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Biomedical subjects

L Zhu

Publications and source records attributed to L Zhu.

At least 361 records · Page 20Linked to original sources
PubMed1996

Changes in beta 4 integrin expression and localization in vivo in response to corneal epithelial injury.

PURPOSE: To determine whether production and localization of beta 4 integrin is altered during in vivo corneal epithelial cell migration in response to debridement wounding. METHODS: Rat corneas were wounded and animals were killed at times ranging from 3 hours to 14 days. At various time points, corneal epithelial integrins were quantitated by gel electrophoresis and immunoblotting of epithelial extracts and then were localized by immunohistochemistry. RESULTS: As early as 6 hours after wounding, an increase in the amount of the beta 4 integrin subunit expressed per microgram of total protein was observed. The level of beta 4 continued to increase until wound closure. By 14 days after wounding, beta 4 expression returned to control levels. The level of expression of beta 1 and alpha (v) integrins were found not to change significantly throughout migration. Immunohistochemical analyses using antibodies against either the beta 4 integrin subunit or HD1, a hemidesmosomal plaque component, showed that in control sections, beta 4 integrin and HD1 codistributed in a linear staining pattern above the basement membrane. As early as 4 hours after wounding, beta 4 was present in both basal and suprabasal epithelial cells, and HD1 was retained at the basal aspect of the epithelial basal cells. CONCLUSIONS: These data show that changes in expression and localization of beta 4 integrin occur in the corneal epithelium in response to debridement wounding in vivo. Previously, we had shown that quantitative changes in beta 4 integrin expression do not occur in an in vitro organ culture model used for the study of corneal epithelial cell migration. Increased beta 4 expression may not be required for migration per se, but it may be play a role in either stabilizing cell:cell or cell:substrate adhesion in vivo or in preparing cells to undergo mitosis during restratification.

Animals↗
PubMed1996

[A PCR marker-based selection for resistance to bacterial blight in rice].

Molecular marker-based selection in plant breeding requires not only suitable molecular markers closely linked to the known genes, but a simple, economic and reliable analyzing technique. We report here a useful PCR marker for genetic diagnostics in breeding for resistance to rice bacterial blight. Xa21 is a newly found gene of rice which confers resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae. We produced two F2 populations between one resistant line IRBB21 containing Xa21 and two susceptible varieties, respectively. One PCR marker, PB78, detected polymorphism between the susceptible varieties and the resistant line. Cosegregation between Xa21 and PB78 was studied in the two F2 populations. The results showed that Xa21 was closely linked to the molecular marker, the crossing over value was 2.48%. Marker-based selection revealed that 100% of the plants with homozygous resistant genotype of PB78 showed resistance to bacterial blight. The available approaches detecting molecular markers in plant breeding are also discussed.

Base Sequence↗
PubMed1996

Immunocytochemical studies of M2 muscarinic receptors in guinea pig atria and ventricles using anti-peptide antibodies.

The localization and density of M2 muscarinic receptors in guinea pig atria and ventricles were studied by immunocytochemical techniques, with anti-peptide antibodies against the second extracellular loop of human muscarinic receptor-2. It was shown that the positive immunoreaction of M2 muscarinic receptor was characterized by brown-yellow granules of variable size and shape, which were located mainly on the cell surface and in the cytoplasm far from nuclei. The positive immunoreactive substances appeared in both atrial and ventricular myocytes, with the density being greater in atria than in ventricles. Pre-incubation with atropine, but not carbachol, significantly reduced the intensity of positive immunoreactivity. This indicates that the binding of antibody to receptor site can be partially blocked by M2 muscarinic receptor antagonist.

Animals↗
PubMed1996

Effects of anti-peptide antibodies against human M2 muscarinic receptors on the cAMP generating system in guinea pig ventricles.

