observed in Xinjiang is reported. Its histo-structure and cell type varied. The neoplastic blood vessels, pericytes, fibroblasts, epithelioid cells with their basement membranes and cell junctions (tight junction and desmosome-like junction), spindle cells with multi-microvilli, phagocytes and mesenchymal cells without any cellular characteristics were found. The nature of these cells and the relation between them are discussed. The authors support the opinion that Kaposi's sarcoma is derived from primitive vasoforming mesenchyme.

Aged↗
PubMed1977

Intercellular junctions, intramembranous particles and cytoskeletal elements of deep cells of the Fundulus gastrula.

The fine structure of motile deep cells of the gastrula stage of Fundulus heteroclitus was studied with transmission electron microscopy, using both thin sectioning and freeze-cleave techniques. Gastrula deep cells form extensive non-junctiona appositions with each other, in which the apposed plasma membranes are parallel and separated by a distance of 26-28 nm. They also form gap junctions. Tight junctions, desmosomes, and extensive interdigitations of apposed plasma membranes were not observed. The plasma membranes of deep cells contain numerous unclustered intramembranous particles. Cytoplasmic microtubules were found, but they appear to be small in number, sparsely distributed, and mainly randomly oriented. Microfilaments are also present and are localized largely in the cortical cytoplasm and in thin cell extensions. The significance of these findings for the contact and locomotory behavior of deep cells is discussed.

Animals↗
PubMed1982

Ultrastructure of odontoblasts in kitten tooth germs as revealed by freeze-fracture.

Fifteen kittens were perfused with 2.5 per cent glutaraldehyde or modified Karnovsky fixative. Distribution and structural features of the three kinds of intercellular junctions; gap junctions, macular tight junctions and desmosome-like junctions were clarified by correlated observations using thin sections and freeze-fracture replicas. Distal junctional complexes of the odontoblasts were composed of both gap and macular tight junctions and sealed extracellular spaces incompletely, because of the poor sealing capacities of macular tight junctions. Therefore, there was no predentine-pulp barrier in the odontoblast layer. Except for the junctional complex, no tight junction was observed in the odontoblasts. Gap junctions and desmosome-like junctions were found between adjacent odontoblasts and between odontoblasts and neighbouring pulp cells. Gap junctions were similar to those of many other tissues but the desmosome-like junctions were different from mature desmosomes in the epithelial cells and showed immature features. Each intercellular junction of odontoblasts is considered to form a site of intercellular communication and cell-to-cell attachment.

Animals↗
PubMed1979

Cell junctions in the cyst envelope in the silkworm testis, Bombyx mori Linné.

The cell junctions of the cyst envelope in the testes of Bombyx mori were examined by electron miscroscopy utilizing a thin-sectioning technique following conventional fixation, tannic acid fixation and lanthanum tracer study, and also using a freeze-fracture technique. There are three kinds of junctions; septate junctions, gap junctions and tight junctions. Septate junctions are of the pleated type. Gap junctions are characterized by four electron-dense lines and three electron-lucent lines in the reduced intercellular spaces seen by thin-sectioning. They are of the "E" type, having clusters of intramembraneous particles on the E-fracture face. The most striking finding is the frequent presence of tight junctions on the fracture planes, while focally fused outer leaflets of the junctional unit membranes are rarely detected on thin-sectioned preparations. Tight junctions are characterized by branching zigzag ridges on the P-fracture face and complementary grooves on the E-fracture face. It is proposed that tight junctions are new morphological evidence of blood-germ cell barrier in an insect.

Animals↗
PubMed2007

Endothelial cell motility is compatible with junctional integrity.

Confluent endothelial cells in culture are generally regarded as a model of resting endothelium in blood vessels (i.e., forming junctions at points of cell-cell contact, losing ability to proliferate in response to growth factors, and remaining stationary). However, incompatibility between junctional integrity and endothelial cell motility remains uncertain. The aim of this study was to determine whether endothelial cells (in colonies generated from differentiating embryonic stem cells in contact with OP9 stromal cell layer) have a resting endothelial phenotype (i.e., lack motility). Time-lapse analyses showed that though endothelial cells were connected to each other through adherens junctions and tight junctions, they were moving continuously within the colonies. Endothelial cell movement was accompanied by formation of lamellipodia, which transiently accumulated green fluorescent protein-tagged beta-actin and p41-Arc (a subunit of the actin-related protein 2/3 complex) at their anterior tips, suggesting that the movement is an active behavior of endothelial cells. Endothelial cell-specific expression of yellow fluorescent protein-tagged vascular endothelial-cadherin and claudin-5 revealed that adherens junctions and tight junctions persisted during endothelial cell migration. Furthermore, intercellular junctions underwent dynamic remodeling at the leading edge of moving endothelial cells. These results suggest that endothelial cells can remain highly motile without losing intercellular junctions.

Actin-Related Protein 2-3 Complex↗
PubMed1978

Development of Sertoli cell junctions in vitro--a freeze-fracture study.

Seminiferous tubules of 1-day-old rats were maintained in organ culture for up to 40 days. Five classes of intercellular junctions between Sertoli cells were observed by the freeze-fracture method as the tissue aged: (a) typical gap junctions; (b) focal tight junctions; (c) macular tight junctions; (d) meandering tight junctions; and (e) extensive tight junctions. The relative proportions of these types of Sertoli cell junctions were quantitated as the organ cultures progressed. The junctional structures observed and classified in organ culture were identical to those seen in vivo, but the timing of their appearance and/or disappearance, as well as their relative proportions, was different from that observed in the developing animal. Extensive tight junctions, with numerous parallel strands, were observed in the 40-day cultures; however, their oblique orientation with respect to the myoid layer was in contrast to the parallel orientation observed in vivo.

