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G Yang

Publications and source records attributed to G Yang.

At least 397 records · Page 22Linked to original sources
PubMed1995

[Ultrastructural study of human yolk sac].

Twenty cases of human yolk sac of different gestation weeks observed by electron microscopy. The wall of yolk sac consisted of endoderm, mesenchyme and mesothelium. Nuclei of the endodermal cell were large and nucleoli were remarkable. The surface of endodermal cell presented a number of microvilli. There were Golgi complex, rough endoplasmic reticulum, glycogen and mitochondria in the cytoplasm of the endodermal cell. The fibroblast-like cell, macrophage-like cell. erythroblast in various mature degree, collagen filament and capillaries were found in the mesenchyme. The mesothelial cell had long, slender microvilli, which were mostly branched. Pinocytotic vesicles in the apical cytoplasm beneath the mesothelial cell membrane were frequent. The differently sized endodermal tubules with well-defined lumen and microvilli were recognized by electron microscopy. Masses of endodermal cells frequently invaginated in the mesenchymal layer, and they often reached the mesothelial layer. These structures of yolk sac were the foundation of finishing synthesis, secretion, translation and hematopoiesis during early organogenesis.

Female↗
PubMed1995

Association of p53 mutations with metastatic prostate cancer.

In prostate cancer, mutation of the p53 tumor suppressor gene has been associated with locally advanced disease and hormone-resistant disease that is predominantly localized to bone. However, little is known regarding the status of the p53 gene in metastatic prostate cancer that has not been treated with hormonal manipulation. We evaluated formalin-fixed, paraffin-embedded malignant tissues from 86 patients with various stages of prostate cancer, including pathologically confined, locally advanced, and metastatic disease, to detect abnormal p53 nuclear protein accumulation using immunohistochemistry. No abnormal p53 immunostaining was detected in 18 patients with prostate cancer confined to the gland. Two tumors from 21 patients with locally advanced disease (extracapsular extension and/or seminal vesicle invasion) had abnormal nuclear p53 accumulation, and a mutation in exon 7 of the p53 gene was detected in tumor DNA from one patient using single-strand conformation polymorphism-direct sequencing analysis. Of the remaining 47 patients studied in whom tissues from the prostate gland and a metastatic site (44 lymph node, 2 bone, and 1 lung) were available, only 3 had received hormonal therapy prior to obtaining metastatic tissue. In four patients both primary and metastatic tumors demonstrated accumulation of p53 protein, whereas seven additional patients exhibited p53 accumulation only at the metastatic site. In three patients the metastatic tumors harbored missense single-base substitutions in exon 5, as detected using single-strand conformation polymorphism-direct sequencing. These results indicate that p53 abnormalities are associated with lymph node metastases derived from prostate cancer patients that had not undergone hormonal therapy.

Adenocarcinoma↗
PubMed1994

Functional expression of the human angiotensinogen gene in transgenic mice.

The renin-angiotensin system is a major determinant of arterial pressure and volume homeostasis in mammals through the actions of angiotensin II, the proteolytic digestion product of angiotensinogen. Molecular genetic studies in several human populations have revealed genetic linkage between the angiotensinogen gene and both hypertension and increased plasma angiotensinogen. Transgenic mice were generated with a human angiotensinogen genomic clone to develop an animal model to examine tissue- and cell-specific expression of the gene and to determine if overexpression of angiotensinogen results in hypertension. Human angiotensinogen mRNA was expressed in transgenic mouse liver, kidney, heart, adrenal gland, ovary, brain, and white and brown adipose tissue and, in kidney, was exclusively localized to epithelial cells of the proximal convoluted tubules. Plasma levels of human angiotensinogen were approximately 150-fold higher in transgenic mice than that found normally in human plasma. The blood pressure of mice bearing the human angiotensinogen gene was normal but infusion of a single bolus dose of purified human renin resulted in a transient increase in blood pressure of approximately 30 mm Hg within 2 min. These results suggest that abnormalities in the angiotensinogen gene resulting in increased circulating levels of angiotensinogen could potentially contribute in part to the pathogenesis of essential hypertension.

Angiotensinogen↗
PubMed1994

Tagged mutations at the Tox1 locus of Cochliobolus heterostrophus by restriction enzyme-mediated integration.

