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Biomedical subjects

Y Luo

Publications and source records attributed to Y Luo.

At least 343 records · Page 19Linked to original sources
PubMed1996

The distribution of collapsin-1 mRNA in the developing chick nervous system.

Collapsin-1 is a secreted glycoprotein that inhibits the extension of specific growth cones in vitro. It has been hypothesized to serve as a repulsive guidance cue for extending growth cones in vivo. Here we report the distribution of collapsin-1 message as demonstrated by in situ hybridization using digoxigenin-labeled RNA probes in wholemounts and tissue sections. In the early chick brain collapsin-1 is expressed in specific regions of the retina, the olfactory bulb, and the diencephalon. In the hindbrain collapsin-1 is first expressed in rhombomere 5 and later in bilaterally symmetric rostrocaudal stripes. Collapsin-1 is expressed in high levels in the ventral horn of the spinal cord and in ventricular stripes that extend rostrally to the hindbrain. In the periphery, collapsin-1 is expressed in the dermamyotome and in ectoderm and epidermis. Based on collapsin's expression patterns we tested axons extending from explants of ventral spinal cord and olfactory bulb for sensitivity to collapsin and show that the former are sensitive to collapsin whereas the latter are not. The distribution of collapsin mRNA is consistent with it playing a role in the organization of sensory axonal projections within the spinal cord and skin.

Animals↗
PubMed1996

Molecular cloning of a protein kinase whose phosphorylation is regulated by genetic adhesion during Chlamydomonas fertilization.

Fertilization in Chlamydomonas is initiated by adhesive interactions between gametes of opposite mating types through flagellar glycoproteins called agglutinins. Interactions between these cell adhesion molecules signal for the activation of adenylyl cyclase through an interplay of protein kinases and ultimately result in formation of a diploid zygote. One of the early events during adhesion-induced signal transduction is the rapid inactivation of a flagellar protein kinase that phosphorylates a 48-kDa protein in the flagella. We report the biochemical and molecular characterization of the 48-kDa protein. Experiments using a bacterially expressed fusion protein show that the 48-kDa protein is capable of autophosphorylation on serine and tyrosine and phosphorylation of bovine beta-casein on serine, confirming that the 48-kDa protein itself has protein kinase activity. This protein kinase exhibits limited homology to members of the eukaryotic protein kinase superfamily and may be an important element in a signaling pathway in fertilization.

Amino Acid Sequence↗
PubMed1996

Loss of heterozygosity on chromosome arm 3p in nasopharyngeal carcinoma.

We have examined 17 primary undifferentiated nasopharyngeal carcinoma biopsies for allelic loss on 3p, comparing the findings in tumors with those in normal lymphocyte DNA from the same patients. Ten polymorphic microsatellite markers were used between 3p13 and 3p26. Allelic loss was observed in 12 samples (70%). Two loci were most frequently affected: D3S1067 (3p21.1-14.3) in 60% and D3S1217 (3p14.2-14.1) in 58%. One tumor seemed to have a homozygous deletion at 3p26, detected by the D3S1297 marker. Analysis of the clinical data showed that an increased number of aberrations in 3p was correlated with more advanced tumor stages.

Adult↗
PubMed1996

Relationships among lactate concentration, blood flow and histopathologic profiles in rat C6 glioma.

Increased capacity for glycolytic metabolism is a well-known characteristic of neoplastic cells. Because lactic acid is the end product of glycolysis, in vivo MRS measurements of tumor lactate concentration ([lac]t) may provide valuable information about tumor metabolism, which will aid the development of therapies and the clinical diagnosis and treatment of tumors. In the present study, several hemodynamic and histologic parameters were evaluated with respect to their influence on [lac]t. Pronounced differences in [lac]t in two distinct populations of tumors suggested a putative perfusion threshold. Above this threshold, [lac]t was independent of hemodynamic and histologic factors including tumor blood flow (measured using MRS and the method of D2O washout), extent of necrosis and inflammatory cell infiltrate. Thus, for most tumors, [lac]t was not determined by any one single factor such as hypoxia, venous clearance, glucose supply, extent of necrosis or degree of inflammatory cell infiltrate. Rather, [lac]t may be equilibrated, at least in part, by an interplay of forces involving hemodynamics and substrate supply. In general, the data are consistent with the hypothesis that elevated lactate in most tumors is related to the high glycolytic activity of adequately perfused, viable neoplastic cells.

