Search PubMed⌕ Search

Biomedical subjects

X Guan

Publications and source records attributed to X Guan.

At least 73 records · Page 4Linked to original sources
PubMed1998

Batch fermentation and optimization of media for Bacillus thuringiensis.

The composition of No. II medium obtained with shaking cultivation contained three factors: nitrogen source, carbon source, and inorganic salts. The relationship between component factors (x(i)) of the media and spore numbers (y) of Bacillus thuringiensis (Bt) was demonstrated by the orthogonal-rotation-combination test. A response surface equation was formed as follows: y = 384 - 7.245x1 + 11.705x2 + 15.475x3 + 14.039x1(2) + 41.831x2(2) - 79.49x3(2) - 35.375x1x2 - 3.375x1x3 - 106.625x2x3. The results showed that this method is simple, practical, and rapid enough for selecting fermentation media for Bt. In addition, the whole course of batch fermentation was also investigated.

Bacillus thuringiensis↗
PubMed1997

The sleep-inducing lipid oleamide deconvolutes gap junction communication and calcium wave transmission in glial cells.

Oleamide is a sleep-inducing lipid originally isolated from the cerebrospinal fluid of sleep-deprived cats. Oleamide was found to potently and selectively inactivate gap junction-mediated communication between rat glial cells. In contrast, oleamide had no effect on mechanically stimulated calcium wave transmission in this same cell type. Other chemical compounds traditionally used as inhibitors of gap junctional communication, like heptanol and 18beta-glycyrrhetinic acid, blocked not only gap junctional communication but also intercellular calcium signaling. Given the central role for intercellular small molecule and electrical signaling in central nervous system function, oleamide- induced inactivation of glial cell gap junction channels may serve to regulate communication between brain cells, and in doing so, may influence higher order neuronal events like sleep induction.

Animals↗
PubMed1997

Formation of circular satellite tobacco ringspot virus RNA in protoplasts transiently expressing the linear RNA.

The most abundant form of the satellite RNA of tobacco ringspot virus (sTRSV RNA) is a linear, unit length molecule of 359 nucleotide residues, designated L-(+)M. A postulated replication scheme for the satellite RNA has as its first, and apparently virus-independent, step the ligation of L-(+)M into the corresponding circular form C-(+)M. We transiently expressed L-(+)M wild type and L-(+)M mutants in tobacco protoplasts using an African cassava mosaic geminivirus vector. Measured extents of C-(+)M accumulation were correlated with computer-predicted folding to suggest wild-type secondary structure elements that might be deleted without reducing ligation. A 127-nucleotide residue mutant L-(+)M was created by replacing, with 7 and 3 residues, respectively, nucleotide residues 53-211 and 268-350, each of which was predicted to form a set of three adjacent imperfect stem-loops in wild-type L-(+)M. The mutant L-(+)M was found to be extensively ligated to C-(+)M in protoplasts and to retain a calculated helix of the wild-type molecule that incorporates the 3' terminal sequence. A trinucleotide in the 3' region was mutated so as to disrupt and restore, respectively, the calculated helix, reducing and restoring, respectively, C-(+)M formation. These results suggest that the 3' stem contributes to the suitability of the small L-(+)M molecules as a substrate for a protoplast RNA ligase and that computed folding of sTRSV RNA may be predictive of sTRSV RNA structure in vivo.

Base Sequence↗
PubMed1997

Steroidogenic factor-1 is an essential transcriptional activator for gonad-specific expression of promoter I of the rat prolactin receptor gene.

The expression of the prolactin receptor is under the control of two putative tissue-specific (PI, gonads; PII, liver) and one common (PIII) promoters (Hu, Z. Z., Zhuang, L., and Dufau, M. L. (1996) J. Biol. Chem. 271, 10242-10246). The three promoter regions were co-localized to the rat chromosomal locus 2ql6, in the order 5'-PIII-PI-PII-3'. To investigate the mechanisms of gonad-specific utilization of PI, the promoter domain, regulatory cis-elements, and trans-factors were identified in gonadal cells. The promoter domain localized to the 152-base pair 5' of the transcriptional start site at -549 is highly active in gonadal cells but has minimal activity in hepatoma cells. It contains a steroidogenic factor 1 (SF-1) element (-668) that binds the SF-1 protein of nuclear extracts from gonadal cells and is essential for promoter activation. A CCAAT box (-623) contributes minimally to basal activity in the absence of the SF-1 element, and two adjacent TATA-like sequences act as inhibitory elements. Thus, PI belongs to a class of TATA-less/non-initiator gene promoters. These findings demonstrate an essential role for SF-1 in transcriptional activation of promoter I of the prolactin receptor gene, which may explain the tissue-specific expression of PI in the gonads but not in the liver and the mammary gland.

Animals↗
PubMed1997

Effects of propranolol on beta-adrenergic receptor of experimental acute myocardial infarction in rats.

