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Biomedical subjects

Q Liu

Publications and source records attributed to Q Liu.

At least 343 records · Page 19Linked to original sources
PubMed1999

Developmental Events Associated with the Critical Stage for Sex Determination in Wild-Rice Florets.

The developmental events of florets and a critical stage for sex determination in two wild-rice populations (Zizania palustris cv. Franklin and Zizania palustris cv. K-2Pi) have been identified. Formation of bisexual florets precedes the development of both male and female florets. Developmental indicators, established by measuring the length of florets and panicles, indicate that the critical stage for sex determination occurs when floret and panicle lengths are 1-2 mm and 3 cm, respectively. The stage of floret development at which sex determination occurs is the same in the two investigated wild-rice populations. Organ suppression in bisexual florets is an essential step for sex determination during the formation of unisexual florets. Histological examination of suppressed stamens or pistils in unisexual florets of wild-rice indicates that cell death does not occur during sex determination. In addition, the length of anthers and pistils in bisexual florets indicates that floral development in the transition zone is normal when compared with the male florets in the male spikelets and female florets in the female spikelets.

Journal Article↗
PubMed1999

Separation of nucleotide oligomers by unitary anion-exchange.

This paper is the first report on the retention behavior of synthetic oligonucleotides and nucleotide oligomers on a continuous-bedmatrix, strong-anion-exchange column. The separation mechanism is predominantly an anion-exchange process, but hydrophobic interaction plays a role as well. The separation is based on the chain length of the oligonucleotide. Both the addition of organic mobile phase modifiers and changes in column temperature affect the retention of oligomers significantly. A volatile buffer system (e.g., triethylamine acetate) could be employed to purify oligonucleotides, and no desalting procedure would be required after the column separation step. The recoveries from the separation are 70% or higher. The maximum loading capacity of an analytical column (35 x 7-mm i.d.) was found to be more than 366 micrograms.

Anion Exchange Resins↗
PubMed1999

Osseointegration of preformed polymethylmethacrylate craniofacial prostheses coated with bone marrow-impregnated poly (DL-lactic-co-glycolic acid) foam.

Osseointegration of bone marrow-PLGA-coated, preformed polymethylmethacrylate cranioplasties offers the possibility of reducing: operative time, periimplant seroma and infection, metallic fixation, and periprosthetic resorption following surgical skull remodeling. These alloplastic materials are FDA-approved but previously have not been used together to promote cranioplasty incorporation. The objective of this study was to determine whether the use of PLGA foam coating improves host osseointegration of preformed, textured, polymethylmethacrylate prosthetic cranioplasties. A critical-sized cranial defect was created in two groups of 10 and one group of three rabbits. The defect was filled with either a textured, preformed polymethylmethacrylate disc or a textured, preformed polymethylmethacrylate disc coated with poly (DL-lactic-co-glycolic acid). Both implants were immersed in autologous bone marrow for 20 minutes before implantation. Half of each group of 10 were killed at 3 weeks, and the remainder at 6 weeks. A third group of three rabbits with excised periosteum was evaluated at 6 weeks. Histologic analysis of the discs determined relative amounts of cancellous bone formation adjacent to the prostheses. Woven trabecular bone was present at each host bone to implant perimeter interface at 3 weeks, with fine fibrous capsular formation around the implants. Thicker, lamellar trabeculae were present at 6 weeks with an increased fibrous layer surrounding both types of implants. Bone formed on the superficial and deep implant surfaces in a noncontiguous fashion. Two of five measures showed that total bone formation was significantly greater in the PLGA-coated implants. Polymethylmethacrylate discs coated with bone marrow-impregnated PLGA foam demonstrate increased bone formation at 3 and 6 weeks as compared with non-coated preformed polymethylmethacrylate discs. Only implants with preserved periosteum showed bone formation away from the host-implant interface (centrally) on the superficial surface at 6 weeks.

Animals↗
PubMed1999

Analysis of TFIIA function In vivo: evidence for a role in TATA-binding protein recruitment and gene-specific activation.

