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1.
The DSL1 complex is a conserved tethering complex at the endoplasmic reticulum that recognizes Golgi-derived COPI vesicles and hands them over to the fusion machinery. The DSL1 complex is the simplest tethering complex of the complexes associated with tethering containing helical rods (CATCHR) family. CATCHR tethering complexes play a role at compartments along the exocytic and endocytic pathways. In this review, different functions of the DSL1 complex are discussed, some open questions with the seemingly straightforward picture are pointed out and alternative functions of the DSL1 complex members are mentioned.  相似文献   

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The significance of muscle cells for the origin of mesoderm in bilateria   总被引:2,自引:0,他引:2  
Muscle tissue may have played a central role in the early evolutionof mesoderm. The first function of myocytes could have beento control swimming and gliding motion in ciliated vermiformorganisms, as it still is in such present-day basal Bilateriaas the Nemertodermatida. The only mesodermal cells between epidermisand gastrodermis in Nemertodermatida are myocytes, and conceivablythe myocyte was, in fact, the original mesodermal cell type.In Nemertodermatida as well as the Acoela, myocytes are subepithelialfiber-type muscle cells and appear to originate from the gastrodermalepithelium by emigration of single cells. Other mesodermal cellsin the acoels are the peripheral parenchyma (connective tissue)and tunica cells of the gonads, and these also arise from thegastrodermis. Musculature in many of the coelomate protostomesand deuterostomes, on the other hand, is in the form of epitheliomuscular(myoepithelial) cells, and this cell type may also have beenan early form of the mesodermal myocyte. The mesodermal bandsin the small annelid Polygordius and in juvenile enteropneustshave cells intermediate between mesenchymal and epithelial intheir histological organization as they develop into myoepithelia.If acoelomates were derived from coelomates by progenesis, thenthe fiber-type muscles of acoelomates could be products of foreshorteneddifferentiation of such tissue. The precise serial patterningof circular muscle cells along the anterior-posterior axis duringembryonic development in the acoel Convoluta pulchra providesa model for early steps in the gradual evolution of segmentationfrom iterated organ systems.  相似文献   

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The interaction of fibronectin fragments with fibroblastic cells   总被引:21,自引:0,他引:21  
We have examined the interaction of the purified cell-binding domain of fibronectin with fibroblastic baby hamster kidney cells. When the cell-binding region of fibronectin is part of a large 75,000-dalton fragment, the direct binding of the tritium-labeled fragment to cells in suspension can be observed. There is a single class of 10(5) sites/cell with an apparent dissociation constant of 4 X 10(-7) M. When the cell-binding region is part of a smaller 11,500-dalton fragment, an interaction with cells can only be observed indirectly via inhibition assays. The apparent affinity of this fragment for the cell surface fibronectin receptor is low. This 11,500-dalton fragment competitively inhibits both the direct binding of soluble [3H]fibronectin to cells in suspension and the spreading of cells on fibronectin-coated substrates, suggesting that the fragment binds to the same receptor site as intact fibronectin. Possible models describing the mechanism of the interaction of fibronectin with its receptor are proposed.  相似文献   

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The interaction of plasma fibronectin with fibroblastic cells in suspension   总被引:28,自引:0,他引:28  
We have examined the interaction of soluble plasma [3H]fibronectin with fibroblastic cells in suspension. Fibronectin labeled by reductive methylation binds to baby hamster kidney cells in serum-free medium in a time-dependent manner at 4, 22, and 37 degrees C, with half-maximal binding occurring in 12-15 min at 22 degrees C. The binding is saturable and reversible. At least 90% of the cell-associated fibronectin is external to the plasma membrane, as judged by trypsin susceptibility of the bound radioactivity. Scatchard analysis of the concentration dependence of binding indicates the presence of a single class of binding sites, even at low input concentrations of fibronectin. There are approximately 5 +/- 1 X 10(5) sites/cell with an apparent dissociation constant of 8.0 +/- 0.5 X 10(-7) M; thus, the binding of soluble fibronectin to these cells is of moderate affinity. This putative fibroblast fibronectin receptor is resistant to trypsin in the presence of physiological concentrations of divalent cations but is susceptible to trypsin in the presence of 5 mM EDTA. Binding of 0.1 mg/ml [3H]fibronectin is 60-80% inhibited by 8 mg/ml unlabeled fibronectin and 95% inhibited by 1 mg/ml purified 75-kDa fibronectin cell-binding domain, but is unaffected by 1 mg/ml 44-kDa collagen-binding domain or 5 mg/ml ovalbumin. The binding parameters determined in this study further define the fibroblast cell-surface fibronectin receptor.  相似文献   

