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Biomedical subjects

F Zhang

Publications and source records attributed to F Zhang.

At least 613 records · Page 34Linked to original sources
PubMed1991

Fluorescence recovery after photobleaching techniques to measure translational mobility in microscopic samples.

The scope of photobleaching applications and the method itself are briefly reviewed. Two current applications in this laboratory are then outlined. First, the use of spatial Fourier transforms to analyze video photobleaching measurements is presented. This method extracts diffusion coefficients using all the image data and it does not require that the initial condition created by photobleaching be known. Second, the use of genetic engineering methods coupled with photobleaching analysis is discussed as means to uncover the structural determinants of membrane protein lateral mobility.

Cytoplasm↗
PubMed1990

Fusion of influenza hemagglutinin-expressing fibroblasts with glycophorin-bearing liposomes: role of hemagglutinin surface density.

Influenza virus gains access to the cytoplasm of its host cell by means of a fusion event between viral and host cell membrane. Fusion is mediated by the envelope glycoprotein hemagglutinin (HA) and is triggered by low pH. To learn how many hemagglutinin trimers are necessary to cause membrane fusion, we have used two NIH 3T3 fibroblast cell lines that express HA protein at different surface densities. On the basis of quantitations of the number of HA trimers per cell and the relative surface areas of the two cell lines, the HAb-2 cells have a 1.9-fold higher plasma membrane surface density than the GP4F cells. The membrane lateral diffusion coefficient and the mobile fraction for HA is the same for both cell lines. A Scatchard analysis of the binding of glycophorin-bearing liposomes to the cells showed 1700 binding sites for the GP4F cells and 3750 binding sites for the HAb-2 cells, with effectively the same liposome-cell binding constant, about 7 x 10(10) M-1. Binding was specific for glycophorin on the liposomes and HA expressed on the cells. A competition experiment employing toxin-containing and empty liposomes allowed us to quantitate the number of liposomes that fused per cell, which was a small constant fraction of the number of bound liposomes. For the HAb-2 cells, about 1 in every 70 bound liposomes fused and for the GP4F cells about 1 in every 300 bound liposomes fused. Hence, the HAb-2 cells showed 4.4 times more fusion per bound liposome, even though the surface density of HA was only 1.9 times greater. We conclude the following: (i) One HA trimer is not sufficient to induce fusion. (ii) The HA bound to glycophorin is not the HA that induces fusion. That is, even though each HA has a binding and a fusion function, those functions are not performed by the same HA trimer.

Animals↗
PubMed1990

Culture and characterization of thymic epithelium from autoimmune NZB and NZB/W mice.

Autoimmune NZB and NZB/W mice display early abnormalities in thymus histology, T cell development, and mature T cell function. Abnormalities in the subcapsular/medullary thymic epithelium (TE) can also be inferred from the early disappearance of thymulin from NZB. It has also been reported that NZB thymic epithelial cells do not grow in culture conditions that support the growth of these cells from other strains of mice. In order to study the contribution of TE to the abnormal T cell development and function in NZB and NZB/W mice, we have devised a culture system which supports the growth of TE cells from these mice. The method involves the use of culture vessels coated with extracellular matrix produced by a rat thymic epithelial cell line. TEA3A1, and selective low-calcium, low-serum medium. In addition TEA3A1 cells have been used as an antigen to generate monoclonal antibodies specific for subcapsular/medullary TE. These antibodies, as well as others already available, have been used to show that the culture conditions described here select for cells displaying subcapsular/medullary TE markers, whereas markers for cortical TE and macrophages are absent.

Animals↗
PubMed1990

Interstitial deletion of the short arm of chromosome 20 in arteriohepatic dysplasia (Alagille syndrome).

