Biomedical subjects

P Li

Publications and source records attributed to P Li.

At least 361 records · Page 20Linked to original sources

PubMed1997

Inscuteable and Staufen mediate asymmetric localization and segregation of prospero RNA during Drosophila neuroblast cell divisions.

When neuroblasts divide, inscuteable acts to coordinate protein localization and mitotic spindle orientation, ensuring that asymmetrically localized determinants like Prospero partition into one progeny. staufen encodes a dsRNA-binding protein implicated in mRNA transport in oocytes. We demonstrate that prospero RNA is also asymmetrically localized and partitioned during neuroblast cell divisions, a process requiring both inscuteable and staufen. Inscuteable and Staufen interact and colocalize with prospero RNA on the apical cortex of interphase neuroblasts. Staufen binds prospero RNA in its 3'UTR. Our findings suggest that Inscuteable nucleates an apical complex and is required for protein localization, spindle orientation, and RNA localization. Stau, as one component of this complex, is required only for RNA localization. Hence staufen also acts zygotically, downstream of inscuteable, to effect aspects of neuroblast asymmetry.

Animals↗

PubMed1997

Comparing the properties of Escherichia coli branching enzyme and maize branching enzyme.

Escherichia coli glycogen branching enzyme (GBE) and maize starch branching enzymes I (SBEI) and II (SBEII) were expressed in E. coli and purified. E. coli GBE branched amylose at a higher rate than did SBEII, but branched amylose at a lower rate than did SBEI. Similar to SBEI, GBE branched amylopectin at a lower rate than did SBEII. High-performance anion-exchange chromatography analysis of the branched products produced by BE revealed the minimum chain length (cl) required for branching. While GBE and SBEII showed the same minimum cl [degree of polymerization (dp) 12] required for branching, SBEI had a slightly higher minimum cl (dp 16) requirement for branching. The major differences between GBE and SBE are their specificities in terms of the size of chains transferred. In comparison with SBE, GBE had a much narrower size range of chains transferred and transferred mainly shorter chains. While SBEI and SBEII produced a large number of chains ranging from dp 6 to over dp 30, GBE predominantly transferred chains ranging from dp 5 to 16 and produced only a very small number of long chains with dp greater than 20. Although it has been reported that SBEI and SBEII preferentially transfer longer and shorter chains, respectively (1), this study further defines the differences between SBEI and SBEII in the size of chains transferred. SBEI predominantly transfers longer chains with dp greater than 10, while producing few shorter chains with dp 3 to 5. In contrast, SBEII preferentially transfers smaller chains with dp 3 to 9, with the most abundant chains being dp 6 and 7. The significance of minimum chain-length requirement by SBE is discussed in setting the invariant size of amylopectin cluster size (9 nm).

1,4-alpha-Glucan Branching Enzyme↗

PubMed1997

Identification and diurnal studies of pineal and serum 5-methoxytryptamine in the rat and quail.

Picomole to femtomole per gland/ml levels of 5-methoxytryptamine (5MT) in the pineal gland and serum of the rat and quail were determined, in the absence of a monoamine oxidase inhibitor, by using the ultra-sensitive technique of capillary column gas chromatography/electron-capture negative ion chemical ionization mass spectrometry. Diurnal rhythms of pineal 5MT with high levels at mid-light and low levels at mid-dark were found in both species, while serum 5MT levels showed less or no diurnal variations. The definitive presence of 5MT in the pineal gland and blood circulation provides further evidence that it is potentially a neurohormone. Whether 5MT is implicated in the photoperiodic responses and/or other physiological functions of animals, however, remains to be investigated.

5-Methoxytryptamine↗

PubMed1997

Molecular evolution of angiosperm mitochondrial introns and exons.

