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Yan Liu

Publications and source records attributed to Yan Liu.

At least 91 records · Page 5Linked to original sources
PubMed2006

trt-1 is the Caenorhabditis elegans catalytic subunit of telomerase.

Mutants of trt-1, the Caenorhabditis elegans telomerase reverse transcriptase, reproduce normally for several generations but eventually become sterile as a consequence of telomere erosion and end-to-end chromosome fusions. Telomere erosion and uncapping do not cause an increase in apoptosis in the germlines of trt-1 mutants. Instead, late-generation trt-1 mutants display chromosome segregation defects that are likely to be the direct cause of sterility. trt-1 functions in the same telomere replication pathway as mrt-2, a component of the Rad9/Rad1/Hus1 (9-1-1) proliferating cell nuclear antigen-like sliding clamp. Thus, the 9-1-1 complex may be required for telomerase to act at chromosome ends in C. elegans. Although telomere erosion limits replicative life span in human somatic cells, neither trt-1 nor telomere shortening affects postmitotic aging in C. elegans. These findings illustrate effects of telomere dysfunction in C. elegans mutants lacking the catalytic subunit of telomerase, trt-1.

Animals↗
PubMed2006

Analysis of tissue-specific region in sericin 1 gene promoter of Bombyx mori.

The gene encoding sericin 1 (Ser1) of silkworm (Bombyx mori) is specifically expressed in the middle silk gland cells. To identify element involved in this transcription-dependent spatial restriction, truncation of the 5' terminal from the sericin 1 (Ser1) promoter is studied in vivo. A 209bp DNA sequence upstream of the transcriptional start site (-586 to -378) is found to be responsible for promoting tissue-specific transcription. Analysis of this 209bp region by overlapping deletion studies showed that a 25bp region (-500 to -476) suppresses the ectopic expression of the Ser1 promoter. An unknown factor abundant in fat body nuclear extracts is shown to bind to this 25bp fragment. These results suggest that this 25bp region and the unknown factor are necessary for determining the tissue-specificity of the Ser1 promoter.

Animals↗
PubMed2006

Fit for Life Boy Scout badge: outcome evaluation of a troop and Internet intervention.

BACKGROUND: This study reports the results of a 9-week intervention on the physical activity levels of adolescent males. METHODS: Participants were 473 10- to 14-year-old Houston Boy Scouts (42 troops) with troops randomly assigned to intervention or control conditions. Data were collected in spring (16 troops) and fall (26 troop) waves during 2003. Intervention participants received a 9-week troop and Internet program to increase physical activity skills, self-efficacy and goal-setting. Physical activity was assessed at baseline, end of the intervention (Post#1) and post-6 months (Post#2) by accelerometer. Minutes of sedentary, light and moderate to vigorous physical activity were calculated. Repeated measure analyses were performed to test differences in physical activity over time between groups with participants nested in troops. RESULTS: A three-way interaction (group * time * wave) that approached significance (P = 0.051) indicated a 12-min reduction in sedentary behavior among spring intervention participants. A significant three-way interaction (P = 0.011) (group * time * wave) indicated a 12-min increase in light intensity activity among the spring intervention group. CONCLUSION: Participation in the Fit for Life badge program resulted in a trend towards a small decrease in sedentary behavior and increased light intensity physical activity among spring participants only. There was no effect on moderate to vigorous physical activity.

Adolescent↗
PubMed2006

Mitochondrial aldehyde dehydrogenase-2 (ALDH2) Glu504Lys polymorphism contributes to the variation in efficacy of sublingual nitroglycerin.

Glyceryl trinitrate (GTN), also known as nitroglycerin, has been used to treat angina and heart failure for more than 130 years. Recently, it was shown that mitochondrial aldehyde dehydrogenase-2 (ALDH2) is responsible for formation of NO, the metabolite needed for GTN efficacy. In the present study, we show that the common G-to-A polymorphism in exon 12 of ALDH2--resulting in a Glu504Lys replacement that virtually eliminates ALDH2 activity in both heterozygotes and homozygotes--is associated with a lack of efficacy of sublingual GTN in Chinese subjects. We also show that the catalytic efficiency (Vmax/Km) of GTN metabolism of the Glu504 protein is approximately 10-fold higher than that of the Lys504 enzyme. We conclude that the presence of the Lys504 allele contributes in large part to the lack of an efficacious clinical response to nitroglycerin; we recommend that this genetic factor be considered when administering nitroglycerin to patients, especially Asians, 30-50% of whom possess the inactive ALDH2*2 mutant allele.

