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H Yu

Publications and source records attributed to H Yu.

At least 55 records · Page 3Linked to original sources
PubMed2003

Post-transcriptional gene silencing in plants by RNA.

RNA silencing, which is termed post-transcriptional gene silencing in plants, is an RNA degradation process through sequence-specific nucleotide interactions induced by double-stranded RNA. In plants, RNA silencing not only serves as a component of the defense mechanism, but also participates in the regulation of endogenous gene expression in a variety of developmental processes. This review elaborates the current progress on the understanding of the molecular basis of RNA silencing including a mechanistic link between the regulation of microRNA and RNA silencing. The practical use of RNA silencing as a reverse genetics approach in plant functional genomics is also discussed.

Gene Silencing↗
PubMed2003

Field evaluation of a test for praziquantel resistance in Schistosoma sp.

A simple rapid test for detecting praziquantel resistance in Schistosoma sp., involving change in shape of miracidia on exposure to praziquantel, was evaluated in China. Tests on miracidia hatched from eggs collected from naturally infected goats were run in a field laboratory in Jiangxi Province and a research laboratory in Shanghai. The mean values in the two laboratories were not significantly different, but the variation between individual samples in the two laboratories suggests that a delineating dose will be required for routine diagnosis of resistance. Confirmation that resistance would have been detected in Schistosoma japonicum must await the isolation of a resistant isolate. The tests suggested that the infection in the goats was susceptible to praziquantel as did chemotherapy of water buffaloes with 25mg/kg. This gave a 95% cure rate on the first treatment and 100% with a second treatment, similar to that found previously in human patients.

Animals↗
PubMed2003

Polymorphism of the insulin gene is associated with increased prostate cancer risk.

High insulin levels are linked with increased cancer risk, including prostate cancer. We examined the associations between prostate cancer with polymorphisms of the insulin gene (INS) and its neighbouring genes, tyrosine-hydroxylase and IGF-II (TH and IGF2). In this study, 126 case-control pairs matched on age, race, and countries of origin were genotyped for +1127 INS-PstI in INS, -4217 TH-PstI in TH, and +3580 IGF2-MspI in IGF2. The homozygous CC genotype of +1127 INS-PstI occurred in over 60% of the population. It was associated with an increased risk of prostate cancer in nondiabetic Blacks and Caucasians (OR=3.14, P=0.008). The CC genotype was also associated with a low Gleason score <7 (OR=2.60, P=0.022) and a late age of diagnosis (OR=2.10, P=0.046). Markers in the neighbouring genes of INS showed only null to modest associations with prostate cancer. The polymorphism of INS may play a role in the aetiology of prostate cancer. Given the high prevalence of the CC genotype and its association with late age of onset of low-grade tumours, this polymorphism may contribute to the unique characteristics of prostate cancer, namely a high prevalence of indolent cancers and the dramatic increase in incidence with age.

Adult↗
PubMed2003

Genotype-phenotype analysis for the polymorphic CA repeat in the insulin-like growth factor-I (IGF-I) gene.

Polymorphic microsatellite dinucleotide (cytosine-adenine, CA) repeats of the insulin-like growth factor-I (IGF-I) gene may have implications in the development of certain types of cancer and osteoporosis. We studied correlations between IGF-I genotypes determined by direct sequencing and plasma IGF-I levels among 113 healthy individuals (60 men and 53 women), who were originally enrolled as controls for hospital-based case-control studies of breast and prostate cancer. On the contrary to an earlier observation, there were no differences in plasma IGF-I levels between those with and without the allele of 19 repeats. With adjustment for other confounders, there were no trends in plasma IGF-I levels with increasing or decreasing the number of CA repeats among all study subjects combined, all Whites or all Blacks, suggesting no overall functional significance of this polymorphism. Opposite trends observed in gender and racial subgroups, i.e., an inverse association between plasma IGF-I levels and the CA repeat length in white women and a positive association in black men, are likely to be chance findings.

Alleles↗
PubMed2003

AMP-activated protein kinase regulation and action in skeletal muscle during exercise.