Numbers of substitutions per site for 15 protein-coding genes and six introns of the plant mitochondria were estimated to compare modes and tempos of evolution between exons and introns, and numbers of insertions-deletions per site also were investigated in introns. Intra-gene homogeneity of numbers of substitutions per site was assessed further among different taxa and between mitochondrial and nuclear paralogs translocated from the mitochondrial genome. Gene-to-gene differences in numbers of substitutions per site were found to be higher for nonsynonymous than synonymous sites, and this could be due to differential selection if mutation rate is assumed constant for the genome. Some mitochondrial genes have evolved as fast as chloroplast genes, thus faster than previously thought. For coxI, relative rate tests showed that woody taxa evolved slower than annuals at synonymous sites. Generation time, population size, and speciation rate are likely factors involved in this rate heterogeneity. Introns were less constrained than their adjacent exons for both overall numbers of substitutions per site and indels, but, on average, overall numbers of substitutions per site for introns were similar to numbers of synonymous substitutions per site for exons. Correlations were generally high between numbers of substitutions and numbers of indels per site for the same intron. Mitochondrial genes transferred to the nucleus had an accelerated rate of substitution per site, which was most significant at synonymous sites. These differences between paralogs in two different genomes are likely the result of different mutation rates.

DNA, Mitochondrial↗

PubMed1997

PRIMO: A primer design program that applies base quality statistics for automated large-scale DNA sequencing.

PRIMO is a computer program that designs walking primers for large-scale DNA sequencing projects. Oligonucleotide primers are predicted automatically, using quality information associated with each base call, eliminating the need for manually viewing the sequence traces or inspecting contig assemblies to determine appropriate locations for primer design. This allows PRIMO to run in batch mode on an arbitrarily large number of templates. For shotgun sequencing, PRIMO reads assembled sequence contigs with corresponding base quality statistics and automatically designs walking primers as needed to extend and join contigs, or improve their overall quality. In the opposite extreme of single-pass or completely directed sequencing, PRIMO reads the unassembled sequence for each template and designs walking primers for extending each read. If the base-calling software does not provide base quality statistics, PRIMO assigns its own measure of base quality determined by the shapes of individual peaks in the trace data for each template. In this way, PRIMO can be used in the finishing stages of a shotgun sequencing project, in sequencing by directed primer walking, or in some intermediate strategy. The code is written in ANSI C and maintained in two versions: one for the Macintosh and the other for UNIX.

Animals↗

PubMed1997

Structure of Pit-1 POU domain bound to DNA as a dimer: unexpected arrangement and flexibility.

Pit-1, a member of the POU domain family of transcription factors, characterized by a bipartite DNA-binding domain, serves critical developmental functions based on binding to diverse DNA elements in its target genes. Here we report a high resolution X-ray analysis of the Pit-1 POU domain bound to a DNA element as a homodimer. This analysis reveals that Pit-1 subdomains bind to perpendicular faces of the DNA, rather than opposite faces of the DNA as in Oct-1. This is accomplished by different spacing and orientation of the POU-specific domain. Contrary to previous predictions, the dimerization interface involves the carboxyl terminus of the DNA recognition helix of the homeodomain, which in an extended conformation interacts with specific residues at the amino terminus of helix alpha1 and in the loop between helices alpha3 and alpha4 of the POU-specific domain of the symmetry related monomer. These features suggest the molecular basis of disease-causing mutations in Pit-1 and provide potential basis for the flexible allostery between protein domains and DNA sites in the activation of target genes.

Amino Acid Sequence↗

PubMed1997

The GDB Human Genome Database Anno 1997.

The value of the Genome Database (GDB) for the human genome research community has been greatly increased since the release of version 6. 0 last year. Thanks to the introduction of significant technical improvements, GDB has seen dramatic growth in the type and volume of information stored in the database. This article summarizes the types of data that are now available in the Genome Database, demonstrates how the database is interconnected with other biomedical resources on the World Wide Web, discusses how researchers can contribute new or updated information to the database, and describes our current efforts as well as planned improvements for the future.

Base Sequence↗

PubMed1997

The bone-bonding polymer Polyactive 80/20 induces hydroxycarbonate apatite formation in vitro.