By using receptor autoradiography to observe the distribution and density of receptors, the effects of propranolol, a beta-blocker, on beta-adrenergic receptor of experimental acute myocardial infarction (AMI) were studied. One week after ligation of proximate left anterior descend (LAD) coronary artery, [3H] DHA binding sites were markedly decreased in both infarct region and non-infarct region. After treatment of propranolol (100 micrograms/kg), the [3H] DHA binding sites were obviously increased in the infarct region, and they were further decreased in the non-infarct region. The ratio of [3H] DHA binding sites of the infarct region to non-infarct region was from 0.24 at LAD ligation to 0.87 after propranolol treatment, which was close to 0.97 of control group (sham operation). The results indicated that the propranolol acted directly on myocardial beta- adrenergic through the receptor regulation of the balance of beta-receptors between the infarct region and non-infarct region, and improvement of the myocardial consonation and contraction synergism, thereby protecting the heart affected by AMI.

Adrenergic beta-Antagonists↗
PubMed1997

Computer simulations of lung morphologies within planar gamma camera images.

A mathematical model and computer code have been developed to unambiguously interpret planar gamma camera images. Specifically, the algorithm permits airway composition of the central, intermediate and peripheral partitions of scans to be determined quantitatively. The algorithm unambigously identifies the spatial coordinates of each of the millions of airways within the adult human lung, and assigns every individual airway to a precise location within the gamma camera image format prescribed by the clinician. This is done on a patient-by-patient basis. The algorithm has evolved from clinical applications of the previous work of Martonen et al. [1]. The objective of the current work was to advance the original protocol and derive an algorithm that was: (1) from a medical perspective, more physiologically realistic; and (2) from a technical perspective, easier to apply in the medical arena. Regarding (1), the major elements of the algorithm are that the outer boundary of the lung is formulated directly from lung perfusion imaging data and that the lung is divided into distinct left and right components. Regarding (2), the algorithm has been written for use with common workstations. It is our hope that the improvements will facilitate applications of the new model-code into aerosol therapy regimens.

Adult↗
PubMed1997

Domain identification by clustering sequence alignments.

A sequence databases are growing rapidly, results from sequence comparison searches using fast search methods such as BLAST and FASTA tend to be long and difficult to digest. In this paper, we present a new method to extract domain information from sequence comparison searches by clustering the resulting alignments according to their similarity to the query sequence. Efficient tree structures and algorithms are used to organize the alignment data such that structurally conserved elements can be easily identified. The hierarchical nature of the data structures used and the flexible X-Window based interface provide an efficient and intuitive means to explore the alignment data at different levels so the main domains as well as distantly related features can be explored.

Algorithms↗
PubMed1996

Gap-junction disassembly and connexin 43 dephosphorylation induced by 18 beta-glycyrrhetinic acid.

Gap-junction channels connect the interiors of adjacent cells and can be arranged into aggregates or plaques consisting of hundreds to thousands of channel particles. The mechanism of channel aggregation into plaques and whether plaques can disaggregate are not known. Many carcinogenic and tumor-promoting chemicals have been identified that inhibit cell-cell gap-junctional coupling. Here, we provide morphological evidence that 18 beta-glycyrrhetinic acid (18 beta-GA), a saponin isolated from licorice root that is an inhibitor of gap-junctional communication, caused the disassembly of gap-junction plaques in WB-F344 rat liver epithelial cells. This effect was dose (5-40 microM) and time dependent (1-4 h treatment). Gap-junction channels in WB-F344 cells are comprised of connexin 43 (Cx43), and the protein is phosphorylated to a species known as Cx43-P2 coincident with the assembly of channels into plaques. Consistent with this, the disassembly of plaques induced by 18 beta-GA was correlated with decreases in Cx43-P2 levels and increases in nonphosphorylated Cx43. Biochemical evidence indicated that these changes in the P2 and NP forms of Cx43 represented 18 beta-GA-induced dephosphorylation of Cx43-P2 and not its degradation or the inhibition of Cx43-NP phosphorylation. Okadaic acid and calyculin A, which are inhibitors of type 1 and type 2A protein phosphatases, prevented the dephosphorylation of Cx43, suggesting that one or both of these phosphatases were involved in Cx43 dephosphorylation. These data indicate that 18 beta-GA causes type 1 or type 2A protein phosphatase-mediated Cx43 dephosphorylation coincident with the disassembly of gap-junction plaques.

Animals↗
PubMed1996

Localization and function of the connexin 43 gap-junction protein in normal and various oncogene-expressing rat liver epithelial cells.

