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Biomedical subjects

L Luo

Publications and source records attributed to L Luo.

At least 37 records · Page 2Linked to original sources
PubMed2001

Mosaic analysis with a repressible cell marker (MARCM) for Drosophila neural development.

We have modified an FLP/FRT-based genetic mosaic system to label either neurons derived from a common progenitor or isolated single neurons, in the Drosophila CNS. These uniquely labeled neurons can also be made homozygous for a mutation of interest within an otherwise phenotypically wild-type brain. Using this new mosaic system, not only can normal brain development be described with unprecedented single cell resolution, but also the underlying molecular mechanisms can be investigated by identifying genes that are required for these developmental processes.

Animals↗
PubMed2001

Tailoring enzymes that modify nonribosomal peptides during and after chain elongation on NRPS assembly lines.

Nonribosomal peptide synthetases are large enzyme complexes that synthesize a variety of peptide natural products through a thiotemplated mechanism. Assembly of the peptides proceeds through amino acid loading, amide-bond formation and chain translocation, and finally thioester lysis to release the product. The final products are often heavily modified, however, through methylation, epimerization, hydroxylation, heterocyclization, oxidative cross-linking and attachment of sugars. These activities are the province of specialized enzymes (either embedded in the multidomain nonribosomal peptide synthetase structure or standalone).

Bacteria↗
PubMed2001

How do dendrites take their shape?

Recent technical advances have made possible the visualization and genetic manipulation of individual dendritic trees. These studies have led to the identification and characterization of molecules that are important for different aspects of dendritic development. Although much remains to be learned, the existing knowledge has allowed us to take initial steps toward a comprehensive understanding of how complex dendritic trees are built. In this review, we describe recent advances in our understanding of the molecular mechanisms underlying dendritic morphogenesis, and discuss their cell-biological implications.

Animals↗
PubMed2001

Cultural values and happiness: an East-West dialogue.

Happiness as a state of mind may be universal, but its meaning is complex and ambiguous. The authors directly examined the relationships between cultural values and experiences of happiness in 2 samples, by using a measurement of values derived from Chinese culture and a measurement of subjective well-being balanced for sources of happiness salient in both the East and the West. The participants were university students-439 from an Eastern culture (Taiwan) and 344 from a Western culture (the United Kingdom). Although general patterns were similar in the 2 samples, the relationships between values and happiness were stronger in the Taiwanese sample than in the British sample. The values social integration and human-heartedness had culture-dependent effects on happiness, whereas the value Confucian work dynamism had a culture-general effect on happiness.

Adolescent↗
PubMed2001

Neoplastic transformation of human osteoblast cells to the tumorigenic phenotype by heavy metal-tungsten alloy particles: induction of genotoxic effects.

Heavy metal-tungsten alloys (HMTAs) are dense heavy metal composite materials used primarily in military applications. HMTAs are composed of a mixture of tungsten (91-93%), nickel (3-5%) and either cobalt (2-4%) or iron (2-4%) particles. Like the heavy metal depleted uranium (DU), the use of HMTAs in military munitions could result in their internalization in humans. Limited data exist, however, regarding the long-term health effects of internalized HMTAs in humans. We used an immortalized, non-tumorigenic, human osteoblast-like cell line (HOS) to study the tumorigenic transforming potential of reconstituted mixtures of tungsten, nickel and cobalt (rWNiCo) and tungsten, nickel and iron (rWNiFe). We report the ability of rWNiCo and rWNiFe to transform immortalized HOS cells to the tumorigenic phenotype. These HMTA transformants are characterized by anchorage-independent growth, tumor formation in nude mice and high level expression of the K-ras oncogene. Cellular exposure to rWNiCo and rWNiFe resulted in 8.90 +/- 0.93- and 9.50 +/- 0.91-fold increases in transformation frequency, respectively, compared with the frequency in untreated cells. In comparison, an equivalent dose of crystalline NiS resulted in a 7.7 +/- 0.73-fold increase in transformation frequency. The inert metal tantalum oxide did not enhance HOS transformation frequency above untreated levels. The mechanism by which rWNiCo and rWNiFe induce cell transformation in vitro appears to involve, at least partially, direct damage to the genetic material, manifested as increased DNA breakage or chromosomal aberrations (i.e. micronuclei). This is the first report showing that HMTA mixtures of W, Ni and Co or Fe cause human cell transformation to the neoplastic phenotype. While additional studies are needed to determine if protracted HMTA exposure produces tumors in vivo, the implication from these in vitro results is that the risk of cancer induction from internalized HMTAs exposure may be comparable with the risk from other biologically reactive and insoluble carcinogenic heavy metal compounds (e.g. nickel subsulfide and nickel oxide).

Alloys↗
PubMed2001

Allelic imbalance on chromosomes 13 and 17 and mutation analysis of BRCA1 and BRCA2 genes in monozygotic twins concordant for breast cancer.

