Biomedical subjects

E Ong

Publications and source records attributed to E Ong.

At least 37 records · Page 2Linked to original sources

PubMed1998

Expression cloning of a human sulfotransferase that directs the synthesis of the HNK-1 glycan on the neural cell adhesion molecule and glycolipids.

The HNK-1 carbohydrate is expressed on various adhesion molecules in the nervous system and is suggested to play a role in cell-cell and cell-substratum interactions. Here we describe the isolation and functional expression of a cDNA encoding a human sulfotransferase that synthesizes the HNK-1 carbohydrate epitope. A mutant Chinese hamster ovary cell line, Lec2, which stably expresses human neural cell adhesion molecule (N-CAM) (Lec2-NCAM), was first established. Lec2-NCAM was co-transfected with a human fetal brain cDNA library, a cDNA encoding the rat glucuronyltransferase that forms a precursor of the HNK-1 carbohydrate, and a vector encoding the polyoma large T antigen. The transfected Lec2-NCAM cells expressing the HNK-1 glycan were enriched by fluorescence-activated cell sorting. Sibling selection of recovered plasmids resulted in a cDNA encoding a sulfotransferase, HNK-1ST, that directs the expression of the HNK-1 carbohydrate epitope on the cell surface. The deduced amino acid sequence indicates that the enzyme is a type II membrane protein. Sequence analysis revealed that there is a short amino acid sequence in the presumed catalytic domain, which is highly homologous to the corresponding sequence in other Golgi-associated sulfotransferases so far cloned. The amount of HNK-1ST transcript is high in fetal brain compared with fetal lung, kidney, and liver. Expression of HNK-1ST resulted in the formation of the HNK-1 epitope on N-CAM and a soluble chimeric form of HNK-1ST was shown to add a sulfate group to a precursor, GlcAbeta1-->3Galbeta1-->4GlcNAcbeta1-->R, forming sulfo-->3GlcAbeta1-->3Galbeta1-->4GlcNAcbeta1-->R. The results combined together indicate that the cloned HNK-1ST directs the synthesis of the HNK-1 carbohydrate epitope on both glycoproteins and glycolipids in the nervous tissues.

Amino Acid Sequence↗

PubMed1998

Oxygen distributions within R3230Ac tumors growing in dorsal flap window chambers in rats.

R3230Ac mammary tumors were grown in transparent window chambers implanted into the dorsal skin flap of 250 g Fischer 344 rats (see Dewhirst et al, 1992). The oxygen pressure distributions in the tumor and host tissue were measured by the oxygen dependent quenching of phosphorescence (see Vinogradov et al, 1996) after injection of Oxyphor R2 (7 mg, 0.3 ml) into the tail vein. The oxygen pressure maps show the R3230Ac tumors to be hypoxic relative to the surrounding tissue. The excitation spectrum for the phosphor has peaks at 419 nm (blue light) and at 524 nm (green light), and the emitted phosphorescence spectrum and lifetime are independent of the wavelength at which the phosphor is excited. The absorption by tissue is much greater for blue light than green light, due to intrinsic chromophores such as cytochromes, hemoglobin, myoglobin etc. Thus, blue excitation measures the oxygen pressures in a much thinner, superficial, surface layer (< 50 microns) than does green excitation, allowing "optical sectioning" of tissue oxygenation. The tissue can be further optically sectioned by making measurements from both sides of the window. Viewed from the tumor side, the superficial layers (blue excitation) of these tumors were hypoxic whereas the host tissue was well oxygenated. The oxygen pressures in the growing edge of the tumors are lower than those in the central core of the tumor, and much lower than those of the host tissue. This result is in agreement with the micro-oxygen electrode measurements of perivascular oxygen pressures reported by Dewhirst and coworkers (1992).

Animals↗

PubMed1998

Developmental regulation of polysialic acid synthesis in mouse directed by two polysialyltransferases, PST and STX.