The bone-bonding polymer known as Polyactive is a block copolymer composed of a polyethylene oxide (PEO) soft segment and a polybutylene terephthalate (PBT) hard segment. This study focuses on the in vitro induction of hydroxyapatite by Polyactive. Our results show that Polyactive is capable of inducing hydroxycarbonate apatite (HCAp) formation from a metastable calcium phosphate solution analogous to a physiological solution. In a 4-day incubation, the HCAp formation extended approximately 100 microm deep from the surface. A great number of globules about 1 microm large were found in the calcified Polyactive. These globules were composed of HCAp crystals embedded in the polymer matrix. There were so many globules in the surface that they connected with each other and formed a calcified layer. Next to the calcified layer was a zone where the globules were scattered. The calcified surface may have acted to promote HCAp growth from the solution, bringing about the formation of a HCAp layer on top of the calcified layer. The transition of solid Polyactive into a Polyactive hydrogel in calcium phosphate solution permitted HCAp formation within the polymer. It is proposed that the COOH groups produced during hydrolysis of Polyactive play an important role in nucleating hydroxyapatite. A remarkable affinity of the PEO segment of the polymer for calcium ions may facilitate moving calcium and phosphate from the solution into the polymer for the growth of HCAp.

Biocompatible Materials↗

PubMed1997

Characterization of mice deficient in interleukin-1 beta converting enzyme.

Interleukin-1 beta converting enzyme (ICE) processes the inactive prolL-1 beta to the proinflammatory mature IL-1 beta. ICE belongs to a family of cysteine proteases that have been implicated in apoptosis. To address the biological functions of ICE, we generated ICE-deficient mice through gene targeting technology. ICE-deficient mice developed normally, appeared healthy, and were fertile. Peritoneal macrophages from ICE-deficient mice underwent apoptosis normally upon ATP treatment. Thymocytes from young ICE-deficient mice also underwent apoptosis when triggered by dexamethasone, gamma irradiation, or aging. ICE-deficient mice had a major defect in the production of mature IL-1 beta and had impaired IL-1 alpha production on LPS stimulation in vitro and in vivo. ICE-deficient mice were resistant to LPS-induced endotoxic shock.

Adenosine Triphosphate↗

PubMed1997

Angiotensin II induces apoptosis of adult ventricular myocytes in vitro.

To determine whether angiotensin II (Ang II) activates the suicide program of myocytes, primary cultures of adult rat ventricular myocytes were exposed to 10(-9) M of Ang II, for 24 h. Ang II resulted in a five-fold increase in programmed myocyte cell death (PMCD) documented by the terminal deoxynucleotidyl transferase assay and confirmed by DNA agarose gel electrophoresis. Ang II stimulation was associated with translocation of the epsilon and delta isoforms of protein kinase C (PKC) which was coupled with an increase in cytosolic Ca2+ in the cells. The PKC inhibitor chelerythrine abolished Ang II-mediated increases in cytosolic Ca2+ and PMCD. Similarly, pretreatment of cells with the intracellular Ca2+ chelator BAPTA/AM inhibited the formation of DNA strand breaks. Conversely, the Ca2+ ionophore A23187 markedly increased PMCD. Finally, the AT1 receptor antagonist, losartan, completely blocked Ang II-induced PMCD, whereas the AT2 receptor antagonist, PD123319, did not attenuate this phenomenon. In conclusion, ligand binding of AT1 receptors on myocytes triggers PMCD by a mechanism involving PKC-mediated increases in cytosolic calcium, which result in internucleosomal DNA fragmentation.

Alkaloids↗

PubMed1997

Metabolism and actions of ADP-riboses in coronary arterial smooth muscle.

