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Biomedical subjects

Y Luo

Publications and source records attributed to Y Luo.

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

A family of molecules related to collapsin in the embryonic chick nervous system.

Signaling molecules with either attractive or repulsive effects on specific growth cones are likely to play a role in guiding axons to their appropriate targets. A chick brain glycoprotein, collapsin, has been shown to be a good candidate for a repulsive guidance cue. We report here the discovery of four new molecules related to collapsin in chick brains. All contain a semaphorin domain. One is structurally very similar to collapsin but is only 50% identical in its amino acid sequence. We have named it collapsin-2. The collapsin-related genes exhibit distinct but overlapping patterns of mRNA expression in the developing spinal cord and the developing visual system. This family of collapsin-related molecules could potentially act as repulsive cues toward specific neuronal populations.

Amino Acid Sequence↗
PubMed1995

Differences in the growth pattern and clinical course of EBV-LMP1 expressing and non-expressing nasopharyngeal carcinomas.

All low differentiated or anaplastic forms of nasopharyngeal carcinoma (NPC) carry multiple copies of EBV-DNA and express EBNA1. The major membrane protein, LMP1, is only expressed in 65% of the tumours. The physiological function of LMP1 in the viral life cycle is unknown, but it has been shown to transform established rodent fibroblasts and immortalised human keratinocytes in vitro, and to increase the likelihood of a malignant transformation. We studied 74 cases collected from the Shanghai and Guanzhou areas in China. LMP1 expression was assessed in tumour biopsies by immunoblotting. Clinical and follow-up data were evaluated according to the classification of WHO. The laboratory and the clinical data were assembled in a mutually independent double blind fashion. Our findings indicate that the LMP1-positive tumours grew faster and more expansively than LMP1-negative tumours, but nevertheless had a better prognosis. LMP1-negative tumours recurred at a higher frequency, and showed an increased tendency to metastasise.

Carcinoma↗
PubMed1995

Failure of intrathymic inoculation of donor-specific splenocytes to prolong cardiac or renal allograft survival in dogs.

The intrathymic inoculation (ITI) of donor splenocytes into potential organ transplant recipients has been demonstrated to result in donor-specific unresponsiveness and greatly prolonged survival of subsequent organ allografts in rodents without the need for long-term pharmacological immunosuppressive therapy. We have studied the effect of the ITI of saline (controls) (groups 1 (n = 6) and 3 (n = 6)) or donor splenocytes (groups 2 (n = 10) and 4 (n = 8)) in dogs that received either pharmacological immunosuppression (with cyclosporine and prednisone, +/- azathioprine/cyclophosphamide) (groups 1 and 2) or rabbit anti-dog antithymocyte globulin (groups 3 and 4) at the time of ITI. Kidney or heart allografting (from the donor of the splenocytes) was carried out 16-74 days after ITI; all but four transplants were performed within 16-22 days after ITI. Mean kidney allograft survival was 6, 10, 9, and 9 days, respectively, in groups 1-4. Mean cardiac allograft survival was 7, 14, 8, and 7 days, respectively. There was no statistical difference in allograft survival between those dogs that received ITI of saline and those that received donor splenocytes. These results would suggest that the protocols developed to date using ITI in rodent species may not be successful in dogs.

Animals↗
PubMed1995

Isolation and structural elucidation of pentacyclic triterpenoids from Maprounea africana.

Pentacyclic triterpenoids based on the taraxer-14-ene skeleton with a C-28 attached carboxylic acid group have been isolated from the roots of Maprounea africana. These compounds were identified as 1 beta,2 alpha-dihydroxyaleuritolic acid 2,3-bis-p-hydroxybenzoate [1], 2 alpha-hydroxyaleuritolic acid 3-p-hydroxybenzoate [2], 2 alpha-hydroxyaleuritolic acid 2,3-bis-p-hydroxybenzoate [4], aleuritolic acid 3-p-hydroxybenzoate [5], aleuritolic acid [6], and aleuritolic acid 3-acetate [7]. Compounds 1 and 2 are new triterpene esters. Compound 3 was previously reported as 7 beta-hydroxymaprounic acid 3-p-hydroxybenzoate [13]. However, based on detailed nmr studies, its structure has been revised.

Magnetic Resonance Spectroscopy↗
PubMed1995

Loss of function effect of RET mutations causing Hirschsprung disease.

We have introduced three Hirschsprung (HSCR) mutations localized in the tyrosine kinase domain of RET into the RET/PTC2 chimaeric oncogene which is capable of transforming NIH3T3 mouse fibroblasts and of differentiating pC12 rat pheochromocytoma cells. The three HSCR mutations abolished the biological activity of RET/PTC2 in both cell types and significantly decreased its tyrosine phosphorylation. By contrast, a rare polymorphism in exon 18 does not alter the transforming capability of RET/PTC2 or its tyrosine phosphorylation. These data suggest a loss of function effect of HSCR mutations which might act through a dominant negative mechanism. Our model system is therefore capable of discriminating between causative HSCR mutations and rare polymorphisms in the tyrosine kinase domain of RET.