Polysialic acid is a developmentally regulated carbohydrate attached to the neural cell adhesion molecule, N-CAM, and abundant in embryonic tissues. There is increasing evidence that polysialic acid reduces N-CAM adhesion, thereby promoting neurite outgrowth and cellular mobility. It has been shown that two enzymes, polysialyltransferase, PST, and sialyltransferase X, STX, form polysialic acid on N-CAM. However, it is not known how these two enzymes contribute to polysialylation. In order to determine how the expression of PST and STX leads to polysialic acid synthesis during mouse development, the expression of PST and STX transcripts were evaluated by Northern blot analysis, competitive reverse transcription-polymerase chain reaction and in situ hybridization, and those results were correlated to the expression of polysialic acid. The results obtained by these analyses demonstrated that both PST and STX transcripts were barely detected at embryonic day 8 (E8) but increased after E9. PST and STX transcripts were present in substantial quantity between E11 and E15, coinciding with the period when maximum synthesis of polysialic acid is required. Ten days after birth, the level of STX transcript declined substantially, whereas the level of PST transcript only gradually declined and persisted in the adult brain. These results, taken together, strongly suggest that PST and STX coordinately synthesize polysialic acid during development. At the same time, they are expressed differentially in tissue-specific and cell-type-specific manners, suggesting that PST and STX may have distinct roles in development and organogenesis.

Animals↗

PubMed1998

Effect of luminance on visual evoked potential amplitudes in normal and disabled readers.

BACKGROUND: Considerable evidence exists that some reading-disabled children have disordered visual processing, specifically in the fast processing magnocellular (M) pathway. METHODS: The extent that varying luminance and temporal frequency affect amplitude and latency of visual evoked potentials (VEPs) in normally achieving and reading-disabled children grades 4 to 6 was measured. Each group consisted of approximately 30 subjects. Monocular and binocular single channel VEPs were recorded using a sinusoidal checkerboard pattern of spatial frequency 14 min arc at 3 different temporal frequencies (1, 4, and 8 Hz), and an 8 Hz flicker fusion stimulus. Stimuli were presented under high and low luminance conditions. The peak of the major positive wave component (P100) of each waveform and the trough of the previous major negative wave component were identified, and the peak to trough amplitude was measured. RESULTS: Statistical analysis of the VEP amplitudes and latencies in response to different experimental conditions was performed using a repeated measure analysis of variance (MANOVA). VEP amplitudes were significantly higher for normal readers across all conditions. Within all subjects, significant effects were found for monocular vs. binocular viewing, temporal frequencies, and high vs. low luminance. Similar analysis of latencies revealed no significant differences. CONCLUSIONS: The presence of a weaker VEP response in reading-disabled children suggests a deficit early in visual processing. The significant difference in VEP amplitudes between the two reading groups provides an objective measure of a deficit in the M pathway that has been implicated in this condition. Whether serial VEP recordings might help to assess the effects of optometric therapy by providing an independent index of therapeutic efficiency is of special interest.

Analysis of Variance↗

PubMed1998

Polysialic acid, a unique glycan that is developmentally regulated by two polysialyltransferases, PST and STX, in the central nervous system: from biosynthesis to function.

Polysialic acid is a developmentally regulated carbohydrate composed of a linear homopolymer of alpha-2,8-linked sialic acid residues. This unique glycan is mainly attached to the neural cell adhesion molecule (N-CAM) and implicated in many morphogenic events of the neural cells by modulating the adhesive property of N-CAM. Recently, the cDNA that encodes polysialyltransferase, which is responsible for the polysialylation of N-CAM, was successfully cloned from three mammalian species. This review focuses on the molecular cloning of human polysialyltransferase, designated PST. It then describes the number of enzymes actually required for the polysialylation of N-CAM using an in vitro polysialyltransferase assay. Comparisons between PST and another polysialyltransferase, sialyltransferase X (STX), are made and it is demonstrated that both enzymes can independently form polysialic acid in vitro, but that during neural development they coordinately but distinctly synthesize polysialic acid on N-CAM. The role of polysialic acid in the central nervous system is also discussed. Finally, evidence that the two polysialyltransferases, PST and STX, apparently have distinct roles in the development of neural cells is provided by using a neurite outgrowth assay.

Animals↗

PubMed1998

Renal transplantation in a heterogeneous population: the thirty-year Montefiore Medical Center experience.

Based on more than 30 years of renal transplantation experience at Montefiore Medical Center we conclude: 1. Improved patient and graft survival can be achieved in the cadaveric transplant recipient despite increasing co-morbidities. 2. Patients at the extremes of age (< 10 or > 60) can undergo renal transplantation safely, with patient and graft survival rates approaching those of the general recipient population. 3. Results of transplantation in African-Americans are as good as non African-Americans at 3 years. Beyond that point the graft survival curves diverge. Well matched (0-1 HLA mismatches) kidneys in the African-American patient do as well if not better than other ethnic groups. However, African-Americans do not receive as many well matched kidneys as others.

Adolescent↗

PubMed1997

Cloning and sequence analysis of two laccase complementary DNAs from the ligninolytic basidiomycete Trametes versicolor.