An autosomal dominant transmission of arteriohepatic dysplasia, or Alagille syndrome, with reduced penetrance and variable expressivity has been suggested from familial pedigrees, but the nature of the genetic defect and its chromosomal localization are not firmly established. We report the case of an 8-year-old boy with arteriohepatic dysplasia, in whom high-resolution chromosome study showed a partial deletion of the short arm of chromosome 20, which encompasses subbands p11.23 to p12.3. In situ hybridization and Southern blotting localized four restriction fragment length polymorphism probes within the deletion and another one distal to the deletion. Because one patient has already been reported to have arteriohepatic dysplasia and deletion of the short arm of chromosome 20, and six additional patients with such a deletion had major features of Alagille syndrome, this syndrome should now be assigned to chromosome 20p.

Bile Ducts↗
PubMed1990

Cell membrane is a major locus for ultraviolet B-induced alterations in accessory cells.

In vitro ultraviolet B (UVB) irradiation of human blood monocytes inhibits their accessory cell function for antigen- and mitogen-induced T cell responses. These studies were designed to characterize the nature of the UVB-induced defect in human monocyte accessory cell function. Irradiated monocytes were deficient in their ability to serve as accessory cells for OKT3-induced T cell activation. In vitro exposure of monocytes to 100 J/m2 UVB completely inhibited the T cell proliferative response (51502 cpm, non-UVB-irradiated; 302 cpm, UVB-irradiated). Analysis of the accessory signals altered by UVB indicated that irradiated monocytes were incapable of binding to OKT3 molecules attached to the CD3 antigen on T cells. Provision of an alternative mechanism for binding of OKT3 molecules by attaching anti-mouse IgG to the bottom of microtiter wells completely restored accessory cell function. Further characterization of the defect demonstrated that UVB radiation did not deplete p72 Fc receptors from the surface of irradiated monocytes. However, UVB exposure did produce a dose-dependent decrease in monocyte membrane expression of ICAM-1. It is proposed that UVB radiation leads to changes within the cell membrane that inhibit the ability of monocytes to express selected molecules necessary for binding of T cells.

Antibodies, Monoclonal↗
PubMed1990

[Effect of monocrotaline on human kidney cells].

The effect of monocrotaline on human kidney cells has been studied by means of monolayer cell culture, cytochemistry and 3H-thymidine incorporation. The result shows that this drug can inhibit cell DNA synthesis, featuring an irreversible damaging action to DNA templet. Also, when the process of glycolysis and saccharide utilization in the cells is inhibited, the amount of lactic acid produced decreases and the pH value becomes higher.

DNA↗
PubMed1990

Preparative slab electrofocusing of methane monooxygenase from a type I methanotroph Methylomonas GYJ3.

The isolation and purification of methane monooxygenase from a type I methanotroph Methylomonas GYJ3 to near homogeneity is reported. The isoelectric focusing in flat-bed granulated gels has resolved the methane monooxygenase into three protein components. The specific activity of the enzyme is 198.4 n mol per min per mg protein, degree of purification 4.13-fold. Recovery of the focused proteins is high and elution simple. Several purification steps may be omitted from the previously published scheme by other techniques.

Isoelectric Focusing↗
PubMed1990

[Circadian rhythm of immune adhesion activity of RBCs in the aged and in patients with kidney deficiency].

The authors observed the variation of immune adhesion activity of RBC of the healthy aged and the Kidney-deficiency patients in different phases of day and night. The results showed that the C3b receptor rosette formation rate of RBC of the aged were in lower level except You phase, while that of the patients were the highest at Mao phase and declined step by step from Mao to Zi phase in a day. The peak and valley values of immune complex rosette of formation rate of RBC of the aged appeared at Mao and Zi phases respectively. But in the Kidney-deficiency patients these rhythms were disappeared. On the basis, the authors discussed the difference and connection between physiological aging and pathological aging.

Aged↗
PubMed1990

[Protective effect of a platelet activating factor antagonist in experimental liver injury].

