Search PubMed⌕ Search

Biomedical subjects

X Gu

Publications and source records attributed to X Gu.

At least 145 records · Page 8Linked to original sources
PubMed1999

External quality assessment survey for hematological laboratories in China.

To evaluate the feasibility of improving external quality assessment (EQA), we set up an experimental EQA survey that included 465 participants in China. During the period of this survey, we checked the quality of the EQA samples, divided the participants into different groups, each laboratory's result was assessed by calculation standard deviation index (SDI). The reference values were determined to evaluate the accuracy for peer groups. The data showed that the stability of the EQA samples was acceptable. Except for WBC count of the Abbott group, the mean, median and reference values for each parameter were very close. We found that the main reason affecting the performance of the participants was not using the reagents. calibrator and QC material recommended by manufacturer. From this survey, we obtain a good reference for future improvement.

Calibration↗
PubMed1999

Reversal of aberrant splicing of beta-thalassemia allele by antisense RNA in vitro and in vivo.

OBJECTIVE: To investigate the reversal of aberrant splicing of beta-thalassemia allele (IVS-2-654 C-->T, beta 654) by antisense RNA in vitro and in vivo. METHODS: The vector expressing antisense RNA which targeted against the aberrant splice sites of beta 654 pre-mRNA was constructed in pcDNA3, and then used to repair the defective splicing of the mutant pre-mRNA in an in vitro transcription and splicing system, as well as in HeLa beta 654 cells and cultured beta 654 erythroid cells by lipid-mediated DNA-transfection method. The effect of the antisense RNA was identified by RT-PCR mediated mRNA quantitative assay as well as globin chain microbiosynthesis. RESULTS: The antisense RNA decreased the aberrant splicing product and restored the correct splicing pattern in vitro and in vivo efficiently. In the in vitro transcription and splicing system, the level of normally spliced mRNA [beta/(beta + beta*)] increased from 0.25 to 0.60. In cultured HeLa beta 654 cells, the level of beta/(beta + beta*) increased from 0.07 to 0.43 on the 15th day after transfection. In cultured beta 654 erythroid cells, the level of mRNA [beta/(beta + beta*)] increased from 0.19 to 0.58 on the 8th day after transfection in beta 654/beta 654 erythroid cells, from 0.02 to 0.38 in beta 654/beta 41-42 erythroid cells, and from 0.45 to 0.83 in beta 654/beta A erythroid cells, respectively. Correspondingly, the ratios of globin chain (beta/alpha) biosynthesis increased from 0.16 to 0.52 on the 8th day after transfection in beta 654/beta 654 erythroid cells, 0.05 to 0.36 in beta 654/beta 41-42 erythroid cells, and 0.42 to 0.81 in beta 654/beta A erythroid cells, respectively. The splicing pattern did not show significant changes as compared to the untreated, as well as to the control antisense fragment. CONCLUSIONS: Antisense RNA transcribed from the expression vector described here could efficiently suppress the aberrant splicing pattern of beta 654 mutant mRNA and restore the correct splicing pathway in vitro and in vivo, leading to the improvement of globin chain biosynthesis in thalassemic cells. Our antisense strategy provides an alternative approach to the gene therapy of beta-thalassemia.

Adolescent↗
PubMed1999

Postoperative radiotherapy for stage I thymoma: a prospective randomized trial in 29 cases.

OBJECTIVE: To determine the effect of postoperative radiotherapy on stage I thymoma. METHODS: Twenty-nine patients with stage I thymoma younger than 65 years, treated between August 1981 and January 1996 were included in this study. All patients were randomly assigned into two groups: surgery alone (13 patients) and surgery with postoperative radiotherapy (16). Staging was based on the surgical and pathologic criteria that the tumor had a complete capsule and without capsular invasion microscopically. Adjuvant radiotherapy was started within 4 weeks after surgery. Megavolage radiation, using the isocentric technique, was administered through an anterior field and/or two anterior oblique wedge fields. For the patients with lymphocytic predominant type, the dose was 50 Gy in 25 daily fractions for 5 weeks; for the patients with epithelial cell type or mixed type, the dose was 60 Gy in 30 daily fractions for 6 weeks. The survival rates were estimated by the Kaplan-Meier method. RESULTS: There was no recurrence and metastasis in either group. No acute and late radiological injuries were found among the patients receiving radiotherapy postoperatively. The 5-year and 10-year survivals were both 92% for the patients treated by surgery alone. However, the survival rates for patients who received radiotherapy were both 88%. There was no difference in the survivals in these two groups. Of the 3 died patients, 1 died of myasthenia gravis and 2 of intercurrent illness. No significant correlation was found between myasthenia gravis and radiotherapy. CONCLUSIONS: Postoperative radiotherapy is unnecessary for the patients with stage I thymoma. No relation is found between radiotherapy and myasthenia gravis.