Animals↗
PubMed1996

B1-insensitive, single-shot localization and water suppression.

A technique for single-shot, localized, water-suppressed in vivo 1H NMR with high immunity to B1 inhomogeneities is described. The single-shot localization is based on complete outer-volume suppression which is achieved with optimized, adiabatic BIR-4 pulses in combination with BO gradient modulation. B1-insensitive water suppression is achieved with BISTRO, a train of selective adiabatic full-passage pulses interleaved with BO gradient crushers. Computer simulations based on the Bloch equations, experimental images of the localized volume, and in vivo 1H spectroscopy experiments demonstrate the excellent spatial localization and water suppression.

Artifacts↗
PubMed1996

Effects of nerve growth factor on axonal retrograde transport after axonal injury of motoneurons.

In this experimental study we coupled nerve growth factor (NGF) with notatin by dicyclohexylcarbodiimide to label NGF and observed the effects of NGF on axonal retrograde transport after axonal injury of motoneurons with the aid of notatin chemiluminescence system. The results showed that NGF could be transported through axon not only to sensory neurons in dorsal root ganglia but also to motoneurons in spinal cord ventral horn.

Animals↗
PubMed1996

An apoptotic response to photodynamic therapy with endogenous protoporphyrin in vivo.

CDF1 mice bearing the colon-26 tumor were treated with aminolevulinic acid (200 mg kg-1) by tail-vein injection, with tumor sites irradiated 4 h later at 633 nm (75-120 J cm-2). 10 h after irradiation, samples of tumors were removed for histology studies and analysis of DNA fragmentation by static gel electrophoresis. The resulting patterns indicate an apoptotic response to photodynamic therapy with endogenously formed protoporphyrin.

Animals↗
PubMed1996

Physiologic levels of beta-amyloid activate phosphatidylinositol 3-kinase with the involvement of tyrosine phosphorylation.

The beta-amyloid protein (A beta) peptide plays an important role in Alzheimer's disease, but the potential actions of physiologic levels of A beta (225-625 pM) have not been explored. We recently showed that picomolar doses of A beta can stimulate tyrosine phosphorylation of neuronal cells and now show that leads to the activation of the lipid kinase phosphatidylinositol 3-kinase (PI3 kinase). Three independent lines of evidence support the hypothesis that A beta is activating PI3 kinase through a tyrosine kinase-mediated mechanism. Immunoblotting studies show that A beta induces tyrosine phosphorylation of p85 as well as association of the p85 subunit of PI3 kinase with tyrosine-phosphorylated proteins. Studies of membrane proteins show that A beta induces a translocation of p85 to membrane-bound glycoproteins, which are likely to be receptors. Finally, direct studies of PI3 kinase activity in both anti-phosphotyrosine immunocomplexes and wheat germ agglutinin precipitates show that A beta increases formation of the product of PI3 kinase. Wortmannin, a selective inhibitor of PI3 kinase, blocks this A beta-stimulated PI3 kinase activity. Thus, physiologic levels of A beta stimulate tyrosine phosphorylation and PI3 kinase activity.

Amyloid beta-Peptides↗
PubMed1996

Cell adhesion-dependent inactivation of a soluble protein kinase during fertilization in Chlamydomonas.

Within seconds after the flagella of mt+ and mt- Chlamydomonas gametes adhere during fertilization, their flagellar adenylyl cyclase is activated several fold and preparation for cell fusion is initiated. Our previous studies indicated that early events in this pathway, including control of adenylyl cyclase, are regulated by phosphorylation and dephosphorylation. Here, we describe a soluble, flagellar protein kinase activity that is regulated by flagellar adhesion. A 48-kDa, soluble flagellar protein was consistently phosphorylated in an in vitro assay in flagella isolated from nonadhering mt+ and mt- gametes, but not in flagella isolated from mt+ and mt- gametes that had been adhering for 1 min. Although the 48-kDa protein was present in the flagella isolated from adhering gametes, we demonstrate that its protein kinase was inactivated by flagellar adhesion. Immunoblot analysis and inhibitor studies indicate that the 48-kDa protein in nonadhering gametes is phosphorylated by a protein tyrosine kinase. In vivo experiments showing that the protein tyrosine phosphatase inhibitor sodium orthovanadate inhibits fertilization suggest that protein dephosphorylation may be required for signal transduction. The 48-kDa protein and its protein kinase may be among the first elements of a novel signalling pathway that couples interaction of flagellar adhesion molecules to gamete activation.

