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Biomedical subjects

Z Yang

Publications and source records attributed to Z Yang.

At least 487 records · Page 27Linked to original sources
PubMed1998

Likelihood ratio tests for detecting positive selection and application to primate lysozyme evolution.

An excess of nonsynonymous substitutions over synonymous ones is an important indicator of positive selection at the molecular level. A lineage that underwent Darwinian selection may have a nonsynonymous/synonymous rate ratio (dN/dS) that is different from those of other lineages or greater than one. In this paper, several codon-based likelihood models that allow for variable dN/dS ratios among lineages were developed. They were then used to construct likelihood ratio tests to examine whether the dN/dS ratio is variable among evolutionary lineages, whether the ratio for a few lineages of interest is different from the background ratio for other lineages in the phylogeny, and whether the dN/dS ratio for the lineages of interest is greater than one. The tests were applied to the lysozyme genes of 24 primate species. The dN/dS ratios were found to differ significantly among lineages, indicating that the evolution of primate lysozymes is episodic, which is incompatible with the neutral theory. Maximum-likelihood estimates of parameters suggested that about nine nonsynonymous and zero synonymous nucleotide substitutions occurred in the lineage leading to hominoids, and the dN/dS ratio for that lineage is significantly greater than one. The corresponding estimates for the lineage ancestral to colobine monkeys were nine and one, and the dN/dS ratio for the lineage is not significantly greater than one, although it is significantly higher than the background ratio. The likelihood analysis thus confirmed most, but not all, conclusions Messier and Stewart reached using reconstructed ancestral sequences to estimate synonymous and nonsynonymous rates for different lineages.

Animals↗
PubMed1998

Arabidopsis Rho-related GTPases: differential gene expression in pollen and polar localization in fission yeast.

The Rho small GTP-binding proteins are versatile, conserved molecular switches in eukaryotic signal transduction. Plants contain a unique subfamily of Rho-GTPases called Rop (Rho-related GTPases from plants). Our previous studies involving injection of antibodies indicated that the pea Rop GTPase Rop1Ps is critical for pollen tube growth. In this study we show that overexpression of an apparent Arabidopsis ortholog of Rop1Ps, Rop1At, induces isotropic cell growth in fission yeast (Schizosaccharomyces pombe) and that green fluorescence protein-tagged Rop1At displays polar localization to the site of growth in yeast. We found that Rop1At and two other Arabidopsis Rops, Rop3At and Rop5At, are all expressed in mature pollen. All three pollen Rops fall into the same subgroup as Rop1Ps and diverge from those Rops that are not expressed in mature pollen, suggesting a coupling of the structural conservation of Rop GTPases to their gene expression in pollen. However, pollen-specific transcript accumulation for Rop1At is much higher than that for Rop3At and Rop5At. Furthermore, Rop1At is specifically expressed in anthers, whereas Rop3At and Rop5At are also expressed in vegetative tissues. In transgenic plants containing the Rop1At promoter:GUS fusion gene, GUS is specifically expressed in mature pollen and pollen tubes. We propose that Rop1At may play a predominant role in the regulation of polarized cell growth in pollen, whereas its close relatives Rop3At and Rop5At may be functionally redundant to Rop1At in pollen.

Amino Acid Sequence↗
PubMed1998

Automatic matching of homologous histological sections.

The role of neuroanatomical atlases is undergoing a significant redefinition as digital atlases become available. These have the potential to serve as more than passive guides and to hold the role of directing segmentation and multimodal fusion of experimental data. Key elements needed to support these new tasks are registration algorithms. For images derived from histological procedures, the need is for techniques to map the two-dimensional (2-D) images of the sectional material into the reference atlas which may be a full three-dimensional (3-D) data set or one consisting of a series of 2-D images. A variety of 2-D-2-D registration methods are available to align experimental images with the atlas once the corresponding plane of section through the atlas has been identified. Methods to automate the identification of the homologous plane, however, have not been previously reported. In this paper we use the external section contour to drive the identification and registration procedure. For this purpose, we model the contours by B-splines because of their attractive properties the most important of which are: 1) smoothness and continuity; 2) local controllability which implies that local changes in shape are confined to the B-spline parameters local to that change; 3) shape invariance under affine transformation, which means that the affine transformed curve is still a B-spline whose control points are related to the object control points through the transformation. In this paper we present a fast algorithm for estimating the control points of the B-spline which is robust to nonuniform sampling, noise, and local deformations. Curve matching is achieved by using a similarity measure that depends directly on the parameters of the B-spline. Performance tests are reported using histological material from rat brains.