Laccases are oxidoreductase enzymes involved in the oxidation of various phenolic compounds. They may play a role in the biodegradation of lignin and in the dechlorination of chlorophenols. The cDNAs encoding laccase LccI and a putative laccase LccIV and the gene for LccI from the white-rot basidiomycete Trametes versicolor were cloned, sequenced and characterized. The genomic DNA of lccI consists of 2128 bp, with the coding region interrupted by 10 introns; the cDNA consists of a 1560 bp open reading frame (ORF). The cDNA of the putative lccIV gene consists of a 1581 bp ORF, with a 794 bp 5' untranslated region. The size of the major transcript for both lccI and lccIV is approximately 2.3 kb. Transcription of lccIV was induced by 2,5-dimethylaniline, whereas the opposite effect was observed for lccI. Laccases I and IV contain highly conserved histidinyl and cysteinyl residues, believed to be involved in binding copper, and share extensive sequence similarity with other laccases produced by both ligninolytic and non-ligninolytic fungi.

Amino Acid Sequence↗

PubMed1997

Irlen lenses do not improve accommodative accuracy at near.

The purpose of the experiment was to determine the influence of Irlen lenses on steady-state accommodation in successful users, as there is speculation that near accommodative dysfunction may be a factor in these patients. Monocular steady-state accommodation in six successful Irlen patients was assessed for near blur stimuli (2, 3, and 4 D) either with nonfiltered spectacle refractive correction or their spectrally broad-band filtered spectacle refractive correction. Accommodation was measured subjectively using a Hartinger coincidence optometer. There was no significant difference in mean level of accommodation between the two conditions. Additionally, there was a small but significant increase in accommodative variability with the filtered prescription. The use of Irlen correction did not have any positive effect on monocular steady-state accommodation at near.

Accommodation, Ocular↗

PubMed1997

Clinical and serological responses to an inactivated influenza vaccine in adults with HIV infection, diabetes, obstructive airways disease, elderly adults and healthy volunteers.

To investigate the clinical and serological responses to an inactivated influenza vaccine (split-virion A/Singapore/6/86-like strains H1N1 (15 ug HA), A/Beijing/353/89-like H3N2 (15 ug HA) and B/Yamagata/16/88-like strain (15 ug HA): MFV-JECT, Merieux, UK) in persons with HIV infection, diabetes, obstructive lung diseases, elderly adults and healthy volunteers. Forty-nine HIV-infected persons received 2 doses of the vaccine at one-month intervals; 34 healthy volunteers, 30 elderly persons, 29 with insulin and non-insulin diabetes and 14 with obstructive airways diseases were vaccinated with one single dose between October 1992 to January 1993. Serological testing of antibody responses was done using haemagglutination assay. Beta2-microglobulin in HIV-infected persons was measured using radioimmunodiffusion between 1st and 2nd dose. Fructosamine levels in diabetic persons were assessed for diabetic control and peak expiratory flow rate (PEFR) was self monitored in persons with lung diseases. All groups apart from the elderly filled in a symptom score chart for the first 5 days following vaccination. A 4-fold rise in titre equal to or more than 1:64 to all the 3 antigens occurred in 20 (58.8%) of healthy volunteers compared with 13 (44.8%) diabetics, 5 (35.7%) with lung diseases, 10 (33.3%) elderly and 13 (26.5%) with HIV infection. A significant correlation of serological response to number of CD4 count in persons with HIV infection was noted (H1N1 P=0.0013, H3N2 P=0.025, BYAM P=0.0018). Mean beta2-microglobulin levels did not change significantly post 1st and 2nd vaccination. Mean fructosamine level did not change significantly. There was no significant change in PEFR. The vaccine was well tolerated. Persons with HIV infection and low CD4 count do not serologically respond well to influenza vaccine even with 2 doses compared to the other 4 groups. The other 4 groups had adequate protective serologic responses. The vaccine was well tolerated in all groups.

Adult↗

PubMed1996

Binding of the cellulose-binding domain of exoglucanase Cex from Cellulomonas fimi to insoluble microcrystalline cellulose is entropically driven.