Clones of rat liver epithelial cells genotypically altered by mutation or by a variety of oncogenes were analyzed by microinjection-dye transfer, immunofluorescence confocal microscopy, and western blotting to determine at what level and to what degree these transformations disrupted gap-junctional intercellular communication (GJIC) mediated by connexin 43 (Cx43). Compared with normal rat liver epithelial cells, cells neoplastically transformed by src, neu, ras, and myc/ras all displayed reduced degrees of GJIC, reduced levels of membrane-associated Cx43 plaques, and hypophosphorylation of Cx43. Confocal analysis further demonstrated that the Cx43 protein was localized, at least in part, to the nucleus rather than to the plasma membrane in the src- and neu-transformed cells, but not in the ras- and myc/ras-transformed cells. Nuclei isolated from WB-neu cells showed substantially higher levels of Cx43 on western blotting than did nuclei from WB-neo control cells, supporting the idea that the nuclear-localized immunopositive material detected by confocal microscopy was Cx43 protein. In a GJIC-deficient mutant rat liver epithelial cell line containing normal numbers of plasma membrane-localized Cx43 plaques that appeared to be reduced in size, the Cx43 protein was also found to be hypophosphorylated. Cells overexpressing myc, on the other hand, displayed a normal degree of GJIC, increased levels of plasma membrane-localized Cx43 plaques, and hyperphosphorylation of the Cx43 protein. Cells expressing raf, previously shown to be GJIC competent, showed Cx43 immunostaining patterns similar to those in normal cells, whereas a cell line established from a tumor induced by injection of these raf-expressing cells into a mouse showed a marked reduction in GJIC and plasma membrane-associated Cx43 immunostaining. These data suggest that altered localization of the gap-junction protein Cx43, mediated in part by changes in the phosphorylation of this protein, contributes to the disruption of GJIC in neoplastically transformed rat liver epithelial cells.

Animals↗
PubMed1996

Reduction of growth and acetyl-CoA carboxylase activity by expression of a chimeric streptavidin gene in Escherichia coli.

The streptavidin gene from Streptomyces avidinii was expressed in E. coli as a non-fusion protein and as a glutathione S-transferase fusion protein. The streptavidin protein accumulated primarily in the inclusion bodies and did not alter cell growth. In contrast, the glutathione-S-transferase-streptavidin fusion protein was soluble. Nondenaturing polyacrylamide gel electrophoresis indicated that the chimeric glutathione-S-transferase-streptavidin protein was present mostly as a monomer, with some detectable polymeric forms. Cells grown in the presence of [3H]-biotin had label specifically associated with the expressed glutathione-S-transferase-streptavidin fusion protein, indicating this protein bound biotin in vivo. The majority of the radiolabeled biotin was associated with polymeric forms of the glutathione-S-transferase-streptavidin protein. The growth rates of biotin auxotrophs of E. coli growing in biotin-deficient media were substantially decreased by the expression of the glutathione-S-transferase-streptavidin gene. The decreased growth rate correlated with a decrease in acetyl-CoA carboxylase activity.

Acetyl-CoA Carboxylase↗
PubMed1996

Identification of three new microsatellite markers in the spinocerebellar ataxia type 2 (SCA2) region and 1.2 Mb physical map.

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease recently mapped to chromosome 12q close to the locus D12S84 by genetic linkage analysis. To generate additional genetic markers in the SCA2 region, we constructed a physical map of the region using yeast artificial chomosome (YAC), P1 artificial chromosome (PAC) and cosmid clones. The physical map was found to agree well with the genetic map. Three novel microsatellite markers were isolated and physically mapped. A novel approach to isolate CAG repeats directly from YAC DNAs is described.

Alleles↗
PubMed1996

Detection of RNA polymerase II promoters and polyadenylation sites in human DNA sequence.

Detection of RNA polymerase II promoters and polyadenylation sites helps to locate gene boundaries and can enhance accurate gene recognition and modeling in genomic DNA sequence. We describe a system which can be used to detect polyadenylation sites and thus delineate the 3' boundary of a gene, and discuss improvements to a system first described in Matis et al. (1995) [Matis S., Shah M., Mural R. J. & Uberbacher E.C. (1995) Proc. First Wrld Conf. Computat. Med., Public Hlth, Biotechnol. (Wrld Sci.) (in press).], which predicts a large subset of RNA polymerase II promoters. The promoter system used statistical matrices and distance information as inputs for a neural network which was trained to provide initial promoter recognition. The output of the network was further refined by applying rules which use the gene context information predicted by GRAIL. We have reconstructed the rule-based system which uses gene context information and significantly improved the sensitivity and selectivity of promoter detection.

Algorithms↗
PubMed1996

Alignments of DNA and protein sequences containing frameshift errors.