We have used the restriction enzyme-mediated integration insertional mutagenesis procedure to tag the Tox1 locus in the filamentous Ascomycete Cochliobolus heterostrophus. Mutations at other, unselected, loci were also identified and a high proportion (30-50%) of them were tagged. This procedure may be of general utility for simultaneously mutating and tagging genes in fungi and in other eukaryotes. The Tox1 locus of C. heterostrophus has been defined by Mendelian analysis as a single genetic element that controls production of T toxin, a linear polyketide involved in virulence of the fungus to its host plant, corn. To tag Tox1, protoplasts of a Tox1+ (T-toxin producing) strain were transformed with a linearized, nonhomologous plasmid along with an excess of the restriction enzyme used to linearize the plasmid. Of 1310 transformants recovered, two produced no detectable T toxin in culture or on corn plants. In each of these transformants, the Tox- mutation mapped at Tox1, was tagged with the selectable marker (hygB) on the transforming plasmid, and was tightly linked to the other tagged Tox- mutation. The two mutations, however, represent two different points of plasmid insertion at the Tox1 locus.

Ascomycota↗
PubMed1994

DNA bending by Cro protein in specific and nonspecific complexes: implications for protein site recognition and specificity.

Scanning force microscopy was used to resolve lambda Cro protein when bound as a single dimer or multiple dimers to its three operator (OR) sites. The bend angles induced by binding of Cro to specific and nonspecific sites were determined and are 69 degrees +/- 11 degrees for specific and 62 degrees +/- 23 degrees for nonspecific complexes. Bending of the nonspecific sites is advantageous for a protein such as Cro that bends its specific site, because it increases the binding specificity of the protein and it can be used by the protein to sample contacts required for the recognition of its target sequence. It is proposed here that bending of nonspecific DNA may be a general property among DNA binding proteins that bend their specific sites.

Base Sequence↗
PubMed1994

Three-dimensional structure of extended chromatin fibers as revealed by tapping-mode scanning force microscopy.

Unfixed chicken erythrocyte chromatin fibers in very low salt have been imaged with a scanning force microscope operating in the tapping mode in air at ambient humidity. These images reveal a three-dimensional organization of the fibers. The planar "zig-zag" conformation is rare, and extended "beads-on-a-string" fibers are seen only in chromatin depleted of histones H1 and H5. Glutaraldehyde fixation reveals very similar structures. Fibers fixed in 10 mM salt appear somewhat more compacted. These results, when compared with modeling studies, suggest that chromatin fibers may exist as irregular three-dimensional arrays of nucleosomes even at low ionic strength.

Animals↗
PubMed1994

Characterization and purification of a macrophage-triggering factor produced in Mycoplasma arginini-infected L5178Y cell cultures.

The supernatant of Mycoplasma arginini-infected murine L5178Y T lymphoma cell cultures (SN-L51) synergizes with small concentrations of IFN-gamma to activate murine peritoneal, thioglycollate-elicited macrophages (M phi) to exhibit cytostatic activity against tumor cells. Treatment of M phi with IFN-gamma and SN-L51 sequentially, but not in the reverse order, activates M phi, which indicates that SN-L51 contains a M phi-triggering factor (MTF). MTF activity could be inhibited by small concentrations of prostaglandin E2, but not by polymyxin B. M phi activated by IFN-gamma plus MTF produce cytostatic effects on tumor cells through a nitric oxide-dependent pathway. MTF activity in SN-L51 is associated with infection of L5178Y cells by M. arginini. Mycoplasma-free L5178Y cells do not produce MTF activity, infection of these L5178Y cells with M. arginini generates the activity, and supernatants of pure M. arginini cultures contain MTF activity. MTF activity is thermostable and resistant to acid, dilute alkali, proteases, and nucleases. MTF was partially purified by ammonium sulfate precipitation, chromatography, electrophoresis, and electroelution. On 12.5% SDS-urea gels, MTF activity migrated with a molecular mass of 2.5 to 4 kDa. MTF activity and the silver staining of this band was resistant to proteinase K; however, Coomassie staining of this band was abolished by proteinase K. The combined data suggest that MTF is either a stable peptide or a peptide linked to lipid or carbohydrate.

Animals↗
PubMed1994

Evidence for nucleophilic catalysis in the aromatic substitution reaction catalyzed by (4-chlorobenzoyl)coenzyme A dehalogenase.

(4-Chlorobenzoyl)coenzyme A dehalogenase catalyzes the hydrolytic dehalogenation of (4-chlorobenzoyl)coenzyme A (4-CBA-CoA) to (4-hydroxybenzoyl)coenzyme A (4-HBA-CoA). Rapid-quench techniques were used in conjunction with [14C]-4-CBA-CoA to test for the formation of a covalent enzyme intermediate during catalysis. The rate of [14C]-4-CBA-CoA (37 microM) consumption in the presence of a 2-fold excess of dehalogenase (75 microM) was determined to proceed at k = 6.5 s-1, coincident with the formation of an enzyme intermediate containing covalently bound radiolabel. The radiolabeled enzyme reached a maximum level at 100 ms, corresponding to 27% of the starting [14C]-4-CBA-CoA, before declining. The kinetics of formation and consumption of the radiolabeled enzyme observed during turnover are consistent with its intermediacy in the overall reaction. A single turnover reaction carried out in 98% 18O-enriched water produced 4-HBA-CoA with 73-75% 16O and 27-25% 18O at the benzoyl ring C(4)-OH. In contrast, a multiple turnover reaction carried out in 93% H2(18)O produced 4-HBA-CoA labeled at the C(4)-OH with 89% 18O and 11% 16O. These results were interpreted as evidence for formation of an aryl enzyme intermediate during 4-CBA-CoA hydrolytic dechlorination in the dehalogenase active site.

