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Biomedical subjects

L Xu

Publications and source records attributed to L Xu.

At least 253 records · Page 14Linked to original sources
PubMed2000

Pluripotent, cytokine-dependent, hematopoietic stem cells are immortalized by constitutive Notch1 signaling.

Hematopoietic stem cells give rise to progeny that either self-renew in an undifferentiated state or lose self-renewal capabilities and commit to lymphoid or myeloid lineages. Here we evaluated whether hematopoietic stem cell self-renewal is affected by the Notch pathway. Notch signaling controls cell fate choices in both invertebrates and vertebrates by inhibiting certain differentiation pathways, thereby permitting cells to either differentiate along an alternative pathway or to self-renew. Notch receptors are present in hematopoietic precursors and Notch signaling enhances the in vitro generation of human and mouse hematopoietic precursors, determines T- or B-cell lineage specification from a common lymphoid precursor and promotes expansion of CD8(+) cells. Here, we demonstrate that constitutive Notch1 signaling in hematopoietic cells established immortalized, cytokine-dependent cell lines that generated progeny with either lymphoid or myeloid characteristics both in vitro and in vivo. These data support a role for Notch signaling in regulating hematopoietic stem cell self-renewal. Furthermore, the establishment of clonal, pluripotent cell lines provides the opportunity to assess mechanisms regulating stem cell commitment and demonstrates a general method for immortalizing stem cell populations for further analysis.

Animals↗
PubMed2000

Beta globin gene inhibition by antisense RNA transcripts.

Sickle cell disease is caused by a mutation in the beta globin gene leading to hemoglobin S (Hb S) production. Several approaches have been explored to prevent Hb S polymerization in red blood cells and the symptoms associated with this disorder. To this end we tested a mammalian expression vector carrying a human beta globin antisense cDNA (pZeobetaAS) fragment in a mouse erythroleukemia cell line expressing the human gamma and beta globin genes. We observed a relative reduction in beta globin mRNA levels compared with gamma mRNA levels in the presence of pZeobetaAS. Moreover, analysis at the protein level showed an average 76% decrease in beta chains and a 517% increase in gamma chain biosynthesis. The inhibitory effect of the antisense vector on globin expression was maintained long term in culture. The expression vector pZeobetaAS was also transfected into primary erythroid progenitors to test its effects on globin genes undergoing normal developmental switching during differentiation. We observed a relative reduction of beta globin mRNA levels compared with gamma mRNA levels. These results support a novel role for antisense cDNA expression vectors as an alternative gene therapy strategy to inhibit betas gene expression in sickle cell disease. Gene Therapy (2000) 7, 438-444.

Anemia, Sickle Cell↗
PubMed2000

Thenar insertion of abductor pollicis longus accessory tendons and thumb carpometacarpal osteoarthritis.

Although the etiology of osteoarthritis of the thumb carpometacarpal (CMC) joint remains unclear, some theories have focused on variations in the local anatomy of the abductor pollicis longus tendon insertion. This cadaver study of 68 specimens analyzed the relationship between a thenar insertion of an accessory abductor pollicis longus tendon and the presence and severity of thumb CMC osteoarthritis. The joint cartilage surfaces were visually graded for degenerative changes. Thirty-five of 68 specimens (51%) had a thenar insertion, most frequently inserting on either the abductor pollicis brevis or opponens pollicis fascia or muscle belly. No significant association between a thenar insertion and thumb CMC arthritis was observed. Conversely, increasing age was noted to have a significant association with degenerative joint disease. Thus, these findings indicate that a thenar slip of the abductor pollicis longus tendon does not correlate with the presence or severity of CMC osteoarthritis.

Adolescent↗
PubMed2000

Molecular cloning and expression patterns of mouse cartilage oligomeric matrix protein gene.

