摘要:

The methylation state of Intracisternal A Particle (IAP) genes in mouse teratocarcinoma cell lines has been investigated as an approach to study the regulation of the expression of these particles. Treatment of the cells with the methylation inhibitor 5‐azacytidine induces the production of the particles in all the cells; the induction is particularly striking in an embryonal carcinoma cell line which is normally devoid of IAPs. The induction is accompanied by decrease in DNA methylation as demonstrated by using the methylation sensitive isoschizomer enzymes MspI and HpaII. Hypomethylation of the IAP genes correlates with accumulation of IAP, specific polyadenylated RNA reinforcing the hypothesis that methylation plays an important role in the control of IAP expressio

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00337.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

A Balbiani ring‐like structure (T‐BR III) is induced at the right telomere on chromosome III by a 35 degrees C heat‐shock. The location of T‐BR III was identified in 3 micron‐semithin sections that were afterwards resectioned to obtain ultrathin sections. These were stained either by uranyl acetate‐lead citrate or PTA. The puff appeared composed of different structures: small compact chromatin bodies, loose chromatin with an apparently fibrillar organization, and granules. The granules, 200‐250 A in diameter, appeared either in linear arrays or in a clustered form. The three components described above were interspersed within the T‐BR without a compartmentalized organization. EDTA preferential ribonucleoprotein staining technique evidenced an EDTA‐positive material within the T‐BR that corresponded to 200‐250 A granules as well as apparently fibrillar structures. However, EDTA did not completely stain some clustered granules. Neither free nor clustered granules were found in T‐BRs formed in the presence of actinomycin D. The significance of the different T‐BR structures in relation to the transcriptional activity

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00338.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Mitochondrial DNA extracted from Rana esculenta oocytes appears heterogeneous in size. The length of these molecules varies continuously from 18,700 bp to 19,700 bp. Each animal is heteroplasmic and can be characterized by the range of the variation (400‐700 bp) and the extreme sizes of the various molecules it carries. The variable region of the genome has been localized between the coding region and the replication origin are

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00339.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The possible physiological targets of pp60src in chicken embryo fibroblasts transformed by Rous sarcoma virus were looked for by a general screening of the modifications of phosphorylation of the major cell phosphoproteins. These modifications were analyzed quantitatively by SDS‐PAGE of total cell proteins on gradient gels, combined with a computerized densitometric evaluation of gel autoradiographies, using cells labeled with either [14C]‐amino acids or with [32P]‐phosphate. A large numbers of proteins, 37 out of the 68 studied, were found to be more phosphorylated in virally transformed cells. The determination of the phosphoamino acid content of proteins which were more phosphorylated in transformed cells and the study of the kinetics of protein phosphorylation in cells infected by a ts mutant, after a shift from the nonpermissive to the permissive temperature, showed that, among these proteins, five displayed a large increase in phosphotyrosine content and an early increase in phosphorylation after the temperature shift. These proteins of 36 K, 41 K, 46 K, 65 K and 280‐300 K doublet are therefore good candidates for being physiological targets of pp60src in t

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00340.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

Incorporation of 5‐bromodeoxyuridine (5‐BUdR) into nuclear DNA severely interrupts the life cycle of Dictyostelium discoideum after the first generation of growth. Loose cellular aggregates are then formed, but no spore or stalk cells are detectable and no other morphological transformations are observed. The perturbation of gene expression in the life cycle has been studied at the protein level by two‐dimensional gel electrophoresis after pulse labelling with 35S‐methionine and also by changes in the patterns of polysomal messenger RNA population. The latter was monitored by hybridisation studies using specific cDNA probes for “vegetative” and “18 hr” messenger RNAs. In the presence of 5‐BUdR major anomalies in polypeptide synthesis were observed after the loose aggregation stage. Some vegetative polypeptides, including actin, which are normally abundant only during growth to the aggregation stage, are oversynthesised during the period 12‐24 hr after starvation. In this same interval the normal decline in the abundance of vegetative mRNA species was not observed. In marked contrast virtually half the normal “18 hr‐specific polypeptides” were poorly synthesised. Likewise, the normal increase in abundance of the corresponding “18 hr‐specific” poly A + RNA species in the polysomes did not occur. No major alteration in the timing of the appearance of new macromolecules during the cell cycle was observed in spite of extensive modification of gene expression by the incorpora