Acyl Coenzyme A↗
PubMed1994

Linker DNA accessibility in chromatin fibers of different conformations: a reevaluation.

New studies on chromatin fiber morphology, using the technique of scanning force microscopy (SFM), have caused us to reexamine recent analysis of nuclease digestion of chromatin. Chicken erythrocyte chromatin fibers, glutaraldehyde-fixed at 0, 10, and 80 mM NaCl, were imaged with the help of SFM. The chromatin fibers possessed a loose three-dimensional 30-nm structure even in the absence of added salt. This structure slightly condensed upon addition of 10 mM NaCl, and highly compacted, irregularly segmented fibers were observed at 80 mM NaCl. This sheds new light upon our previously reported analysis of the kinetics of digestion by soluble and membrane-immobilized micrococcal nuclease [Leuba, S. H., Zlatanova, J. & van Holde, K. (1994) J. Mol. Biol. 235, 871-880]. While the low-ionic-strength fibers were readily digested, the highly compacted structure formed at 80 mM NaCl was refractory to nuclease attack, implying that the linkers were fully accessible in the low-ionic-strength conformation but not in the condensed fibers. We now find that cleavage of the linker DNA by a small molecule, methidiumpropyl-EDTA-Fe(II), proceeds for all types of conformations at similar rates. Thus, steric hindrance is responsible for the lack of accessibility to micrococcal nuclease in the condensed fiber. Taken in total the data suggest that reexamination of existing models of chromatin conformation is warranted.

Animals↗
PubMed1994

Terminin (Tp 63/60), a novel cell senescence-related protein, is present in the aging human hippocampus.

We have previously identified a cell senescence-related, detergent-insoluble cytoplasmic protein referred to as terminin, and have presented the development-dependent modification of terminin polypeptides in rat brain. In the present study, we characterize biochemically and immunocytochemically terminin expression in human hippocampus. By immunoblotting with a monoclonal antibody (mab 1.2) against terminin, we identified a 63 kDa polypeptide (Tp63) in the detergent-insoluble fraction of human brain proteins, which can be identified by either one- or two-dimensional electrophoresis. The 63 kDa protein in immunoprecipitates of human hippocampus was found to share a peptide pattern with the 60 kDa terminin (Tp60) previously found in rat brain, as demonstrated by in situ peptide mapping, suggesting that the human 63 kDa protein is a homologue of the rat Tp60. By immunocytochemistry, terminin immunoreactivity was demonstrated throughout the neuronal layers in the human hippocampus. The pyramidal cell layer in hippocampus proper and subiculum, as well as the granule cells in the dentate gyrus, gave rise to immunoreactivity for terminin. It was observed that in the cornu Ammonis, the highest terminin immunoreactivity was present in the pyramidal neurons of CA1. At the cellular level terminin was localized intraneuronally, as demonstrated by confocal microscopy of double staining with both mab 1.2 and an anti-neurofilament antibody. Taken together, the present study establishes that terminin is expressed in abundance in aging human CNS neurons.

Aged↗
PubMed1994

Expression of terminin, a senescence-related cytoplasmic protein, in the aging rat brain.

Terminin is a cytoplasmic protein expressed in irreversibly growth-arrested senescent fibroblast cultures and in terminally differentiated cells of various epithelia. In the present study, terminin was identified by immunohistochemistry in the cytoplasm of neurons and glia of aging rat brain using the monoclonal antibody (Mab) 1.2. Few terminin-positive neurons were observed in 3-month-old brain. At 18 months, terminin immunoreactivity was noted in dentate gyrus granule cells, in hippocampal fibre projections and in neuronal perikarya of deep cerebellar nuclei (but not in cerebellar cortex). In 33-month brain, terminin immunoreactivity in the dentate gyrus was more intense than at 18 months but immunoreactive fibre bundles in the hippocampus were no longer seen. At 33 months, the cerebellar granule cell layer contained terminin-positive horizontal interneurons and received immunoreactive axonal projections not seen in the younger preparations. In addition, ubiquitous low-level terminin expression was noted in neurons of the cerebral cortex, hippocampus and cerebellum of the 33-month-old animals. Thus, in the rat CNS, an increase in terminin appears to be a physiologic marker of neuronal aging. Small numbers of terminin-positive neuroglia were present in gray and white matter of 3-month-old brain and became increasingly more abundant in the 18- and 33-month-old animals. However, even in senescent brains, terminin-positive neuroglia represented a very small fraction of the entire glial pool. Terminin expression in slowly renewing neuroglial populations may identify those cells in which degeneration and death are imminent.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

Transfusion-related transmissible diseases: detection by polymerase chain reaction-amplified genes of the microbial agents.