OBJECTIVE: To develop transgenic mice harboring mutations in the COMP gene as animal models for pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), autosomal dominant disorders characterized by early onset osteoarthritis and epiphyseal abnormalities. As a first step in generating a mouse model for COMP mutations, we have cloned the cDNA of mouse COMP and examined its tissue expression pattern. DESIGN: Total mRNA was isolated from the skeletal tissues of newborn C57BL/6j mice and used as a template for oligo(dT) first-strand cDNA synthesis. The cDNA was used for PCR amplification of COMP using three oligonucleotide primer pairs designed from the published rat COMP cDNA sequence. Nested PCR was used to complete the sequence between the amplified fragments. The entire cDNA was sequenced and the expression pattern of the corresponding transcripts examined by Northern hybridizations. RESULTS: A full-length COMP cDNA was isolated. Analysis showed that the entire translated region of the mouse COMP gene is 2268 bp and the derived amino acid sequence shows 90% homology to human COMP. Of eight adult mouse non-cartilage tissues tested, COMP expression was detected only in testis.

Achondroplasia↗
PubMed2000

Cortical mechanisms for auditory spatial illusions.

Frequency transformation by the external ears provides the spectral cues for localization of broadband sounds in the vertical plane. When human subjects listen to spectrally-impoverished narrowband sounds presented in a free field, the perceived locations vary with the centre frequency and are largely independent of the actual source locations. The present study explored the substrate of spatial illusion by examining the responses of cortical neurons to narrowband stimuli. Single-unit responses were recorded in area A2 of anaesthetized cats. Broadband noise bursts were presented at 14 locations in the vertical median plane, from 60 degrees below the front horizon, up and over the head, to 20 degrees below the rear horizon. Narrowband (1/6-oct) noise bursts were presented at + 80 degrees elevation. An artificial neural network was trained to recognize the spike patterns elicited by broadband noise and, thereby, to register the spike patterns with sound-source elevation. When the trained network was presented with neural responses elicited by narrowband noise, the elevation estimated by the neural network varied with the centre frequency of the narrowband stimuli. Consistent with psychophysical results in human, the locations associated with a given centre frequency could be predicted by comparing the stimulus spectrum with the directional transfer functions of the cat's external ear. The results support the hypothesis that full spike patterns (including spike counts and spike timing) of cortical neurons code information about sound location and that the auditory cortical neurons play a pivotal role in localization behaviour.

Acoustic Stimulation↗
PubMed2000

Regulation of the rat BB1 RNA during normal rat lung development.

BB1 was recently cloned from the WI-38 human fetal lung cell line. Human BB1 (hBB1) is expressed by multiple tissues, including lung. Because inhibition of BB1 translation using antisense oligodeoxynucleotides resulted in prevention of G1 traversal in cultured cells, we hypothesized that BB1 gene expression would be regulated during lung development with greater expression during periods of active lung growth. To gain insight into the expression of BB1 during lung development, a rat BB1 (rBB1) homologue was cloned and used in Northern hybridization analyses and in situ hybridization histochemistry (ISHH). Northern hybridization analyses of fetal and postnatal rat lung demonstrate that rBB1 RNA abundance is relatively low on fetal days E17 through E19, with a small peak of expression occurring on fetal day E20, then increases at birth with peak expression in adult lung. ISHH correlates with the Northern hybridization data and reveals rBB1 RNA expression throughout lung from E17 to E21 in both epithelium and mesenchyme. In postnatal lung, more intense expression of BB1 was observed than in fetal lung, localizing BB1 transcripts to proximal and distal airways and mesenchymal cells surrounding airways. Proliferating cell nuclear antigen (PCNA) was identified in lung sections adjacent to those used for ISHH and it was found that BB1 expression was present in PCNA-positive cells; however, BB1 expression was not limited to PCNA-positive cells in either the fetal or postnatal periods. This was most apparent in adult (60-day) rat lung where essentially no PCNA-positive cells were detected, but intense BB1 expression was detected in airway epithelium and surrounding mesenchyme. These studies demonstrate developmental regulation of BB1 during lung development. The findings are consistent with BB1 action in cell growth-related processes of fetal and early postnatal lung; however, the distribution of BB1 expression in relation to PCNA localization suggests that BB1 participates in cellular functions in addition to cell proliferation.

Amino Acid Sequence↗
PubMed2000

A peptide vaccine that prevents experimental autoimmune myasthenia gravis by specifically blocking T cell help.

