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Biomedical subjects

W Lin

Publications and source records attributed to W Lin.

At least 217 records · Page 12Linked to original sources
PubMed1995

Neurofilaments help maintain normal morphologies and support elongation of neurites in Xenopus laevis cultured embryonic spinal cord neurons.

Neurofilament number and subunit composition, which are highly regulated during development, have been proposed to help regulate axonal diameter and stability. From experiments on dissociated cell cultures of Xenopus laevis embryonic spinal cord, we have obtained direct evidence that neurofilaments help maintain the structural integrity of newly developing axons. An anti-neurofilament monoclonal antibody specific for Xenopus NF-M and the cell lineage tracer, lysinated FITC-dextran, were coinjected into a single blastomere of 2-cell stage embryos. Within neurons descended from the injected blastomere, this antibody specifically confined neurofilaments to the cell body for the first two days of culture, as assayed by immunocytochemical staining with antiserum against the low molecular weight neurofilament protein XNIF. Although whole IgGs and Fab fragments both affected neurofilament distribution, the whole IgGs were more effective. For the first 9 hr of culture, neurites containing anti-NF-M developed normally. By 21 hr, they were shorter than those of sibling control neurons within the same dish, and many became morphologically abnormal. Defects included large variations in diameter, poorly defined separations between the growth cone and neurite, and more collateral branching. Despite these abnormal features, neurons containing anti-NF-M had normal distributions of alpha-tubulin immunoreactivity and phalloidin-stained F-actin. These latter observations argued that defects resulted from the absence of neurofilaments rather than from interference of the movement of other structural materials essential for axonal growth. These results support the hypothesis that neurons use neurofilaments to help maintain the characteristic shapes of axons against the increasing structural demands placed upon the elongating process.

Animals↗
PubMed1995

[An analysis of complications after implantation of saline-filled silicone prosthesis for augmentation mammaplasty in 294 cases].

Complications after implantation of saline-filled silicone prosthesis for augmentation mammaplasty were analyzed in 294 patients after being followed for 3-5 years. The complications included hematoma, infection, capsular contraction, rupture of the implant, exposure of the implant, psychataxia and poor contour etc. Conditions in which these complications occurred, causes, clinical malifestations, prevention and treatment are discussed.

Breast Diseases↗
PubMed1994

Novel bacterial P-type ATPases with histidine-rich heavy-metal-associated sequences.

Menkes disease and Wilson disease are human disorders of copper metabolism. It has recently been shown that both are due to mutations in P-type ATPase copper transport molecules. Related heavy metal transporting ATPases have been described in several strains of bacteria. In an effort to isolate other mammalian metal transporters, we screened a human small intestine library with probes homologous to conserved sequences in the known proteins. Two novel cDNAs were isolated, which encode new members of this family. Surprisingly, they were both of bacterial origin, most likely derived from E. coli sequences transduced during library construction.

Adenosine Triphosphatases↗
PubMed1994

Use of human leukocyte-specific monoclonal antibodies for clinically immunophenotyping lymphocytes of rhesus monkeys.

The rhesus monkey (Macaca mulatta) is an important experimental animal frequently utilized for studies of infectious diseases, immunity, hematopoiesis, and transplantation. Since the structure of cell surface molecules is phylogenetically conserved, monoclonal antibodies raised against human leukocyte antigens can sometimes recognize the homologous determinant on monkey leukocytes. To facilitate better utilization of this animal model, we tested 89 commercially available monoclonal antibodies which define 27 human cell surface antigens for reactivity with rhesus monkey PBL. Certain antigens which delineate clinical useful lymphocyte subsets such as CD2, CD4, CD8, CD14, CD16, CD20, and MHC class II are apparently well conserved since most human cell-specific antibodies identified the homologous cell subset in monkeys. However, other antigens such as CD3, CD19, CD45, and CD56 were identified infrequently by human cell-specific antibodies. FITC-modification of antibodies which had no effect on their binding to human cells occasionally inhibited antibody binding to monkey cells. Nevertheless, an adequate number of cross-reactive monoclonal antibodies was identified to allow gating of lymphocytes for accurate flow cytometric analysis and quantitation of the major lymphocyte subsets of the rhesus monkey. The T lymphocyte subset distribution in blood and lymphoid tissue of rhesus monkeys was similar to man. However, the B subset was significantly larger in monkeys. The daily variation in absolute PBL subset size was marked and found to be due mainly to daily fluctuations in total lymphocyte number.