Adult↗
PubMed1999

[The effects of lead poisoning on expression of nerve growth factor gene of submandibular gland in mice].

OBJECTIVE: To study the toxicity of lead poisoning to submandibular gland and its effects on nerve growth factor (NGF) gene expression in mice. METHODS: An experimental model with lead poisoning was established and its histopathological changes in the submandibular gland of mice were observed under light and electronic microscopes. Effects of lead poisoning on expression of NGF mRNA in submandibular gland were analyzed quantitatively by human NGF DNA probe labelled with digoxin with in situ hybridization. RESULTS: Body weight of the mice with experimental lead poisoning reduced, and their lead levels in blood and submandibular gland increased. Lobular atrophy, fibrous hypertrophy, angiectasis of the stroma and enlargement of lobule interstitial in mouse submandibular gland with lead poisoning could be found under light and electron microscopes. Their rough surfaced endoplasmic reticulum was extended and mitochondrion swollen. Graphic analysis showed that diameters of the secretory striate ducts and granular tubules decreased in the mice with lead poisoning. Results of in situ hybridization indicated that hybridized signals in the granular and secretory striate ducts and granular tubules reduced significantly, and NGF mRNA expression decreased. CONCLUSION: Lead is toxic to the submandibular gland of mice and can affect their NGF gene expression.

Animals↗
PubMed1999

[Vegetables rich in carotenoids on the vitamin A status of children].

Vitamin A (VA) deficiency is still an important nutritional problem in our country. In order to determine whether plant carotenoids ingestion can improve VA nutrition, a study by using yellow and dark green vegetables was conducted in two classes of a kindergarten for ten weeks in September through December in 1996. The VA nutritional status was marginal to adequate among 41 children (5.3-6.6 year-old), and serum retinols in 39% of these children were below 0.30 mg/L. Each child in class A was provided with about 238 g/d of green and yellow vegetables (spinach, Chinese chive, carrots, and red yams) and 34 g/d of light colored vegetables (cabbage, Chinese cabbage, potato, cucumber, turnip and winter melon). Each child in class B consumed the usual diet with only 56 g/d of green and yellow vegetables and 193 g/d of light colored vegetables. Serum retinol concentration collected before and after the intervention were used to assess VA nutritional status. The results showed that vitamin A nutrition was improved by increasing the intake of green and yellow vegetables. Serum retinol was sustained in the group fed green and yellow vegetables and decreased in the group fed light colored vegetables. Thus, dietary green and yellow vegetables could provide adequate VA nutrition in these children.

Carotenoids↗
PubMed1999

Pilot study of schistosomiasis control in Poyang lake region.

AIM: To perform a longitudinal survey of the control of schistosomiasis in Fanhu Village hyperendemic for schistosomiasis, Poyang Lake region of Jiangxi Province from 1992 to 1996. METHODS: Annual mass chemotherapy and health education were implemented in all investigated individuals, in 1996, artesunate was used in high risk population in transmission season as a prophylactic measure. RESULTS: The prevalence of S. japonicum infection reduced from 26.0% in 1992 to 10.7% in 1994, the intensity of infection (geometric mean of EPG of feces) in residents decreased from 1.92 in 1992 to 0.55 in 1994, and the morbidity indicators such as hepatomegaly and splenomegaly in the cases also have been improved significantly after chemotherapy. In 1995, both the infection rate and intensity of infection of schistosomiasis were recurred from 10.7% and 0.55 in 1994 to 18.4% and 1.04 respectively due to the floods. In 1996, the infection rate reduced to 5.0% and the intensity of infection also decreased to 0.25 due to the additional measure. CONCLUSION: A mass chemotherapy in conjunction with health education and oral artesunate for preventing reinfection in transmission season is effective for the control of schistosomiasis in lake regions.

Adolescent↗
PubMed1999

Microvascular changes in the retrobulbar optic nerve in idiopathic intracranial hypertension.