Isothermal titration microcalorimetry is combined with solution-depletion isotherm data to analyze the thermodynamics of binding of the cellulose-binding domain (CBD) from the beta-1,4-(exo)glucanase Cex of Cellulomonas fimi to insoluble bacterial microcrystalline cellulose. Analysis of isothermal titration microcalorimetry data against two putative binding models indicates that the bacterial microcrystalline cellulose surface presents two independent classes of binding sites, with the predominant high-affinity site being characterized by a Langmuir-type Ka of 6.3 (+/-1.4) x 10(7) M-1 and the low-affinity site by a Ka of 1.1 (+/-0.6) x 10(6) M-1. CBDCex binding to either site is exothermic, but is mainly driven by a large positive change in entropy. This differs from protein binding to soluble carbohydrates, which is usually driven by a relatively large exothermic standard enthalpy change for binding. Differential heat capacity changes are large and negative, indicating that sorbent and protein dehydration effects make a dominant contribution to the driving force for binding.

Binding Sites↗

PubMed1995

Solution structure of a cellulose-binding domain from Cellulomonas fimi by nuclear magnetic resonance spectroscopy.

Multidimensional, multinuclear nuclear magnetic resonance spectroscopy combined with dynamical simulated annealing has been used to determine the structure of a 110 amino acid cellulose-binding domain (CBD) from Cex, a beta-1,4-glycanase from the bacterium Cellulomonas fimi (CBDcex). An experimental data set comprising 1795 interproton NOE-derived restraints, 50 phi, 34 chi 1, and 106 hydrogen bond restraints was used to calculate 20 final structures. The calculated structures have an average root-mean-square (rms) deviation about the mean structure of 0.41 A for backbone atoms and 0.67 A for all heavy atoms when fitted over the secondary structural elements. Chromatography, ultracentrifugation, and 15N NMR relaxation experiments demonstrate that CBDcex is a dimer in solution. While attempts to measure NOEs across the dimer interface were unsuccessful, a computational strategy was employed to generate dimer structures consistent with the derived data set. The results from the dimer calculations indicate that, while the monomer topologies produced in the context of the dimer can be variable, the relative positioning of secondary structural elements and side chains present in the monomer are restored upon dimer formation. CBDcex forms an extensive beta-sheet structure with a beta-barrel fold. Titration with cellohexaose, [beta-D-glucopyranosyl-(1,4)]5-D-glucose, establishes that Trp 54 and 72 participate in cellulose binding. Analysis of the structure shows that these residues are adjacent in space and exposed to solvent. Together with other proximate hydrophilic residues, these residues form a carbohydrate-binding cleft, which appears to be a feature common to all CBDs of the same family.

Actinomycetales↗

PubMed1995

Macrophage inflammatory protein 1-alpha mRNA expression in an immortalized microglial cell line and cortical astrocyte cultures.

Macrophage inflammatory protein 1 (MIP-1) is a recently characterized inflammatory and chemokinetic cytokine. Proinflammatory stimuli have been shown to induce expression of MIP-1 by macrophages. We hypothesized that microglia and astrocytes express MIP-1 alpha because of their many immunologic similarities to macrophages. MIP-1 alpha mRNA was examined with quantitative reverse transcription and polymerase chain reaction in an immortalized mouse microglial cell line (BV-2) and in mouse cortical astrocyte cultures. We found that in both the BV-2 microglial cell line and in astrocyte cultures, MIP-1 alpha mRNA was strongly induced by lipopolysaccharide and the phorbol ester PMA. MIP-1 alpha mRNA was reduced by dBcAMP, interferon-gamma, and PGE1. Dexamethasone decreased MIP-1 alpha mRNA levels in astrocyte cultures, but not in BV-2 microglial cells. Interleukin-1 beta, tumor necrosis factor alpha, and MIP-1 alpha had no effect on MIP-1 alpha mRNA expression. These findings demonstrate that MIP-1 alpha mRNA is expressed by cultured glial cells and is regulated by proinflammatory and anti-inflammatory stimuli. MIP-1 alpha may be expressed by microglia and astrocytes in vivo, and may help modulate cerebral inflammation.

Animals↗

PubMed1995

Leukemia inhibitory factor mRNA is expressed in cortical astrocyte cultures but not in an immortalized microglial cell line.

Leukemia inhibitory factor (LIF) is a multifunctional cytokine synthesized by a variety of cell types. In the nervous system LIF affects neuronal differentiation, and may be important during cerebral infection and inflammation. To clarify the cellular source of LIF in the brain, we examined the expression of LIF mRNA by primary cortical astrocyte cultures and an immortalized microglial cell line. The microglial cell line did not express LIF mRNA in response to pro-inflammatory agents such as lipopolysaccharide (LPS) that induced expression of other cytokine mRNAs. In contrast, primary astrocyte cultures grown in serum-containing medium expressed LIF mRNA constitutively, and this expression was regulated by pro-inflammatory and anti-inflammatory stimuli. Agents which activate the cAMP and protein kinase C second messenger systems also increased LIF mRNA in astrocyte cultures. These results suggest that astrocytes, but not microglia, may be an important source of LIF during cerebral inflammation and infection.