Animals↗
PubMed1994

Role of histidine 373 in the catalytic activity of coagulation factor XIII.

Factor XIII catalysis proceeds via formation of thioester acyl enzyme intermediate involving an active site cysteine residue at position 314. The contribution of other residues to catalysis has not been established. Earlier studies of the pH dependence of factor XIII activity suggested the existence of a putative active site histidine. We used chemical modification and oligonucleotide directed site-specific mutagenesis to investigate the role of histidines. Photo-oxidation with methylene blue resulted in a complete loss of catalytic activity under conditions that oxidized histidine but did not affect the essential cysteine. Single substitution of each of the 14 histidine residues in the a-subunit of factor XIII by asparagine or alanine led to mutants with catalytic activities generally not significantly different from the wild-type recombinant enzyme. The only exceptions were the H373N and H373A mutants that were poorly expressed, had no detectable rate of [14C]putrescine incorporation into dimethylcasein, and failed to cross-link fibrin gamma-chains. Thus, the a-subunit His-373 may function in the active site of factor XIII, by analogy with papain's mechanism, as a histidinium cation that increases the nucleophilicity of the essential Cys-314. Decreased expression levels of His-373 mutants also indicate that this residue may be critical for enzyme stability.

Binding Sites↗
PubMed1994

Structure-function relationships in the 47-kDa antenna protein and its complex with the photosystem II reaction center core: insights from picosecond fluorescence decay kinetics and resonance Raman spectroscopy.

We report the fluorescence decay kinetics and the vibrational properties of chlorophyll a bound to the 47-kDa antenna protein (CP47) of spinach photosystem II. The chlorophyll fluorescence of CP47 samples decays with four lifetimes (tau = 75.8 ps, 1.05 ns, 3.22 ns, and 5.41 ns). The 75.8-ps and 3.22-ns components are associated with chlorophyll a bound to relatively intact centers, the 1.05-ns component corresponds to chlorophyll bound to centers that are slightly perturbed, and the the 5.41-ns phase probably originates from centers that are severely denatured. The resonance Raman spectrum of CP47 at 441.6 nm (this work) and at 406.7 nm [de Paula, J. C., Ghanotakis, D. F., Bowlby, N. R., Dekker, J. P., Yocum, C. F., & Babcock, G. T. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.), Vol. I, pp 643-646, Kluwer Academic Publishers, Dordrecht, The Netherlands] shows heterogeneity in the C = O stretching region. This part of the spectrum monitors the environment of the keto group at position 9 of the chlorophyll a molecule. We show that several structurally distinct pools of chlorophyll a are bound to CP47. Four of these may be distinguished by their C9 = O stretching frequencies (nu C = O = 1670, 1688, 1693, and 1701 cm-1). By analyzing the resonance enhancement pattern of these modes, we ascribe the 1693-cm-1 vibration to denatured centers. Of the remaining populations, we propose that the 1670-cm-1 vibration is consistent with a hydrogen bond between the C9 = O group of chlorophyll a and the protein. We elaborate on the role of this chromophore-protein interaction in the mechanism of energy transfer within the 47-kDa antenna protein.

Chlorophyll↗
PubMed1994

Cloning and developmental expression of the chick type II and type III TGF beta receptors.

To address the role of peptide growth factors in chick organogenesis, we have focused on TGF beta 2 and have cloned the chick Type II and Type III TGF beta receptors. The chick Type II receptor is a serine/threonine kinase with a ligand binding profile identical to the human receptor and a divergent N-terminus when compared to the mammalian receptors. The chick Type III receptor is a beta-glycan that demonstrates a binding profile identical to the rat receptor and contains a single transmembrane spanning domain and short cytoplasmic tail that are highly conserved when compared to the mammalian receptors. Both the Type II and Type III TGF beta receptors are coexpressed during chick embryogenesis in the developing heart, lung, and eye, and are developmentally upregulated in parallel in the heart and lung. Levels of both receptor proteins and mRNAs also increase in cardiocytes cultured from different developmental stages, in agreement with the increase in Type II and Type III receptor mRNA levels observed in the developing heart. Although exhibiting different temporal or spatial profiles from the receptors, TGF beta 2 is also expressed in the developing heart, lung, and eye. These findings are consistent with recent data indicating that co-expression of both the Type II and Type III TGF beta receptors is required for high affinity binding of TGF beta 2 by the Type II receptor and suggest that TGF beta 2 and the Type II and Type III TGF beta receptors participate in heart, lung, and eye development.