The detection of blood-borne microbes by PCR has broadly and rapidly progressed in the past 5 years as briefly described in this article. This progress has been largely because of the scientific developments made at Roche Molecular Systems by Sninsky et al through collaborations with academic and Government institutions. This unprecedented cooperation propels the continuing work at Roche Molecular Systems to bring the PCR technology into routine laboratory diagnosis. Whether the success of EIA in virtual elimination of hepatitis and retroviral infections can be matched by the cost-effectiveness of putative application of PCR in screening blood supply remains to be determined.

Bacterial Infections↗
PubMed1994

Rare detection of hepatitis B and hepatitis C virus genomes by polymerase chain reaction in seronegative donors with elevated alanine aminotransferase.

BACKGROUND: Since screening for antibody to hepatitis C virus (HCV) was introduced in 1990, posttransfusion hepatitis has been reduced to nearly background levels. This has led to reconsideration of the value of testing donated blood for elevated alanine aminotransferase (ALT). The contribution of ALT testing in detecting seronegative infection was evaluated by the performance of polymerase chain reaction (PCR) for hepatitis B virus (HBV) or HCV in plasma from ALT-elevated blood units. STUDY DESIGN AND METHODS: Testing was performed on 375 units of plasma, derived from an equivalent of 47,500 blood donations, with a highly sensitive hemi-nested PCR procedure. Using a triplet of primers directed at the conserved regions of HBV DNA and 5'-noncoding regions of HCV RNA, the hemi-nested PCR assay can reliably amplify 10 viral molecules to levels detectable in ethidium bromide-stained agarose gels. Pools of plasma from groups of four donors were screened with hemi-nested PCR. For any reactive pools, the plasma from individual donors was retested twice on different aliquots. RESULTS: Two of 375 units, both with midrange ALT elevation, were repeatedly reactive in hemi-nested PCR (one each for HBV DNA and HCV RNA). However, samples from the two suspect donors tested 9 and 5 months later revealed no seroconversion, elevated ALT, or viral genomes in hemi-nested PCR. CONCLUSION: The lack of confirmed HBV or HCV infection in this study representing an estimated 47,500 voluntary blood donations suggests that routine ALT testing for further prevention of posttransfusion hepatitis after exclusion of HBV- and/or HCV-seropositive blood may be superfluous.

Alanine Transaminase↗
PubMed1994

Toxin-deficient mutants from a toxin-sensitive transformant of Cochliobolus heterostrophus.

Tox1 is the only genetic element identified which controls production of T-toxin, a linear polyketide involved in the virulence of Cochliobolus heterostrophus to its host plant, corn. Previous attempts to induce toxin-deficient (Tox-) mutants, using conventional mutagenesis and screening procedures, have been unsuccessful. As a strategy to enrich for Tox- mutants, we constructed a Tox1+ strain that carried the corn T-urf13 gene (which confers T-toxin sensitivity) fused to a fungal mitochondrial signal sequence; the fusion was under control of the inducible Aspergillus nidulans pelA promoter which, in both A. nidulans and C. heterostrophus, is repressed by glucose and induced by polygalacturonic acid (PGA). We expected that a transformant carrying this construction would be sensitive to its own toxin when the T-urf13 gene was expressed. Indeed, the strain grew normally on medium containing glucose but was inhibited on medium containing PGA. Conidia of this strain were treated with ethylmethanesulfonate and plated on PGA medium. Among 362 survivors, 9 were defective in T-toxin production. Authenticity of each mutant was established by the presence of the transformation vector, proper mating type, and a restriction fragment length polymorphism tightly linked to the Tox1+ locus. Progeny of each mutant crossed to a Tox1+ tester segregated 1:1 (for wild type toxin production vs. no or reduced toxin production), indicating a single gene mutation in each case. Progeny of each mutant crossed to a Tox1- tester segregated 1:1 (for no toxin production vs. no or reduced toxin production) indicating that each mutation mapped at the Tox1 locus. Availability of Tox- mutants will permit mapping in the Tox1 region without interference from a known Tox1 linked translocation breakpoint.

Ascomycota↗