Molecular sequences, like all experimental data, are subject to error. Many current DNA sequencing protocols have very significant error rates and often generate artefactual insertions and deletions of bases (indels) which corrupt the translation of sequences and compromise the detection of protein homologies. The impact of these errors on the utility of molecular sequence data is dependent on the analytic technique used to interpret the data. In the presence of frameshift errors, standard algorithms using six-frame translation can miss important homologies because only subfragments of the correct translation are available in any given frame. We present a new algorithm which can detect and correct frameshift errors in DNA sequences during comparison of translated sequences with protein sequences in the databases. This algorithm can recognize homologous proteins sharing 30% identity even in the presence of a 7% frameshift error rate. Our algorithm uses dynamic programming, producing a guaranteed optimal alignment in the presence of frameshifts, and has a sensitivity equivalent to Smith-Waterman. The computational efficiency of the algorithm is O(nm) where n and m are the sizes of two sequences being compared. The algorithm does not rely on prior knowledge or heuristic rules and performs significantly better than any previously reported method.

Algorithms↗
PubMed1996

Gap junction endocytosis and lysosomal degradation of connexin43-P2 in WB-F344 rat liver epithelial cells treated with DDT and lindane.

Treatment of WB-F344 rat liver epithelial cells with DDT (1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane) or lindane induces a loss of gap junction plaques and a decrease in the phosphorylated gap junction protein connexin43-P2 (Cx43-P2), which is associated with the plaques. In this study we have considered several mechanisms. The loss of junctional plaques could be due to disaggregation of junctional particles or to endocytosis of the plaques, while the loss of Cx43-P2 could be due to dephosphorylation or degradation. Immunohistochemical analyses of DDT- or lindane-treated cells revealed a reduction in plasma membranous Cx43-positive gap junction plaques coincident with the appearance of Cx43-positive punctate cytoplasmic structures. The cytoplasmic Cx43-positive structures eventually disappeared after 4 h treatment. Diffuse Cx43-positive plasma membranous staining was not seen following DDT or lindane treatment. Western blot analyses of these cells indicated that Cx43-P2 decreased in a time-dependent manner that paralleled the disappearance of gap junction plaques from the plasma membrane. The loss of Cx43-P2 was not due to dephosphorylation, since no increase in non-phosphorylated (Cx43-NP) or other phosphorylated (Cx43-P1) forms of the protein were evident. The decrease in Cx43-P2 and the disappearance of cytoplasmic Cx43-positive structures were prevented by colchicine and chloroquine, which suggests that Cx43-P2-containing plaques were internalized and degraded in lysosomes. In addition, two small (approximately 18 and approximately 22 kDa) bands appeared in Western blots coincident with the loss of Cx43-P2 and may be degradation products of the protein. These immunohistochemical and biochemical data strongly suggest that the loss of gap junction plaques and of Cx43-P2 in WB-F344 cells treated with DDT and lindane were due to endocytosis of the plaques and degradation of Cx43-P2 in lysosomes.

Animals↗
PubMed1996

[Antimicrobial properties of Flos Lonicerae against oral pathogens].

The antimicrobial effect of Flos Lonicerae on oral pathogens was studied. The results showed that 73.9% of the tested pathogens were inhibited at a concentration below 6.25mg/ml. Streptococci mutants, actinomyces viscosus and bacteroides melaninogenicus were comparatively more sensitive to Flos Lonicerae.

Actinomyces viscosus↗
PubMed1996

Collaborative study on evaluation of immunodiagnostic assays in schistosomiasis japonica by treatment efficacy assessment. Collaboration Group.

OBJECTIVE: This paper is the summary of "National Symposium on the Value of Immunodiagnostic Assays in Schistosomiasis by Treatment Effects Assessment" which was directed by the Expert Advisory Committee for Schistosomiasis of the Ministry of Public Health. This symposium was held to evaluate the diagnostic effects of the new system of detection in the sensitivity and specificity by treatment assessment. MATERIALS AND METHODS: Twelve laboratories with 14 assay systems participated in this collaborative study, in which, 450 sera were detected by double blind trial using a classical antibody detection with ELISA as a control. RESULTS: The results showed that 6 test systems were superior or close to the classical antibody detection, especially in evaluating the value of treatment effects. CONCLUSIONS: It is unanimously recognized that much progress has been made in the research of immunodiagnosis of schistosomiasis in China, but many problems remain to be solved and worth further studying.

Animals↗
PubMed1996

[Effects of electroacupuncture on the subcutaneous mast cells of zusanli acupoint in rat with unilateral sciatic nerve transection].

Electroacupuncture could induce the convergence and degranulation of subcutaneous mast cells in acupoints. After unilateral transection of sciatic nerve, we studied the numbers of subcutaneous mast cells and its degranulation in bilateral Zusanli and Xiajuxu acupoints with electroacupuncture in Zusanli. We found that sciatic nerve transection could reduce the total numbers of mast cells and the degranulation numbers of mast cells in Zusanli. The results suggested peripheral nerves play an important role in the convergence and degranulation of mast cells in acupoints by electroacupuncture induction.

Acupuncture Points↗