Amino Acid Sequence↗
PubMed1994

Three-dimensional time-of-flight MR angiography with variable TE (VARIETE) for fat signal reduction.

Uniform fat saturation over a large region of interest remains a problem in time-of-flight (TOF) magnetic resonance angiography applications. We demonstrate that a variable echo time with an opposed phase value at low spatial slice select frequencies can effectively reduce most of the fat signal in an otherwise standard three-dimensional TOF acquisition. We evaluated this method at 1.5 T using a short TE = 5.3 ms and a long TE = 6.75 ms for different values of the slice encoding gradient (i.e., different kz values). Shorter echo time (TE = 5.3 msec) was used at higher spatial slice select frequencies, but all echoes have the same gradient structures. By keeping the number of slice encoding steps with longer echoes to a minimum, field inhomogeneity effects on flow compensation remained small. A magnetization transfer saturation pulse was used to suppress signal of brain parenchyma. Overall, highly uniform and selective fat signal reduction was obtained while maintaining superior flow compensation in all volunteer studies.

Adipose Tissue↗
PubMed1994

Maturation of neurites in mixed cultures of spinal cord neurons and muscle cells from Xenopus laevis embryos followed with antibodies to neurofilament proteins.

Dissociated cell cultures of Xenopus laevis embryonic spinal cord have proved useful for studying the differentiation of neuronal ionic channels and membrane properties and for examining the dynamics of microtubules in developing neurons. To examine their usefulness for studying neurofilaments in developing neurites, we prepared similar cultures from stage 22 embryos. Between 3 and 55 h after plating, these cultures were fixed and immunostained with antibodies directed against various epitopes of neurofilament proteins from X. laevis. These antibodies were specific for nonphosphorylated epitopes of the two low molecular weight Xenopus neurofilament proteins (Xenopus NF-L and the Xenopus neuronal intermediate filament protein, XNIF), both phosphorylated and nonphosphorylated epitopes of the Xenopus middle molecular weight neurofilament protein (NF-M), and a nonphosphorylated epitope of the Xenopus high molecular weight neurofilament protein (NF-H). The emergence of these neurofilament proteins in culture was compared to the time course previously reported for them in Xenopus spinal cord neurons in situ. To facilitate the comparison of times in culture to developmental stages, the age of cultured neurons was converted to an equivalent Nieuwkoop and Faber normal stage using data presented here on the effect of changing temperature on developmental rates of X. laevis. With the exception of the nonphosphorylated epitope of NF-H, which is indicative of the most mature axons found in situ, the emergence of the other neurofilament protein antibody epitopes closely paralleled that previously reported for these antibodies in situ. Thus, with respect to XNIF, NF-M, and NF-L, the neurites of cultured neurons were typical of young, embryonic Xenopus laevis spinal cord axons. This system should prove useful for studying both the function of these neurofilament proteins during the early stages of axonal development and the dynamics of their transport.

Animals↗
PubMed1994

Preparation of sterically stabilized human serum albumin nanospheres using a novel Dextranox-MPEG crosslinking agent.

Human serum albumin (HSA) nanospheres with a size less than 200 nm in diameter were prepared using a modified coacervation method and crosslinking with methyl polyethylene glycol modified oxidized Dextram (Dextranox-MPEG) which created a sterically stabilizing polyethylene oxide surface layer surrounding the nanospheres. The crosslinking efficiency and the surface characteristics of glutaraldehyde and Dextranox-MPEG crosslinked HSA nanospheres were determined and compared. The zeta potential of the Dextranox-MPEG crosslinked particles was significantly lower than that of glutaraldehyde stabilized particles. The existence of a hydrated steric barrier surrounding the nanospheres was confirmed by an electrolyte and pH induced flocculation test. The Dextranox-MPEG crosslinked nanospheres showed a significantly reduced plasma protein adsorption on the particle surface compared with glutaraldehyde crosslinked nanospheres.