Administration, Sublingual↗
PubMed2006

Enhancement and sustainment of internal stochastic resonance in unidirectional coupled neural system.

In this study, the collective dynamical behavior of two unidirectionally, linearly coupled neurons was investigated. Our investigation illustrates that, depending on the coupling strength, the internal stochastic resonance (ISR) effect observed in one of the two neurons could be amplified or sustained by the other. The amplification of ISR is enhanced as the coupling strength is increased from 0. However, when the coupling strength is increased above a certain level, the amplification of ISR is reduced, implicating that there exists an optimal coupling strength for the information flow between two neurons. As the coupling strength is increased further, i.e., above the critical level, synchronization of the two subsystems is achieved, yet the two subsystems exhibit the same magnitude response to the external noise, suggesting that the information transmission among coupled subunits could not be improved by further enhancing their coupling strength. And similar phenomena could also be obtained for the nonidentical case.

Journal Article↗
PubMed2006

Location of phenothiazine in sodium dodecyl sulfate/n-pentanol/water microemulsions.

The location of phenothiazine (PTZ) in sodium dodecyl sulfate (SDS)/n-pentanol (n-C5H11OH)/water microemulsions is studied by cyclic voltammetry at a Pt electrode. The results indicate that PTZ exists in the membrane phase of microemulsion droplets with its N atom or S atom toward the polar head of the surfactant. In addition, we examine the effect of the compositions and structures of the microemulsions, pH, temperature, and the inorganic salts on the location distribution for PTZ in the membrane phase of the microemulsions. The results show that the location distribution for PTZ in the membrane phase of the microemulsions is mainly dependent on the hydrogen bond between the -NH in PTZ and n-pentanol (or the -SO4- of SDS) and on the electrostatic interaction between the S atom (or N atom) in PTZ and the polar head of SDS.

Journal Article↗
PubMed2006

[Effect of carbon dioxide pneumoperitoneum during laparoscopic surgery on morphology of peritoneum].

OBJECTIVE: To investigate the influence of carbon dioxide (CO2) pneumoperitoneum during laparoscopic surgery on morphology of peritoneum. METHODS: Forty patients with myoma of uterus or simple ovarian cyst excluding peritonitis were randomly divided into 2 equal groups to undergo laparoscopic surgery with CO2 pneumoperitoneum or laparotomy respectively. Specimens of parietal peritoneum were obtained at different time points, 0, 30, 90, and 120 min after the beginning of observation, i.e. e, insufflation or opening of the peritoneal cavity, to undergo transmission electron microscopy and scanning electron microscopy to observe the morphological changes of mesothelial cells. RESULTS: In the laparotomy group, up to the time point of 60 min, there was no marked change of mesothelial cells. Intercellular cleft were occasionally found since 90 min and became significant 120 min after. However, in the CO2 pneumoperitoneum group bulging up of mesothelial cells was evident immediately at the time of filling of CO2, intercellular spaces could be found 30 min later, 60 min later intercellular cleft deep to the underlying basement membrane could be seen and the basement membrane lost its continuity and became uncovered, and 120 min later such changes became more significant and a small amount of lymphocytes and macrophages were found in the intercellular clefts. CONCLUSION: Carbon dioxide pneumoperitoneum during laparoscopic surgery causes significant morphological changes in the peritoneum duration of insufflation dependently.

Carbon Dioxide↗
PubMed2006

Novel fluorescent markers for hypoxic cells of naphthalimides with two heterocyclic side chains for bioreductive binding.

Novel naphthalimides with two heterocyclic side chains of 2-nitroimidazole for bioreductive binding were designed, synthesized, and used as fluorescent markers for hypoxic cells. Their evaluation for imaging tumor hypoxia was carried out in V79 cells, CHO cells, and 95D cells in vitro by using fluorescence scan ascent. A2 and A4 showed a very large differential fluorescence between hypoxic and oxic cells (V79 cells) in vitro and are promising candidate markers for hypoxic cells.