The present study was conducted to observe the effect of platelet activating factor antagonist-WEB 2086 on the galactosamine/endotoxin (GalN/E)-induced rat liver injury. The results showed that the WEB 2086 (1, 20 or 40 mg/kg, ip) diminished significantly GaIN/E induced elevations of ALT.AST and ACP in the serum (P less than 0.01). Histological changes of the liver were also found to be improved significantly by WEB 2086 administration. Additionally, WEB 2086 decreased significantly the GaIN/E-induced increase of Malondialdehyde (MDA) and Myeloperoxidase (MPO) in the liver (P less than 0.05-0.01), and prevented the decreasing of superoxide dismutase (SOD) in the liver (P less than 0.01). The results obtained with WEB 2086 confirm that platelet activating factor (PAF) has an important role in the pathophysiology of liver injury, PAF-antagonists may have protective effects on liver injury.

Animals↗
PubMed1990

[Observation of efficacy of different dialytic therapies in renal transplantation preparation].

Fifty-seven cadaveric renal transplantations in fifty-five cases were analysed of them, thirty cases were prepared by continuous ambulatory peritoneal dialysis (CAPD group); twenty-seven transplantations in twenty-five cases were prepared by hemodialysis (HD group). Our data show that there is no significant difference in the survival duration between CAPD group and HD group; that there is also no significant difference in the survival duration between the two groups treated with the same immunosuppressive drugs, and that patients prepared by CAPD have a low risk of peritonitis after transplantation. It is better not to remove the Tenckhoff catheter until the graft function is stable so that it can be used for the transient peritoneal dialysis in the case of the insult of graft function or for the sampling of the peritoneal effusion for diagnosis of suspectable peritonitis after renal transplantation.

Adult↗
PubMed1989

[Evaluation of antipyrine clearance in chronic liver diseases].

Antipyrine (AP) clearance was determined in 23 cases with liver cirrhosis (LC), 12 with chronic active hepatitis (CAH), 12 with hepatocellular carcinoma (mcHCC), 20 with non-hepatic diseases and 70 healthy controls. ICG Clearance was performed simultaneously in 9 cases of them. The results showed that AP clearance was significantly decreased in patients with LC and moderately decreased in CAH and HCC, its diagnostic sensitivity in LC was significantly higher than that of GPT. The significant positive correlation between the AP and ICG clearance was noted and AP clearance also well correlated with serum albumin level and prothrombin time. It is suggested that AP clearance may be used as a quantitative test to determine the reserve capacity of liver and as a substitutive test for ICG clearance.

Adolescent↗
PubMed1988

Molecular characterization of ataxia telangiectasia T cell clones. II. The clonal inv(14) in ataxia telangiectasia differs from the inv(14) in T cell lymphoma.

We compared inversions of chromosome 14 in an ataxia telangiectasia clone and in a malignant T cell line (SUP-T1). The R-banding chromosome analysis showed a clear difference between the distal breakpoint of the two inversions. Fine mapping of the distal breakpoint in the ataxia telangiectasia inv(14) was performed by in situ hybridization. We conclude that this breakpoint is centromeric to the immunoglobulin heavy chain locus and to the D14S1 anonymous locus. Our results favor the existence of an unknown oncogene in band 14q32.1.

Ataxia Telangiectasia↗
PubMed1987

The fragile X site in somatic cell hybrids: an approach for molecular cloning of fragile sites.

Fragile X syndrome is a common form of mental retardation associated with a fragile site on the human X chromosome. Although fragility at this site is usually evident as a nonstaining chromatid gap, it remains unclear whether or not actual chromosomal breakage occurs. By means of somatic cell hybrids containing either a normal human X or a fragile X chromosome and utilizing two genes that flank the fragile site as markers of chromosome integrity, segregation of these markers was shown to be more frequent if they encompass the fragile site under appropriate culture conditions. Hybrid cells that reveal marker segregation were found to contain rearranged X chromosomes involving the region at or near the fragile site, thus demonstrating true chromosomal breakage within this area. Two independent translocation chromosomes were identified involving a rodent chromosome joined to the human X at the location of the fragile site. DNA analysis of closely linked, flanking loci was consistent with the position of the breakpoint being at or very near the fragile X site. Fragility at the translocation junctions was observed in both hybrids, but at significantly lower frequencies than that seen in the intact X of the parental hybrid. This observation suggests that the human portion of the junctional DNA may contain part of a repeated fragility sequence. Since the translocation junctions join heterologous DNA, the molecular cloning of the fragile X sequence should now be possible.