Chemistry, Pharmaceutical↗
PubMed1994

Automated enumeration of CD34+ cells in peripheral blood and bone marrow.

We have developed a rapid and accurate method to enumerate the number of CD34+ cells in peripheral blood, bone marrow, and leukopheresis samples. The method consists of a two-tube assay and a dedicated software program for data acquisition and analysis. The first reagent combination consists of (a) a nucleic acid dye to identify nucleated cells, (b) a CD45 monoclonal antibody labeled with PE/CY5 to discriminate progenitor cells from mature lymphoid, neutrophil, erythroid, and monocytic cells, (c) an IgG1 control antibody labeled with PE to establish the boundary between specific and nonspecific staining, and (d) a known number of fluorescent beads to determine an absolute count of cells. In the second reagent combination the IgG1 control antibody is replaced by a CD34 antibody labeled with PE that is used to identify the CD34+ cells in the location established by the control reagent combination. The software program uses the fluorescent beads to adjust the forward light scatter, orthogonal light scatter, and three fluorescence detectors of the flow cytometer. The expected location of the CD34+ cells is then established with the control reagent combination followed by the enumeration of the CD34+ cells per microliter of sample with the reagent combination containing the CD34 antibody. This method is sensitive enough to detect CD34+ cells in peripheral blood of normal donors and can reliably determine an increase in CD34+ cells in the peripheral blood of patients treated with chemotherapy and/or growth factors. The method alleviates some of the difficulties encountered when small numbers of CD34+ cells are enumerated. The system allows for more precise evaluations of the grafts used for bone marrow transplantation.

Antigens, CD↗
PubMed1994

Immunopathogenic events in acute infection of rhesus monkeys with simian immunodeficiency virus of macaques.

Infection of the rhesus monkey with simian immunodeficiency virus of macaques (SIVmax) was employed to explore the early immune events associated with the initial containment of an acute AIDS virus infection. In nine rhesus monkeys infected intravenously with uncloned SIVmac strain 251, high-level p27 plasma antigenemia was usually detected transiently from approximately day 7 through day 21 following virus inoculation. SIVmac replication in lymph nodes measured by in situ RNA hybridization closely paralleled the time course and magnitude of viremia. The containment of SIVmac spread by 3 to 4 weeks following infection suggests an efficient, early immune control of this virus infection. Anti-SIVmac antibodies were first detected in the blood at approximately day 14. At the time antigenemia was decreased or cleared, SIVmac neutralizing antibodies were present. A rise in circulating and lymph node CD8+ T cells also occurred coincident with the clearance of antigenemia and persisted thereafter. These CD8+ lymphocytes in lymph nodes had increased expression of both major histocompatibility complex class II and the adhesion molecule LFA-1; they also demonstrated decreased expression of the naive T-cell-associated CD45RA molecule. SIVmac-specific cytotoxic T-lymphocyte precursors were detected in both blood and lymph node by 7 days post-virus inoculation. These studies indicate that both virus-specific humoral and cellular immune mechanisms in blood and lymph node are associated with the clearance of viremia that occurs within the first month of infection of rhesus monkeys with SIVmac.

Animals↗
PubMed1994

Optimizing three-dimensional time-of-flight MR angiography with variable repetition time.

PURPOSE: To implement and evaluate a variable repetition time (TR) modification of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography. MATERIALS AND METHODS: Variable- and constant-TR 3D TOF MR angiography of the intracranial vasculature was performed in 20 healthy volunteers and 10 patients with known or suspected cerebrovascular disease. Total acquisition time was short and held constant for all studies. Frequency-selective fat saturation (FS) and magnetization transfer saturation (MTS) pulses were applied. The associated maximum-intensity projection (MIP) images were evaluated quantitatively for contrast-to-noise (C/N) and qualitatively for depiction of vessels that exhibit slow flow. RESULTS: Variable-TR MIP images exhibited improved C/N and depiction of small peripheral vessels and venous structures when compared with constant-TR MIP images. These observations were consistent for all studies. CONCLUSIONS: The variable-TR modification improved the depiction of intracranial vessels that exhibit slow flow.