Animals↗
PubMed2006

Synthesis and evaluation of novel 8-oxo-8H-cyclopenta[a]acenaphthylene-7-carbonitriles as long-wavelength fluorescent markers for hypoxic cells in solid tumor.

Novel bioreductive and long-wavelength fluorescent markers for hypoxic cells in solid tumor, 9-isocyano-8H-acenaphtho[l,2-b]pyrrol-8-one with the side chain of 2-nitroimidazole, were designed, synthesized, and evaluated in V79 379A Chinese hamster cells in vitro. Compounds A(2) and A(4) showed good hypoxic-oxic fluorescence differential in vitro (V79 cells) by using fluorescence scan ascent.

Acenaphthenes↗
PubMed2006

Prediction of chromatographic relative retention time of polychlorinated biphenyls from the molecular electronegativity distance vector.

Using the molecular electronegativity distance vector (MEDV) descriptors derived directly from the molecular topological structures, the gas chromatographic relative retention times (RRTs) of 209 polychlorinated biphenyls (PCBs) on the SE-54 stationary phase were predicted. A five-variable regression equation with the correlation coefficient of 0.9964 and the root mean square errors of 0.0152 was developed. The descriptors included in the equation represent degree of chlorination (nCl), nonortho index (Ino), and interactions between three pairs of atom types, i.e., atom groups -C= and -C=, -C= and >C=, -C= and -Cl. It has been proved that the retention times of all 209 PCB congeners can be accurately predicted as long as there are more than 50 calibration compounds. In the same way, the MEDV descriptors are also used to develop the five- or six-variable models of RRTs of PCBs on other 18 stationary phases and the correlation coefficients in both modeling stage and LOO cross-validation step are not lower than 0.99 except two models.

Chromatography, Gas↗
PubMed2006

Speciation of chromium by selective separation and preconcentration of Cr(III) on an immobilized nanometer titanium dioxide microcolumn.

Nanometer titanium dioxide immobilized on silica gel (immobilized nanometer-scale TiO2 particles) was prepared by a sol-gel method and characterized by X-ray diffraction and scanning electron microscopy. The adsorptive behavior of Cr(III) and Cr(VI) on immobilized nanometer TiO2 was assessed. Cr(III) was selectively sorbed on immobilized nanometer TiO2 in the pH range of 7-9, while Cr(VI) was found to remain in solution. A sensitive and selective method has been developed for the speciation of chromium in water samples using an immobilized nanometer TiO2 microcolumn and inductively coupled plasma atomic emission spectrometry. Under optimized conditions (pH 7.0, flow rate 2.0 mL/min), Cr(III) was retained on the column, then eluted with 0.5 mol/L HNO3 and determined by ICP-AES. Total chromium was determined after the reduction of Cr(VI) to Cr(III) by ascorbic acid. The adsorption capacity of immobilized nanometer TiO2 for Cr(III) was found to be 7.04 mg/g. The detection limit for Cr(III) was 0.22 ng/mL and the RSD was 3.5% (n = 11, c = 100 ng/ mL) with an enrichment factor of 50. The proposed method has been applied to the speciation of chromium in water samples with satisfactory results.

Adsorption↗
PubMed2006

Proteomic dissection of plant development.

Plant development is controlled by complex endogenous genetic programs and responses to environmental cues. Proteome analyses have recently been introduced to plant biology to identify proteins instrumental in these developmental processes. To date most plant proteome studies have been employed to generate reference maps of the most abundant soluble proteins of plant organs at a defined developmental stage. However, proteomics is now also utilized for genetic studies comparing the proteomes of different plant genotypes, for physiological studies analyzing the influences of exogenous signals on a particular plant organ, and developmental studies investigating proteome changes during development. Technical advances are now beginning to allow a proteomic dissection of individual cell types, thus greatly increasing the information revealed by proteome analyses.