3T3 Cells↗
PubMed1995

Rotenoids mediate potent cancer chemopreventive activity through transcriptional regulation of ornithine decarboxylase.

For the discovery of new cancer chemopreventive agents, we have studied the potential of plant extracts to inhibit phorbol ester-induced ornithine decarboxylase (ODC) activity in cell culture. Four active rotenoids were obtained from the African plant Mundulea sericea (Leguminosae). These isolates were highly potent when evaluated for inhibition of chemically induced preneoplastic lesions in mammary organ culture and inhibition of papillomas in the two-stage mouse skin model, and they appear to function by a unique mechanism at the level of ODC messenger RNA expression. Based on our findings, rotenoids can be regarded as promising new chemopreventive or anticancer agents.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1995

Arachidonic acid, but not sodium nitroprusside, stimulates presynaptic protein kinase C and phosphorylation of GAP-43 in rat hippocampal slices and synaptosomes.

Activation of protein kinase C (PKC) and phosphorylation of its presynaptic substrate, the 43-kDa growth-associated protein GAP-43, may contribute to the maintenance of hippocampal long-term potentiation (LTP) by enhancing the probability of neurotransmitter release and/or modifying synaptic morphology. Induction of LTP in rat hippocampal slices by high-frequency stimulation of Schaffer collateral-CA1 synapses significantly increased the PKC-dependent phosphorylation of GAP-43, as assessed by quantitative immunoblotting with a monoclonal antibody that recognizes an epitope that is specifically phosphorylated by PKC. The stimulatory effect of high-frequency stimulation on levels of immunoreactive phosphorylated GAP-43 was not observed when 4-amino-5-phosphonovalerate (50 microM), an N-methyl-D-aspartate (NMDA) receptor antagonist, was bath-applied during the high-frequency stimulus. This observation supports the hypothesis that a retrograde messenger is produced postsynaptically following NMDA receptor activation and diffuses to the presynaptic terminal to activate PKC. Two retrograde messenger candidates--arachidonic acid and nitric oxide (sodium nitroprusside was used to generate nitric oxide)--were examined for their effects in hippocampal slices on PKC redistribution from cytosol to membrane as an indirect measure of enzyme activation and PKC-specific GAP-43 phosphorylation. Bath application of arachidonic acid, but not sodium nitroprusside, at concentrations that produce synaptic potentiation (100 microM and 1 mM, respectively) significantly increased translocation of PKC immunoreactivity from cytosol to membrane as well as levels of immunoreactive, phosphorylated GAP-43. The stimulatory effect of arachidonic acid on GAP-43 phosphorylation was also observed in hippocampal synaptosomes. These results indicate that arachidonic acid may contribute to LTP maintenance by activation of presynaptic PKC and phosphorylation of GAP-43 substrate. The data also suggest that nitric oxide does not activate this signal transduction system and, by inference, activates a distinct biochemical pathway.

Animals↗
PubMed1995

Boundaries of the nicking region for the F plasmid transfer origin, oriT.

The extent of the F plasmid oriT nicking region was determined from the properties of successive substitution mutations in the region from base pair 121 to base pair 174 and from KMnO4 probing of DNA structural distortions induced in vivo by tra gene products. Nicking and transfer assays indicated that the left margin of oriT lies predominantly at the nick site, and that the nicking domain primarily lies within 17 bp to the right of the nick. Some mutants that were proficient for nicking showed reduced frequencies of termination, indicating that oriT nicking does not guarantee efficient termination. DNA in the vicinity of the nick (G137, T138, G140, and T141 on the nicked strand) showed elevated sensitivity to KMnO4 when tra gene products were present in the donor. Bases C145, C146, C147, C149, and G150 on the unnicked strand also became more sensitive to oxidation under tra+ conditions. The bases preferentially oxidized by KMnO4 lie within the nicking domain, as defined by the substitution mutants, and they include dinucleotides that can produce kinks in the DNA. Base pairs in the nicking region are calculated to be more thermodynamically stable than base pairs in the flanking regions.

Base Sequence↗
PubMed1995

The D1 and D12 subunits are both essential for the transcription termination factor activity of vaccinia virus capping enzyme.

Transcription termination by vaccinia virus RNA polymerase during synthesis of early mRNAs requires a virus-encoded termination factor (VTF). VTF is but one of many activities associated with the vaccinia virus mRNA capping enzyme, a heterodimer of 95- and 33-kDa subunits encoded by the D1 and D12 genes, respectively. Although the three catalytic domains involved in cap formation have been assigned to individual subunits or portions thereof, the structural requirements for VTF activity are unknown. We now report that both full-length subunits are required for transcription termination. The 844-amino acid D1 subunit by itself, which is fully active in triphosphatase and guanylyltransferase functions, has no demonstrable VTF activity in vitro. Neither does the D12 subunit by itself. The heterodimeric methyltransferase domain of D1 (residues 498 to 844) and D12 subunits also has no VTF activity. VTF is not affected by a K-to-M mutation of the guanylyltransferase active site at position 260 (K260M) that abolishes enzyme-GMP complex formation or by a H682A/Y683A double mutation of the D1 subunit, which abrogates methyltransferase activity. Thus, the structural requirements for termination are distinct from those for nucleotidyl transfer and methyl transfer.