Adult↗
PubMed1994

Effect of intratracheal dexamethasone on oleic acid-induced lung injury in the rat.

The therapeutic efficacy of single-dose intratracheal dexamethasone (2.5 mg/kg) in oleic acid-induced acute lung injury in the rat was established by showing significant improvement in bronchoalveolar lavage parameters and lung compliance at 24 h after oleic acid as compared with animals not treated with oleic acid. An equivalent dose of intraperitoneal dexamethasone demonstrated no therapeutic benefit at 24 h after oleic acid. The therapeutic effect of this single-dose intratracheal dexamethasone regimen was accompanied by recovery to normal bronchoalveolar parameters and lung compliance at 7 days, in contrast to previous observations made with high-dose sustained intraperitoneal dexamethasone (4 mg/kg for 7 days). This improved benefit:toxicity ratio of intratracheal dexamethasone compared with systemic dexamethasone may be due to enhanced topical anti-inflammatory potency relative to systemic potency and toxicity.

Animals↗
PubMed1994

Combinatorial expression of three zebrafish genes related to distal-less: part of a homeobox gene code for the head.

We describe analysis of zebrafish distal-less-related homeobox genes that may serve as specifiers of positional information in anterior regions of the CNS and in peripheral structures. We isolated three zebrafish genes, dlx2, dlx3, and dlx4, by screening embryonic cDNA libraries. Comparisons of the predicted sequences of the Dlx2, Dlx3, and Dlx4 proteins with distal-less proteins from other species suggest that vertebrate distal-less genes can be divided into four orthologous groups. We observed similarities but also unique features of the expression patterns of the zebrafish dlx genes. Among the three genes, dlx3 alone is expressed during gastrulation. Shortly after gastrulation, cells in the ventral forebrain rudiment express dlx2 and dlx4, but not dlx3, and hindbrain neural crest cells express only dlx2. Presumptive precursor cells of the olfactory placodes express dlx3 and dlx4 but not dlx2. Transcripts of dlx3 and dlx4 are present in overlapping subsets of cells in the auditory vesicle and in cells of the median fin fold, whereas dlx2 is never expressed in the auditory vesicle and only at low levels in localized regions of the median fin fold. Cells of the visceral arches and their primordia express all three dlx genes, but with different developmental time courses. We suggest that combinatorial expression of the dlx genes is part of a homeobox gene code specifying pattern formation or cell fate determination in the forebrain, in peripheral structures of the head, and in the fins.

Amino Acid Sequence↗
PubMed1994

Short versus long echo time for cranial MR angiography in children and adults.

PURPOSE: To evaluate the ability of short-echo-time (TE) versus long-TE three-dimensional time-of-flight MR angiography sequences to decrease phase-related signal loss and refocus signal from blood in intracranial MR angiography of adults and children. METHODS: We evaluated 3-D time-of-flight cranial MR angiography in 33 cases (18 children and 15 adults) using two sequences. The longer-echo reference sequence had a TE of 8.0 milliseconds and a field echo of 6.5 milliseconds; the shorter-echo sequence had a TE of 5.1 and a field echo of 4.2 milliseconds. Repetition time, flip angle, and matrix were constant. The bandwidth for the longer-echo sequence was 130 Hz, 195 Hz for the shorter-echo sequence. RESULTS: The greatest improvement in diagnostic images was for children; significant and mildly improved signal recovery was demonstrated in 15 and 2 cases, respectively, of a total of 18 studies. This allowed improved diagnostic assessment. However, in the adult group significantly and mildly improved signal recovery were present in only 2 and 6 cases, respectively, of a total of 15 studies. In the group of children and adults combined, decreased lumen definition and peripheral vessel visibility were present in 24 and 30 of 33 cases, respectively, because of higher signal from background tissue when the shorter-TE field-echo sequence was used and, hence, reduced vascular contrast. CONCLUSION: The use of a short-field-echo/TE sequence is therefore recommended as the initial study in children but as a secondary examination in areas of abnormality in adults. This study illustrates the improved signal recovery from phase-related sources and improved visibility of intracranial stenosis in children with the use of a short-echo sequence. In adults, the short-echo sequence should not be used for the initial screening but reserved for secondary evaluation.

Adolescent↗