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We have previously reported the presence and regulation of an acetylcholine-hydrolyzing enzyme in high density suspension cultures of WRL-10A fibroblasts where its activity increases 100-fold when growth is arrested. Substrate specificity, substrate inhibition, and product identification studies indicate that this enzyme is acetylcholinesterase (AChE, EC 3.1.1.7). Treatment of whole cells with 5 mM diazotized sulfanilic acid revealed that most of the AChE is located on the external surface of the cell membrane. It was also found that the enzyme is released in the medium at a rate of 0.5 U/h/mg cell protein and that within a 24-h period the de novo synthesized and liberated AChE is equivalent to 90% of the activity associated with the cells. No similar synthesis of AChE was found in six order fibroblastic cell lines examined. These and related findings indicating that acetylcholine is also present in high density populations of WRL-10A cells suggest that this unique phenotype may be used profitably in exploring further the relationship between components of the cholinergic system and non-neuronal cell growth.  相似文献   

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4F2 monoclonal antibody recognizes a 120-kD glycoprotein on the surface of human spread fibroblastic cells of embryonic and neoplastic origin, but it does not bind to normal spread adult fibroblasts. Flow cytometric analysis reveals that human adult fibroblasts become 4F2-positive when they are analyzed as round-shaped cells; this means that, in normal adult cells, 4F2 antigen behaves as a cryptic molecule. Thus, the basic difference between embryonic, neoplastic and normal adult cells consists in a different organization in the architecture of the cell membrane, since in embryonic and neoplastic cells there is a continuous expression of the 4F2 antigen independently of the cell shape and cell cycle phase. Quantitative flow cytometry shows that the mean surface density (MSD) of the 4F2 antigen 1, does not vary as a function of the cell cycle; 2, is inversely related to cell size and "metabolic time". This suggests that at the plateau phase the surface organization of G1 resting cells changes as a function of the number of days spent in culture; and 3, sarcoma and SV40-transformed cells show significantly increased MSD levels of the 4F2 antigen in comparison with normal cells of similar size. Electrophoretic analysis under reducing conditions confirms the quantitative differences in the expression of the 4F2 antigen described with the cell sorter. It also reveals, in a way different from that previously found with lymphoid cells, the coexistence of two molecules (85 and 73 kD) in the heavy chain regions. The 73 kD is, however, much more strongly expressed in the fibrosarcoma than in the embryonic cells. Finally, it shows that 4F2 antigen is a very useful tool for studying the organization and the structure of the cell membrane of human fibroblasts and can provide new insights to understand better the developmental and transformation processes.  相似文献   

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The origin of the mesoderm and the subsequent formation of the coelom in the larvae of the brachiopod species Notosaria nigricans and Calloria inconspicua is documented in detail at the ultrastructural level. During gastrulation, the blastocoel is completely displaced by the invaginating archenteron. Initial mesoderm formation was observed in late wedge-shaped to early three-lobed stages in both species. Proliferation of mesodermal cells from the archenteral epithelium mainly occurs in the dorsolateral (C. inconspicua) and caudolateral (N. nigricans) parts of the archenteral wall. Thus, a compact mesodermal cell mass pushes its way towards the subepidermal basal lamina. During further development of the larva, the mesoderm is separated from the archenteral epithelium by an extracellular matrix secreted frontad from behind. As a result, a single coelomic anlage is formed. The initial mesoderm in both species is of archenteral/endodermal origin. Considering endodermal origin as the crucial character for enterocoely, coelom formation through proliferation of a compact, endodermally derived mesodermal cell mass in Brachiopoda is clearly identified as enterocoely. Endodermal origin of mesoderm and, therefore, of the coelomic epithelium is hypothesised as a synapomorphy of Brachiopoda and Deuterostomia. As a consequence: (1) Brachiopoda and Deuterostomia are considered sister groups, (2) Brachiopoda group within Radialia and (3) lophophorates (”Tentaculata”) remain as a paraphyletic grouping. Accepted: 26 November 1999  相似文献   