The effects of anti-peptide antibodies (Ab) against the second extracellular loop of human muscarinic receptor-2 on the cAMP generating system in guinea pig ventricles were studied. These effects were compared with those of the muscarinic receptor agonist carbachol (Carb). It was shown that: (1) both Carb and Ab were able to inhibit the isoproterenol (Iso)-stimulated cAMP production of ventricles in a dose-dependent manner. Carb at 2 microM, 10 microM and 50 microM decreased Iso-stimulated cAMP production by 8.0 +/- 1.1, 15.8 +/- 1.2 and 28.4 +/- 1.7%, respectively; whereas Ab at 50 nM, 100 nM and 400 nM decreased it by 5.8 +/- 0.4, 16.8 +/- 1.4 and 30.6 +/- 2.5%, respectively. (2) Both Carb and Ab could also inhibit the basal cAMP content of ventricles significantly. Carb at 10 microM and Ab at 100 nM decreased it by 46.9 +/- 4.2% and 60.2 +/- 4.6%, respectively. (3) The inhibitory effects of both Ab and Carb on Iso-stimulated cAMP production were significantly prevented by atropine at 1.5 microM. (4) The inhibitory effect of Ab at 100 nM was almost completely abolished by the peptide (700 nM) used as immunogen. These findings suggest that the antibodies exhibit a stimulatory muscarinic activity similar to carbachol in the inhibitory modulation of cAMP production.

Animals↗
PubMed1996

Effects of anti-peptide antibodies against human M2 muscarinic receptors on cardiac function in rats in vivo.

The effects of anti-peptide antibodies (Ab) against the second extracellular loop of human muscarinic receptor-2 on cardiac function in rats in vivo were studied. These effects were compared with those of the muscarinic receptor agonist, carbachol (Carb). It was shown that: (1) both Carb and Ab administered intravenously in the same doses of 0.4 nmol, 1.0 nmol, and 2.0 nmol were able to inhibit the maximal rate of rise of ventricular pressure (+dp/dt max) in a dose-dependent manner. (2) The isoproterenol (Iso)-induced increase in HR and +dp/dt max were also markedly inhibited by Carb and Ab. Administration of 1.0 nmol Carb decreased the Iso-stimulated increase of HR from 13.6 +/- 2.0 to 4.9 +/- 0.7% and decreased the increase of +dp/dt max from 27.9 +/- 3.2 to 4.8 +/- 0.6%, respectively; whereas Ab decreased the HR to 6.5 +/- 1.1% and +dp/dt max to 13.5 +/- 1.2%, respectively. (3) Both the inhibitory effects of Carb and Ab could be significantly blocked by atropine (1.4 nmol). These findings suggest that the Ab display a stimulatory muscarinic activity similar to Carb in inhibiting the cardiac function as evidenced by its negative chronotropic and inotropic effects.

Animals↗
PubMed1996

PCR analysis of half-seeds of cereal crops and its application in marker-assisted selection and breeding.

A simple and rapid PCR method was adapted to DNA analysis of cereal seeds. Half-seeds of rice, wheat, and maize were treated with an extraction buffer and the resulting supernatants were used in PCR and RAPD reactions. PCR products amplified from the half-seed DNA extracts were identical with that from leaf tissue DNA extracts when the same specific primers were used in PCR reactions. The remaining half-seeds with embryos could still germinate normally. The half-seed PCR analysis was applied to the identification of resistant genotypes of rice bacterial blight, and it was proved effective in plant breeding and genetic studies.

Breeding↗
PubMed1996

[Effect of electro-acupuncture and transcutaneous electric nerve stimulation on experimental diabetes and its neuropathy].