Activation of transcription can occur by the facilitated recruitment of TFIID to promoters by gene-specific activators. To investigate the role of TFIIA in TFIID recruitment in vivo, we exploited a class of yeast TATA-binding protein (TBP) mutants that is activation and DNA binding defective. We found that co-overexpression of TOA1 and TOA2, the genes that encode yeast TFIIA, overcomes the activation defects caused by the TBP mutants. Using a genetic screen, we isolated a new class of TFIIA mutants and identified three regions on TFIIA that are likely to be involved in TBP recruitment or stabilization of the TBP-TATA complex in vivo. Amino acid replacements in only one of these regions enhance TFIIA-TBP-DNA complex formation in vitro, suggesting that the other regions are involved in regulatory interactions. To determine the relative importance of TFIIA in the regulation of different genes, we constructed yeast strains to conditionally deplete TFIIA levels prior to gene activation. While the activation of certain genes, such as INO1, was dramatically impaired by TFIIA depletion, activation of other genes, such as CUP1, was unaffected. These data suggest that TFIIA facilitates DNA binding by TBP in vivo, that TFIIA may be regulated by factors that target distinct regions of the protein, and that promoters vary significantly in the degree to which they require TFIIA for activation.

DNA-Binding Proteins↗
PubMed1999

Hypersensitive site 2 specifies a unique function within the human beta-globin locus control region to stimulate globin gene transcription.

The human beta-globin locus control region (LCR) harbors both strong chromatin opening and enhancer activity when assayed in transgenic mice. To understand the contribution of individual DNase I hypersensitive sites (HS) to the function of the human beta-globin LCR, we have mutated the core elements within the context of a yeast artificial chromosome (YAC) carrying the entire locus and then analyzed the effect of these mutations on the formation of LCR HS elements and expression of the genes in transgenic mice. In the present study, we examined the consequences of two different HS2 mutations. We first generated seven YAC transgenic lines bearing a deletion of the 375-bp core enhancer of HS2. Single-copy HS2 deletion mutants exhibited severely depressed HS site formation and expression of all of the human beta-globin genes at every developmental stage, confirming that HS2 is a vital, integral component of the LCR. We also analyzed four transgenic lines in which the core element of HS2 was replaced by that of HS3 and found that while HS3 is able to restore the chromatin-opening activity of the LCR, it is not able to functionally replace HS2 in mediating high-level globin gene transcription. These results continue to support the hypothesis that HS2, HS3, and HS4 act as a single, integral unit to regulate human globin gene transcription as a holocomplex, but they can also be interpreted to say that formation of a DNase I hypersensitive holocomplex alone is not sufficient for mediating high-level globin gene transcription. We therefore propose that the core elements must productively interact with one another to generate a unique subdomain within the nucleoprotein holocomplex that interacts in a stage-specific manner with individual globin gene promoters.

Animals↗
PubMed1999

Elevated cyclin E levels, inactive retinoblastoma protein, and suppression of the p27(KIP1) inhibitor characterize early development of promyeloid cells into macrophages.