PURPOSE: To examine the microvascular changes in the retrobulbar optic nerve in idiopathic intracranial hypertension (PTC). METHODS: Both optic nerves from a 29-year-old man with a two year history of PTC were examined histologically and morphometrically. A semi-automated image analysis system and paraphenylenediamine (PPD) stain were employed to resolve sufficiently the microvascular images for counts and measurement. RESULTS: There were 150 vessels distributed in the optic nerves which revealed the following: The average lumen of the vessels in outer sectors were larger than those of the inner sector vessels (168.17 microns 2 vs. 46.99 microns 2; p = 0.0338; OD; and 251.96 microns 2 vs. 130.02 microns 2; p = 0.029; OS) while in the normal control optic nerve the outer and inner area lumens were reversed in size-differential, but this did not show a statistical difference. The thickness of the PTC optic nerve vessel walls in the outer sectors was also greater than that of the walls in the inner sectors (4.95 microns vs. 2.67 microns; p = 0.013; OD and 5.25 microns vs. 3.34 microns; p = 0.019; OS); the same measurements in the normal optic nerve showed a reversed ratio, which was opposite that of the experimental group and but not statistically different. CONCLUSION: This pattern of microvascular changes is consistent with the selective axonal loss in the peripheral area of each optic nerve as much more severe than that in the inner sectors.

Adult↗
PubMed1999

Intracellular interaction of Hsp47 and type I collagen in corneal endothelial cells.

PURPOSE: Previous studies by the current investigators showed that type I collagen was posttranslationally regulated in corneal endothelial cells (CECs). These cells synthesize type I procollagen and degrade it intracellularly; however, when CECs are modulated with fibroblast growth factor-2 and/or corneal endothelium modulation factor, they synthesize and secrete type I collagen. Heat shock protein 47 (Hsp47), an endoplasmic reticulum resident protein, is known to function as a molecular chaperon in regulating procollagen folding and/or assembly. The interaction of Hsp47 with type I procollagen synthesis in CECs was also studied. METHODS: Expression of proteins was analyzed by radioactive labeling or immunoblot analysis. The steady state level of type I collagen and Hsp47 mRNAs was determined by northern blot analysis. Coprecipitation using immunoprecipitation followed by immunoblotting was performed to determine the association profile between Hsp47 and type I procollagen. Subcellular localization of Hsp47 and type I procollagen was determined by immunofluorescent staining. RESULTS: Normal and modulated cells expressed Hsp47 and Hsp70. The relative amount of Hsp47 produced by modulated cells was much higher than that of control cells, but the expression level of Hsp70 was the same in control and modulated cells. The steady state levels of type I collagen transcripts were higher in normal cells than in modulated cells, whereas modulated cells contained a much higher steady state level of Hsp47 mRNA. Type I procollagen was found to be associated with Hsp47 when analyzed by coprecipitation or cross-linking. The cytoplasmic localization profile of Hsp47 and type I collagen was different in normal cells, although a colocalization profile was observed to some degree. These two proteins were predominantly colocalized in the Golgi area in modulated CECs. CONCLUSIONS: Hsp47 may be involved in the synthesis and/or intracellular transport of type I collagen in CECs. Modulated cells that secrete type I collagen into the extracellular matrix express a higher level of Hsp47 than do control cells.

Animals↗
PubMed1998

Identification of two Escherichia coli pseudouridine synthases that show multisite specificity for 23S RNA.

Several putative Escherichia coli pseudouridine (Psi) synthases have been identified by iterative searching of genomic databases for ORFs homologous to known Psi synthases [Gustafsson et al. (1996) Nucleic Acids Res. 24, 3756-3762]. Of these, yceC and yfiI were proposed to encode Psi synthases which modify 23S rRNA. In the present work, yceC and yfiI were cloned and overexpressed in E. coli, and the encoded enzymes, YceC and YfiI, were purified to homogeneity. Both proteins converted Urd residues of rRNA to Psi, thus confirming their identities as Psi synthases. However, in in vitro experiments both enzymes extensively modified Urd residues of both 23S rRNA and 16S rRNA. Gene-disruption of yceCresulted in the absence of Psi modification at positions U955, 2504, and 2580 of 23S RNA, thus identifying these sites as in vivo targets for YceC. Likewise, yfiI disruption resulted in the absence of Psi modification at positions U1911, 1917, and possibly 1915 of 23S RNA. Disruption of yceC did not affect the growth under the conditions tested, whereas yfiI-disrupted cells showed a dramatic decrease in growth rate. Since YceC and YfiI hypermodify RNA in vitro, factors in addition to ribonucleotide sequence must contribute to the in vivo specificity of these enzymes.

Bacterial Proteins↗
PubMed1998

The efficient cellular uptake of high density lipoprotein lipids via scavenger receptor class B type I requires not only receptor-mediated surface binding but also receptor-specific lipid transfer mediated by its extracellular domain.