To study genetic changes associated with the development of breast cancer and the extent of its hereditary predisposition, paraffin-embedded tissue samples were obtained from monozygotic twin pairs concordant for breast cancer through the linked Swedish Twin and Cancer Registries. DNA samples extracted from the matched tumour and normal tissues of nine twin pairs were analysed for allelic imbalance using a series of microsatellite markers on chromosomes 13 and 17, containing loci with known tumour suppressor genes. Multiple losses of constitutional heterozygosity (LOH), consistent with a loss of large genomic region, the whole chromosome or chromosome arm, was found in at least three pairs of twins. One double mitotic crossover was identified in one tumour sample in a pair concordant for LOH at multiple loci on both chromosomes. Recombination breakpoints were mapped to regions delineated by D13S218 and D13S263, and D13S155 and D13S279, respectively. In general, no genetic effect of losing the same allele within a twin pair was found. However, for one marker at chromosome 13 (D13S328, between the BRCA2 and the RB-1 loci) and two markers on chromosome 17 (D17S786, distal to the p53 locus, and D17S855, an intragenic BRCA1 marker) the proportion of twin pairs with the same LOH was significantly higher than expected. These regions may reflect hereditary genomic changes in our sample set. In addition, tumour DNA samples from a subset of 12 twin pairs were analysed for BRCA1 and BRCA2 mutations using exon-by-exon single-strand conformation polymorphism analysis. Two unclassified BRCA2 variants, with a putative pathogenic effect, were identified, but no pathogenic alterations were found in the BRCA1 gene.

Adult↗
PubMed2001

A model of dynamic side-chain--side-chain interactions in the alpha-lactalbumin molten globule.

Proteins in the molten globule state contain high levels of secondary structure, as well as a rudimentary, nativelike tertiary topology. Thus, the structural similarity between the molten globule and native proteins may have a significant bearing in understanding the protein-folding problem. To explore the nature of side-chain--side-chain interactions in the alpha-lactalbumin (alpha-LA) molten globule, we determined the effective concentration for formation of the 28--111 disulfide bond in 14 double-mutant proteins, each containing two hydrophobic core residues replaced by alanine. We compared our results with those of single-alanine substitutions using the framework of double-mutant cycle analysis and found that, in the majority of cases, the effects of two alanine substitutions are additive. Based on these results, we propose a model of side-chain-side-chain interactions in the alpha-LA molten globule, which takes into consideration the dynamic nature of this partially folded species.

Alanine↗
PubMed2001

Neurotoxic effect of high dose of L-(+)-2-amino-3-phosphonopropionic acid in rats after intracaudatal injection.

AIM: To investigate neurotoxic effect of L-(+)-2-amino-3-phosphonopropionic acid (L-AP3), a partial agonist/antagonist of metabotropic glutamate receptors (mGluRs), and explore the underlying mechanisms. METHODS: Consciousness and behavior of rats were evaluated after injection of L-AP3, D-(+)-2-amino-3-phosphonopropionic acid (D-AP3, an isomer of L-AP3) or L-(+)-2-amino-4-phosphonobutyric acid (L-AP4, an agonist of mGluRs) into right caudatum. Brain water, Na+, K+, and Ca2+ contents as well as the permeability of blood brain barrier (BBB) were determined 6 h after treatment of these chemicals. Histological changes at the same time point were also observed. RESULTS: Rats treated with L-AP3 600 nmol but not 60 nmol became somnolentia. Inject ion of L-AP3 600 nmol induced a great increase of brain water, Na+, and Ca2+ contents, and a decrease of brain K+ content (P < 0.01). Meanwhile, the permeability of BBB was also increased (P < 0.01). Electron microscopic study revealed remarkable swelling of astrocytes and degenerative changes of neurons in chemical-treated caudatum. The neurotoxic effect of L-AP3 was not mimicked by D-AP3 or L-AP4 (P < 0.05). DL-2-Amino-5-phosphonovaleric acid, an antagonist of N-methyl-D-aspartate (NMDA) receptors, attenuated the changes induced by L-AP3 (P < 0.05), whereas (+/-)-alpha-methyl-(4-carboxyphenyl)glycine, a non-subtype specific antagonist of mGluRs, failed to block the effect of L-AP3. CONCLUSION: Intracaudatal injection of L-AP3 induced neurotoxic effect characterized by vasogenic brain edema, neuronal degeneration, and high brain Ca2+ content. Neurotoxic effect of L-AP3 was stereoselective and might be mediated by phospholipase C activation and partially involvement of NMDA receptors.

Alanine↗
PubMed2001

Fluoxetine inhibits dendrite atrophy of hippocampal neurons by decreasing nitric oxide synthase expression in rat depression model.