Plant Development↗
PubMed2006

Comparative proteome analyses of maize (Zea mays L.) primary roots prior to lateral root initiation reveal differential protein expression in the lateral root initiation mutant rum1.

The embryonically preformed primary root is the first root type of maize that emerges after germination. In this study the abundant soluble proteins of 2.5-day-old primary roots of wild-type and lateral root mutant rum1 seedlings were compared before the initiation of lateral roots. In CBB-stained 2-D gels, among 350 detected proteins 14 were identified as differentially accumulated (>twofold change; t-test: 95% significance) in wild-type versus rum1 primary roots. These proteins which were identified via ESI MS/MS are encoded by 12 different genes. Functionally, these proteins are involved in lignin biosynthesis, defense, and the citrate cycle. Nine of these genes were further analyzed at the RNA expression level. This study represents the first comparative proteomic analysis of maize primary roots prior to lateral root initiation and will contribute to a better understanding of the molecular basis of root development in cereals.

Blotting, Northern↗
PubMed2006

Comparison of extraction versus nonextraction orthodontic treatment outcomes for borderline Chinese patients.

INTRODUCTION: The purpose of this study was to compare orthodontic treatment outcomes in Chinese patients with borderline problems treated with and without extractions. METHODS: Records of 39 borderline patients treated at the Faculty Clinic of the Peking University Orthodontic Department were evaluated retrospectively by 5 associate professors. Sixteen patients had been treated without extractions, and 23 had 4 first or second premolars extracted. Each judge evaluated the posttreatment records independently for tooth alignment, overbite, overjet, midline symmetry, lateral occlusion, and facial profile, and rated them on a scale from 1 to 5. RESULTS: The only statistically significant difference between the extraction and nonextraction groups was for facial profile, with the judges preferring the extraction profiles. Fifteen soft-tissue cephalometric variables were measured to determine the source of the difference, and 6 showed statistically significant differences. When profile changes from pretreatment to posttreatment were examined, significant differences in treatment-associated changes between extraction and nonextraction groups were all related to the lower lip and chin. CONCLUSIONS: In this sample of Chinese borderline orthodontic patients, Chinese clinicians had a statistically significant preference for the facial profiles of the extraction patients, but no statistically significant preferences for tooth alignment, overbite, overjet, midline symmetry, or posterior occlusion. Extraction treatment increases the inclination of the chin and reduces protrusion of the lower lip compared with nonextraction treatment, and this might explain the difference.

Asian People↗
PubMed2006

The transcription factor MEF/ELF4 regulates the quiescence of primitive hematopoietic cells.

The transcriptional circuitry that regulates the quiescence of hematopoietic stem cells is largely unknown. We report that the transcription factor known as MEF (or ELF4), which is targeted by the t(X;21)(q26;q22) in acute myelogenous leukemia, regulates the proliferation of primitive hematopoietic progenitor cells at steady state, controlling their quiescence. Mef null HSCs display increased residence in G0 with reduced 5-bromodeoxyuridine incorporation in vivo and impaired cytokine-driven proliferation in vitro. Due to their increased HSC quiescence, Mef null mice are relatively resistant to the myelosuppressive effects of chemotherapy and radiation. Thus, MEF plays an important role in the decision of stem/primitive progenitor cells to divide or remain quiescent by regulating their entry to the cell cycle.

Animals↗
PubMed2006

Epm2a suppresses tumor growth in an immunocompromised host by inhibiting Wnt signaling.

The genetic mechanisms responsible for increased incidence of lymphoma in immunocompromised individuals have not been fully elucidated. We show that, in a line of TCR transgenic TG-B mice, an insertional mutation in one allele of the Epm2a locus and epigenetic silencing of another led to a high rate of lymphoma with early onset. Overexpressing Epm2a suppressed the growth of established tumor cells and the development of lymphoma in the TG-B mice, while specific silencing of the locus increased tumorigenesis in the immune-deficient host. Downregulation of Epm2a expression is widespread among mouse and human lymphoma cell lines. Epm2a-encoded laforin is a phosphatase for GSK-3beta and an important repressor in the Wnt signaling pathway. Inactivation of Epm2a resulted in increased Wnt signaling and tumorigenesis.

Animals↗