Cyclin-dependent kinase inhibitors such as p27(KIP1) have recently been shown to lead to cellular differentiation by causing cell cycle arrest, but it is unknown whether similar events occur in differentiating promyeloid cells. Hematopoietic progenitor cells undergo lineage-restricted differentiation, which is accompanied by expression of distinct maturation markers. Here we show that the classical growth factor insulin-like growth factor I (IGF-I) potently promotes vitamin D(3)-induced macrophage differentiation of promyeloid cells, as assessed by measurement of a coordinate increase in expression of the integrin alpha subunit CD11b, the CD14 lipopolysaccharide receptor, and the macrophage-specific esterase, alpha-naphthyl acetate esterase, as early as 24 h following initiation of terminal differentiation. Addition of IGF-I to cells undergoing vitamin D(3)-induced differentiation also leads to an early increase in expression of cyclin E, phosphorylation of the retinoblastoma tumor suppressor protein, and a doubling of the cell number. Early expression of CD11b (24 h) is simultaneously accompanied by inhibition in the expression of p27(KIP1). Cell cycle analysis with propidium iodide revealed that CD11b expression at 24 h following initiation of differentiation occurs at all phases of the cell cycle instead of only those cells arrested in G(0)/G(1). Similarly, development of a novel double-labeling intra- and extracellular flow-cytometric technique demonstrated that single cells expressing the mature leukocyte differentiation antigen CD11b can also incorporate the thymidine analog bromodeoxyuridine. Likewise, expression of the intracellular DNA polymerase delta cofactor/proliferating-cell nuclear antigen at 24 h is also simultaneously expressed with the surface marker CD11b, indicating that these cells continue to proliferate early in their differentiation program. Finally, at 24 h following induction of differentiation, IGF-I promoted a fourfold increase in the uptake of [(3)H]thymidine by purified populations of CD11b-expressing cells. Taken together, these data demonstrate that the initial steps associated with terminal macrophage differentiation occur concomitantly with progression through the cell cycle and that these very early differentiation events do not require the accumulation of p27(KIP1).

Cell Cycle↗
PubMed1999

Development of intrinsic tone in isolated pulmonary arterioles.

In isolated porcine pulmonary arterioles with endothelium, intraluminal diameter measured at a transmural pressure of 20 mmHg decreased spontaneously from 233 +/- 11 to 171 +/- 12 micrometer in 135 min. This intrinsic constriction was not prevented by indomethacin, tetraethylammonium, or superoxide dismutase. Indomethacin plus NG-nitro-L-arginine methyl ester caused initial constriction and BQ-123 or BQ-123 plus BQ-788 caused initial dilation, but these treatments did not prevent subsequent progressive constriction. In pulmonary arterioles with endothelium exposed to calcium-free conditions and pulmonary arterioles without endothelium, the intraluminal diameter measured at a transmural pressure of 20 mmHg was constant at 239 +/- 16 and 174 +/- 7 micrometer, respectively. Thus the spontaneous development of tone in isolated pulmonary arterioles required extracellular calcium and resulted from 1) time-independent smooth muscle contraction caused by mechanisms intrinsic to smooth muscle and 2) time-dependent contraction caused by decreasing activity of endothelium-derived relaxing factors other than nitric oxide, vasodilator prostaglandins, and hyperpolarizing factors acting on calcium-dependent potassium channels or increasing activity of endothelium-derived contracting factors other than endothelin-1, vasoconstrictor prostaglandins, and superoxide anions. Further investigation is indicated to identify these unknown mechanisms and determine their role in pulmonary vasoreactivity.

Animals↗
PubMed1999

Endurance exercise causes interaction among stress hormones, cytokines, neutrophil dynamics, and muscle damage.

We analyzed adaptation mechanisms regulating systemic inflammatory response of the stressed body by using an experimental challenge of repeated exercise bouts and accompanying muscle inflammation. Eight untrained men bicycled at 90 W for 90 min, 3 days in a row. Exercise induced peripheral neutrophilia with a leftward shift of neutrophil nucleus and neutrophil priming for oxidative activity determined by luminol-dependent chemiluminescence. Plasma growth hormone and interleukin-6 rose significantly after exercise and were closely correlated with the neutrophil responses. Serum creatine kinase and myoglobin levels as muscle damage markers rose after exercise in "delayed onset" and were closely correlated with the preceding neutrophil responses. These exercise-induced responses were strongest on day 1, but the magnitude gradually decreased with progressive daily exercise. In contrast, the magnitude of catecholamine responses to exercise sessions gradually rose, possibly suppressing neutrophil oxidative responses. These results indicate that stress-induced systemic release of bioactive substances may determine neutrophil mobilization and functional status, which then may affect local tissue damage of susceptible organs.

Adult↗
PubMed1999

Constriction to hypoxia-reoxygenation in isolated mouse coronary arteries: role of endothelium and superoxide.