Adenosine Triphosphate↗
PubMed1996

EcoCELLs: tools for mesocosm scale measurements of gas exchange.

We describe the use of a unique plant growth facility, which has as its centerpiece four 'EcoCELLs', or 5x7 m mesocosms designed as open-flow, mass-balance systems for the measurement of carbon, water and trace gas fluxes. This system is unique in that it was conceived specifically to bridge the gap between measurement scales during long-term experiments examining the function and development of model ecosystems. There are several advantages to using EcoCELLs, including (i) the same theory of operation as leaf level gas exchange systems, but with continuous operation at a much larger scale; (ii) the ability to independently evaluate canopy-level and ecosystem models; (iii) simultaneous manipulation of environmental factors and measurement of system-level responses, and (iv) maximum access to, and manipulation of, a large rooting volume. In addition to discussing the theory, construction and relative merits of EcoCELLs, we describe the calibration and use of the EcoCELLs during a 'proof of concept' experiment. This experiment involved growing soybeans under two ambient CO2 concentrations (approximately 360 and 710 micromoles mol-1). During this experiment, we asked 'How accurate is the simplest model that can be used to scale from leaf-level to canopy-level responses?' in order to illustrate the utility of the EcoCELLs in validating canopy-scale models.

Calibration↗
PubMed1996

Rapid initiation of apoptosis by photodynamic therapy.

Photodynamic therapy (PDT) of neoplastic cell lines is sometimes associated with the rapid initiation of apoptosis, a mode of cell death that results in a distinct pattern of cellular and DNA fragmentation. The apoptotic response appears to be a function of both the sensitizer and the cell line. In this study, we examined photodynamic effects of several photosensitizers on murine leukemia P388 cells. Two drugs, a porphycene dimer (PcD) and tin etiopurpurin (SnET2), which localized at lysosomal sites, were tested at PDT doses that resulted in 50% loss of viability (LD50), measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. An oligonucleosomal pattern of DNA degradation was observed within 1 h after irradiation. Neither sensitizer antagonized PDT-mediated internucleosomal DNA cleavage by the other. Very high PDT doses with either agent abolished this rapid internucleosomal cleavage. Exposure of cells to high concentrations of either sensitizer in the dark also resulted in rapid DNA fragmentation to nucleosomes and nucleosome multimers; this effect was not altered by the antioxidant 6-hydroxy-2,5,7,8-tetramethyl-chroman-2-carboxylic acid (trolox), although the latter could protect cells from cytotoxicity and apoptotic effects caused by LD50 PDT doses. Photodamage from two cationic sensitizers, which localized at membrane sites, caused rapid DNA cleavage to 50 kb particles; however, no further fragmentation was detected after 1 h under LD10, LD50 or LD95 PDT conditions. Moreover, the presence of either cationic sensitizer inhibited the rapid internucleosomal cleavage induced by SnET2 or PcD photodamage. The site of photodynamic action may therefore be a major determinant of the initiation and rate of progression of apoptosis.

Animals↗
PubMed1996

Delayed oxidative photodamage induced by photodynamic therapy.

Apoptotic DNA fragmentation was observed 60 min after photodynamic therapy of murine leukemia cells in culture, using either of two photosensitizers with predominantly lysosomal targets. When the radical scavengers trolox or alpha-tocopherol succinate were present during irradiation, the subsequent appearance of apoptotic cells was prevented, as was phototoxicity. Addition of either scavenger during the 60 min after irradiation provided only partial protection from apoptosis and phototoxicity; this protection was abolished if the addition was delayed for 10 min. These results are consistent with a model whereby long-persisting photoproducts continue the initiation of apoptosis for approximately 10 min after irradiation has ceased.

Animals↗
PubMed1996

A novel method for monitoring Mycobacterium bovis BCG trafficking with recombinant BCG expressing green fluorescent protein.