Myasthenia gravis (MG) and its animal model, experimental autoimmune (EA) MG, are caused by T cell-dependent autoantibodies that react with the nicotinic acetylcholine receptor (AChR) on muscle and interfere with neuromuscular transmission. Thus, selective inactivation of CD4(+) AChR-specific T helper cells should lower AChR Ab levels and ameliorate disease. In the Lewis rat model of EAMG, alpha chain residues 100-116 of the AChR represent the dominant T cell epitope, which is important in helping Ab responses to this autoantigen. In the present report, we have applied a new design technique that requires no knowledge of Ag receptor sequences on errant T cells in order to develop a synthetic peptide vaccine against T cells reactive with the aforementioned T cell epitope. Immunization with the peptide 1) induced polyclonal and monoclonal Ab, which inhibited AChR 100-116 stimulation of AChR-sensitized lymphocytes and recognized Vbeta15 containing T cell receptors on AChR 100-116-specific T cell lines and clones; 2) lowered AChR Ab levels; 3) reduced the loss of muscle AChR; and 4) lessened the incidence and severity of EAMG. These findings suggest a new strategy for the functional abrogation of epitope-specific T cells that could have potential application to human autoimmune diseases.

Amino Acid Sequence↗
PubMed2000

Reproducibility of gastric myoelectrical activity and the water load test in patients with dysmotility-like dyspepsia symptoms and in control subjects.

Gastric dysrhythmias and normal gastric myoelectrical activity have been recorded in patients with functional dyspepsia. The aim of this study was to determine the reproducibility of gastric myoelectrical patterns and responses to a water load in patients with dysmotility-like functional dyspepsia and healthy control subjects. We studied 24 patients with dysmotility-like functional dyspepsia and 24 age-matched control subjects. Gastric myoelectrical activity was assessed using cutaneous electrodes to record electrogastrograms (EGGs) before and after the subjects ingested water until full. The EGGs with water load tests were repeated 1 week apart. The patients ingested significantly smaller volumes of water at both week 1 and 2 (358 +/- 26 mL and 349 +/- 30 mL) compared to control subjects (557 +/- 35 mL and 560 +/- 27 mL, p < 0.01). Gastric dysrhythmias were found in 4 of 24 (16.7%) control subjects at each visit and in 14 (58%) and 12 (50%) of the dyspeptic patients at week 1 and 2, respectively. Of 14 patients, 2 (14.3%) had gastric dysrhythmias at week 1 but had normal gastric rhythms at week 2. Thus, reproducibility was 100% in the control subjects and 91.7% in the patients. In conclusion, some variability in EGG pattern occurred, but gastric myoelectrical activity and responses to the water load test were generally consistent and reproducible in patients with dysmotility-like functional dyspepsia and in healthy control subjects.

Adolescent↗
PubMed2000

Glaucoma screening using the scanning laser polarimeter.

PURPOSE: To determine the ability of scanning laser polarimetry (GDx Nerve Fiber Analyzer; Laser Diagnostic Technologies, Inc., San Diego, CA) to separate normal eyes and those considered likely to have glaucoma in a public glaucoma screening. METHODS: A 2-day public glaucoma screening program was held at two different institutions. Each subject underwent ophthalmologic examination, Humphrey perimetry (24-2 Fastpac program), and imaging using scanning laser polarimetry (GDx) in each eye for allocation into a diagnostic category: normal, ocular hypertensive, glaucoma suspect, or glaucoma. Results from the normal and glaucoma groups were analyzed, using modulation parameters calculated from a measurement band located 1.8 disc diameters from the disc, and selected parameters provided automatically by GDx software. Receiver operating characteristic curves were used to depict the sensitivity/specificity relationship at different GDx parameter cutoff levels. RESULTS: Of 200 subjects, 197 were classified; 122 were classified as normal, 23 were classified with ocular hypertension, 30 were classified as glaucoma suspects, and 22 were classified with definite glaucoma. Three subjects had ocular diseases other than glaucoma. The maximum area under the receiver operating characteristic curve for modulation parameters was 0.935, and for the GDx software parameters was 0.901. CONCLUSIONS: Scanning laser polarimetry may be useful in glaucoma screening.