In this paper, the experimental diabetic rats induced by streptozotocin (STZ, i.p. 50 mg/kg) were divided into three groups, electro-acupuncture (EA group, n = 8), transcutaneous electric nerve stimulation (TENS group, n = 8), at bilateral Shenshu and Zusanli points for 20 minutes once every 2-3 days for five weeks, and without any treatment (DM group, n = 6) respectively. As compared with the DM group, the increased plasma glucose levels was lowered significantly in EA group (P < 0.05) and slightly in TENS group (P > 0.05) by the end of the sixth week. And the symtoms of polyphagia, polydipsia and polyuria were attenuated in EA group. The motor nerve conduction velocity slowing was prevented or corrected after a course of four and six weeks treatment in EA and TENS group respectively. In the DM and TENS groups the pain threshold was lowered at 6-20 days after injection of STZ, but elevated in EA group, their differences were of significance (P < 0.05). In general, the efficiency of EA treatment on experimental diabetes and its neuropathy was better than that of TENS therapy.

Animals↗
PubMed1996

[Clinico-pathologic study of leiomyomatosis peritonealis disseminata].

In order to study the relationship between the clinical preseentation of leiomyomatosis peritonealis disseminata (LPD) and their pathological changes as well as the differenciation of this tumor from other tumors, clinical pathological analysis was performed on the 3 cases of LPD admitted to our hospital from 1959 to 1996. Results showed that the masses in the abdomen of all three cases were found to be multiple well circumscribed nodules protruding from the serosal surface. Histological examination revealed that the nodules were composed of interlaced bundles of smooth muscle tissue. Immunohistochemical studies found that they were positive for vimentin, desmin and actin. The results of this study indicate that LPD is a benign proliferation of smooth muscle that occurs in the abdominal cavity of women during the reproductive years of life and should be distinguished from well differentiated leiomyosarcomas.

Actins↗
PubMed1995

Solution structure of a cisplatin-induced DNA interstrand cross-link.

The widely used antitumor drug cis-diamminedichloroplatinum(II) (cisplatin or cis-DDP) reacts with DNA, cross-linking two purine residues through the N7 atoms, which reside in the major groove in B-form DNA. The solution structure of the short duplex [d(CAT-AGCTATG)]2 cross-linked at the GC:GC site was determined by nuclear magnetic resonance (NMR). The deoxyguanosine-bridging cis-diammineplatinum(II) lies in the minor groove, and the complementary deoxycytidines are extrahelical. The double helix is locally reversed to a left-handed form, and the helix is unwound and bent toward the minor groove. These findings were independently confirmed by results from a phase-sensitive gel electrophoresis bending assay. The NMR structure differs markedly from previously proposed models but accounts for the chemical reactivity, the unwinding, and the bending of cis-DDP interstrand cross-linked DNA and may be important in the formation and repair of these cross-links in chromatin.

Antineoplastic Agents↗
PubMed1995

The structure of a novel DNA duplex formed by human centromere d(TGGAA) repeats with possible implications for chromosome attachment during mitosis.

The solution structure of the DNA duplex [GTGGAATGGAAC]2 containing a tandem repeat of the human centromere (TGGAA)n unit has been determined by two-dimensional nuclear magnetic resonance (2D-NMR), distance geometry (DG) and molecular dynamics/energy minimization (MD/EM) methods. This remarkably stable "self-complementary" antiparallel duplex contains a tandem repeated motif in which unpaired guanine residues from opposite strands intercalate and costack between sheared G.A pairs. Twelve independent refined structures were determined from the NMR data and found to converge to a single family of closely related structures with pair-wise r.m.s.d. values of 0.55 +/- 0.25 Angstrum. All sugar residues are in the normal C2'-endo conformation except for the unpaired guanosines, which are in the unusual C3'-endo conformation. The guanosine residues of the bracketing G.A pairs have high-antiglycosidic torsion angles and zeta backbone torsion angles close to the trans domain. The structure exhibits many unusual interstrand interactions, including base-sugar stacking, base-phosphate hydrogen bonding and cross-strand base stacking. The [GGA]2 unit contains a stack of four contiguous guanine residues, all of which have their hydrogen-bonding surface (N2H-N1H-O6-N7) exposed to solvent and available for interaction with other bases or ligands. This unexpected property may explain the unique morphology and function of the human centromere in mitosis.

Base Sequence↗
PubMed1995

N-terminus and lysine side chain pKa values of melittin in aqueous solutions and micellar dispersions measured by 15N NMR.