Physical exercise increases muscle glucose uptake, enhances insulin sensitivity and leads to fatty acid oxidation in muscle. The AMP-activated protein kinase (AMPK) is an energy-sensing enzyme that is strongly activated during muscle contraction due to acute decreases in ATP/AMP and phosphocreatine/creatine ratios. Accumulating evidence suggests that AMPK plays an important role in mediating these metabolic processes. Furthermore, AMPK has been implicated in regulating gene transcription and therefore may play a role in some of the cellular adaptations to training exercise. There is also evidence that changes in AMPK activity result in altered cellular glycogen content, suggesting that this enzyme regulates glycogen metabolism. Recent studies have shown that the magnitude of AMPK activation and associated metabolic responses are affected by factors such as glycogen content, exercise training and fibre type. In summary, AMPK regulates several metabolic pathways during acute exercise and modifies the expression of many genes involved in the adaptive changes to exercise training.

AMP-Activated Protein Kinases↗
PubMed2003

Genetic delineation of sibling species of the pest fruit fly Bactocera (Diptera: Tephritidae) using microsatellites.

Using a large set of microsatellites, the genetic relationships between three closely related Australian fruit fly species, Bactrocera tryoni (Froggatt), B. neohumeralis (Hardy) and B. aquilonis(May) were investigated. Bactrocera tryoni and B. neohumeralis are sympatric, while B. aquilonisis allopatric to both. The sympatric species, B. tryoni and B. neohumeralis, were found to be genetically distinct. It is likely that despite differences in mating time between these two species, some gene flow still occurs. In contrast, the sibling species B. tryoni and B. aquilonis were found to be closely related, despite allopatry. The level of genetic divergence was similar to that found within eastern Australian populations of B. tryoni. Consideration of all available genetic data suggests that this similarity is not due to recent (i.e. within the last 30 years) displacement of B. aquilonis by B. tryoni from the B. aquilonis region (north-western Australia). Instead the data suggests that, at least in the areas sampled, asymmetrical hybridization may have occurred over a longer timescale.

Animals↗
PubMed2003

Inferring modes of colonization for pest species using heterozygosity comparisons and a shared-allele test.

Long-range dispersal of a species may involve either a single long-distance movement from a core population or spreading via unobserved intermediate populations. Where the new populations originate as small propagules, genetic drift may be extreme and gene frequency or assignment methods may not prove useful in determining the relation between the core population and outbreak samples. We describe computationally simple resampling methods for use in this situation to distinguish between the different modes of dispersal. First, estimates of heterozygosity can be used to test for direct sampling from the core population and to estimate the effective size of intermediate populations. Second, a test of sharing of alleles, particularly rare alleles, can show whether outbreaks are related to each other rather than arriving as independent samples from the core population. The shared-allele statistic also serves as a genetic distance measure that is appropriate for small samples. These methods were applied to data on a fruit fly pest species, Bactrocera tryoni, which is quarantined from some horticultural areas in Australia. We concluded that the outbreaks in the quarantine zone came from a heterogeneous set of genetically differentiated populations, possibly ones that overwinter in the vicinity of the quarantine zone.

Animals↗
PubMed2002

Ergodic chaos-based communication schemes.

Recent studies have shown the applicability of synchronized chaotic systems to the area of communications in different ways. At the same time synchronization based signal recovery and estimation of parameters severely suffer due to the presence of channel noise. By exploiting the ergodic properties of chaotic signals effectively, a simple technique called the mean-value method is introduced. This method is shown to be capable of estimating chaos system parameters from the transmitted chaotic signal efficiently for a low signal-to-noise ratio. A suitable demodulator has been designed for ergodic chaotic parameter modulation scheme for digital signal communication. Further, the mean-value technique incorporates a noncoherent receiver to recover analog information signal from the chaos masked signal efficiently. It is found that the proposed chaotic masking scheme is robust even in the presence of strong noise. In addition, this scheme has the potential advantage of a very simple hardware realization, which promises enhanced signal recovery performances.

Journal Article↗
PubMed2002

Multi-layered microcapsules for cell encapsulation.

Mechanical stability, complete encapsulation, selective permeability, and suitable extra-cellular microenvironment, are the major considerations in designing microcapsules for cell encapsulation. We have developed four types of multi-layered microcapsules that allow selective optimization of these parameters. Primary hepatocytes were used as model cells to test these different microcapsule configurations. Type-1 microcapsules with an average diameter of 400 microm were formed by complexing modified collagen with a ter-polymer shell of 2-hydroxyethyl methylacrylate (HEMA), methacrylic acid (MAA) and methyl methacrylate (MMA), resulting in a capsule thickness of 2-5 microm. Cells in these microcapsules exhibited improved cellular functions over those cultured on collagen monolayers. Type-II microcapsules were formed by encapsulating the Type-I microcapsules in another 2-5 microm ter-polymer shell and a approximately 5 microm collagen layer between the two ter-polymer shells to ensure complete cell encapsulation. Type-II microcapsules comprised of a macro-porous exoskeleton with materials such as alumina sol-gel coated on the Type-I microcapsules. Nano-indendation assay indicated an improved mechanical stability over the Type-I microcapsules. Type-IV microcapsules were created by encapsulating Type-III microcapsules in another 2-5 microm ter-polymer shell, with the aim of imparting a negatively charged smooth surface to minimize plasma protein absorption and ensure complete cell encapsulation. The permeability for nutrient exchange, cellular functions in terms of urea production and mechanical stability of the microcapsules were characterized. The advantages and limitations of these microcapsules for tissue engineering are discussed.