The class B type I scavenger receptor, (SR-BI), is a member of the CD36 superfamily of proteins and is a physiologically relevant, high affinity cell surface high density lipoprotein (HDL) receptor that mediates selective lipid uptake. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated uptake via coated pits and vesicles (e.g. the low density lipoprotein receptor pathway) in that it involves efficient transfer of the lipids, but not the outer shell proteins, from HDL to cells. The abilities of SR-BI and CD36, both of which are class B scavenger receptors, to bind HDL and mediate cellular uptake of HDL-associated lipid when transiently expressed in COS cells were examined. For these experiments, the binding of HDL to cells was assessed using either 125I- or Alexa (a fluorescent dye)-HDL in which the apolipoproteins on the surface of the HDL particles were covalently modified. Lipid transfer was measured using HDL noncovalently labeled by the fluorescent lipid 1,1'-dioctadecyl-3,3, 3',3'-tetramethylindocarbocyanine perchlorate. Although both mSR-BI and human CD36 (hCD36) could mediate the binding of HDL in a punctate pattern across the surfaces of cells, only mSR-BI efficiently mediated the transfer of lipid to the cells. Analysis of point mutants established that the major sites of fatty acylation of mSR-BI are Cys462 and Cys470 and that fatty acylation is not required for receptor clustering, HDL binding, or efficient lipid transfer. Generation of mSR-BI/hCD36 domain swap chimeras showed that the differences in lipid uptake activities between mSR-BI and hCD36 were not due to differences between their two sets of transmembrane and cytoplasmic domains but rather result from differences in their large extracellular loop domains. These results show that high affinity binding to a cell surface receptor is not sufficient to ensure efficient cellular lipid uptake from HDL. Thus, SR-BI-mediated binding combined with SR-BI-dependent facilitated transfer of lipid from the HDL particle to the cell appears to be the most likely mechanism for the bulk of the selective uptake of cholesteryl esters from HDL to the liver and steroidogenic tissues.

Amino Acid Sequence↗
PubMed1998

Integrin-mediated signalling of gelatinase B secretion in colon cancer cells.

The progression of colon cancer has been linked to both cell adhesion molecules called integrins and matrix-degrading enzymes called metalloproteinases. Herein we report that the alpha v beta 6 integrin expressed in colon cancer cells induces gelatinase B secretion through the C-terminal cytoplasmic extension unique to the beta 6 integrin subunit, and that this ligand-independent event involves activation of the protein-kinase-C pathway.

Antigens, Neoplasm↗
PubMed1998

Improvement of interferon-gamma sialylation in Chinese hamster ovary cell culture by feeding of N-acetylmannosamine.

Because the presence of sialic acid can extend circulatory lifetime, a high degree of sialylation is often a desirable feature of therapeutic glycoproteins. In this study, the incomplete intracellular sialylation of interferon-gamma (IFN-gamma), produced by Chinese hamster ovary cell culture, was minimized by supplementing the culture medium with N-acetylmannosamine (ManNAc), a direct intracellular precursor for sialic acid synthesis. By introducing 20 mM ManNAc into the culture medium, incompletely sialylated biantennary glycan structures were reduced from 35% to 20% at the Asn97 glycosylation site. This effect was achieved without affecting cell growth or product yield. The intracellular pool of CMP-sialic acid, the nucleotide sugar substrate for sialyltransferase, was also extracted and quantified by HPLC. Feeding of 20 mM ManNAc increased this intracellular pool of CMP-sialic acid by nearly thirtyfold compared with unsupplemented medium. When radiolabeled ManNAc was used to trace the incorporation of the precursor, it was found that supplemental ManNAc was exclusively incorporated into IFN-gamma as sialic acid and that, at 20 mM ManNAc feeding, nearly 100% of product sialylation originated from the supplemental precursor.

Animals↗
PubMed1998

[A molecular variant of angiotensinogen gene is associated with myocardial infarction in Chinese].

OBJECTIVE: A molecular variant of the angiotensinogen(AGT) gene with threonine instead of methionine at position 235(i.e.,with M235T polymor- phism) has been shown to be associated with essential hypertension, preeclampsia, coronary atherosclerosis, coronary heart disease(CHD), myocardial infarction(MI) in Caucasians and in Japanese. The purpose of the present study was to assess whether the M235T polymorphism was associated with MI in a Chinese population. METHODS: M235T polymorphism in exon 2 of AGT gene was determined by polymerase chain reaction(PCR) and restriction endonuclease analysis in a study of 57 patients with MI and 76 non-CHD individuals as control. RESULTS: The frequencies of T235 allele(0.82) and 235TT genotype (0.70) in the MI group were higher than those in the control subjects(0.63 and 0.42 respectively, P=0.013 and P<0.025). AGT gene 235TT genotype was at significantly increased risk of MI(odds ratio 3.65, P=0.016) in analysis adjusted for several main CHD risk factors. CONCLUSION: There is a significant association between AGT gene 235TT genotype and MI, this genotype might be an independent risk for MI in Chinese population.