Melittin (MLT) is a 26-amino acid cytolytic peptide from the Apis mellifera honey bee. It is known to exist as an alpha-helical tetramer, as an alpha-helical monomer, or as a monomeric random coil depending on solvent conditions. The charge state of MLT is believed to be a major factor in determining its aggregation properties and its interaction with lipids. Several, contradictory, indirect measurements of the pKa values of the three lysine groups in MLT have been reported. In the present study, high-resolution 15N NMR at 50.6 MHz was used to directly measure the pKa values of the amino groups of the Gly-1, Lys-7, Lys-21, and Lys-23 residues of MLT. Specifically, the pH dependence of MLT 15N chemical shifts was measured separately for the isotopically enriched backbone nitrogen of Gly-1 and the side chain nitrogen atoms of Lys-7, Lys-21, and Lys-23 at a MLT concentration of 1.2 mM and a temperature of 23 degrees C. Measurements were made for MLT in potassium phosphate buffer, in neat water, and in 1-myristoyl-2-hydroxyl-sn-glycero-3-phosphocholine (MMPC) lipid micelles. The experiments showed for MLT tetramer in aqueous phosphate buffer that the amino nitrogen of Gly-1 has a pKa of 8.15, and that the Lys-7, Lys-21, and Lys-23 side chain nitrogen atoms have pKa values of 10.21, 10.03, and 10.24 respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Structure of the gene for the catalytic subunit of human DNA polymerase delta (POLD1).

We have isolated genomic DNA clones covering the gene for human DNA polymerase delta catalytic subunit (POLD1) and its 5' flanking sequence. This gene is divided into 27 exons and is distributed over at least 32 kb of DNA. The exons and most of the introns are relatively small. The sizes of the exons range from 55 to 201 bp. Seven introns are smaller than 100 bp. Intron 1 is the largest intron, with a size of greater than 10 kb. All of the intron-exon junctions match well with the reported consensus sequences. Multiple copies of the Alu repetitive sequence and the variable number of tandem repeats were found in several introns. Transcription of POLD1 appears to initiate at multiple sites. The major start site was 53 nucleotides upstream of the ATG start codon. The sequence of the promoter and upstream DNA is G+C rich and does not contain a TATA sequence. Several potential transcription factor-binding sites, including the AP2-, CTF-, Ets1-, GCF-, MBF-1-, NF-E1-, and Sp1-binding sites, were found in this region. A 1.8-kb pol delta promoter DNA directed the expression of a luciferase reporter gene when transfected into HeLa cells.

Base Sequence↗
PubMed1995

p107 uses a p21CIP1-related domain to bind cyclin/cdk2 and regulate interactions with E2F.

The kinase activities of the cyclin/cdk complexes can be regulated in a number of ways. The most recently discovered mechanism of regulation is the association of cdk inhibitors (CKIs), such as p21, p27, and p57, with these complexes. In this report we demonstrate that the pRB-related protein p107, like the p21 family of cdk inhibitors, can inhibit the phosphorylation of target substrates by cyclin A/cdk2 and cyclin E/cdk2 complexes, and the associations of p107 and p21 with cyclin/cdk2 rely on a structurally and functionally related interaction domain. Furthermore, interactions between p107 or p21 with cyclin/cdk2 complexes are mutually exclusive. In cells treated with DNA-damaging agents elevated levels of p21 cause a dissociation of p107/cyclin/cdk2 complexes to yield p21/cyclin/cdk2 complexes. Finally, the consequences of cyclin/cdk2 interactions with p107 have been examined. The activation of the p107-bound cyclin/cdk kinases leads to dissociation of p107 from the transcription factor E2F. Together, these results suggest that cyclin/cdk complexes can be regulated by protein molecules from different families in a mutually exclusive manner in response to certain signals and that these inhibitory proteins may have a potential role in regulating macromolecular assembly.

Amino Acid Sequence↗