Animals↗
PubMed1998

Control of sympathetic outflows by the hypothalamic paraventricular nucleus.

1. The functional role of the paraventricular nucleus (PVN) has been examined by studying its connections with cardiovascular neurons in the medulla and spinal cord and its influence on activity in several sympathetic nerves. 2. Chemical stimulation of neurons within the PVN can elicit pressor responses and can excite reticulo-spinal vasomotor neurons in the rostral ventrolateral medulla (RVLM). 3. The PVN-RVLM excitation is blocked by kynurenic acid applied iontophoretically in the vicinity of RVLM-spinal neurons, suggesting this is a glutamate-dependent pathway. 4. Electrical stimulation of PVN neurons evoked action potentials in RVLM neurons after 27 ms with a small variability. 5. Anterograde and retrograde labelling of PVN and RVLM neurons revealed PVN terminals closely associated with RVLM-spinal neurons and showed that the PVN is connected to the spinal cord via three pathways. 6. Chemical activation of PVN neurons can produce a pattern of activation of cardiovascular neurons similar to that occurring in defence against plasma volume expansion. 7. It is concluded that the PVN connections with the RVLM and spinal cord are important to a role in defending against life-threatening disturbances.

Animals↗
PubMed1998

A DnaK homolog in Myxococcus xanthus is involved in social motility and fruiting body formation.

Myxococcus xanthus is a gram-negative soil bacterium which exhibits a complex life cycle and social behavior. In this study, two developmental mutants of M. xanthus were isolated through Tn5 transposon mutagenesis. The mutants were found to be defective in cellular aggregation as well as in sporulation. Further phenotypic characterization indicated that the mutants were defective in social motility but normal in directed cell movements. Both mutations were cloned by a transposon-tagging method. Sequence analysis indicated that both insertions occurred in the same gene, which encodes a homolog of DnaK. Unlike the dnaK genes in other bacteria, this M. xanthus homolog appears not to be regulated by temperature or heat shock and is constitutively expressed during vegetative growth and under starvation. The defects of the mutants indicate that this DnaK homolog is important for the social motility and development of M. xanthus.

Bacterial Proteins↗
PubMed1998

Chemotaxis in Borrelia burgdorferi.

Borrelia burgdorferi is a motile spirochete which has been identified as the causative microorganism in Lyme disease. The physiological functions which govern the motility of this organism have not been elucidated. In this study, we found that motility of B. burgdorferi required an environment similar to interstitial fluid (e.g., pH 7.6 and 0.15 M NaCl). Several methods were used to detect and measure chemotaxis of B. burgdorferi. A number of chemical compounds and mixtures were surveyed for the ability to induce positive and negative chemotaxis of B. burgdorferi. Rabbit serum was found to be an attractant for B. burgdorferi, while ethanol and butanol were found to be repellents. Unlike some free-living spirochetes (e.g., Spirochaeta aurantia), B. burgdorferi did not exhibit any observable chemotaxis to common sugars or amino acids. A method was developed to produce spirochete cells with a self-entangled end. These cells enabled us to study the rotation of a single flagellar bundle in response to chemoattractants or repellents. The study shows that the frequency and duration for pausing of flagella are important for chemotaxis of B. burgdorferi.

Adaptation, Physiological↗
PubMed1998

Methylation of FrzCD defines a discrete step in the developmental program of Myxococcus xanthus.