Aged↗
PubMed1998

Estimation of evolutionary distances under stationary and nonstationary models of nucleotide substitution.

Estimation of evolutionary distances has always been a major issue in the study of molecular evolution because evolutionary distances are required for estimating the rate of evolution in a gene, the divergence dates between genes or organisms, and the relationships among genes or organisms. Other closely related issues are the estimation of the pattern of nucleotide substitution, the estimation of the degree of rate variation among sites in a DNA sequence, and statistical testing of the molecular clock hypothesis. Mathematical treatments of these problems are considerably simplified by the assumption of a stationary process in which the nucleotide compositions of the sequences under study have remained approximately constant over time, and there now exist fairly extensive studies of stationary models of nucleotide substitution, although some problems remain to be solved. Nonstationary models are much more complex, but significant progress has been recently made by the development of the paralinear and LogDet distances. This paper reviews recent studies on the above issues and reports results on correcting the estimation bias of evolutionary distances, the estimation of the pattern of nucleotide substitution, and the estimation of rate variation among the sites in a sequence.

Animals↗
PubMed1998

Molecular recognition of tRNA by tRNA pseudouridine 55 synthase.

Escherichia coli tRNA pseudouridine 55 synthase catalyzes pseudouridine formation at U55 in tRNA. A 17 base oligoribonucleotide analog of the T-arm was equivalent to intact native tRNA as a substrate for pseudouridine 55 synthase, viz., the features for substrate recognition by this enzyme are completely contained within the T-arm. The structures and activities of mutant tRNAs and T-arms were used to analyze substrate recognition by pseudouridine 55 synthase. The 17-mer T-arm was an excellent substrate for the synthase, while disruption of the stem structure of the 17-mer T-arm eliminated activity. Kinetic data on tRNA mutants lacking single T-stem base pairs indicated that only the 53:61 base pair, which maintains the 7 base loop size, was essential for activity. The identities of individual bases in the stem were unimportant provided base pairing was intact. A major function of the T-stem appears to be the maintainence of a stable stem-loop structure and proper presentation of the T-loop to pseudouridine 55 synthase. The 7 base T-loop could be expanded or contracted by 1 base and still retain activity, albeit with a 30-fold reduction in kcat. Kinetic analysis of T-loop mutants revealed the requirement for U54, U55, and A58, and a preference for C over U at position 56. Base substitutions at loop nonconserved position 59 or semiconserved positions 57 or 60 were well tolerated. Comparison of pseudouridine 55 synthase and tRNA (m5U54)-methyltransferase revealed that both enzymes required the stem-loop structure. However, pseudouridine 55 synthase was not stringent for a 7 base loop and recognized a consensus base sequence within the T-loop, while tRNA (m5U54)-methyltransferase recognized the secondary structure of the 7 member T-loop with only a specific requirement for U54, the T-loop substrate site. We conclude that recognition of tRNA by pseudouridine 55 synthase resides in the conformation of the T-arm plus four specific bases of the loop.

Base Composition↗
PubMed1998

A conserved aspartate of tRNA pseudouridine synthase is essential for activity and a probable nucleophilic catalyst.

tRNA pseudouridine synthase I catalyzes the conversion of uridine to pseudouridine at positions 38, 39, and/or 40 in the anticodon loop of many tRNAs. Pseudouridine synthase I was cloned behind a T7 promoter and expressed in Escherichia coli to about 20% of total soluble proteins. Fluorouracil-substituted tRNA caused a time-dependent inactivation of pseudouridine synthase I and formed a covalent complex with the enzyme that involved the FUMP at position 39. Asp60, conserved in all known and putative pseudouridine synthases, was mutated to amino acids with diverse side chains. All Asp60 mutants bound tRNA but were catalytically inactive and failed to form covalent complexes with fluorouracil-substituted tRNA. We conclude that the conserved Asp60 is essential for pseudouridine synthase activity and propose mechanisms which involve this residue in important catalytic roles.

Amino Acid Sequence↗
PubMed1998

Early metazoan divergence was about 830 million years ago.

From a total of 22 nuclear genes, we estimate that the divergence time between Drosophila and vertebrates was about 830 million years ago (mya), which is significantly (1% level) earlier than the Cambrian explosion indicated by the early triploblastic fossils (<600 mya).

Amino Acid Sequence↗