Animals↗
PubMed2002

Membrane potential dependent modulations of calcium oscillations in insulin-secreting INS-1 cells.

This study was undertaken to examine the role of K(+) channels on cytosolic Ca(2+) ([Ca(2+)](i)) in insulin secreting cells. [Ca(2+)](i) was measured in single glucose-responsive INS-1 cells using the fluorescent Ca(2+) indicator Fura-2. Glucose, tolbutamide and forskolin elevated [Ca(2+)](i) and induced [Ca(2+)] oscillations. Whereas the glucose effect was delayed and observed in 60% and 93% of the cells, in a poorly and a highly glucose-responsive INS-1 cell clone, respectively, tolbutamide and forskolin increased [Ca(2+)](i) in all cells tested. In the latter clone, glucose induced [Ca(2+)](i) oscillations in 77% of the cells. In 16% of the cells a sustained rise of [Ca(2+)](i) was observed. The increase in [Ca(2+)](i) was reversed by verapamil, an L-type Ca(2+) channel inhibitor. Adrenaline decreased [Ca(2+)](i) in oscillating cells in the presence of low glucose and in cells stimulated by glucose alone or in combination with tolbutamide and forskolin. Adrenaline did not lower [Ca(2+)](i) in the presence of 30mM extracellular K(+), indicating that adrenaline does not exert a direct effect on Ca(2+) channels but increases K(+) channel activity. As for primary b-cells, [Ca(2+)](i) oscillations persisted in the presence of closed K(ATP) channels; these also persisted in the presence of thapsigargin, which blocks Ca(2+) uptake into Ca(2+) stores. In contrast, in voltage-clamped cells and in the presence of diazoxide (50mM), which hyperpolarizes the cells by opening K(ATP) channels, [Ca(2+)](i) oscillations were abolished. These results support the hypothesis that [Ca(2+)](i) oscillations depend on functional voltage-dependent Ca(2+) and K(+) channels and are interrupted by a hyperpolarization in insulin-secreting cells.

Adrenergic alpha-Agonists↗
PubMed2002

Calcium-stimulated short-circuit currents in the canine proximal colonic epithelium: effects of DK-PGD2, a metabolite of prostaglandin D2.

Prostaglandin D2 (PGD2) has marked inhibitory effects on the canine proximal colonic epithelium set up in Ussing chambers. These effects involved a receptor that is pharmacologically distinct from the classical DP, presumably the recently identified CRTH2/DP2 variety. The mechanism underlying these effects was studied using 13,14-dihydro-15-keto-PGD2 (DK-PGD2), a stable metabolite of the parent prostanoid. The metabolite quickly reversed short circuit currents (I(sc)) stimulated by diverse agonists. Greater inhibitory effects were seen with stimulants such as carbachol and cyclopiazonic acid (CPA) rather than with forskolin or protein kinase A activators. Since the same stimulants were differentially affected by removal and replacement of serosal Ca2+, we tested the possibility that the prostanoid inhibited basolateral Ca2+ entry. In the absence of serosal Ca2+, tissues primed with CPA demonstrated concentration-dependent increases in I(sc), to cumulative additions of Ca2+ or Sr2+, though the former was more potent. Cl- removal and pretreatment with bumetanide virtually abolished responses, suggesting that the increase in I(sc) reflected Ca2+ dependent Cl- secretion. Though responses were insensitive to the L-type channel antagonist, verapamil, a marked inhibition was seen in the presence of metal cations (Gd3+, Cd2+, and La3+). Pretreatment with DK-PGD2 inhibited responses to Ca2+ in CPA-primed tissues. Thus, basolateral Ca2+ entry via store-operated Ca2+ channels may be the locus for the inhibitory effects of PGD2 in this tissue. These results could indicate a potential transduction mechanism for the novel DP receptor variously called CRTH2 or DP2.