Diagnostic Techniques, Ophthalmological↗
PubMed2000

Nonequilibrium molecular dynamics simulations of transport and separation of gas mixtures in nanoporous materials

The nonequilibrium molecular dynamics simulations of transport and separation of a binary gas mixture through a porous membrane with interconnected pores of distributed sizes are reported. The membrane is modeled by a three-dimensional disordered molecular network of interconnected pores consisting of tens of thousands of atoms, based on a Voronoi tessellation of space. Results are presented for transport and adsorption of the gases, including the existence of an optimal pore structure for maximum separation of the gases.

Journal Article↗
PubMed2000

Individual differences in external-ear transfer functions of cats.

Knowledge of the direction-dependent filter characteristics of the external ears is useful for the study of spatial hearing in experimental animals. The present study examined individual differences in the directional components of external-ear transfer functions (directional transfer functions, DTFs) among 24 anesthetized cats. Ears were fixed in a frontal position. Inter-cat differences in DTFs were quantified across a mid-frequency range from 8 to 16 kHz and across 30 locations in the horizontal plane and vertical midline. Across cats, DTFs showed similar direction dependence, but tended to differ in regard to the center frequencies of spectral features, such as spectral peaks and notches. Certain mid-frequency notches, for instance, varied in frequency across cats by nearly a factor of 2. Scaling of DTFs in frequency could reduce the overall differences between pairs of cats. Scale factors that minimized inter-cat differences ranged as high as 1.57 and correlated moderately with cats' body weights. Nevertheless, appreciable individual differences remained after frequency scaling. Inter-cat differences in DTFs were substantially larger than differences that resulted from variability in positioning the ears. The results suggest some guidelines regarding the conditions under which it is acceptable to apply DTF measurements from one cat to another.

Acoustics↗
PubMed2000

Phospholipase D and RalA cooperate with the epidermal growth factor receptor to transform 3Y1 rat fibroblasts.

3Y1 rat fibroblasts overexpressing the epidermal growth factor (EGF) receptor (EGFR cells) become transformed when treated with EGF. A common response to oncogenic and mitogenic stimuli is elevated phospholipase D (PLD) activity. RalA, a small GTPase that functions as a downstream effector molecule of Ras, exists in a complex with PLD1. In the EGFR cells, EGF induced a Ras-dependent activation of RalA. The activation of PLD by EGF in these cells was dependent upon both Ras and RalA. In contrast, EGF-induced activation of Erk1, Erk2, and Jun kinase was dependent on Ras but independent of RalA, indicating divergent pathways activated by EGF and mediated by Ras. The transformed phenotype induced by EGF in the EGFR cells was dependent upon both Ras and RalA. Importantly, overexpression of wild-type RalA or an activated RalA mutant increased PLD activity in the absence of EGF and transformed the EGFR cells. Although overexpression of PLD1 is generally toxic to cells, the EGFR cells not only tolerated PLD1 overexpression but also became transformed in the absence of EGF. These data demonstrate that either RalA or PLD1 can cooperate with EGF receptor to transform cells.

Animals↗
PubMed2000

Essential roles for ankyrin repeat and transactivation domains in induction of T-cell leukemia by notch1.

Notch receptors participate in a conserved signaling pathway that controls the development of diverse tissues and cell types, including lymphoid cells. Signaling is normally initiated through one or more ligand-mediated proteolytic cleavages that permit nuclear translocation of the intracellular portion of the Notch receptor (ICN), which then binds and activates transcription factors of the Su(H)/CBF1 family. Several mammalian Notch receptors are oncogenic when constitutively active, including Notch1, a gene initially identified based on its involvement in a (7;9) chromosomal translocation found in sporadic T-cell lymphoblastic leukemias and lymphomas (T-ALL). To investigate which portions of ICN1 contribute to transformation, we performed a structure-transformation analysis using a robust murine bone marrow reconstitution assay. Both the ankyrin repeat and C-terminal transactivation domains were required for T-cell leukemogenesis, whereas the N-terminal RAM domain and a C-terminal domain that includes a PEST sequence were nonessential. Induction of T-ALL correlated with the transactivation activity of each Notch1 polypeptide when fused to the DNA-binding domain of GAL4, with the exception of polypeptides deleted of the ankyrin repeats, which lacked transforming activity while retaining strong transactivation activity. Transforming polypeptides also demonstrated moderate to strong activation of the Su(H)/CBF1-sensitive HES-1 promoter, while polypeptides with weak or absent activity on this promoter failed to cause leukemia. These experiments define a minimal transforming region for Notch1 in T-cell progenitors and suggest that leukemogenic signaling involves recruitment of transcriptional coactivators to ICN1 nuclear complexes.

