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H H Cheng

Publications and source records attributed to H H Cheng.

At least 19 recordsLinked to original sources
PubMed2006

Stability of Marek's disease virus 132-bp repeats during serial in vitro passages.

The Marek's disease virus (MDV) genome contains 2 sets of 132-bp tandem repeat sequences. An increase in 132-bp repeat units has been associated with attenuation of oncogenicity during in vitro passage. By cloning entire genomes, we demonstrated that the copy number of 132-bp repeats can differ within an individual MDV genome. The stability of the 132-bp repeats during cell passage depended on the initial copy number. When both sets of repeats contained 2 copies, the copy number remained stable, while if even 1 set of repeats contained 6 copies, repeat expansion occurred relatively quickly. This expansion did not affect the in vitro growth curve. However, when MDV clones with low and high copy numbers were passed together, genomes with expanded repeats rapidly predominated, mimicking the behavior of naturally-occurring MDV. These results suggest that the preponderance of high-copy repeats after passage reflects intracellular copy number within individual infected cells rather than an influence on the spread of the virus.

Animals↗
PubMed2006

Molecular epidemiology of long-term colonization of Candida albicans strains from HIV-infected patients.

Twenty-one Candida albicans isolates from three HIV-infected patients were collected over a period of 3 years and characterized for fluconazole susceptibility, infectivity and genetic relatedness. Fluconazole resistance was found in five isolates, four exhibited dose-dependent susceptibility and the remainder were fully susceptible to this agent. Pulsed-field gel electrophoresis of SfiI restriction digests of the genomic DNA from the isolates revealed that isolates from the same swab specimen were identical despite differences in susceptibility to fluconazole and isolates recovered over time from the three patients retained clonally related DNA fingerprints within each patient. This small-scale study confirms the persistence of oral colonization of C. albicans strains in HIV-infected patients. Clinical data also suggests that the primary infecting strain may become a persistent colonist in the oral cavity once the immune function of the patient has been restored.

Adult↗
PubMed2006

Safrole-induced Ca2+ mobilization and cytotoxicity in human PC3 prostate cancer cells.

The effect of the carcinogen safrole on intracellular Ca2+ mobilization and on viability of human PC3 prostate cancer cells was examined. Cytosolic free Ca2+ levels ([Ca2+]i) were measured by using fura-2 as a probe. Safrole at concentrations above 10 microM increased [Ca2+]i in a concentration-dependent manner with an EC50 value of 350 microM. The Ca2+ signal was reduced by more than half after removing extracellular Ca2+ but was unaffected by nifedipine, nicardipine, nimodipine, diltiazem, or verapamil. In Ca2+-free medium, after treatment with 650 microM safrole, 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) failed to release Ca2+. Neither inhibition of phospholipase C with U73122 nor modulation of protein kinase C activity affected safrole-induced Ca2+ release. Overnight incubation with 0.65-65 microM safrole did not affect cell viability, but incubation with 325-625 microM safrole decreased viability. Collectively, the data suggest that in PC3 cells, safrole induced a [Ca2+]i increase by causing Ca2+ release from the endoplasmic reticulum in a phospholipase C- and protein kinase C-independent fashion, and by inducing Ca2+ influx. Safrole can decrease cell viability in a concentration-dependent manner.

Calcium Channel Blockers↗
PubMed2006

Effect of riluzole on Ca2+ movement and cytotoxicity in Madin-Darby canine kidney cells.