Myxococcus xanthus is a gram-negative soil bacterium which undergoes fruiting body formation during starvation. The frz signal transduction system has been found to play an important role in this process. FrzCD, a methyl-accepting taxis protein homologue, shows modulated methylation during cellular aggregation, which is thought to be part of an adaptation response to an aggregation signal. In this study, we assayed FrzCD methylation in many known and newly isolated mutants defective in fruiting body formation to determine a possible relationship between the methylation response and fruiting morphology. The results of our analysis indicated that the developmental mutants could be divided into two groups based on their ability to show normal FrzCD methylation during development. Many mutants blocked early in development, i.e., nonaggregating or abnormally aggregating mutants, showed poor FrzCD methylation. The well-characterized asg, bsg, csg, and esg mutants were found to be of this type. The defects in FrzCD methylation of these signaling mutants could be partially rescued by extracellular complementation with wild-type cells or addition of chemicals which restore their fruiting body formation. Mutants blocked in late development, i.e., translucent mounds, showed normal FrzCD methylation. Surprisingly, some mutants blocked in early development also exhibited a normal level of FrzCD methylation. The characterized mutants in this group were found to be defective in social motility. This indicates that FrzCD methylation defines a discrete step in the development of M. xanthus and that social motility mutants are not blocked in these early developmental steps.

Bacterial Proteins↗
PubMed1998

Results from 5 years of nationwide DNA fingerprinting of Mycobacterium tuberculosis complex isolates in a country with a low incidence of M. tuberculosis infection.

Results from DNA fingerprint analyses of Mycobacterium tuberculosis complex isolates from tuberculosis (TB) patients diagnosed during 5 years in Denmark are presented. The lack of success in eradicating TB in this low-incidence country may be explained by an unrecognized high frequency of active TB transmission (57%) among native Danes. Only two strains of M. tuberculosis are responsible for 40% of all clustered cases of TB among Danes.

Adolescent↗
PubMed1998

Diversity of DNA fingerprints of Mycobacterium tuberculosis isolates in the United States.

To investigate the diversity of IS6110 fingerprints of Mycobacterium tuberculosis isolates in the United States and to determine if matching IS6110 fingerprints represent recent interstate tuberculosis transmission, we performed restriction fragment length polymorphism analysis of M. tuberculosis isolates from 1,326 patients in three geographically separated states. Seven hundred ninety-five different IS6110 fingerprint patterns were generated, and pattern diversity was similar in each state. Ninety-six percent of the fingerprint patterns were observed in only one state, demonstrating that most IS6110 fingerprint patterns are confined to a single geographic location. Of the IS6110 fingerprint patterns that were shared by isolates from more than one state, most isolates with 1 to 5 IS6110 copies were separable by pTBN12 fingerprinting whereas those with > 15 copies were not. One high-copy-number M. tuberculosis strain had identical IS6110 and pTBN12 fingerprints and included 57 isolates from three states. Epidemiological data demonstrated significant recent transmission of tuberculosis within each city but not among the states. This suggests that identical fingerprints of isolates from geographically separate locations most likely reflect interstate tuberculosis transmission in the past, with subsequent intrastate spread of disease. Further evaluation of M. tuberculosis strains that cause outbreaks in different geographic locations will provide insight into the epidemiological and bacteriological factors that facilitate the spread of tuberculosis.

DNA Fingerprinting↗
PubMed1998

Demonstration of an early and a late phase of ischemic preconditioning in mice.

It is unknown whether ischemic preconditioning (PC; either early or late) occurs in the mouse. The goal of this study was to answer this question and to develop a reliable and physiologically relevant murine model of both early and late ischemic PC. A total of 201 mice were used. In nonpreconditioned open-chest animals subjected to 30 min of coronary occlusion followed by 24 h of reperfusion, infarct size (tetrazolium staining) averaged 52% of the region at risk. When the 30-min occlusion was performed 10 min after a PC protocol consisting of six cycles of 4-min occlusion and 4-min reperfusion, infarct size was reduced by 75%, indicating an early PC effect. When the 30-min occlusion was performed 24 h after the same PC protocol, infarct size was reduced by 48%, indicating a late PC effect. In mice in which the 30-min occlusion was followed by 4 h of reperfusion, infarct size was similar to that observed after 24 h of reperfusion, indicating that a 4-h reperfusion interval is sufficient to detect the final extent of cell death in this model. Fundamental physiological variables (body temperature, arterial oxygenation, acid-base balance, heart rate, and arterial pressure) were measured and found to be within normal limits. Taken together, these results demonstrate that, in the mouse, a robust infarct-sparing effect occurs during both the early and the late phases of ischemic PC, although the early phase is more powerful. This murine model is physiologically relevant, provides reliable measurements, and should be useful for elucidating the cellular mechanisms of ischemic PC in genetically engineered animals.