AIM: To study the effect of fluoxetine on dendrite atrophy of hippocampal neurons in rat depression model. METHODS: CMS (chronic mild stress), mimicking human depression, was used as the animal depression model. The neurons shape and numbers of nitric oxide synthase positive cells in the hippocampal subfields were measured by Nissl staining and histochemical staining of NADPH (nicotinamide adenine dinucleotide phosphate)-diaphorase respectively. RESULTS: CMS deforms neurons in the hippocampal formation, and fluoxetine can renormalize the deformed neurons by inhibiting the nitric oxide synthase catalyzing the over-production of NO, which lead subsequently to the morphological abnormality in the circumscribed area of brain. CONCLUSION: Fluoxetine, an antidepressant, renormalizes dendrite atrophy of hippocampal neurons by inhibiting nitric oxide synthase overexpression in rat chronic mild stress model.

Animals↗
PubMed2001

Magnetic resonance imaging in distinguishing malignant from benign pleural disease.

OBJECTIVE: To explore the role of magnetic resonance imaging (MRI) in distinguishing malignant from benign pleural disease. METHODS: All 64 patients were examined with both computed tomography (CT) and MRI. The morphologic features of pleural lesions and MR signal intensity on T1-weighted, T2-weighted and contrast-enhanced T1-weighted images were evaluated. RESULTS: Mediastinal pleural involvement, circumferential pleural thickening, nodularity, irregularity of pleural contour, and infiltration of the chest wall and/or diaphragm were most suggestive of a malignant cause on CT and MR images. Contrary to what has been reported in the literature, pleural thickness greater than 1 cm either on CT or on MRI did not reveal a significant difference between malignant and benign pleural disease (P > 0.05, chi-square test). Using morphologic features in combination with signal intensity features, MRI had a sensitivity of 98% and a specificity of 92% in the detection of pleural malignancy. CONCLUSIONS: Compared with those on CT, the morphologic features on MRI allowed a mostly equal and in some cases superior detection and evaluation of the spread of pleural disease. In combination with signal intensity and morphologic features, MRI is very useful in distinguishing malignant from benign pleural disease.

Adult↗
PubMed2000

ADP is the cognate ligand for the orphan G protein-coupled receptor SP1999.

P2Y receptors are a class of G protein-coupled receptors activated primarily by ATP, UTP, and UDP. Five mammalian P2Y receptors have been cloned so far including P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11. P2Y1, P2Y2, and P2Y6 couple to the activation of phospholipase C, whereas P2Y4 and P2Y11 couple to the activation of both phospholipase C and the adenylyl cyclase pathways. Additional ADP receptors linked to Galpha(i) have been described but have not yet been cloned. SP1999 is an orphan G protein-coupled receptor, which is highly expressed in brain, spinal cord, and blood platelets. In the present study, we demonstrate that SP1999 is a Galpha(i)-coupled receptor that is potently activated by ADP. In an effort to identify ligands for SP1999, fractionated rat spinal cord extracts were assayed for Ca(2+) mobilization activity against Chinese hamster ovary cells transiently transfected with SP1999 and chimeric Galpha subunits (Galpha(q/i)). A substance that selectively activated SP1999-transfected cells was identified and purified through a series of chromatographic steps. Mass spectral analysis of the purified material definitively identified it as ADP. ADP was subsequently shown to inhibit forskolin-stimulated adenylyl cyclase activity through selective activation of SP1999 with an EC(50) of 60 nM. Other nucleotides were able to activate SP1999 with a rank order of potency 2-MeS-ATP = 2-MeS-ADP > ADP = adenosine 5'-O-2-(thio)diphosphate > 2-Cl-ATP > adenosine 5'-O-(thiotriphosphate). Thus, SP1999 is a novel, Galpha(i)-linked receptor for ADP.

3T3 Cells↗
PubMed2000

A statistical mechanical model for predicting B-DNA curvature and flexibility.

A statistical mechanical model taking into account the symmetric twisting, tilting, sliding fluctuations and asymmetric rolling fluctuations has been proposed to predict the macroscopic curvature and flexibility of B-DNA. Based on the statistical data of structural parameters of double helix in nucleic acid database and the related theoretical analysis, the equilibrium angular parameters (Omega, rho and tau) describing the orientation of successive base-pair planes, the translation parameters (D(y)) along the long axis of neighboring base-pair step and the corresponding force constants are arranged for ten dimers appropriately. Under the assumption of independent angular parameters, independent base-pair steps and a simple energy function, we can calculate the macroscopic curvature and the flexibility of DNA sequences through the transformation matrix and the Boltzmann ensemble average. The predictions on curvature and flexibility of DNA have been compared with the corresponding experimental data. The agreement is remarkably good. It is demonstrated that the lowering of the temperature does increase the DNA curvature.

Animals↗
PubMed2000

Small GTPases Rac and Rho in the maintenance of dendritic spines and branches in hippocampal pyramidal neurons.