Animals↗
PubMed2002

Recent developments in depsipeptide research.

This review focuses on the major developments in depsipeptide research since 1995. Depsipeptides are bio-oligomers composed of hydroxy and amino acids linked by amide and ester bonds. Many depsipeptides show very promising biological activities, including anticancer, antibacterial, antiviral, antifungal, anti-inflammatory, and anti-clotting or anti-antherogenic properties. In this report depsipeptides exhibiting these properties are discussed. Their isolation, structural determination, and notable structural features are discussed, but their biological properties and therapeutic potentials are emphasized. Depsipeptides have shown the greatest therapeutic potential as anticancer agents. Four depsipeptides have entered clinical trials for cancer treatment. Among the antiviral compounds discovered, the callipeltins and the quinoxapeptins are particularly promising due to their inhibitory activities against HIV. These compounds have the potential to be developed as anti-AIDS drugs or to serve as lead compounds for the discovery of structurally related anti-AIDS compounds. Antifungal compounds, such as the jaspamides, may lead to therapies against many of the opportunistic infections that accompany AIDS. Anti-inflammatory compounds such as SCH217048 act as neurokinin antagonists and may lead to anti-inflammatory treatments. Some depsipeptides such as micropeptins and A90720A have been found to be effective plasmin inhibitors, which have implications as treatments for cardiovascular diseases. Compounds such as SCH58149 help control the levels of HDL and LDL.

Anti-Inflammatory Agents↗
PubMed2002

[Expression and prognostic significance in epithelial ovarian cancer].

BACKGROUND: Insulin-like growth factor binding protein-3 (IGFBP-3) is a glycoprotein with specific binding affinity to peptide hormones insulin-like growth factors (IGFs) which are potent mitogens for a variety of cells. IGFBP-3 can inhibit the activities of IGFs by interfering with the interaction between IGFs and their receptor IGF-IR. Epithelial ovarian cancer (EOC) tissues express IGFBP-3, IGFs and IGF-IR. Moreover, high levels of IGF-I and IGF-IR have been shown in epithelial ovarian cancer, and IGF-I stimulates the growth of ovarian cancer. METHODS: We measured IGFBP-3 levels in ovarian cancer tissues of 147 consecutive patients and we examined its association with clinical and pathological features of the disease and patient survival. The average age of the patients in the study was 55 years and the median follow-up time was 37 months. IGFBP-3 levels were measured in the tissue extracts by a commercial ELISA kit and non-parametric statistics and the Cox regression survival analysis were used to determine the associations of IGFBP-3 with clinical and pathologic variables as well as with patient survival. RESULTS: High IGFBP-3 levels resulted significantly associated with some of the favorable prognostic features of the disease, including early clinical stage (p=0.048), small size of residual tumor (p=0.007), and optimal debulking result (p=0.007). High IGFBP-3 was also associated with a significantly reduced risk for disease progression (RR=0.52, p=0.034) and we showed an inverse dose-dependent relationship between IGFBP-3 and disease progression-free survival (p=0.033). However, the association with disease progression-free survival was no longer statistically significant in a multivariate analysis. An association between IGFBP-3 and overall survival was not shown. CONCLUSIONS: This study suggest that IGFBP-3 may play a role in the progression of epithelial ovarian cancer.

Adult↗
PubMed2001

A quantitative method to measure telomerase activity by bioluminescence connected with telomeric repeat amplification protocol.

Telomerase is expected to be a new biomarker for cancer diagnosis. The telomeric repeat amplification protocol (TRAP) is a sensitive method to detect telomerase activity. However, TRAP and its modified protocols are not always suitable for measuring telomerase activity of a large number of clinical samples to diagnosis cancer because these methods generally require a time-consuming detection step such as gel electrophoresis. To improve the procedure for mass diagnosis, we applied bioluminescence to replace the detection step. Telomerase activity is measured by evaluating the amount of inorganic pyrophosphate generated in PCR amplification of telomerase elongation product, with use of the sensitive enzymatic luminometric inorganic pyrophosphate detection assay (ELIDA). TRAP connected with ELIDA (TRAP-ELIDA) can quantitatively detect telomerase activity within linearity from 2 to 1000 cell equivalents. The ELIDA signals accorded with results of TRAP-SYBR green staining, and the results of ELIDA were significantly correlated to those of TRAP connected with an enzyme-linked immunosorbent assay (TRAP-ELISA) (r(2) = 0.992, P < 0.001). TRAP-ELIDA is a simple and sensitive method to quantify telomerase activity without time-consuming gel electrophoresis. Because TRAP-ELIDA measures telomerase activity with a luminometer, it could be applied to a large number of clinical samples at the same time.

