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Biomedical subjects

Y Xu

Publications and source records attributed to Y Xu.

At least 1,315 records · Page 73Linked to original sources
PubMed1981

Plasmid deoxyribonucleic acid replication in Streptomyces griseus.

A series of electron micrographs showing the presence of different molecular forms representing various replication stages of plasmid deoxyribonucleic acid from Streptomyces griseus was obtained. Based upon an analysis of these electron micrographs, a tentative model for plasmid deoxyribonucleic acid replication in S. griseus is proposed.

DNA Replication↗
PubMedDate not supplied

Regional myocardial blood volume and flow: first-pass MR imaging with polylysine-Gd-DTPA.

The authors investigated the utility of an intravascular magnetic resonance (MR) contrast agent, poly-L-lysine-gadolinium diethylenetriaminepentaacetic acid (DTPA), for differentiating acutely ischemic from normally perfused myocardium with first-pass MR imaging. Hypoperfused regions, identified with microspheres, on the first-pass images displayed significantly decreased signal intensities compared with normally perfused myocardium (P < .0007). Estimates of regional myocardial blood content, obtained by measuring the ratio of areas under the signal intensity-versus-time curves in tissue regions and the left ventricular chamber, averaged 0.12 mL/g +/- 0.04 (n = 35), compared with a value of 0.11 mL/g +/- 0.05 measured with radiolabeled albumin in the same tissue regions. To obtain MR estimates of regional myocardial blood flow, in situ calibration curves were used to transform first-pass intensity-time curves into content-time curves for analysis with a multiple-pathway, axially distributed model. Flow estimates, obtained by automated parameter optimization, averaged 1.2 mL/min/g +/- 0.5 (n = 29), compared with 1.3 mL/min/g +/- 0.3 obtained with tracer microspheres in the same tissue specimens at the same time. The results represent a combination of T1-weighted first-pass imaging, intravascular relaxation agents, and a spatially distributed perfusion model to obtain absolute regional myocardial blood flow and volume.

Animals↗
PubMedDate not supplied

Activation of oncogene c-Ha-ras in gastric cancer of Chinese patients.

A transforming gene was cloned from a focus of rat fibroblast cell line Rat 1 transfected with DNA of a gastrocarcinoma cell line. The transforming gene is the activated form of oncogene c-Ha-ras, and the lesion was identified as a single nucleotide substitution at codon 12 by sequencing. We further used polymerase chain reaction (PCR)-restriction analysis to detect the mutations at codon 12 of c-Ha-ras. By using this method, 11 cases out of 24 solid tumors and 3 cell lines of gastric cancer were shown to contain mutations, and there was a strong correlation between mutations and metastasis and survival of the patients. The role of the activated c-Ha-ras in tumorigenesis of stomach cancer was further proved through the assay in which the malignant phenotypes of the c-Ha-ras-transformed cells were partially inhibited by blocking the c-Ha-ras expression with antisense oligonucleotides or exogenous plasmid expressing antisense RNA.

Asian People↗
PubMedDate not supplied

Influences of fulvic acid on bioavailability and toxicity of selenite for wheat seedling and growth.

The influences of fulvic acid (FA) on bioavailability and toxicity of selenite for wheat seedling and growth were studied by greenhouse hydroponic experiment. The results showed that seed germination, embryo development, and growth were stimulated by selenite in the concentration range of 0.1-1.0 mg/L. In the presence of FA, the stimulation effects were more obviously observed. However, when the concentration of selenite exceeded 1.0 mg/L, toxic effects were observed for most of the measured indicators. The presence of FA could reduce the bioavailability of Se and could antagonize the toxic effects of Se. The reasons for the antagonism were caused by the inhibitory effects of FA on uptake of Se by plants and by the stimulating effects of FA on plant growth.

Benzopyrans↗
PubMedDate not supplied

Variant forms of galanin isolated from porcine brain.

In a peptide concentrate, prepared from acid extracts of porcine brain, several galanin-like immunoreactive peptides were detected and two of these were purified. Characterization of the peptides by sequence analysis, mass spectrometry, and capillary zone electrophoresis identified them as a N-terminally nine residue elongated form of galanin, preprogalanin(24-61) amide, and as an N-terminally four residue truncated form of galanin corresponding to preprogalanin(37-61) amide. The former finding suggests that the removal of the signal peptide in preprogalanin occurs by enzymatic cleavage between glycine-23 and leucine-24. The presence of truncated galanin might refer to a mechanism, where galanin is inactivated by removal of functionally important amino acid residues from the N-terminus.

Amino Acid Sequence↗
PubMedDate not supplied

Expression of CYP4A isoforms in developing rat placental tissue and rat trophoblastic cell models.

Maintaining fatty acid homeostasis during pregnancy is critical for normal fetal development. As an organ that controls nutrient supply from the mother to the fetus, the placenta plays a significant role in guiding fatty acid transfer to the developing fetus. The cytochrome P450 4A (CYP4A) subfamily of metabolizing enzymes is a group of structurally and functionally conserved proteins that are specialized in the omega/omega-1 hydroxylation of saturated and unsaturated fatty acids and their derivatives. To understand the function of the CYP4A system in the placenta and its significance in maintaining fetal fatty acid homeostasis, information about the placental expression of individual CYP4A isoforms is required. In the present study, we have elucidated the temporal and spatial patterns of expression of the four known rat CYP4A isoforms (CYP4A1, CYP4A2, CYP4A3, and CYP4A8) in the junctional and labyrinthine zones of the developing rat chorioallantoic placenta as well as two rat trophoblastic cell lines, HRP-1 and Rcho-1, using semi-quantitative RT-PCR and immunohistochemical analyses. The mRNA from the four rat CYP4A isoforms was detected in the developing rat placenta with CYP4A1 exhibiting the strongest expression (4A1 > 4A2 >> 4A3 approximately equal to 4A8). CYP4A1 was also detected by immunohistochemical staining in the developing rat placenta. We also observed CYP4A1 in both HRP-1 and Rcho-1 cells by RT-PCR, suggesting the utility of these cells as in vitro tools to study the effects of xenobiotics on placental fatty acid metabolism. Establishing the expression of CYP4A isoforms in these tissues and cell models provides a framework for further investigation of their functional and physiological significance in guiding proper fetal development.

Allantois↗
PubMedDate not supplied

Pathological findings in the intestinal tract and liver of chicks after exposure to Salmonella serotypes Typhimurium or Kedougou.

Day-old chicks were inoculated either via the feed or by direct oral inoculation with salmonellas which were either invasive or non-invasive (serotypes Typhimurium and Kedougou, respectively). Colonization of the alimentary tract and visceral organs, determined by microbiological examination, occurred more quickly in birds inoculated orally with S. serotype Typhimurium compared with feed-challenged birds. By contrast, S. serotype Kedougou remained confined to the alimentary tract. In birds inoculated either orally or via the feed, S. serotype Typhimurium, but not serotype Kedougou, was identified in the lamina propria of the caecum by immunostaining. Electron microscopic examination confirmed that the organisms were within macrophages.

Animal Feed↗