摘要:

AbstractMC3T3‐E1 cells grown with ascorbic acid express sequentially osteoblastic marker proteins such as alkaline phosphatase (ALPase) and then form a mineralized extracellular matrix (ECM) as a consequence of osteoblastic differentiation. To explore the functional roles of ALPase in the process of osteoblastic maturation, an inducible expression vector for antisense ALPase RNA was constructed and stably transfected into MC3T3‐E1 cells. The expression of antisense ALPase RNA in the differentiated MC3T3‐E1 transfectants reduced markedly the ALPase activity, which resulted in a significant decrease in the deposition of minerals upon prolonged culture. These findings demonstrated directly that ALPase participated in the mineralizationo

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0060

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe nucleolar organization has been studied in spreads of cells either untreated or treated with hypotonic salt solution for different periods. A network corresponding to the nucleolonema becomes evident with progressive hypotonic treatment. The network reveals units comparable to the rDNA transcriptional units in length and is associated with tufts of fibrils and granules. Spread preparations from cycloheximide treated cells reveal a thread‐like axis and often ‘Christmas tree’‐like configurations within these units. Spacers joining the units can also be detected. It is supposed that the transcriptional units move outwards with their transcriptional products where the processing takes place. In loose nucleoli, this network forms the nucleolonema, which remains associated with the granules, the processed transcriptional products. In compact nucleoli the network is obliterated by the granules and they form the major component of the nucleoli. Such organization represents all the events in the transcription and processing of riboso

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0061

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThis study describes the adhesion of human osteoblasts, culturedin vitro, to proteins of the extracellular matrix, the biosynthesis of integrins, their topography and organization in focal contacts. The adhesion of osteoblasts to laminin, type I collagen, vitronectin and fibronectin was 77–100%, in 2h and at 55nmsubstrata concentration, and it was accompained by spreading of the cells. Adhesion to fibronectin (FN), laminin (LN) and type I collagen (COL) was inhibited by antibodies to the β1 integrin and antibodies to the α5 chain affected adhesion only to fibronectin. Using a panel of polyclonal antibodies against α2, α3, α5, αv, β1andβ3 integrins we detected synthesis of α3β1, α5β1, αvβ3, and an αvβ1‐like dimer by immunoprecipitation of metabolically labelled cell lysates. Studies of immunolocalization demonstrated the presence of the same integrins identified in lysates, plus α4, α1 and β5 subunits. In cells adhering in the presence of serum we showed organization of β3 and αv integrins in focal contacts. In cells adhering to fibronectin α5 and β1 integrins were localized in focal contacts. In cells spread on laminin or type I collagen none of the integrins investigated was l

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0062

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractConstitutively migrating malignant rat liver epithelial cells obtained by Ha ras transformation exhibit a fibroblastoid phenotypein vitro. The cells deposit the anti‐adhesive extracellular matrix (ECM) protein tenascin into their ECM migration tracks. The serum‐free medium conditioned by these constitutively migrating cells contains an epithelial migration‐stimulating activity (eMSA) that is neither cell‐type‐, nor species‐specific. This eMSA fractionates in the range of 30 to 50kDa and binds to Mono‐Q, Mono‐S, and with low affinity to heparin—Sepharose. The conditioned medium also induces the expression of the serine proteinase inhibitor PAI‐1. Both migration and expression of PAI‐1 are inhibited by cyclic AMP, as previously shown for the migration of the non‐transformed liver epithelial cells induced by several growth factors that act through tyrosine kinase receptors. These results suggest that the eMSA might act through signal transduction pathways similar to those of the growth factors previously studied. It is postulated that the eMSA, through both autocrine and paracrine mechanisms, is at least partially responsible for the malignant phenoty

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0063

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractWe have investigated the effects of altered cell shape on the regulation of the 92kDa type IV collagenase. In MDCK cells, anti‐E‐cadherin antibodies alter cell shape by disrupting normal cell—cell contacts, while sodium butyrate causes a marked flattening and spreading of cells. The disruption of cell—cell contacts led to a faint expression of the 92kDa collagenase. This effect was enhanced by sodium butyrate, which by itself did not induce collagenase expression. In contrast, stromelysin expression was not regulated in these conditions. Although mRNA expression was enhanced, the secreted collagenase activity was not altered in these conditions in either cell line. Examination of cytoskeletal and extracellular matrix proteins and cell—cell and cell—matrix adhesion proteins by immunofluorescence and Western blot revealed a disruption of the actin network, tight junctions, and fibronectin deposition by anti E‐cadherin antibodies, and alterations in actin, cytokeratin 8, cytokeratin 14, laminin and β1 integrin induced by sodium butyrate. Thus, the induction of collagenase expression in epithelial cells by disrupted cell—cell adhesion and sodium butyrate is associated with changes in cell sha

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0064

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe three‐dimensional structure of the extracellular substratum was found to regulate reversibly the morphology, proliferation and collagen synthesis of perisinusoidal stellate cells (lipocytes, i.e. fat‐storing ‘Ito’ cells). On non‐coated polystyrene and type I collagen‐coated culture dishes, the cells spread well and extended their cellular processes. On the surface of type I collagen gels, the cells gathered and formed a mesh‐like structure. However, in type I collagen gel where the cells were surrounded by type I collagen three‐dimensionally, the cells extended their fine cellular processes and resembled the star‐shaped stellate cells seenin vivo. The cell proliferation was more prominent in culture dishes coated with type I collagen or in polystyrene culture dishes than on or in type I collagen gels. The collagen synthesis was affected in the same manner. These data indicate that the nature and the three‐dimensional structure of the extracellular matrix (ECM) can regulate morphology, proliferation and functions of the perisinusoidal stellate cells. In order to examine the reversibility of these regulations, we liberated cultured cells with trypsin or with purified bacterial collagenase and re‐seeded them onto or into each substratum. The cells changed their shape, rate of proliferation and collagen synthesis according to each new substratum. These results indicate that the three‐dimensional structure of ECM reversibly regulates the morphology, proliferation rate and functions of the perisi

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0065

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

AbstractThe tight junctions between Sertoli cells were examined by freeze‐fracture in 3‐month‐old prenatally irradiated rats, whose seminiferous tubules are devoid of germ cells. The replicas from irradiated tubules show elaborate interdigitations of the lateral membranes of Sertoli cells and very extensive tight junctions. These junctions are characterized by a great number of continuous parallel or complex interweaving strands of intramembranous particles, preferentially associated with E fracture faces. The presence of highly cross‐linked tight junctional strands is compatible with an epithelium deprived of germ cells, with a reduced need for flexibility. Anomalous ectoplasmic specializations, consisting of groups of cisternae arranged perpendicularly to the lateral surface, are found in the irradiated tubules. These structures may be involved in a storage mechanism of redundant lateral membrane resulting from the elimination of germ cells. Typical gap junctions, intercalated between the tight junctional strands, are larger and more frequently found in treated animals than in controls. These findings indicate that a very tight permeability barrier seems to be established in the irradiated testis even in the absence of germ cells. Thus, the formation and maintenance of Sertoli tight junctions do not appear to be directly dependent on the presence of germ cells. Nevertheless, the alterations detected in the tight junction architecture and in the ectoplasmic specializations indicate that maturing germ cells probably contribute to the functional organization of the blood—testis barrier in the norm

ISSN:1065-6995    

DOI:10.1006/cbir.1996.0066

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY