Biomedical subjects

C Yang

Publications and source records attributed to C Yang.

At least 37 records · Page 2Linked to original sources

PubMed1999

Conservation of ARS elements and chromosomal DNA replication origins on chromosomes III of Saccharomyces cerevisiae and S. carlsbergensis.

DNA replication origins, specified by ARS elements in Saccharomyces cerevisiae, play an essential role in the stable transmission of chromosomes. Little is known about the evolution of ARS elements. We have isolated and characterized ARS elements from a chromosome III recovered from an alloploid Carlsberg brewing yeast that has diverged from its S. cerevisiae homeologue. The positions of seven ARS elements identified in this S. carlsbergensis chromosome are conserved: they are located in intergenic regions flanked by open reading frames homologous to those that flank seven ARS elements of the S. cerevisiae chromosome. The S. carlsbergensis ARS elements were active both in S. cerevisiae and S. monacensis, which has been proposed to be the source of the diverged genome present in brewing yeast. Moreover, their function as chromosomal replication origins correlated strongly with the activity of S. cerevisiae ARS elements, demonstrating the conservation of ARS activity and replication origin function in these two species.

Conserved Sequence↗

PubMed1999

DNA sequence and functional analysis of homologous ARS elements of Saccharomyces cerevisiae and S. carlsbergensis.

ARS elements of Saccharomyces cerevisiae are the cis-acting sequences required for the initiation of chromosomal DNA replication. Comparisons of the DNA sequences of unrelated ARS elements from different regions of the genome have revealed no significant DNA sequence conservation. We have compared the sequences of seven pairs of homologous ARS elements from two Saccharomyces species, S. cerevisiae and S. carlsbergensis. In all but one case, the ARS308-ARS308(carl) pair, significant blocks of homology were detected. In the cases of ARS305, ARS307, and ARS309, previously identified functional elements were found to be conserved in their S. carlsbergensis homologs. Mutation of the conserved sequences in the S. carlsbergensis ARS elements revealed that the homologous sequences are required for function. These observations suggested that the sequences important for ARS function would be conserved in other ARS elements. Sequence comparisons aided in the identification of the essential matches to the ARS consensus sequence (ACS) of ARS304, ARS306, and ARS310(carl), though not of ARS310.

Amino Acid Sequence↗

PubMed1999

Fourth branchial arch sinus: clinical presentation, diagnostic workup, and surgical treatment.

OBJECTIVES/HYPOTHESIS: Abnormalities of the fourth branchial arch are much less common than those of the second arch and present in a different manner. The authors report their experience with five cases of fourth arch sinuses. METHODS: Retrospective chart review of patients at a tertiary care center. RESULTS: All patients presented in the first or second decade of life, and all but one had left-sided neck involvement. Four patients presented with recurrent low neck inflammatory episodes, and one with respiratory compromise. Diagnostic studies performed included ultrasound, computed tomography (CT) scan, barium swallow, magnetic resonance imaging, and fine-needle aspiration. Barium contrast studies and CT scan were the most useful in demonstrating a fourth arch sinus tract preoperatively. Surgical treatment with an emphasis on complete exposure of the recurrent laryngeal nerve and exposure of the lateral piriform sinus to facilitate complete sinus tract excision was successful in all patients. CONCLUSION: The clinical history of recurrent low neck inflammatory episodes in young patients, especially on the left side, should raise the suspicion of this entity. Investigation using barium swallow in combination with CT scanning is useful. Excision of the sinus tract taking care not to injure the recurrent laryngeal nerve is curative.

Adolescent↗

PubMed1999

Stabilization of the i-motif by intramolecular adenine-adenine-thymine base triple in the structure of d(ACCCT).

The crystal structure of d(ACCCT), solved by molecular replacement, shows a four-stranded i-motif conformation, where two parallel duplexes intercalate with one another in opposite orientations. Each duplex is stabilized by hemi-protonated C-C+ base pairing between parallel strands, and a string of water molecules bridge the cytosine N4 atoms to phosphate O atoms. This structure of d(ACCCT) shows examples of reversed Hoogsteen and Watson-Crick base pairing in both intermolecular and intramolecular manners to stabilize the tetraplex. Noticeably, the four-stranded complex is further stabilized at one end by a three-base hydrogen-bonding network, in which two adenines and a thymine form four hydrogen bonds via a reverse Hoogsteen and an asymmetric adenine-adenine base pairing. The structure of d(ACCCT) shows a similar local structure to that found in the d(TAA) part of the crystal structure of d(TAACCC) and provides further structural evidence that these base arrangements are essential for stabilizing these novel DNA super-secondary structures.

Adenine↗

PubMed1999

Optics systems for the home laboratory: caveat emptor.

A careful and detailed evaluation of different multilayer optics (Osmic Cross-coupled Max-Flux Optics and Osmic Confocal Max-Flux Optics) compared with MSC/Yale Total-Reflection Mirrors has been completed. This report provides a detailed comparison of usable flux, spectral purity, divergence, beam profile and data quality for these systems. The most striking results have been obtained using either the Osmic #4 or #7 Confocal Max-Flux Optic, which were designed for 0. l and 0.2 mm focal spots, respectively, in conjunction with a 0.3 mm focal spot. These optic configurations provide a 5.8-fold and 8.2-fold increase in flux through a 0.2 mm aperture, respectively, compared with the MSC/Yale Mirrors.

Crystallography, X-Ray↗

PubMed1999

A nonlinear axisymmetric model with fluid-wall interactions for steady viscous flow in stenotic elastic tubes.

Arteries with high-grade stenoses may compress under physiologic conditions due to negative transmural pressure caused by high-velocity flow passing through the stenoses. To quantify the compressive conditions near the stenosis, a nonlinear axisymmetric model with fluid-wall interactions is introduced to simulate the viscous flow in a compliant stenotic tube. The nonlinear elastic properties of the tube (tube law) are measured experimentally and used in the model. The model is solved using ADINA (Automatic Dynamic Incremental Nonlinear Analysis), which is a finite element package capable of solving problems with fluid-structure interactions. Our results indicate that severe stenoses cause critical flow conditions such as negative pressure and high and low shear stresses, which may be related to artery compression, plaque cap rupture, platelet activation, and thrombus formation. The pressure filed near a stenosis has a complex pattern not seen in one-dimensional models. Negative transmural pressure as low as -24 mmHg for a 78 percent stenosis by diameter is observed at the throat of the stenosis for a downstream pressure of 30 mmHg. Maximum shear stress as a high as 1860 dyn/cm2 occurs at the throat of the stenoses, while low shear stress with reversed direction is observed right distal to the stenosis. Compressive stresses are observed inside the tube wall. The maximal principal stress and hoop stress in the 78 percent stenosis are 80 percent higher than that from the 50 percent stenosis used in our simulation. Flow rates under different pressure drop conditions are calculated and compared with experimental measurements and reasonable agreement is found for the prebuckling stage.

Animals↗

PubMed1999

Phylogenetic analysis of Cryptosporidium parasites based on the small-subunit rRNA gene locus.

Biological data support the hypothesis that there are multiple species in the genus Cryptosporidium, but a recent analysis of the available genetic data suggested that there is insufficient evidence for species differentiation. In order to resolve the controversy in the taxonomy of this parasite genus, we characterized the small-subunit rRNA genes of Cryptosporidium parvum, Cryptosporidium baileyi, Cryptosporidium muris, and Cryptosporidium serpentis and performed a phylogenetic analysis of the genus Cryptosporidium. Our study revealed that the genus Cryptosporidium contains the phylogenetically distinct species C. parvum, C. muris, C. baileyi, and C. serpentis, which is consistent with the biological characteristics and host specificity data. The Cryptosporidium species formed two clades, with C. parvum and C. baileyi belonging to one clade and C. muris and C. serpentis belonging to the other clade. Within C. parvum, human genotype isolates and guinea pig isolates (known as Cryptosporidium wrairi) each differed from bovine genotype isolates by the nucleotide sequence in four regions. A C. muris isolate from cattle was also different from parasites isolated from a rock hyrax and a Bactrian camel. Minor differences were also detected between C. serpentis isolates from snakes and lizards. Based on the genetic information, a species- and strain-specific PCR-restriction fragment length polymorphism diagnostic tool was developed.

Animals↗

PubMed1999

Partial protection against Plasmodium vivax blood-stage infection in Saimiri monkeys by immunization with a recombinant C-terminal fragment of merozoite surface protein 1 in block copolymer adjuvant.

Merozoite surface protein 1 is a candidate for blood-stage vaccines against malaria parasites. We report here an immunization study of Saimiri monkeys with a yeast-expressed recombinant protein containing the C terminus of Plasmodium vivax merozoite surface protein 1 and two T-helper epitopes of tetanus toxin (yP2P30Pv20019), formulated in aluminum hydroxide (alum) and block copolymer P1005. Monkeys immunized three times with yP2P30Pv20019 in block copolymer P1005 had significantly higher prechallenge titers of immunoglobulin G (IgG) antibodies against the immunogen and asexual blood-stage parasites than those immunized with yP2P30Pv20019 in alum, antigen alone, or phosphate-buffered saline (PBS) (P < 0.05). Their peripheral blood mononuclear cell proliferative responses to immunogen stimulation 4 weeks after the second immunization were also significantly higher than those from the PBS control group (P < 0.05). Upon challenge with 100,000 asexual blood-stage parasites 5 weeks after the last immunization, monkeys immunized with yP2P30Pv20019 in block copolymer P1005 had prepatent periods longer than those for the control alone group (P > 0.05). Three of the five animals in this group also had low parasitemia (peak parasitemia, </=20 parasites/microliter of blood). Partially protected monkeys had significantly higher levels of prechallenge antibodies against the immunogen than those unprotected (P < 0.05). There was also a positive correlation between the prepatent period and titers of IgG antibodies against the immunogen and asexual blood-stage parasites and a negative correlation between accumulated parasitemia and titers of IgG antibodies against the immunogen (P < 0.05). These results indicate that when combined with block copolymer and potent T-helper epitopes, the yeast-expressed P2P30Pv20019 recombinant protein may offer some protection against malaria.

Adjuvants, Immunologic↗

PubMed1999

Detection of phylogenetically diverse human immunodeficiency virus type 1 groups M and O from plasma by using highly sensitive and specific generic primers.

The high degree of genetic diversity within human immunodeficiency virus type 1 (HIV-1), which includes two major groups, M (major) and O (outlier), and various env subtypes within group M (subtypes A to J), has made designing assays that will detect all known HIV-1 strains difficult. We have developed a generic primer set based on the conserved immunodominant region of transmembrane protein gp41 that can reliably amplify as few as 10 copies/PCR of viral DNA from near-full-length clones representing group M subtypes A to H (subtypes I and J were not available). The assay is highly sensitive in detecting plasma viral RNA from HIV-1 strains of diverse geographic origins representing different subtypes of HIV-1 group M as well as HIV-1 group O. Of the 253 group M plasma specimens (subtypes A, 68 specimens; B, 71; C, 19; D, 27; E, 23; F, 33; and G, 12), 250 (98.8%) were amplified by using the gp41 M/O primer set. More importantly, all 32 (100%) group O plasma samples were also amplified with these primers. In vitro spiking experiments further revealed that the assay could reliably detect as few as 25 copies/ml of viral RNA and gave positive signals in HIV-1-seropositive specimens with plasma copy numbers below the limits of detection by all commercially available viral load assays. In addition, analysis of five seroconversion panels indicated that the assay is highly sensitive for early detection of plasma viremia during the "window period." Thus, the highly sensitive assay will be useful for early detection of HIV-1 in clinical specimens from all known HIV-1 infections, regardless of their genotypes and geographic origins.

Acquired Immunodeficiency Syndrome↗

PubMed1999

Spatial coherence of forward-scattered light in a turbid medium.

We study spatially coherent forward-scattered light propagating in a turbid medium of moderate optical depth (0-9 mean free paths). Coherent detection was achieved by using a tilted heterodyne geometry, which desensitizes coherent detection of the attenuated incident light. We show that the degree of spatial coherence is significantly higher for light scattered only once in comparison with that for multiply scattered light and that it approaches a small constant value for large numbers of scattering events.

Extraterrestrial Environment↗

PubMed1999

Testing the efficacy of a recombinant merozoite surface protein (MSP-1(19) of Plasmodium vivax in Saimiri boliviensis monkeys.

Saimiri boliviensis monkeys were immunized with the yeast-expressed recombinant protein yP2P30Pv200(19). The antigen consisted of the C-terminus (amino acid Asn1622-Ser1729) of the merozoite surface protein 1 of the Plasmodium vivax Salvador I strain. Two universal T helper cell epitopes (P2 and P30) of tetanus toxin and six histidine residues for purification purposes were attached to the N- and C-termini, respectively. Four groups of five monkeys were given three immunizations at four-week intervals with either 250 microg of yP2P30Pv200(19) formulated with nonionic block copolymer P1005, 250 microg of antigen adsorbed to alum, 250 microg of antigen in phosphate-buffered saline (PBS), or PBS alone. Five weeks after the last immunization, each animal was inoculated with 100,000 parasitized erythrocytes of the Salvador I strain of P. vivax. Animals were splenectomized one week after challenge to increase parasite densities; after seven weeks of infection, animals were treated. Eighteen weeks later, the animals were rechallenged with the homologous parasite. Following the first challenge, three monkeys immunized with the antigen with P1005 were protected; no animals were protected from rechallenge. One monkey immunized with yP2P30Pv200(19) with alum was protected; no protection was seen after rechallenge. Two monkeys immunized with antigen alone were protected; none were protected from rechallenge. One control animal had a low parasite count following primary infection; none were protected against rechallenge. Adverse reactions were only observed with animals receiving P1005. It is proposed that splenectomy of the monkeys prevented adequate assessment of the efficacy of this antigen. Identification of a monkey host that supports high density parasitemia without splenectomy appears needed before further testing of blood-stage vaccines against P. vivax.

Adjuvants, Immunologic↗

PubMed1999

Role of eicosanoids in the pathogenesis of murine cerebral malaria.

Because microvascular damage is a common feature of cerebral malaria, we have examined the role eicosanoid metabolites (prostaglandins and leukotrienes) in experimental cerebral malaria. Eighty ICR mice were infected with Plasmodium berghei ANKA, with 40 uninfected mice as controls. Half of the infected mice were treated on days 4 and 5 with aspirin, a prostaglandin synthesis inhibitor. Infected mice started to die of cerebral malaria on day 6, and by day 17, all infected mice died. In contrast, all infected mice treated with aspirin died by day 12. Infected mice had increased phospholipase A2 mRNA expression in the spleen and cyclooxygenase 1 (COX1) and COX2 expression in the brain. At the peak of cerebral malaria, infected mice had higher serum leukotriene B4 levels than control mice, and aspirin-treated infected mice had higher serum leukotriene B4 levels than untreated infected mice. These results suggest that prostaglandins are protective whereas leukotrienes are detrimental in cerebral malaria.

Animals↗

PubMed1999

Cytokine production in rhesus monkeys infected with Plasmodium coatneyi.

Plasmodium coatneyi infection in rhesus monkeys has been used as a model for studying human malaria. Cytokine production in this model, however, has so far not been examined. In this study, four rhesus monkeys were infected with P. coatneyi, with another four animals serving as uninfected controls. Blood samples were taken for the determination of daily parasitemia, and cytokine and prostaglandin E2 (PGE2) levels at days 0, 3, 5, 7, and 10. All inoculated animals became infected, with synchronized appearance of ring-stage parasites. Infected monkeys had increased plasma levels of proinflammatory cytokines (interleukin-1beta, interferon-gamma, and tumor necrosis factor-alpha) during the late stage of the infection. They also had increased production of ciliary neurotrophic factor. In conjunction with the production of proinflammatory cytokines, infected monkeys also had gradual increases in the production of PGE2. A continued definition of the P. coatneyi/rhesus monkey animal model should be useful for the elucidation of the immunopathogenesis of human malaria.

Animals↗

PubMed1999

The physiological response of thrombopoietin (c-Mpl ligand) to thrombocytopenia in the rat.

It has been suggested that circulating levels of thrombopoietin (TPO) are determined primarily by platelet and megakaryocyte clearance of TPO and not by changes in hepatic TPO production. The experimental evidence accumulated so far to support this hypothesis is incomplete. We have therefore developed a new model of non-immune thrombocytopenia in the rat and used it to assess the relationship of TPO (c-mpl ligand) to the platelet mass. 14 d following the administration of busulphan, the platelet count reached a nadir of <2% of its initial value and remained at this level for up to 6 d. Circulating TPO was measured by two different bioassays which were sensitive enough to measure normal levels of TPO and levels rose from 106 +/- 29 pg/ml in animals with a normal platelet count to 2015 +/- 544 pg/ml in those with thrombocytopenia. These elevated levels of TPO were solely a response to the low platelet count since transfusion of a normal mass of platelets into the thrombocytopenic animals returned the TPO levels exactly to normal. The increase in TPO levels in thrombocytopenic animals was not due to increased TPO production since the thrombocytopenic animals did not show any increase in TPO mRNA in total or polysome-associated hepatic RNA. Rather, rat platelets were able to bind and stoichiometrically remove TPO from thrombocytopenic plasma via high-affinity receptors (Kd = 38 +/- 10 pm; 233 +/- 32 receptors/platelet). These results serve as a proof that the circulating level of TPO is determined not by alterations in TPO transcription or translation but by the ability of the platelet mass to bind and remove TPO from the circulation.

Animals↗

PubMed1999

Modifications to standard guidelines and changes in blood pressure readings: use of an automatic blood pressure device.

The purpose of the study was to determine what effect modifications to American Heart Association (AHA) guidelines produce when taking blood pressures with an automatic device. Eight blood pressure measurements were taken at least 2 minutes apart; two with standard AHA guidelines and six with modifications. Findings of this study suggest that elevation of the arm can have a significant effect on both the systolic and diastolic blood pressure. Two modifications, talking and placing the arm beside the trunk, raised the diastolic pressure. However, some modifications did not have a statistically significant effect. Techniques used to take blood pressures with an automatic device can have a significant effect on the readings.

Adult↗

PubMed1999

The expression of insulin-like growth factor II, hepatitis B virus X antigen and p21 in experimental hepatocarcinogenesis in tree shrews.

The purpose of this paper was to study the mechanism of synergistic effect in hepatocarcinogenesis induced by hepatitis B virus (HBV) infection and aflatoxin B1 (AFB1) intake. Immunohistochemical staining was used in formalin-fixed, paraffin-embedded sections of cancer and liver tissues. The incidence of hepatocellular carcinomas (HCCs) was 52.9% in experimental tree shrews that received both HBV and AFB1. It was significantly higher than that of animals exposed to HBV (11.1%, Group B), or (AFB1) (15.8%, group C) alone. HCC was not found in the control animals (group D). The expressions of insulin-like growth factor II (IGF-II) were 82.4%, 22.2%, 26.3% and 0 in groups A, B, C and D, respectively. The significant differences of IGF-II were observed between groups A and B, C and D (P < 0.05). The expressions of p21 were 29.4%, 11.1%, 15.8% and 0 in group A, B, C and D, respectively. The positive rate of hepatitis B x antigen (HbxAg) was significantly higher in the group A than that in the group B (52.9% vs. 11.1%, P < 0.05). The parallel relations between the incidence of HCC and the overexpressions of these genes protein have been found in each group. On the other hand, the expressions of these genes in tumour-bearing tree shrews were significantly higher than that in nontumour-bearing animals. These findings suggest a synergistic effects of HBV and AFB1 in activation of these genes in tree shrews. Overexpressions of these genes may take an important role in the course of hepatocarcinogenesis in tree shrews.

Aflatoxin B1↗

PubMed1999

Synergistic effect of hepatitis B virus and aflatoxin B1 in hepatocarcinogenesis in tree shrews.

An animal experiment with tree shrews was performed to detect the synergistic effects of hepatitis B virus (HBV) infection and dietary aflatoxin B1 (AFB1) in hepatocarcinogenesis. Adult healthy tree shrews (Tupaia belangeri chinensis) were divided into four groups: Group A (HBV + AFB1)--animals were infected with human HBV serum at first, then fed AFB1 diluted with milk, 150 ug/kg.bw/day, 6 days/week for 105 weeks. Group B (HBV)--animals were infected with human HBV as Group A, but no AFB1 treatment. Group C (AFB1)--animals were treated with AFB1 as Group A but no HBV infection. Group D--animals were treated neither with human HBV nor AFB1. During the experiment, blood samples and liver biopsies were taken regularly from all animals in each group. All the animals were sacrificed on the 160th week when the experiment ended. The samples of sera and liver tissues were checked for HBV markers and histological changes. Hepatocellular carcinomas (HCCs) were found only in Group A and Group C, with incidences of 67% and 30% respectively. The average time for HCC occurrence in Group A and Group C was 120.3 +/- 16.6 and 153.3 +/- 5.8 weeks respectively (P < 0.01). Even though no HCC occurred in Group B, 1 animal which died before the end of the experiment showed two large hepatocellular nodules. These results showed that there is synergistic effect between HBV and AFB1 in tree shrews' hepatocarcinogenesis, even though the hepatocarcinogenic effect played by HBV alone is rather weak.

Aflatoxin B1↗

PubMed1998

Modulation of aromatase expression in the breast tissue by ERR alpha-1 orphan receptor.

We have previously identified a silencer element (S1) that is situated between promoters I.3 and II of the human aromatase gene and that down-regulates the action of these promoters. We recently applied the yeast one-hybrid approach to screen a human breast tissue hybrid cDNA expression library for genes encoding the proteins binding to the silencer region. Most proteins identified from this approach belong to the nuclear receptor superfamily. Fifty % of the positive clones encode for ERR alpha-1, and other positive clones include EAR-2, EAR-3 (COUP-TF1), RAR gamma, and p120E4F. Because ERR alpha-1 was found to be the major protein interacting with S1, we decided to examine the regulatory action of ERR alpha-1 on promoter I.3 of the human aromatase gene. Using a reporter plasmid that includes the aromatase genomic fragment containing promoter I.3 and S1, ERR alpha-1 was found to have a positive regulatory function in breast cancer SK-BR-3 cells. Gel mobility shift assays have confirmed that ERR alpha-1 binds to S1 in a dose-dependent manner, and DNase I footprinting analysis has revealed that ERR alpha-1 binds to a region, 5'-AAGGTCAGAAAT-3', which is within S1 and between 96 and 107 bp relative to the transcriptional start site of promoter I.3. In addition, despite the fact that the nuclear receptor SF1 was shown previously to bind to the same site and to mediate a cAMP response in ovary, our yeast one-hybrid screening did not find any SF-1 clones. Gel mobility shift assays further revealed that SF-1 can bind to the silencer element with an affinity comparable with ERR alpha-1. Because our reverse transcription-PCR analysis was not able to detect SF1 mRNA in breast cancer tissue or in SK-BR-3 cells, it is thought that SF1 protein is not expressed in breast cancer tissue. Two ERR alpha-1 RNA variants with differences at the 5'-end have been reported. Our reverse transcription-PCR analysis identified the shorter variant in 28 of 32 breast tumor specimens and the longer variant in only 1 specimen. In addition, the shorter variant was detected in breast cancer SK-BR-3 cells as well as in a breast tumor fibroblast line WS3TF. The results suggest that ERR alpha-1 is one of the nuclear proteins interacting with S1 in breast cancer tissue. It is thought that the silencer element in the human aromatase gene may function differently in different tissues because of distinct expression patterns of transcription factors.

Aromatase↗