The aim of the present study was to determine the role of endothelium and superoxide in the responses of isolated mouse coronary arteries to hypoxia-reoxygenation. Isolated mouse coronary artery was cannulated, pressurized at 60 mmHg, and constantly superfused with recirculating Krebs-Ringer bicarbonate solution for continuous measurement of intraluminal diameter (ID) by video microscopy. Under a no-flow condition, hypoxia (0% O(2), 30 min) caused vasoconstriction. Reoxygenation caused a further vasoconstriction (ID change from 111.4 +/- 11.1 to 91 +/- 16.5 microm) that was significantly reduced by removal of endothelium (ID change from 105.4 +/- 27 to 109.9 +/- 23.4 microm). Cu/Zn superoxide dismutase (150 U/ml) did not alter the hypoxic vasoconstriction but abolished the reoxygenation-caused endothelium-dependent vasoconstriction. Hypoxia-reoxygenation markedly enhanced the generation of superoxide that was significantly reduced by either removing the endothelium or treated these endothelium-intact vessels with superoxide dismutase. These results suggest that, in isolated mouse coronary arteries, hypoxia causes vasoconstriction that is independent of endothelium, whereas reoxygenation causes vasoconstriction that is mediated by enhanced generation of superoxide from endothelium.

Animals↗
PubMed1999

Immunohistochemical detection of somatostatin receptor subtypes sst1 and sst2A in human somatostatin receptor positive tumors.

Although in situ hybridization has been used to examine the distribution of messenger RNA for somatostatin receptor subtypes (sst) in human tumors, the cellular localization of sst1 and sst2A receptors has not been reported. In this study, we describe the cellular localization of human sst1 and sst2A receptor proteins in both cryostat- and paraffin-embedded sections of 25 human tumor tissues using two recently developed polyclonal antibodies. Six somatostatin (SS) receptor (SSR) positive tumors (two gastrinomas, three carcinoids, one pheochromocytoma) and one SSR negative tumor (renal cell carcinoma), selected by positive and negative SSR autoradiography, respectively, were studied by both immunohistochemistry and Western blot analysis. The six SSR positive tumors expressed sst2A, while 4 of 5 expressed sst1 as well. The SSR negative tumor did not express either sst1 or sst2A. Western blot analysis of wheat germ agglutinin purified membrane proteins confirmed the presence of the sst1 and sst2A glycosylated receptors. The paraffin-embedded sections gave best information with respect to the subcellular localization. Sst1 immunoreactivity was observed both on the membrane and in the cytoplasm, while sst2A showed predominantly membrane-associated immunoreactivity. This subcellular distribution of sst1 or sst2A receptors was confirmed in paraffin-embedded sections of 8 additional intestinal carcinoids, 5 gastrinomas and 5 pheochromocytomas. Sst1 receptors were detected in 7 out of 8 carcinoids, in all gastrinomas, and in 4 out of 5 pheochromocytomas, while 6 out of 8 carcinoids, all gastrinomas, and 3 out of 5 pheochromocytomas expressed sst2A receptors. In conclusion, sst1 and sst2A receptors show a differential subcellular localization in human SSR positive tumors. The use of SSR subtype selective antibodies to detect the subcellular distribution of SSR subtypes in individual tumor cells is an important step forward to understand more about the pathophysiological role of the different SSR subtypes in human tumors.

Adrenal Gland Neoplasms↗
PubMed1999

Detection of virtually all mutations-SSCP (DOVAM-S): a rapid method for mutation scanning with virtually 100% sensitivity.