Animals↗
PubMed2000

Rival Penalized Competitive Learning based approach for discrete-valued source separation.

This paper presents an approach based on Rival Penalized Competitive Learning (RPCL) rules for discrete-valued source separation. In this approach, we first build a connection between the source number and the cluster number of observations. Then, we use the RPCL rule to automatically find out the correct number of clusters such that the source number is determined. Moreover, we tune the de-mixing matrix based on the cluster centers instead of the observation themselves, whereby the noise interference is considerably reduced. The experiments have shown that this new approach not only quickly and automatically determines the number of sources, but also is insensitive to the noise in performing blind source separation.

Algorithms↗
PubMed2000

Colocalization of dihydropyridine and ryanodine receptors in neonate rabbit heart using confocal microscopy.

Because of undeveloped T tubules and sparse sarcoplasmic reticulum, Ca(2+)-induced Ca(2+) release (CICR) may not be the major mechanism providing contractile Ca(2+) in the neonatal heart. Spatial association of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs), a key factor for CICR, was examined in isolated neonatal rabbit ventricular myocytes aged 3-20 days by double-labeling immunofluorescence and confocal microscopy. We found a significant increase (P < 0.0005) in the degree of colocalization of DHPR and RyR during development. The number of voxels containing DHPR that also contained RyR in the 3-day-old group (62 +/- 1.8%) was significantly lower than in the other age groups (76 +/- 1.3 in 6-day old, 75 +/- 1.2 in 10-day old, and 79 +/- 0.9% in 20-day old). The number of voxels containing RyR that also contained DHPR was significantly higher in the 20-day-old group (17 +/- 0.5%) compared with the other age groups (10 +/- 0.7 in 3-day old, 11 +/- 0.6 in 6-day old, and 11 +/- 0.5% in 10-day old). During this period, the pattern of colocalization changed from mostly peripheral to mostly internal couplings. Our results provide a structural basis for the diminished prominence of CICR in neonatal heart.

Animals↗
PubMed2000

Characterization of RyR1-slow, a ryanodine receptor specific to slow-twitch skeletal muscle.

Two distinct skeletal muscle ryanodine receptors (RyR1s) are expressed in a fiber type-specific manner in fish skeletal muscle (11). In this study, we compare [(3)H]ryanodine binding and single channel activity of RyR1-slow from fish slow-twitch skeletal muscle with RyR1-fast and RyR3 isolated from fast-twitch skeletal muscle. Scatchard plots indicate that RyR1-slow has a lower affinity for [(3)H]ryanodine when compared with RyR1-fast. In single channel recordings, RyR1-slow and RyR1-fast had similar slope conductances. However, the maximum open probability (P(o)) of RyR1-slow was threefold less than the maximum P(o) of RyR1-fast. Single channel studies also revealed the presence of two populations of RyRs in tuna fast-twitch muscle (RyR1-fast and RyR3). RyR3 had the highest P(o) of all the RyR channels and displayed less inhibition at millimolar Ca(2+). The addition of 5 mM Mg-ATP or 2.5 mM beta, gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) to the channels increased the P(o) and [(3)H]ryanodine binding of both RyR1s but also caused a shift in the Ca(2+) dependency curve of RyR1-slow such that Ca(2+)-dependent inactivation was attenuated. [(3)H]ryanodine binding data also showed that Mg(2+)-dependent inhibition of RyR1-slow was reduced in the presence of AMP-PCP. These results indicate differences in the physiological properties of RyRs in fish slow- and fast-twitch skeletal muscle, which may contribute to differences in the way intracellular Ca(2+) is regulated in these muscle types.

Adenine Nucleotides↗