Animals↗
PubMed1998

The distribution of the matricellular protein thrombospondin 2 in tissues of embryonic and adult mice.

Mice that lack the matricellular protein thrombospondin 2 (TSP2) develop a pleiotropic phenotype characterized by morphological changes in connective tissues, an increase in vascular density, and a propensity for bleeding. Furthermore, dermal cells derived from TSP2-null mice display adhesion defects, a finding that implicates TSP2 in cell-matrix interactions. To gain a better understanding of the participation of TSP2 in the development and maturation of the mouse, we examined its distribution in embryonic and adult tissues. Special attention was paid to the presence of TSP2 in collagen fibers, because collagen fibrils in the TSP2-null mouse appear to be irregular in size and contour by electron microscopy. Immunohistochemical analysis of Day 15 and Day 18 embryos revealed TSP2 in areas of chondrogenesis, osteogenesis, and vasculogenesis, and in dermal and other connective tissue-forming cells. Distinctly different patterns of deposition of TSP2 were observed in areas of developing cartilage and bone at Days 15 and 18 of embryonic development. A survey of adult tissues revealed TSP2 in dermal fibroblasts, articular chondrocytes, Purkinje cells in the cerebellum, Leidig cells in the testis, and in the adrenal cortex. Dermal fibroblasts were also shown to synthesize TSP2 in vitro. The distribution of TSP2 during development is in keeping with its participation in the formation of a variety of connective tissues. In adult tissues, TSP2 is located in the pericellular environment, where it can potentially influence the cell-matrix interactions associated with cell movement and tissue repair.

Age Factors↗
PubMed1998

Extension of in vitro life-span of gamma-irradiated human embryo cells accompanied by chromosome instability.

We studied the effect of repeated irradiation with a low dose rate (about 0.0012 cGy per min) of 60Co gamma-rays on the in vitro life-span of human embryo (HE) cells. HE cells were cultured in an incubator that was set in a 60Co gamma-ray-irradiation room, and the irradiation was repeated throughout the life-span of the HE cells (for about 150 to 160 days) on every day base. During this period, the cells accumulated 106 to 123 cGy. The life-span of the irradiated cells prolonged 1.14 to 1.35 times when compared to that of non-irradiated cells. The incidence of cells with chromosome bridge and micronuclei significantly increased in the irradiated cells. Although the number of chromosomes gradually changed with repetition of culture in both non-irradiated and irradiated cells, the frequencies of aneuploid cells in irradiated cells were about two times higher than that in non-irradiated cells. These results indicate that repeated irradiation with a low dose of gamma-rays produces chromosome instability, and it may be a cause of numerical chromosome abnormalities and life-span extension of irradiated cells.

Aneuploidy↗
PubMed1998

Telomerase activity, telomere length, and chromosome aberrations in the extension of life span of human embryo cells induced by low-dose X-rays.

We examined whether the shortening of telomere structure is related to in vitro cellular aging after multiple low-dose irradiation. We used three strains of HE cells (HE23, HE31, and HE40) exhibiting different levels of telomerase activity and irradiated these cells twice a week with a dose of 2 cGy or 4 cGy of X-rays until they senesced. The cells were in total exposed to doses of 52-208 cGy of X-rays. Only the HE31 cells, which had no telomerase activity, experienced an increase in the number of cell divisions, reaching a maximum of 120-124% of the non-irradiated controls. However, in two strains which did exhibit telomerase activity in an early passage in culture, no extension of cell life span was found. Telomerase-positive cells completely lost all telomerase activity when the cells were subcultured several times without irradiation. In the HE31 cells where the life span was extended, the ratio of cell having a long telomere was higher than those of the other two cells (HE23 and HE40). Cytogenetic analysis revealed that the life span extension due to multiple low-dose irradiation which was observed in HE31 cells did not correlate with specific chromosome alterations. Our results suggest that the telomerase activity remaining in the cells at an early passage does not correlate with the extension of life span in vitro by X-irradiation. The factor other than telomerase activity may play an important role in the regulation of telomere length and the extension of life span.

Cell Division↗
PubMed1998

Childhood diabetes in China. Enormous variation by place and ethnic group.