Dideoxy fingerprinting (ddF) was used as a tool to search for a generic set of conditions with sufficient power to detect virtually all mutations. For each condition tested, a very large sample of mutation-containing, single-stranded segments (about 1500) were analyzed with ddF. Correlation coefficients identified pairs of conditions in which single-strand conformation polymorphism (SSCP) mobilities were poorly correlated. The data strongly suggest that tertiary structure (e.g., base-sugar and sugar-sugar interactions) rather than secondary structure is the predominant determinant of mobility shifts by SSCP. Five conditions were selected with sufficient redundancy to detect all the mutations. The sensitivity of detection of virtually all mutations-SSCP (DOVAM-S) was determined by blinded analyses on samples containing additional mutations scattered throughout the eight exons and splice junctions in the factor IX gene. The factor IX gene sequence (2.5 kb) was scanned in one lane by 15 PCR-amplified segments (125 kb of sequence scanned per gel). All of the 84 single-base substitutions were detected in the blinded analyses, the first consisting of 50 hemizygous mutant and wild-type (WT) samples and the second consisting of 50 heterozygous mutant and WT samples. DOVAM-S is estimated to be five times faster than fluorescent DNA sequencing for the detection of virtually all mutations when the five conditions are applied.

Biotechnology↗
PubMed1999

REF Select: expert system software for selecting restriction endonucleases for restriction endonuclease fingerprinting.

REF Select, expert system software, has been developed to assist in the selection of optimal restriction endonucleases for restriction endonuclease fingerprinting (REF), a method for rapid and sensitive mutation screening of long DNA segments (1-2 kb). The REF method typically involves six separate digestions with up to two restriction endnonucleases used in each digestion. If done manually, performing a comprehensive review of the large number of possible sets of restriction endonucleases that could be used (over 10(19) in the example presented here) and making an optimal choice is not feasible. Furthermore, the typical nonoptimal manual selection takes approximately 8 h by someone experienced with REF. REF Select enables a comprehensive review of the possible sets and a consistent, objective and fast selection of an optimal set by using a two-step strategy: the selection of sets that meet specific constraints, which is followed by a ranking of those sets by an optimality score. Based on our experience with REF, we chose default selection and ranking parameters to help the user get started quickly. These parameters form a knowledge base that can be customized and then saved by the user. In conclusion, REF Select facilitates the general application of REF by serving as an expert system for the selection of optimal restriction endonucleases. We demonstrated REF Select using an example segment from the human p53 gene.

Algorithms↗
PubMed1999

[The expression of p16, CDK4 and pRb in hepatocellular carcinomas].

OBJECTIVE: To make an analysis of the expression of p16 gene, CDK4 and retinoblastoma protein(pRb) in human hepatocellular carcinoma(HCC). METHODS: Application of immunohistochemistry to 40 cases of HCC and their adjacent liver tissues. RESULTS: The abnormal expressions of p16, CDK4 and pRb were 94.44%(34/36), 40.00%(16/40) and 45.71%(16/35) respectively. Rb protein was strongly stained in 13/34(38.23%) cases lacking or weak staining with p16, which showed a negative relation between the expressions of Rb and p16. The abnormal expressions of both p16 and Rb were 15/34(44.11%) cases, indicating that except p16, there are some other ways to regulate Rb. In 14 cases of CDK4 overexpression, most of them (92.85%) presented p16 aberration, 50.00% of them were observed with pRb abnormal expression, 46.15% of them were along with the alterations of both p16 and pRb. There was no significant correlation between p16 or CDK4 or pRb abnormal expression and HCC malignant grade. CONCLUSION: The data show that the aberrant expression of p16, CDK4 and pRb may play a role in the carcinogenesis of HCC. The changes of p16 expression is prominent.

Carcinoma, Hepatocellular↗
PubMed1999

[Mutation analysis of p16 gene in non-small cell lung carcinomas].

OBJECTIVE: To investigate the role of p16 gene in the tumorigenesis of non-small cell lung carcinomas (NSCLC). METHODS: Homozygous deletion and mutation of exon 2 of p16 genes in 40 NSCLC tissues were analyzed using PCR and dsDNA direct sequencing technique. RESULTS: In 2 NSCLC tissues, homozygous deletions of p16 gene were detected; in 14 NSCLC tissues, 19 point mutations and a frameshift were detected. CONCLUSION: Point mutations of p16 gene were frequent and might play a role in the initiation and progression of NSCLC. Nt380 in this gene was a hot spot of mutation.