Adenosine Triphosphate↗
PubMed2001

DAF-16-dependent and independent expression targets of DAF-2 insulin receptor-like pathway in Caenorhabditis elegans include FKBPs.

The daf-2 insulin-like receptor pathway regulates development and life-span in Caenorhabditis elegans. Reduced DAF-2 signaling leads to changes in downstream targets via the daf-16 gene, a fork-head transcription factor which is regulated by DAF-2, and results in extended life-span. Here, we describe the first identification of genes whose expression is controlled by the DAF-2 signaling cascade. dao-1, dao-2, dao-3, dao-4, dao-8 and dao-9 are down-regulated in daf-2 mutant adults compared to wild-type adults, whereas dao-5, dao-6 and dao-7 are up-regulated. The latter genes are negatively regulated by DAF-2 signaling and positively regulated by DAF-16. Positive regulation by DAF-2 on dao-1, dao-4 and dao-8 was mediated by DAF-16, whereas daf-16 mediates only part of DAF-2 signaling for dao-2 and dao-9. Regulation by DAF-2 is most likely DAF-16 independent for dao-3 and hsp-90. RNA levels of dao-5 and dao-6 showed elevated expression in daf-2 adults, as well as being strongly expressed in dauer larvae. In contrast, hsp-90 transcript levels are low in daf-2 mutant adults though they are enriched in dauer larvae, indicating overlapping but not identical mechanisms of efficient life maintenance in stress-resistant dauer larvae and long-lived daf-2 mutant adults. dao-1, dao-8 and dao-9 are homologs of the FK506 binding proteins that interact with the mammalian insulin pathway. dao-3 encodes a putative methylenetetrahydrofolate dehydrogenase. DAO-5 shows 33 % identity with human nucleolar phosphoprotein P130. dao-7 is similar to the mammalian ZFP36 protein. Distinct regulatory patterns of dao genes implicate their diverse positions within the signaling network of DAF-2 pathway, and suggest they have unique contributions to development, metabolism and longevity.

Aging↗
PubMed2001

Beyond synexpression relationships: local clustering of time-shifted and inverted gene expression profiles identifies new, biologically relevant interactions.

The complexity of biological systems provides for a great diversity of relationships between genes. The current analysis of whole-genome expression data focuses on relationships based on global correlation over a whole time-course, identifying clusters of genes whose expression levels simultaneously rise and fall. There are, of course, other potential relationships between genes, which are missed by such global clustering. These include activation, where one expects a time-delay between related expression profiles, and inhibition, where one expects an inverted relationship. Here, we propose a new method, which we call local clustering, for identifying these time-delayed and inverted relationships. It is related to conventional gene-expression clustering in a fashion analogous to the way local sequence alignment (the Smith-Waterman algorithm) is derived from global alignment (Needleman-Wunsch). An integral part of our method is the use of random score distributions to assess the statistical significance of each cluster. We applied our method to the yeast cell-cycle expression dataset and were able to detect a considerable number of additional biological relationships between genes, beyond those resulting from conventional correlation. We related these new relationships between genes to their similarity in function (as determined from the MIPS scheme) or their having known protein-protein interactions (as determined from the large-scale two-hybrid experiment); we found that genes strongly related by local clustering were considerably more likely than random to have a known interaction or a similar cellular role. This suggests that local clustering may be useful in functional annotation of uncharacterized genes. We examined many of the new relationships in detail. Some of them were already well-documented examples of inhibition or activation, which provide corroboration for our results. For instance, we found an inverted expression profile relationship between genes YME1 and YNT20, where the latter has been experimentally documented as a bypass suppressor of the former. We also found new relationships involving uncharacterized yeast genes and were able to suggest functions for many of them. In particular, we found a time-delayed expression relationship between J0544 (which has not yet been functionally characterized) and four genes associated with the mitochondria. This suggests that J0544 may be involved in the control or activation of mitochondrial genes. We have also looked at other, less extensive datasets than the yeast cell-cycle and found further interesting relationships. Our clustering program and a detailed website of clustering results is available at http://www.bioinfo.mbb.yale.edu/expression/cluster (or http://www.genecensus.org/expression/cluster).

Algorithms↗