To better understand intracellular and extracellular trafficking of Mycobacterium bovis bacillus Calmette-Guérin (BCG) when used as an intravesical agent in the treatment of transitional cell carcinoma (TCC) of the bladder, recombinant BCG (rBCG) expressing the jellyfish green fluorescent protein (GFP) was created. When the MB49.1 murine TCC cell line was incubated with GFP-expressing rBCG, internalization of the pathogen could be directly visualized by UV microscopy and quantitated by flow cytometry. The in vitro internalization of the GFP rBCG by the bladder tumor cells was temperature dependent, occurring most readily at 37 degrees C and being severely inhibited at 4 degrees C. Optimum internalization was achieved in vitro at a 10:1 BCG-to-tumor cell ratio over 24 h during which approximately 16% of the tumor cells became infected. Cytochalasin B, a phagocytosis inhibitor, abrogated the ingestion by almost 100% at a concentration of 200 micrograms/ml, indicating that contractile microfilaments likely played an important role in this process. By using mitomycin, a DNA cross-linking reagent, to inhibit proliferation of MB49.1 cells, clearance of about 40% of the green rBCG was achieved by 3 days postinfection. No significant difference between the GFP rBCG and wild-type BCG was observed in the ability to induce the expression of cell membrane proteins of major histocompatibility classes I and II, ICAM-I and -II, B7-1 and -2, of Fas from MB49.1 cells or cytokine production from mouse spleen cells. These results indicate that GFP rBCG may serve as a useful substitute for wild-type BCG in future studies of in vivo trafficking experimental and clinical immunotherapy.

Animals↗
PubMed1996

Rapamycin resistance tied to defective regulation of p27Kip1.

The potent antiproliferative activity of the macrolide antibiotic rapamycin is known to involve binding of the drug to its cytosolic receptor, FKBP12, and subsequent interaction with targets of rapamycin, resulting in inhibition of p70 S6 kinase (p70S6K). However, the downstream events that lead to inhibition of cell cycle progression remain to be elucidated. The antiproliferative effects of rapamycin are associated with prevention of mitogen-induced downregulation of the cyclin-dependent kinase inhibitor p27Kip1, suggesting that the latter may play an important role in the growth pathway targeted by rapamycin. Murine BC3H1 cells, selected for resistance to growth inhibition by rapamycin, exhibited an intact p70S6K pathway but had abnormally low p27 levels that were no longer responsive to mitogens or rapamycin. Fibroblasts and T lymphocytes from mice with a targeted disruption of the p27Kip1 gene had impaired growth-inhibitory responses to rapamycin. These results suggest that the ability to regulate p27Kip1 levels is important for rapamycin to exert its antiproliferative effects.

Animals↗
PubMed1996

Developmental regulation of cytochrome oxidase subunit VIa isoforms in cardiac and skeletal muscle.

Physiological requirements for mitochondrial respiration change during fetal and postnatal development of cardiac and skeletal muscle, particularly after the abrupt transition from the hypoxic fetal environment to the oxygen-rich milieu of the neonate. This study defines the pattern of expression of nuclear genes encoding the muscle-specific (H) and non-muscle-specific (L) isoforms of cytochrome oxidase (COX) subunit VIa during pre- and postnatal development of striated muscles in the mouse. In the early embryo, COX VIa-L was the predominant isoform expressed in all tissues. COX VIa-H mRNA was detectable as early as day 8 postcoitum (pc) in the heart, but not until gestational day 14 in skeletal myofibers of the tongue, diaphragm, and other skeletal muscles. At late fetal stages up until birth (days 16-18 pc), COX VIa-L and COX VIa-H were both expressed in striated myocytes, although the L form remained the dominant isoform. In postnatal animals, however, expression of COX VIa-H increased whereas COX VIa-L decreased in a reciprocal manner. Activation of the COX VIa-H gene also was observed during differentiation of nurine myogenic cells in culture and was followed by diminished expression of the COX VIa-L isoform in maturing myotubes, as in the intact animal. We conclude that regulation of nuclear genes encoding subunits of COX is a component of the developmental programs that govern cardiac and skeletal muscle differentiation and maturation in the mammalian fetus and neonate. COX VIa-L, the predominant isoform in all fetal tissues, is gradually replaced by the muscle-specific H isoform in both cardiac and skeletal muscles, although this transition is not complete until after birth.

Aging↗