The present study examined the metabolism of ADP-ribose (ADPR) and cyclic ADP-ribose (cADPR) in small bovine coronary arterial homogenates and characterized the effects of these nucleotides on the activity of potassium (K+) channels in coronary smooth muscle cells. ADPR and cADPR were produced from NAD+ (1mM) by homogenates from small bovine coronary arteries. The conversion rate was 2.81 +/- 0.19 nmol/min/100 micrograms protein for ADPR and 1.37 +/- 0.03 nmol/min/100 micrograms protein for cADPR. In patch clamp experiments, ADPR produced a concentration-dependent increase in the activity of a calcium activated K (Kca) channel in inside-out membrane patches of coronary arterial smooth muscle cells at concentrations of 0.1, 1 and 10 microM. The open state probability (NPo) of Kca channel was maximally increased 5-fold at a concentration of 10 microM. cADPR reduced the activity of Kca channel at concentrations of 1 and 10 microM. The NPo was decreased by 45% and 75%, respectively. The results indicate that there is an enzymatic pathway in the coronary arterial smooth muscle to produce ADPR and cADPR. These nucleotides may play a role in the control of coronary vascular tone by altering the activity of the Kca channel in vascular smooth muscle cells.

Adenosine Diphosphate Ribose↗

PubMed1997

Palliative gastrojejunostomy. A minimally invasive approach.

Palliative bypass for neoplastic gastric outlet obstruction should be minimally invasive. We designed a laparoscopically assisted approach that appears to meet the need. The proximal jejunum is exteriorized by laparoscopy via an epigastric trocar-site incision. An EEA anvil is installed in the exteriorized jejunum, which is returned to the abdomen. Through this mini-incision, the anterior wall of the stomach is opened for insertion of the EEA stapler, which penetrates the posterior gastric wall. When snapped to the anvil and fired, an antecolic gastrojejunostomy is created. No mortality or anastomotic leak occurred in two cases. The operation and recovery appeared to be faster than historic controls. This operation is minimally invasive and expeditious, ideal for patients requiring palliative bypass.

Biopsy↗

PubMed1997

AZT blocks down-regulation of IL-2 and IFN-gamma gene expression in HIV acutely infected cells.

HIV infection causes dysregulation of cytokine gene expression in CD4+ T cells of the infected host. Azidothymidine (AZT) inhibits HIV replication by blocking reverse transcription. Using a one-stop cell-to-cell HIV infection model, we have investigated the expression of several key cytokines in HIV infected T cells in the absence or presence of AZT treatment. Acute HIV infection of T cells resulted in dramatic down regulation of the expression of IL-2 and INF-gamma mRNA. While beta-actin mRNA levels remained constant in both AZT-free and AZT treated cultures after HIV infection, it was found that AZT blocked the down regulation of IL-2 mRNA and INF-gamma mRNA in CD4+ T cells acutely infected with HIV.

CD4-Positive T-Lymphocytes↗

PubMed1997

Nucleotide sequence of the murine leukaemia virus amphotropic strain 4070A integrase (IN) coding region and comparative structural analysis of the inferred polypeptide.

The complete nucleotide sequence of the integrase (IN) protein coding region of the murine leukaemia virus (MLV) amphotropic strain 4070A is presented. The sequence comprises 1,224 nucleotides, encoding a 408-residue polypeptide of M(r) 46,312. Alignment of the inferred 4070A IN amino acid sequence with the IN proteins of other MLV showed that substitutions are confined largely to segments within the N- and C-terminal domains. In the N-terminal domain the majority of substitutions occur as contiguous 2- to 6-residue blocks, whereas in the C-terminal domain they occur as isolated entities except within a short segment characterized by deletions/insertions. Selection appears to act on the C-terminal 19 residues of IN rather than on the N-terminal residues of ENV (encoded by overlapping reading frames), suggesting a functional role for this segment. Phylogenetic analyses grouped the sequences into two clusters, one comprising IN from the amphotropic strain 4070A and three ecotropic MLV (CAS-BR-E, Moloney and Friend), the other consisting of IN from three ecotropic MLV (two radiation-induced viruses and AKV) and a mink cell focus-forming (MCF) MLV virus. The same dichotomy and cluster composition was obtained from analysis of the long terminal repeat (LTR) regions from these viruses (consistent with the functional interrelationship of IN and LTR) but not from analysis of envelope protein sequences (consistent with the functional independence of ENV proteins from both IN and LTR). Secondary structure predictions supported features determined from the catalytic domain of human immunodeficiency virus and avian sarcoma virus IN, and identified probable structures within the relatively long N- and C-terminal domains of MLV IN proteins.