Base Sequence↗
PubMed1995

Cloning, functional characterization, and mechanism of action of the B-cell-specific transcriptional coactivator OCA-B.

Biochemical purification and cognate cDNA cloning studies have revealed that the previously described transcriptional coactivator OCA-B consists of a 34- or 35-kDa polypeptide with sequence relationships to known coactivators that function by protein-protein interactions. Studies with a recombinant protein have proved that a single OCA-B polypeptide is the main determinant for B-cell-specific activation of immunoglobulin (Ig) promoters and provided additional insights into its mechanism of action. Recombinant OCA-B can function equally well with Oct-1 or Oct-2 on an Ig promoter, but while corresponding POU domains are sufficient for OCA-B interaction, and for octamer-mediated transcription of a histone H2B promoter, an additional Oct-1 or Oct-2 activation domain(s) is necessary for functional synergy with OCA-B. Further studies additional Oct-1 or Oct-2 activation domain(s) is necessary for functional synergy with OCA-B. Further studies show that Ig promoter activation by Oct-1 and OCA-B requires still other general (USA-derived) cofactors and also provide indirect evidence that distinct Oct-interacting cofactors regulate H2B transcription.

Amino Acid Sequence↗
PubMed1995

[Measurement of the reserve function of inspiratory muscle and its clinical significance].

The principles of measuring inspiratory muscle tension-time index (TTim) and the ratio of the works of inspiration over the maximal works of inspiration (Wi/Wi(max)) were investigated and their formulae were deduced, i.e. TTim = (Pi x Ti)/(MIP x Ttot) and Wi/Wi(max) = (Pi x VT)/(MIP x IC). The importance of the inspiratory pressure and the maximal inspiratory pressure (MIP) measured at function residual capacity (FRC) level was emphasized. Both TTim and Wi/Wi(max) were measured in 35 normal subjects and 89 patients with chronic obstructive pulmonary disease (COPD). The results showed that normal value of TTim was 0.0253 +/- 0.0055 which corresponds to the normal value of the diaphragm tension-time index (TTdi = 0.02-0.03) reported by Bellemare. Patients with COPD had a mean TTim much higher than that of normals (P < 0.01). The works of inspiration (Wi) in patients with COPD increased, while the maximal works of inspiration (Wi(max)) declined, so Wi/Wi(max) became significantly greater than that of normals (P < 0.01). The results also showed that there was a linear relationship between Pi/Pimax and TTim or Wi/Wimax (r = 0.7891, 0.9738, 0.6459, 0.9327, P < 0.01). Therefore, we suggest that both TTim and Wi/Wimax can be used as clinical indices to reflect the reserve function of inspiratory muscles.

Adult↗
PubMed1995

[Preconcentration of trace chromium in natural water with activated carbon and its determination by colorimetry].

The adsorption and desorption behavior of chromium was studied. Trace chromium in water could be adsorbed on activated carbon at pH 9-10, then eluted with 0.5% sulfuric acid and determined by colorimetry. The content of chromium could be concentrated by 100 times. For sample, the coefficient of variation of 8 parallel determinations was 7.7%. The proposed method has been applied to the determination of trace chromium in natural waters with the recovery of 71.4%-90.0%, and with the detection limit of 0.04 microgram/L.

Carbon↗
PubMed1995

[The application of halo assay in analysis of cell chromatin structure].

Halo assay, a method for quantitative analysis of chromatin structure in cell, was developed recently. Due to visualization, feasibility, rapidity, and sensitivity of the method, it has been applied in radiobiology and cancer research. According to previous reports, with some improvement, this method has been established in our laboratory. Employing halo assay, the chromatin structure of two kinds of cell strain with similar genetic background and different radiosensitivity was analyzed and the results show that radiosensitive strain has looser chromatin structure than radioresistant one. It is possible that this difference is related to their different radiosensitivity, thus it's a proof for the relation of chromatin structure and radiosensitivity.

Animals↗
PubMed1995

[Effects of Sichuan herba Epimedii on the concentration of plasma middle molecular substances and sulfhydryl group of "yang-deficiency" model animal].

The effects of tonifying the kidney and strengthening the "Yang" produced by the extracts of Chinese herbs Epimedium wushanense and E. pubescens were studied in this paper. The results showed that both two herbs could decrease the concentration of plasma middle molecular substances and increase the concentration of plasma sulfhydryl group of "Yang-deficiency" model mice, thus suggesting that the above-said tonifying and strengthening effects of Herba Epimedii may result from its effects on middle molecular substances and sulfhydryl group, so as to strengthen the body resistance and eliminate the invading pathogenic factors.

Animals↗