Animals↗
PubMed1987

Identification of a complex associated with processing and polyadenylation in vitro of herpes simplex virus type 1 thymidine kinase precursor RNA.

Cleavage and polyadenylation of substrate RNAs containing the herpes simplex virus type 1 (HSV-1) thymidine kinase (tk) gene polyadenylation signal region were examined in HeLa cell nuclear extract. 3'-End RNA processing was accurate and efficient and required ATP and Mg2+. Cleavage, but not polyadenylation, occurred in the presence of EDTA or when ATP was replaced with 3' dATP (cordycepin) or AMP(CH2)PP, a nonhydrolyzable analog of ATP. Processing in vitro and in vivo showed the same signal element requirements: a series of substrates containing linker scanning, internal deletion, and small insertion mutations was processed with the same relative efficiencies and at the same sites in vitro and in vivo. A complex involved in 3'-end RNA processing was identified by gel mobility shift analysis. This complex formed rapidly, reached a maximum level after 20 to 30 min, and was much reduced after 2 h. Very little complex was formed at 0 degree C or with substrates lacking a polyadenylation signal. Entry of 32P-labeled tk substrate into the complex could be prevented by addition of excess 35S-labeled tk or adenovirus L3 precursor RNAs. Competition was not observed with tk RNAs lacking a complete polyadenylation signal.

Adenosine Triphosphate↗
PubMed1986

Fine-structure analysis of the processing and polyadenylation region of the herpes simplex virus type 1 thymidine kinase gene by using linker scanning, internal deletion, and insertion mutations.

Most eucaryotic mRNAs are polyadenylated. In higher eucaryotes, the sequence AATAAA is located 7 to 30 base pairs (bp) upstream from the site of processing and polyadenylation and is a critical part of the signal for processing and polyadenylation. Efficient cleavage and polyadenylation also require sequences downstream of polyadenylation sites. The herpes simplex virus type 1 thymidine kinase (tk) gene contains two copies of the AATAAA hexanucleotide and a GT box (18 of 19 consecutive residues are G or T) previously shown to be required for efficient processing and polyadenylation of tk mRNA (C. N. Cole and T. P. Stacy, Mol. Cell. Biol., 5:2104-2113). To define further the sequence requirements for efficient polyadenylation, we prepared linker scanning, internal deletion, and small insertion mutations in the polyadenylation region of the tk gene. These mutations were analyzed by S1 nuclease protection analysis of cytoplasmic RNA isolated from transfected Cos-1 monkey kidney cells. When the proximal AATAAA was deleted, no tk mRNA polyadenylated in the normal region was detected, whereas replacement of the second AATAAA with an XbaI linker had no effect on polyadenylation. When various portions of the GT box were replaced with linker, the amount of tk mRNA produced was reduced to 23 to 82% of the normal amount, but polyadenylation in the normal region was never abolished. Thus, no single portion of the GT box was absolutely required. In some cases, extended transcripts, polyadenylated at a cryptic site within pBR322, were detected. A spacing of 6 bp between AATAAA and the GT box was too short for efficient processing and polyadenylation. A spacing of 30 bp appeared to work almost as efficiently as did the wild-type spacing of 18 bp. Taken together, these results indicate that efficient polyadenylation requires both AATAAA and downstream GT-rich sequences. In addition, processing and polyadenylation are affected both qualitatively and quantitatively by sequences at polyadenylation sites and at more distant locations.

Animals↗