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Platelet-derived growth factor (PDGF) increases the mitogenic activity of epidermal growth factor (EGF) in several cells lines, including BALB/C-3T3. PDGF-treated BALB/C-3T3 cells manifest a reduced capacity to bind 125I-labeled EGF due to a loss of high affinity EGF receptors. Cholera toxin potentiates the ability of PDGF to both decrease EGF binding and initiate mitogenesis. Whether PDGF increases EGF sensitivity via its effects on EGF receptors is not known and requires a more complete understanding of the mechanism by which PDGF decreases EGF binding. 12-O-tetradecanoylphorbol 13-acetate (TPA) also reduces EGF binding in BALB/C-3T3 and other cells, presumably by activating protein kinase C and, consequently, inducing the phosphorylation of EGF receptors at threonine-654. PDGF indirectly activates protein kinase C, and EGF receptors in PDGF-treated WI-38 cells are phosphorylated at threonine-654. Thus, the effects of PDGF on EGF binding may also be mediated by protein kinase C. We investigated this hypothesis by comparing the actions of PDGF and TPA on EGF binding in density-arrested BALB/C-3T3 cells. Both PDGF and TPA caused a rapid, transient, cycloheximide-independent loss of 125I-EGF binding capacity. The actions of both agents were potentiated by cholera toxin. However, whereas TPA allowed EGF binding to recover, PDGF induced a secondary and cycloheximide-dependent loss of binding capacity. Most importantly, PDGF effectively reduced binding in cells refractory to TPA and devoid of detectable protein kinase C activity. These findings indicate that PDGF decreases EGF binding by a mechanism that involves protein synthesis and is distinct from that of TPA.  相似文献   

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The induction of antigen-specific T cell tolerance and its maintenance in the periphery is critical for the prevention of autoimmunity. Recent evidence shows that dendritic cells (DC) not only initiate T cell responses, but are also involved in silencing of T cell immune responses. The functional activities of DC are mainly dependent on their state of activation and differentiation, that is, terminally differentiated mature DC can efficiently induce the development of T effector cells, whereas immature DC are involved in maintenance of peripheral tolerance. The means by which immature DC maintain peripheral tolerance are not entirely clear, however, their functions include the induction of anergic T cells, T cells with regulatory properties as well as the generation of T cells that secrete immunomodulatory cytokines. This review summarizes the current knowledge about the immunoregulatory role of immature DC that might act as guardians for the induction and maintenance of T cell tolerance in the periphery.  相似文献   

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In mammalian cells most microtubules are enriched in tyrosinated alpha-tubulin (tyr-tubulin). Other subclasses of microtubules are present in variable amounts and some are enriched in detyrosinated alpha-tubulin (glu-tubulin). We examined the effect of cell-cell interactions on the level of glu-tubulin in microtubules. This was studied by quantitative immunofluorescence using antibodies against tyr- and glu-tubulin. We found that in cells which have established cell-cell contacts, the ratio of glu-/tyr-tubulin is higher than in isolated cells. We also examined the effect of cell-cell interactions on the glu-/tyr-tubulin ratio by using the antibody blocking method of Schulze and Kirschner [42]. Microtubules containing mainly tyr-tubulin had been blocked first by a polyclonal antibody against tyr-tubulin and several layers of secondary antibodies. The unblocked microtubules were then labeled by a monoclonal antibody against alpha-tubulin. Since the coating efficiency of microtubules by the anti-tyr tubulin depends on the amount of tyr-tubulin in each microtubule, this procedure allows the visualization of microtubules enriched or depleted in tyr-tubulin in specific domains of each cell. Microtubules were more extensively blocked in subconfluent than in confluent cells and preferentially at the periphery of the cytoplasm. In cells present at the margin of an artificial wound produced in a confluent monolayer, the amount of blocked microtubules increased slowly with time (between 2 and 4 h). These results are consistent with the hypothesis that cell-cell contacts lead to increased tubulin dytyrosination both in fibroblastic and epithelial cells.  相似文献   

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A furosemide-sensitive, ouabain-insensitive [86Rb+] uptake is described in glioma cells in culture which is dependent upon external Na+, K+, and Cl? concentrations. This transport activity was also inhibited by bumetanide at 100-fold lower concentrations than furosemide. Furosemide-sensitive swelling of glioma cells is demonstrated and this activity is dependent upon external Na+ and K+ in a manner similar to [86Rb+] uptake. This transport activity was not detected in neuroblastoma cells and the possible relevance of these findings to extracellular K+ buffering by glia is discussed.  相似文献   

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Replication initiation is a key event in the cell cycle of all organisms and oriC , the replication origin in Escherichia coli , serves as the prototypical model for this process. The minimal sequence required for oriC function was originally determined entirely from plasmid studies using cloned origin fragments, which have previously been shown to differ dramatically in sequence requirement from the chromosome. Using an in vivo recombineering strategy to exchange wt oriC s for mutated ones regardless of whether they are functional origins or not, we have determined the minimal origin sequence that will support chromosome replication. Nearly the entire right half of oriC could be deleted without loss of origin function, demanding a reassessment of existing models for initiation. Cells carrying the new DnaA box-depleted 163 bp minimal oriC exhibited little or no loss of fitness under slow-growth conditions, but were sensitive to rich medium, suggesting that the dense packing of initiator binding sites that is a hallmark of prokaryotic origins, has likely evolved to support the increased demands of multi-forked replication.  相似文献   

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