Intercellular bridges between granulosa cells and the oocyte in the elasmobranch Raya asterias.
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In the present ultrastructural study intercellular bridges, connecting somatic granulosa cells to oocyte, have been detected for the first time and their modifications have been followed during Raja oogenesis. Intercellular bridges make their first appearance in small previtellogenic follicles as connecting devices between small cells and the oocyte. Later on, when the follicular epithelium becomes polymorphic and multilayered, for the presence of small, large, and pyriform-like cells, intercellular bridges link the oocyte and the different granulosa cells. Intercellular bridges contain ribosomes, whorl of membranes, mitochondria and vacuoles. Such cytoplasmic components are present also in the cell apex of large and pyriform-like cells thus suggesting, in agreement with other species (Motta et al. J. Exp. Zool., 1996;276:223-241) they may flow toward the oocyte. In this regard the presence of intercellular bridges during the oogenesis of cartilagineous fish may represent a crucial event of the active cooperation between granulosa cells and the oocyte. (+info)
Isolation and characterization of mammalian homologues of Caenorhabditis elegans lin-7: localization at cell-cell junctions.
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In Caenorhabditis elegans, the vulval induction is mediated by the let-23 receptor tyrosine kinase (RTK)/ Ras signaling pathway. The precise localization of the let-23 RTK at the epithelial junctions is essential for the vulval induction, and requires three genes including lin-2, -7, and -10. The mammalian homologue of lin-2 has been identified as a protein interacting with a neuronal adhesion molecule, neurexin, and named CASK. CASK has recently been reported to interact with syndecans and an actin-binding protein, band 4.1, at epithelial and synaptic junctions, and to play central roles in the formation of cell-cell junctions. The product of C. elegans lin-7 directly interacts with let-23 RTK and localize it at epithelial junctions. Here, we report three rat homologues of lin-7 ubiquitously expressed in various tissues. These homologues are accumulated at the junctional complex region in cultured Madin-Darby canine kidney cells, and are also localized at the synaptic junctions in neurons. The mammalian homologues of lin-7 may be implicated in the formation of cell-cell junctions. (+info)
Intercalated duct cells in the chicken pancreatic islet with special reference to the alloxan administration.
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The intercalated duct cells were observed in the A and B islets of the chicken pancreas. These cells adhered with each other by intercellular junctional complexes at the apical side. They had many microvilli projecting into the lumen. Abluminally, they displayed extended slender cytoplasmic processes between islet endocrine cells. Administration of alloxan resulted to denser cytoplasm and a more prominent thickening of cytoplasmic processes of the intercalated duct cells, although the blood glucose levels did not show appreciable changes by the treatment. The intercalated duct epithelial cells appeared clearly as stellate cells. The lysosomes increased in size and number with passage of time after alloxan administration. The present findings may suggest that intercalated ducts are not only anatomically important as a structure passing through the islet but also play physiologically by protecting the islet endocrine cells. (+info)
The fate of E- and P-cadherin during the early stages of apoptosis.
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Caspases are responsible for the proteolysis of many cytoskeletal proteins in apoptotic cells. It has been demonstrated here that during cisplatin-induced apoptosis of human embryo retinoblasts both E- and P-cadherin were degraded by caspases, giving initially major polypeptide products of apparent molecular weights 48 K and 104 K respectively. This proteolysis occurred over a similar time-scale to the observed degradation of PARP and to the onset of DNA fragmentation but appreciably later than p53 induction and cleavage of Mdm2 and p21. Addition of caspase inhibitors such as Z-VAD-FMK inhibited apoptosis and cadherin degradation. Co-immunoprecipitation studies carried out on viable cells confirmed previously observed complexes between cadherins and alpha and beta catenin and between the catenins themselves. These interactions were sustained in apoptotic cells as long as the protein components remained intact. Using confocal microscopy it has been shown that cytoskeletal changes associated with apoptosis precede degradation of catenins and cadherins by several hours. In particular, after addition of cisplatin relatively rapid (within 3 h) re-localization of adherens junction proteins from the cell periphery to the cytoplasm was observed whereas little cadherin or catenin degradation occurred until 10 h. We conclude that neither caspase-mediated degradation of cytoskeletal components nor disruption of adherens junction protein-protein interactions is required for morphological change. (+info)
Activation of the protein kinase Akt/PKB by the formation of E-cadherin-mediated cell-cell junctions. Evidence for the association of phosphatidylinositol 3-kinase with the E-cadherin adhesion complex.
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E-cadherins are surface adhesion molecules localized at the level of adherens junctions, which play a major role in cell adhesiveness by mediating calcium-dependent homophylic interactions at sites of cell-cell contacts. Recently, E-cadherins have been also implicated in a number of biological processes, including cell growth and differentiation, cell recognition, and sorting during developmental morphogenesis, as well as in aggregation-dependent cell survival. As phosphatidylinositol (PI) 3-kinase and Akt play a critical role in survival pathways in response to both growth factors and extracellular stimuli, these observations prompted us to explore whether E-cadherins could affect intracellular molecules regulating the activity of the PI 3-kinase/Akt signaling cascade. Using Madin-Darby canine kidney cells as a model system, we show here that engagement of E-cadherins in homophylic calcium-dependent cell-cell interactions results in a rapid PI 3-kinase-dependent activation of Akt and the subsequent translocation of Akt to the nucleus. Moreover, we demonstrate that the activation of PI 3-kinase in response to cell-cell contact formation involves the phosphorylation of PI 3-kinase in tyrosine residues, and the concomitant recruitment of PI 3-kinase to E-cadherin-containing protein complexes. These findings indicate that E-cadherins can initiate outside-in signal transducing pathways that regulate the activity of PI 3-kinase and Akt, thus providing a novel molecular mechanism whereby the interaction among neighboring cells and their adhesion status may ultimately control the fate of epithelial cells. (+info)
Cutting edge: combined treatment of TNF-alpha and IFN-gamma causes redistribution of junctional adhesion molecule in human endothelial cells.