Carcinoma, Non-Small-Cell Lung↗
PubMed1999

Structural and functional characterization of Kv6.2 a new gamma-subunit of voltage-gated potassium channel.

We have cloned and functionally expressed Kv6.2, a new member of the Kv6 subfamily of voltage-gated potassium channel subunits. The human Kv6.2 (KCNF2) gene was mapped at 18q22-18q23. Kv6.2 mRNA is preferentially expressed in rat and human myocard. Rat and human Kv6.2 subunits appear to be unable to form functional Kv channels in a heterologous expression system, but, when coexpressed with Kv2.1 alpha subunits, heteromultimeric Kv channels were formed mediating voltage-activated delayed-rectifier type outward currents. Their kinetics and conductance-voltage relationship were different from those mediated by homomultimeric Kv2.1 channels. Yeast two-hybrid reporter assays indicated that Kv6.2 amino-termini are able to interact specifically with the Kv2.1 amino-terminus. It is proposed that this protein protein interaction underlies Kv2.1/Kv6.2 subunit assembly and the expression of functional heteromultimeric Kv2.1/Kv6.2 channels. The most resiliant feature of the Kv2.1/Kv6.2 channels was their submicromolar sensitivity to the antiarrhythmic drug propafenone. The data suggest that delayed-rectifier type channels containing Kv6.2 subunits may contribute to cardiac action potential repolarization.

Amino Acid Sequence↗
PubMed1999

[The cDNA clone and sequence analysis of the coding region of human augmenter of liver regeneration (hALR) gene].

OBJECTIVE: To obtaining cDNA clone of the coding region of human augmenter of liver regeneration(hALR) as a basis for further study. METHODS: Total RNA of human fetal liver was extracted as a template. First strand of cDNA was synthesised by reverse transcription with olig(dT)-primer and then amplified by PCR with the primers designed by ourself. The size of PCR product was about 380 bp. it was subcloned into pUC19 and was sequenced by auto-sequencing instrument. The sequence of hALR was analysed with PCGENE program. RESULT: The cDNA of integrity coding region of hALR was obtained. Its size was 378 bp. The sequence homology of our hALR compared with rat ALR and human ALR recently reported were 86.5% and 99.2%, respectively. CONCLUSION: It was also suggested that hALR takes part in growth regulation of fetal liver during human fetus late development.

Animals↗
PubMed1999

[Construction of human combinatorial immunoglobulin library containing HBsAb on the surface of phage].

OBJECTIVE: To construct a human recombinant immunoglobulin library containing HBsAb. METHODS: The mRNA isolated from peripheral blood lymphocytes of two blood donors with HBsAb were reversely transcribed to the first strand cDNA with oligo-(dT) primer. Human immunoglobulin kappa light chains and heavy chains Fd genes were amplified respectively by PCR with designed oligo nucleotide primers and the first strand cDNA templates. The kappa light chain genes were first cloned into PComb3Hss vector to construct a human recombinant light chain library. The heavy chain genes were subsequently inserted into the corresponding sites of kappa-PComb3Hss plasmid to generate a combinatorial kappa-Fd-PComb3Hss plasmid. The plasmid transformed into E.Coli.XLI-Blue and the E.Coli.XLI-Blue infected by help phage. RESULTS: The constructed light chains library size was 1.5 x 10(5), and the recombinant frequency of kappa chain genes was 57% and the human combinatorial Fab immunoglobulin library was 5 x 10(5) members and the recombinant frequency of Fab genes was 50%. Finally, the titer of phages in the phage antibody library containing HBsAb was 5 x 10(14) CFU/ml. CONCLUSION: Our work in constructing human immunoglobulin combinatorial library containing HBsAb will be beneficial to further study on selecting Fab phage antibodies of HBsAg from the library.

Hepatitis B Antibodies↗