Animals↗
PubMedDate not supplied

Glycerol disrupts tight junction-associated actin microfilaments, occludin, and microtubules in Sertoli cells.

Intratesticular injections of glycerol have been shown to result in a marked and prolonged reduction of spermatogenesis, accompanied by increased permeability of the blood-testis barrier. Because the permeability of the blood-testis barrier is regulated by Sertoli cell tight junctions, and tight junction organization is regulated by the cytoskeleton, we undertook to examine the effects of glycerol treatment on cytoskeletal actin microfilaments and microtubules, and on the tight junction protein, occludin, in Sertoli cells. Adult rats received a single intratesticular injection of either saline (controls) or a 10% glycerol solution. At 24 hours and 7, 15, and 21 days after injection, testes were collected and prepared for routine histology, cryosectioning, or whole seminiferous tubule immunohistochemical staining; and the preparations were viewed by light and confocal microscopy. In saline-injected testes, Sertoli cells had a cytoskeletal and junctional organization that resembled that of normal testes. F-actin microfilaments, located in the basal region, were arranged in regular bundles or chords that circumscribed the perimeter of each Sertoli cell at the level of the tight junction. Occludin colocalized with tight junction-associated actin filament distribution and microtubules formed a geometric array associated with spermatogenic cells. In contrast, in glycerol-treated Sertoli cells, microfilament and microtubule organization and occludin distribution were partially or completely disrupted. From these results we conclude that glycerol treatment either directly or indirectly disrupts tight junction-associated F-actin and occludin and tubulin organization in rat Sertoli cells. Perturbation of the tight junction-associated proteins could explain the increase in permeability of the blood-testis barrier observed after glycerol treatment. Impaired spermatogenesis following glycerol treatment is likely a consequence of a leaky blood testis barrier and disrupted Sertoli cell cytoskeleton. Glycerol injections may serve as a useful tool in studying the relationship between cytoskeletal organization and the stabilization of Sertoli-Sertoli cell junctions.

Actins↗
PubMed1983

Fluid-overload pulmonary oedema in mice: the intercellular junctions of bronchiolar epithelium and arterial endothelium.

It has been reported previously that fluid leaks through the intercellular junctions of arterial endothelium and bronchiolar epithelium in fluid-overload pulmonary oedema in mice. In this study, freeze fracture technique was used to see morphological changes in the intercellular junctions at these sites. In arterial endothelium, the intercellular junction consists of a combination of gap junctions and tight junctions. In this experiment, only the tight junctions were disrupted. In bronchiolar epithelium, the tight junction was disrupted. The other sites in the vascular system and respiratory surface did not show any changes in the morphology of intercellular junctions. Thus, this study confirms the previous study and provides some structural correlation for the changes of permeability in fluid-overload pulmonary oedema.

Animals↗
PubMed1982

Intercellular junctions of the hen parathyroid gland. A freeze-fracture study.

The fine structure of the intercellular junctions of the hen parathyroid gland was studied using freeze-fracture replicas and thin sections. In the conventional thin sections, desmosomes, intermediate junctions (maculae adherentes) and gap junctions were observed, and in the lanthanum-fixed sections, tight junctions (maculae occludentes) were demonstrated as well. In the freeze-fracture replicas, desmosomes, gap junctions, tight junctions and combination forms of gap and tight junctions occurred, but intermediate junctions were not identified. Junctional complexes (zonulae occludentes) were not encountered in any preparations. The gap junctions varied in size and shape; they ranged from irregularly shaped, minute assemblages of particles to large aggregations of a round or elliptic outline. Both the tight junctions and the combination forms of gap and tight junctions also exhibited a variety of shape and dimension, and, depending on the form of the tight junctional strands, they were classified into three types: type I consisted of a simple line of strands; type II consisted of a closed network of strands; and type III consisted of an open network of strands. The combination forms were more numerous than the typical tight junctions. The possible significance of these junctions is discussed in relation to the function of the parathyroid parenchymal cell.

Animals↗
PubMed1977

Adult rat hepatocytes in primary monolayer culture. Ultrastructural characteristics of intercellular contacts and cell membrane differentiations.

Primary monolayer cultures were obtained in 60-mm petri dishes by incubating 3 X 10(6) isolated hepatocytes at 37 degrees C in Dulbecco's medium supplemented with 17% fetal calf serum. The ultrastructure of monolayer cells was examined after various incubation periods. Within 4 h of plating, the isolated spherical cells adhere to the plastic surface, establish their first contacts by numerous intertwined microvilli, and form new hemidesmosomes. After 12 h of culture, wide branched trabeculae of flattened polyhedral cells extend in all directions. Finally, after 24 h of culture, bile canaliculi are reconstituted, and a biliary polarity is recovered: the Golgi elements, which are scattered throughout the cytoplasm in the isolated cells, are reassembled in front of the newly formed bile canalculi, symmetrically in the adjacent cells; lysosomes are concentrated in that region, and microtubules reappear. Concomitantly, plasma membrane differentiations, namely desmosomes and tight junctions, develop. Tight junctions sealing the bile ducts constitute a barrier to the passage of ruthenium red and horseradish peroxidase. De novo formation of these junctions was studied by the freeze-etching technique: 10-nm particles compose a network of anastomosed linear arrays in the vicinity of the bile canaliculi; in the next step of differentiation, the particles fuse, form short ridge segments and finally continuous branched smooth strands, characteristic of the mature tight junction.

Cell Adhesion↗