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Proinflammatory cytokines such as TNF-alpha and IFN-gamma induce cell adhesion molecules in endothelial cells and promote transmigration of leukocytes across endothelial cells. However, when those two were administered together, leukocyte transmigration paradoxically decreased. We cloned a human and bovine homologue of the junctional adhesion molecule (JAM), a novel molecule at the tight junction, and examined the effects of proinflammatory cytokines on JAM in HUVECs. The combined treatment of TNF-alpha plus IFN-gamma caused a disappearance of JAM from intercellular junctions. However, flow cytometry, cell ELISA, and subcellular fractionation analysis demonstrated that the amount of JAM was not reduced. This suggested that JAM changed its distribution in response to proinflammatory cytokines. This redistribution of JAM might be involved in a decrease in transendothelial migration of leukocytes at inflammatory sites. (+info)
Role of actin stress fibres in the development of the intervertebral disc: cytoskeletal control of extracellular matrix assembly.
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Orientation of collagen fibrils is a key event in the development of many tissues. In the intervertebral disc, the outer annulus fibrosus comprises lamellae of parallel collagen fibres, the direction of orientation of the long axis of which alternates in angle between lamellae. In development, this organisation is preceded by the formation of sheets of oriented fibroblasts, which then deposit the oriented lamellae. Here, using fluorescent labelling, confocal and electron microscopic techniques on developmental series, we show that the orientation of cells in lamellae is associated with the formation of adherens junctions intercellularly, involving cadherins and vinculin, and longitudinal stress fibres (label for filamentous actin and tropomyosin) intracellularly. The stress fibres direct the initial elongation of cells and control the deposition of oriented extracellular matrix via junctional complexes with the matrix involving vinculin and alpha 5 beta 1 integrins, which in turn promote the formation of oriented fibronectin at the cell surface; oriented collagen is deposited between cells at the same stages. Shortly after birth, the stress fibres disappear, probably because cells now gain orientational cues from the matrix, and are undergoing differentiation-related changes to form fibrocartilage cells. Dev Dyn 1999;215:179-189. (+info)
Organ preservation solutions increase endothelial permeability and promote loss of junctional proteins.
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OBJECTIVE: To investigate the effects of the organ preservation solutions UW and Plegisol on endothelial permeability; occludin and vascular endothelial (VE)-cadherin content in human umbilical vein endothelial cells (HUVEC); and junctional localization of these proteins after exposure to these solutions. SUMMARY BACKGROUND DATA: Organ preservation for transplantation is limited by several challenges, including loss of tissue function, tissue injury, and tissue edema. Occludin and VE-cadherin are responsible for maintaining and regulating the endothelial solute barrier. Several studies have noted organ edema and dysfunction with preservation, as well as gaps between endothelial cells suggesting that disorganization of junctional proteins (e.g., occludin and VE-cadherin) is responsible for interstitial edema. METHODS: HUVEC monolayers were treated with 4 degrees C UW and Plegisol for 3 and 6 hours and then reperfused with normal buffer. Permeability was examined using FITC-dextran tracer during the reperfusion phase. Occludin and VE-cadherin content at different time points was measured by Western blotting. Treated groups were also examined by immunofluorescence for occludin, VE-cadherin, and F-actin. RESULTS: Compared with untreated controls, cold preservation for 3 and 6 hours increased endothelial permeability after rewarming, which appears to depend on the duration of cold exposure. Monolayers exposed to 3 hours of cold preservation did not have increased permeability in the first hour after rewarming but had significantly increased permeability after the first hour and all subsequent time points. Monolayers exposed to 6 hours of cold preservation had increased permeability after the first hour and at all later time points. Western blotting demonstrated that occludin content was decreased to a similar extent with all solutions after 3 hours of cold preservation. Six hours of cold preservation in Plegisol reduced the occludin content significantly compared with UW and control. VE-cadherin content was unchanged after 3 hours of cold preservation but was dramatically reduced in all groups at 6 hours. Immunofluorescent staining demonstrated junctional gap formation and discontinuous staining of occludin and VE-cadherin with all cold preservation protocols; changes in F-actin organization were observed at 3 and 6 hours after cold preservation. CONCLUSION: The changes in occludin, VE-cadherin, and F-actin content and organization and increased permeability associated with cold storage demonstrate that alterations of the tight and adherens junctions may underlie organ edema associated with cold organ preservation. These data also suggest that novel strategies to maintain the content and integrity of endothelial junctional proteins may provide an important therapeutic avenue for organ preservation. (+info)