Riluzole is a drug used in the treatment of amyotrophic lateral sclerosis; however, its in vitro action is unclear. In this study, the effect of riluzole on intracellular Ca2+ concentration ([Ca2+]i) in Madin-Darby canine kidney (MDCK) cells was investigated using the Ca2+ -sensitive fluorescent dye, fura-2. Riluzole (100-500 microM) caused a rapid and sustained increase of [Ca2+]i in a concentration-dependent manner (EC50 = 150 microM). Some 40 and 50% of this [Ca2+]i increase was prevented by the removal of extracellular Ca2+ and the addition of La3+, respectively, but was unchanged by dihydropyridines, verapamil and diltiazem. In Ca2+ -free medium, thapsigargin - an inhibitor of the endoplasmic reticulum (ER) Caz+ -ATPase--caused a monophasic [Ca2+]i increase, after which the increasing effect of riluzole on [Ca2+]i was attenuated by 70%; in addition, pre-treatment with riluzole abolished thapsigargin-induced [Ca2+]i increases. U73122, an inhibitor of phospholipase C (PLC), abolished ATP (but not riluzole)-induced [Ca2+]i increases. At concentrations of 250 and 500 microM, riluzole killed 40 and 95% cells, respectively. The cytotoxic effect of riluzole (250 microM) was unaltered by pre-chelating cytosolic Ca2+ with BAPTA. Collectively, in MDCK cells, riluzole rapidly increased [Ca2+]i by stimulating extracellular Ca2+ influx via an La3+ -sensitive pathway and intracellular Ca2+ release from the ER via, as yet, unidentified mechanisms. Furthermore, riluzole caused Ca2+ -unrelated cytotoxicity in a concentration-dependent manner.

Animals↗
PubMed2005

Distribution and susceptibility to amphotericin B and fluconazole of Candida spp. isolated from Taiwan.

Susceptibilities to amphotericin B and fluconazole of 628 clinical yeast strains collected from 22 hospitals in Taiwan were determined. A total of 53 isolates (8.4%) were resistant to fluconazole. Each hospital had different resistance rate to fluconazole ranging from 0% to 24%. None of the 186 isolates from eight of the 22 hospitals was resistant to fluconazole. In contrast, isolates from nine of the remaining 14 hospitals had greater than 10% resistance rate to fluconazole. Consistently, 88.9% (8/9) fluconazole-resistant C. albicans isolates were from hospitals having a high resistance rate to fluconazole. The prevalence of various Candida spp. in each hospital was different. A positive association was found between the prevalence of C. tropicalis and the resistance rate to fluconazole for individual hospitals. Although only three isolates (0.5%) were resistant to amphotericin B, a co-resistance to both amphotericin B and fluconazole was observed, which highlights the emerging problem of drug resistance.

Amphotericin B↗
PubMed2005

Development and validation of a PCR-RFLP assay to evaluate TVB haplotypes coding receptors for subgroup B and subgroup E avian leukosis viruses in White Leghorns.

The cellular receptor of subgroup B avian leukosis virus (ALVB) is encoded by a gene at the tumour virus B (TVB) locus. TVB alleles encode specific receptors permitting infection by exogenous ALVB or avian leukosis virus subgroup D (ALVD) as well as endogenous avian leukosis virus subgroup E (ALVE), and thus susceptibility is dominant to resistance. Two single nucleotide polymorphisms at the TVB locus have been reported distinguishing three TVB alleles (TVB*S1, TVB*S3 and TVB*R). We have developed a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay using the two single nucleotide polymorphisms to define three observed allelic haplotypes and to identify the six possible TVB genotypes consisting of the three haplotypes in defined laboratory strains of chickens. One additional potential allelic haplotype and four genotypes were also briefly discussed. Chickens from parents heterozygous for different TVB alleles were challenged with Rous sarcoma viruses of subgroup ALVB and ALVE to induce wing-web tumours. Tumour incidences were evaluated between chickens of the genotypes determined with this newly developed PCR-RFLP assay. Importantly, chickens typed with this assay as TVB*S3/*S3 were resistant to infection by ALVE only, and those TVB*R/*R were resistant to both ALVE and ALVB. Furthermore, a vast majority of chickens with the susceptible TVB*S1/- genotypes developed a tumour. This PCR-RFLP assay enables a relatively rapid assessment of all six anticipated TVB genotypes in experimental strains of chickens undergoing segregation for TVB*S1, TVB*S3, and TVB*R alleles. This non-infectious assay should be further evaluated for the capacity to select and breed commercial chickens for genetic resistance to infections by ALVB, ALVD and ALVE.