The shape of dendritic trees and the density of dendritic spines can undergo significant changes during the life of a neuron. We report here the function of the small GTPases Rac and Rho in the maintenance of dendritic structures. Maturing pyramidal neurons in rat hippocampal slice culture were biolistically transfected with dominant GTPase mutants. We found that expression of dominant-negative Rac1 results in a progressive elimination of dendritic spines, whereas hyperactivation of RhoA causes a drastic simplification of dendritic branch patterns that is dependent on the activity of a downstream kinase ROCK. Our results suggest that Rac and Rho play distinct functions in regulating dendritic spines and branches and are vital for the maintenance and reorganization of dendritic structures in maturing neurons.

Animals↗
PubMed2000

The HIV-1 Env protein signal sequence retards its cleavage and down-regulates the glycoprotein folding.

Secretory proteins and most membrane proteins are synthesized with a signal sequence that is usually cleaved from the nascent polypeptide chain, during its transport, into the lumen of the endoplasmic reticulum (ER). We have analyzed the kinetics of the cleavage of the HIV-1 Env protein signal sequence from gp160 and gp120 in HeLa, BHK, and Jurkat cells. Furthermore, we have determined the effects of this cleavage on the association of the gp160 and gp120 glycoproteins with the ER protein calnexin and the effects of the signal sequence cleavage on protein folding. The cleavage of the HIV-1 Env protein signal sequence on both gp160 and gp120 occurred very slowly in all three cell lines with a t(1/2) of 45-60 min. The core glycosylated and signal-sequence-retained forms of gp160 and gp120 associated with calnexin while the signal-sequence-cleaved forms of gp160 and gp120 had disassociated from calnexin and correctly folded as determined by their ability to associate with the CD4 cellular receptor. Further analysis of the folding state of gp160 and gp120 in nonreducing SDS-PAGE revealed that the signal-sequence-retained and calnexin-associated forms of gp160 and gp120 migrated as broad, diffuse bands, whereas the signal-sequence-cleaved or CD4-associated forms of gp160 and gp120 migrated as single sharper bands. The cause of this retardation in the rate of folding and intracellular transport of HIV-1 glycoproteins was localized to their signal sequences by fusing the vesicular stomatitis virus G protein with the HIV-1 Env protein signal sequence and expressing this chimeric protein in mammalian cells. The HIV-1 Env protein signal sequence on the VSV-G protein also confers a reduced rate of cleavage and slow intracellular transport and folding of the chimeric G protein. These results provide direct evidence that in vivo the HIV-1 glycoprotein signal sequence inhibits the folding of HIV-1 Env protein. Our data also suggest a direct correlation between the rate of the signal sequence cleavage and protein folding.

Calcium-Binding Proteins↗
PubMed2000

A B cell superantigen-induced persistent "Hole" in the B-1 repertoire.

The bacterial toxin protein A from Staphylococcus aureus (SpA) interacts with B cell antigen receptors encoded by variable region heavy chain (V(H)) clan III genes via a V region framework surface that has been highly conserved during the evolution of the adaptive immune system. We have investigated the consequences of exposure to this prototypic B cell superantigen, and found that treatment of neonates or adults induces a T cell-independent deletion of a large supraclonal set of susceptible B cells that includes clan III/V(H) S107 family-expressing lymphocytes. In studies of different SpA forms, the magnitude of the induced deletion directly correlated with the V(H)-specific binding affinity/avidity. Upon cessation of SpA exposure, the representation of conventional splenic (B-2 subset) lymphocytes normalized; however, we found that the V(H) family-restricted deficit of peritoneal B-1 cells persisted. SpA treatment also induced a persistent loss of splenic S107-mu transcripts, with a loss of certain natural antibodies and specific tolerance to phosphorylcholine immunogens that normally recruit protective antimicrobial responses dominated by the S107-expressing B-1 clone, T15. These studies illustrate how a B cell superantigen can exploit a primordial Achilles heel in the immune system, for which B-1 cells, an important source of natural antibodies and host immune responses, have special susceptibility.

Adult↗
PubMed2000

A hypercycle theory of proliferation of viruses and resistance to the viruses of transgenic plant.

A set of dynamical equations for the proliferation of two typical viruses TMV and PVY has been derived from the reaction equations describing their replication, assembly and translation. These equations can be seen as the generalization of hypercycle theory to the system. The quantitative explanation on the phenomena of proliferation of plant virus and the mechanism of resistance to the disease of transgenic plant is offered. The phenomenon of specific cessation of minus-strand RNA accumulation in the proliferation of TMV, the cross-protection of plant viruses and the mechanism of resistance to viruses of transgenic plant are discussed based on the computer simulation of the proliferation of viruses and the prediction of the secondary structure of the genomic RNA.

Computer Simulation↗