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00341.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The relationship between membrane lipid fluidity and expression of HLA‐DR and cALL (CALLA) antigens was studied in a human non T non B acute lymphoblastic leukemia cell line (Reh). The membrane fluidity was modulated by treatment with cholesteryl hemisuccinate or phospholipids (e.g. egg lecithin) and monitored by fluorescence polarization. HLA‐DR and CALLA expression was measured in an indirect immunofluorescence test with a Fluorescence Activated Cell Sorter (FACS 440), on 24, 48, 72 and 96 hour‐cultured cells. Significant antigenic modulation was obtained with cholesteryl hemisuccinate treatment on 48 hour‐cells where a slight increase in HLA‐DR and a marked decrease in CALLA were observed. In contrast no antigenic modification was observed on lecithin‐tr

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00342.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

HLA class I and class II (HLA‐DR (human I‐E equivalent) and DQ (human I‐A equivalent] antigens were localized by immunofluorescence technique on thin frozen sections of normal human jejunum using a panel of monomorphic monoclonal antibodies. HLA class I (A, B and C) and HLA‐DR molecules were found in the basolateral membrane of enterocytes; HLA‐DR were also detected in a patchy distribution in the apical part of enterocytes; HLA‐DQ molecules (the human equivalent of the murine I‐A molecular subset) were not detected on normal enterocytes. All three molecules were detected on the membrane of lymphocytes and monocytes present in the l

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00343.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The mechanism by which macrophages recognize tumor cells is still unknown. We have studied interactions between rat liver macrophages and rat L 5222 leukemia cells. These tumor cells, but not normal leukocytes or erythrocytes, adhere to freshly isolated macrophages in vitro. Binding of tumor cells by macrophages can be inhibited by N‐acetyl‐D‐galactosamine, D‐galactose and more potently by glycoproteins with terminal N‐acetyl‐D‐galactosamine or D‐galactose residues. Tumor cell adhesion is calcium‐dependent. The relevant leukemia cell membrane structures which bear terminal beta‐D‐galactosyl or related residues have been determined as trypsin‐ and pronase‐sensitive, and hence may presumably be glycoproteins. The tumor cell receptor on liver macrophages appears to be a lectin with the carbohydrate specificity N‐acetyl‐D‐galactosamine greater than D

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00344.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time‐dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8‐Br‐cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00345.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY

摘要:

The hepatopancreas of the lobster has recently been found to be a rich source of material from which to isolate arthopod gap junctions biochemically (Finbow et al., 1983a; 1984). It has therefore been studied here to assess the features of these intercellular junctions and any others that may be present, in vivo. The tissue consists of columnar epithelial cells which possess apical microvilli and basal infoldings. In thin sections the lateral borders of these cells are characterized by desmosomes and smooth septate junctions as well as by gap junctions. The desmosomes exhibit no apparent freeze fracture profile but the septate junctions display parallel rows of ridges or aligned intramembranous particles (IMPs) with complementary grooves on the other membrane half; these IMPs shift in their preferential fracturing plane depending on whether the tissue has first been fixed, always remaining on the EF if unfixed. The IMPs or connexons, of which the gap junctions are composed, fracture onto the E face, leaving complementary pits on the P face, regardless of whether the tissue is fixed or not. At the base of the pancreatic cells, the lateral borders are thrown into interdigitating folds which display endocytotic profiles and possible internalization of junction‐bearing membranes. This phenomenon, which is readily visualized both after tracer incubation and in replicas, may represent junctional degradation relating to membrane turnove

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1985.tb00346.x

出版商:Blackwell Publishing Ltd    

年代:1985

数据来源: WILEY