Alleles↗
PubMed2005

Microsatellite markers associated with resistance to Marek's disease in commercial layer chickens.

The objective of the current study was to identify QTL conferring resistance to Marek's disease (MD) in commercial layer chickens. To generate the resource population, 2 partially inbred lines that differed in MD-caused mortality were intermated to produce 5 backcross families. Vaccinated chicks were challenged with very virulent plus (vv+) MD virus strain 648A at 6 d and monitored for MD symptoms. A recent field isolate of the MD virus was used because the lines were resistant to commonly used older laboratory strains. Selective genotyping was employed using 81 microsatellites selected based on prior results with selective DNA pooling. Linear regression and Cox proportional hazard models were used to detect associations between marker genotypes and survival. Significance thresholds were validated by simulation. Seven and 6 markers were significant based on proportion of false positive and false discovery rate thresholds less than 0.2, respectively. Seventeen markers were associated with MD survival considering a comparison-wise error rate of 0.10, which is about twice the number expected by chance, indicating that at least some of the associations represent true effects. Thus, the present study shows that loci affecting MD resistance can be mapped in commercial layer lines. More comprehensive studies are under way to confirm and extend these results.

Animals↗
PubMed2004

A comprehensive screen for chicken proteins that interact with proteins unique to virulent strains of Marek's disease virus.

Genetic resistance to Marek's disease (MD) has been proposed as a method to augment current vaccinal control of MD. Although it is possible to identify QTL and candidate genes that are associated with MD resistance, it is necessary to integrate functional screens with linkage analysis to confirm the identity of true MD resistance genes. To help achieve this objective, a comprehensive 2-hybrid screen was conducted using genes unique to virulent Marek's disease virus (MDV) strains. Potential MDV-host protein interactions were tested by an in vitro binding assay to confirm the initial two-hybrid results. As a result, 7 new MDV-chicken protein interactions were identified and included the chicken proteins MHC class II beta (BLB) and invariant (Ii) chain (CD74), growth-related translationally controlled tumor protein (TPT1), complement component Clq-binding protein (C1QBP), retinoblastoma-binding protein 4 (RBBP4), and alpha-enolase (ENO1). Mapping of the encoding chicken genes suggests that BLB, the gene for MHC class II beta chain, is a positional candidate gene. In addition, the known functions of the chicken proteins suggest mechanisms that MDV might use to evade the chicken immune system and alter host gene regulation. Taken together, our results indicate that integrated genomic methods provide a powerful strategy to gain insights on complex biological processes and yield a manageable number of genes and pathways for further characterization.

Animals↗
PubMed2003

Study of air pollutants in Hong Kong using energy dispersive X-ray fluorescence.

Airborne particulate samples were collected from various reference sites in Hong Kong and the energy dispersive X-ray fluorescence (EDXRF) intensities for 19 chemical elements were recorded. Principal component analysis (PCA) was employed so that the variances of these 19 original variables were captured by a few new indices called principal components or PCs. Data points for similar sources were automatically grouped together in a plot of the first three PCs (PC plot). Data for the monitoring site Mong Kok were located within the area defined by vehicular emissions. As such, the main air pollutant at this site was concluded to originate from vehicular emissions. A fraction of data for the Causeway Bay monitoring site also fell into this same identified area, so the main air pollutant could also be vehicular emissions. Some of the data located either on or outside the border can be explained in terms of meteorology.

Air Pollutants↗
PubMed2003

Mapping quantitative trait loci associated with resistance to coccidiosis and growth.