Animals↗

PubMed1995

Nearwork-induced transient myopia: a critical review.

The literature on nearwork-induced transient myopia (NITM) is reviewed, with NITM being defined as the short-term myopic far point shift immediately following a sustained near visual task. A majority of these investigations demonstrated the presence of NITM for a variety of test parameters, e.g., visual acuity, contrast sensitivity and far point. Overall, these studies reported relatively small myopic shifts, with a mean of approximately 0.40 D and a range from 0.12 to 1.30 D. The subsequent decay is characterized by an exponential function with a relatively short time course. While the precise etiology and implications of NITM remain unclear, speculations regarding its origin and relevance to clinical myopia are discussed. Studies that did not demonstrate NITM are also reviewed.

Accommodation, Ocular↗

PubMed1995

Vergence adaptation and the order of clinical vergence range testing.

When measuring horizontal relative vergence ranges, the conventional clinical procedure is to assess the base-in (or divergence) range before the base-out (or convergence) determination. The rationale for this order of testing is that the convergence responses stimulated during the base-out measurements may produce vergence adaptation (i.e., a fusional aftereffect), which may temporarily bias the subsequent base-in values in the base-out direction. However, the effect of reversing this order of testing (i.e, base-out before base-in) has not been directly evaluated. Accordingly, the present study compared distance base-in vergence ranges measured both before and after base-out testing at separate test sessions. Additionally, tonic vergence (TV) was assessed before and after each vergence range measurement. The results indicated that base-out vergence range testing stimulated vergence adaptation, and furthermore produced a statistically significant reduction in the subsequently measured base-in recovery value. However, the magnitude of this shift was less than the estimated degree of repeatability of the vergence range measurement. Therefore, a more appropriate order of testing would be to assess the heterophoria compensating range first in order to obtain accurate results during this more critical measurement.

Adaptation, Ocular↗

PubMed1995

Purification of human interleukin-2 using the cellulose-binding domain of a prokaryotic cellulase.

Engineering gene fusions which introduce an affinity tag linked to the target polypeptide by a specific protease cleavage site is widely used to facilitate recombinant protein purification. A fusion protein CBDAPT-IL-2, comprised of the cellulose-binding domain (CBD) and Pro-Thr (PT) rich linker of the Cellulomonas fimi endo-beta-1,4-glucanase A (CenA) and a factor Xa cleavage sequence (IleGluGlyArg) fused to the N terminus of human interleukin-2, was produced in Escherichia coli, Streptomyces lividans and mammalian COS cells. CBDAPT-IL-2, secreted from S. lividans or COS cells or recovered from the insoluble fraction of E. coli, could be purified by adsorption on cellulose. The intact fusion protein adsorbed to cellulose was hydrolyzed in situ with factor Xa to release active interleukin-2.

Actinomycetales↗

PubMed1995

Effect of target proximity on transient myopia induced by equidioptric stimuli.

Transient myopia may be exhibited after sustained focus on a near target. This appears to be related to the within-task accommodative response. Although proximally induced accommodation has been shown to produce considerable transient myopia under open-loop conditions, its effect under naturalistic closed-loop conditions remains unclear. Accordingly, the present study examined the effect of target distance on transient myopia for equidioptric stimuli (5 D). A Canon R-1 autorefractor was used to assess the pre- and post-task refractive state objectively. Two tasks were performed monocularly and consisted of either accommodating on a near target at 20 cm (5 D) or a far target at 6 m viewed through a -5 D lens. The former task involved both blur and proximally induced accommodation, whereas the latter consisted of a blur stimulus only. Similar amounts of transient myopia were found under both conditions. These equivalent responses may be related to the relatively small output of proximally induced accommodation believed to be present under closed-loop conditions.

Accommodation, Ocular↗

PubMed1994

Non-S-layer glycoproteins in eubacteria.

Glycoproteins are proving to be quite common in prokaryotes. Those in S-layers are the best understood in terms of structure. Numerous eubacteria produce non-S-layer glycoproteins about which relatively little is known. The glycans on such proteins and the nature and sites of their linkages to proteins are novel in those glycoproteins which have been examined in any detail. The possible functions of the glycans are mostly not understood. Eubacterial non-S-layer glycoproteins and the glycosylation systems producing them deserve more attention.

Amino Acid Sequence↗