OBJECTIVE: To investigate the incidence rate of IDDM in China. RESEARCH DESIGN AND METHODS: The Chinese IDDM registry was established in 1991 as part of the World Health Organization's Multinational Project for Childhood Diabetes (DiaMond) project. Twenty-two centers were developed to monitor the incidence of IDDM in children < 15 years of age. The population under investigation includes > 20 million individuals, representing approximately 7% of the children in China. Capture-recapture methods were used to estimate the ascertainment. RESULTS: The overall ascertainment-corrected IDDM incidence rate in China was 0.51 per 100,000, the lowest rate ever reported. There was a 12-fold geographic variation (0.13-1.61 per 100,000). In general, the incidence rate was higher in the north and the east. There was a sixfold difference among ethnic groups (highest: Mongol group, 1.82 per 100,000; lowest: Zhuang group, 0.32 per 100,000). CONCLUSIONS: China has an extremely low overall IDDM incidence rate. China also has the greatest geographic and ethnic variation seen for any country.

Adolescent↗
PubMed1998

Use of antimicrobial spray applied with an inside-outside birdwasher to reduce bacterial contamination on prechilled chicken carcasses.

Antimicrobial sprays applied using a modified inside-outside birdwasher to reduce Salmonella typhimurium and total aerobic bacteria on prechilled chicken carcasses were evaluated in a poultry processing pilot plant. Four chemicals, including trisodium phosphate (TSP, 10%), lactic acid (LAC, 2%), cetylpyridinium chloride (CPC, 0.5%), and sodium bisulfate (SBS, 5%) were selected to be tested as antimicrobial agents. Each chicken carcass was inoculated by spraying the outside and inside of each carcass with S. typhimurium at 10(5) CFU per carcass. The inoculated carcasses then were passed through the birdwasher and sprayed with selected chemicals at 35 degrees C at a pressure of 413 kPa for 17 s. After a 60-s setting time on a shackle line, the carcasses were sprayed with tap water to rinse off chemical residue. All the chemical treatments reduced Salmonella on the chicken carcasses by approximately 2 log10 CFU per carcass. Total aerobes on the chicken carcasses, however, were reduced by 2.16, 1.66, 1.03, and 0.74 log10 CFU per carcass after spraying with 0.5% CPC, 5% SBS, 2% LAC, or 10% TSP, respectively. Spray treatments of both SBS and LAC caused slight discoloration in part of the chicken skin. The most effective antimicrobial spray treatment for reducing both Salmonella and total aerobes on prechilled chicken carcasses was 0.5% CPC.

Animals↗
PubMed1998

Studies on the creatine kinase MM isoforms of normal and Duchenne muscular dystrophic patients.

OBJECTIVE: To study the changes of creatine kinase MM (CK-MM) isoforms in Duchenne muscular dystrophy (DMD) patients. METHODS: Serum samples from 49 DMD patients and 40 control subjects were collected for CK-MM isoforms measurement. CK-MM isoforms were separated within 30 minutes by electrophoresis on agarose gel with a discontinuous buffer system at constant current of 30 mA and low voltage of 200-300 V, then measured by fluorescence scanning. RESULTS: Significant differences of MM2/MM1 ratio were found between DMD patients and control subjects (P < 0.05) as well as among the three different age groups of DMD patients (P < 0.05). CONCLUSIONS: CK-MM isoforms may present useful information for the early diagnosis and evaluation of DMD and the ratio of MM2/MM1 can be considered as a specific indicator of the degree of seriousness for DMD patients.

Adolescent↗
PubMed1998

[Epidemiologic and experimental studies on epidemic haemorrhagic fever virus in pigs].

In order to study the roles of pigs with epidemic haemorrhagic fever virus, epidemiologic and experimental studies were carried out in pigs. Aetiological, serological and polymerase chain reaction (PCR) techniques were performed. Results showed that not only pigs could be infected with EHFV under natural or experimental conditions but susceptible to EHFV as well. Virus may disseminate to many organs of the animals through blood and cause transient pathologic changes. EHFV duplicates inside the animal bodies and be excreted to cause pollution of environment. It is possible that pigs serve as sources of EHF infection. Our research data also showed for the first time that EHEV were vertically transmitted through the placenta of pigs. There was no evidence showing that people raising pigs were symptomatically sick due to EHF infection.

Animals↗