To map QTL associated with disease resistance to avian coccidiosis and growth, two commercial broiler lines with different degrees of resistance to the disease were crossed to generate an F1 generation that was intercrossed to produce 314 F2 generation offspring. The F2 offspring were inoculated with sporulated oocysts of Eimeria maxima. Five disease-associated phenotypes were measured after the infection. Intertrait comparisons revealed that oocyst shedding was a good parameter for evaluating disease resistance or susceptibility. One hundred nineteen microsatellite markers, covering 80% of the chicken genome with an average marker interval of 25 cM, were used for genotyping of F1 parents and F2 offspring. Statistical analysis based on the data of four families revealed a locus on chromosome 1 associated with oocyst shedding (logarithm of odds = 3.46). The genetic mechanism of this locus appeared additive. The genomic scan also identified three potential growth QTL on chromosomes 1, 6, and 8. These results provide the foundation for further investigation to validate the QTL.

Animals↗
PubMed2003

Identification of chicken lymphocyte antigen 6 complex, locus E (LY6E, alias SCA2) as a putative Marek's disease resistance gene via a virus-host protein interaction screen.

Marek's disease virus (MDV) is a naturally occurring oncogenic avian herpesvirus that causes neurological disorders and T cell lymphoma disease in domestic chickens. Identification and functional characterization of the individual factors involved in Marek's disease (MD) resistance or pathogenesis will enhance our understanding of MDV pathogenesis and further genetic improvement of chickens. To study the genetic basis for resistance to MD, a strategy that combined protein-protein interaction screens followed by linkage analysis was performed. The MDV protein US10 was used as the bait in an E. COLI two-hybrid screening of a cDNA library derived from activated splenic T cells. The chicken LY6E, also known as SCA2 and TSA1, was found to specifically interact with US10. This interaction was confirmed by an in vitro protein-binding assay. Furthermore, LY6E was found to be significantly associated with MD traits in an MD resource population comprised of commercial chickens. Previously, LY6E was implicated in two independent DNA microarray experiments evaluating differential gene expression following MDV infection. Given that LY6E is involved in T cell differentiation and activation, we suggest that LY6E is a candidate gene for MD resistance and deserves further investigation on its role in MDV pathogenesis, especially with respect to the binding of US10.

Animals↗
PubMed2002

Development and mapping of microsatellite markers derived from chicken chromosome-specific libraries.

Chromosome-specific painting probes and libraries were developed for chicken Macrochromosomes 1, 2, 3, and 4 by chromosome microisolation and microcloning. Fluorescent in situ hybridization results using the painting probes on normal chicken metaphase chromosomes indicated the purity and specificity of each probe. Chromosome-specific libraries for chicken Macrochromosomes 1, 2, 3, and 4 were prepared in a phage vector. Fifty-two additional unique microsatellite markers of the (AC)n type were developed from these chromosome-specific libraries. These markers were mapped on the East Lansing reference population to increase the marker density on the four macrochromosomes. Results of the current study suggest that development of markers from chromosome-specific libraries is very useful for constructing high-density linkage maps for chicken macrochromosomes.

Animals↗
PubMed2001

Localization to chicken chromosome 5 of a novel locus determining salmonellosis resistance.

Clear genetic differences in the susceptibility of chickens to visceral infection by Salmonella have been observed and it has been possible to identify resistant and susceptible lines of inbred chickens. We report here the results of experiments to map directly the gene(s) controlling this trait in chickens by examining crosses between highly susceptible and highly resistant lines. In the mapping panel, a region on chicken Chromosome (Chr) 5 was found to have a large effect on resistance, and this effect was observed in three separate resource populations. Mapping of additional marker loci in the region of the resistance gene further localized it to a region of approximately 2 cM, close to the genes for creatine kinase (CKB) and dynein (DNCH1). This region shows conserved synteny with telomeric regions of human Chr 14 and mouse Chr 12. On the basis of this conserved synteny, this resistance gene seems unlikely to correspond to the previously identified salmonellosis resistance genes Lps (located on mouse Chr 4) or Nos(2) (located on mouse Chr 11). There was no association between Nramp1 and resistance in these crosses, although this gene was shown to contribute to resistance in other crosses. The homologous human and mouse regions at present contain no likely candidate genes for this trait. Thus this appears to be a novel resistance gene, which we designate SAL1.

Animals↗