Amino Acid Sequence↗

PubMed1997

Coronary artery stenosis in rats affects beta-adrenergic receptor signaling in myocytes.

OBJECTIVE: The purpose of this study was to determine whether the early chronic ischemic cardiomyopathy produced by non-occlusive coronary artery constriction was characterized by alterations in the regulation of beta-adrenoreceptor (beta-AR) signaling. METHODS: Coronary artery narrowing was surgically induced in rats and the animals sacrificed at 7 and 14 days. The changes in the biochemical properties of the multiple components of the beta-AR pathway were examined in enzymatically dissociated myocytes. RESULTS: Coronary stenosis, involving an average 55% reduction in luminal diameter, was associated with left ventricular failure and right ventricular dysfunction at both time intervals. A decrease in the quantity of beta-AR was detected at 7 days and preceded the loss of high-affinity binding sites. This regulatory modification was characterized by a reduction in beta 1 and beta 2 receptors and a shift in the isoproterenol dose response curve indicating a functional correlation between the decrease in beta-AR and attenuated inotropic support of the myocardium. The percentage of beta-AR binding agonist with high affinity decreased significantly at 14 days along with a further reduction in the density of beta 1 and beta 2 receptors. Reconstitution studies with cyc S49 lymphoma cells did not detect an impairment of Gs alpha functional activity, but the quantity of Gi alpha was increased at both intervals. Finally, activation of the catalytic unit of adenylyl cyclase by forskolin and GTP was not altered by coronary stenosis, however, basal cyclic AMP in myocytes was depressed at 14 days. CONCLUSIONS: Coronary stenosis induces distinct and progressive modifications in the beta-AR signaling cascade which may contribute to the impaired ventricular performance in this model of myocardial ischemia.

Adrenergic beta-Agonists↗

PubMed1997

Basal nitric oxide expresses endogenous cardioprotection during reperfusion by inhibition of neutrophil-mediated damage after surgical revascularization.

Ischemia-reperfusion damages endothelium and impairs basal production of nitric oxide. Basally released nitric oxide is cardioprotective by its inhibition of neutrophil activities. Loss of endogenous nitric oxide with endothelial injury may occur during two phases: cardioplegic ischemia and reperfusion (aortic declamping). This study tested the hypothesis that inhibition of endogenously released nitric oxide in hearts subjected to regional ischemia, cardioplegic arrest, and reperfusion (1) restricts endogenous cardioprotection and permits neutrophil-mediated damage and (2) expresses damage during the reperfusion phase. L-Nitro-arginine was used to block basal nitric oxide production. In 22 anesthetized dogs, the left anterior descending artery was ligated for 90 minutes followed by 1 hour of arrest with cold multidose (every 20 minutes) blood cardioplegia. Dogs were divided into three groups: the first group received standard unsupplemented blood cardioplegia (group 1, n = 8), in the second group L-nitro-arginine was administered as an additive to blood cardioplegic solution (1 mmol) and as an infusion during reperfusion (34 mg/kg) (group 2, n = 7), and in the third group L-nitro-arginine was administered only at reperfusion (group 3, n = 7). The ligature was released during the second infusion of cardioplegic solution. Infarct size (triphenyltetrazolium chloride) was increased in group 3 (L-nitro-arginine only at reperfusion) compared with that in group 1 (standard blood cardioplegia) (49% +/- 6% vs 34% +/- 2%, respectively), but was not further extended in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion) (56% +/- 3%, p > 0.05 vs group 3), which suggests primarily a reperfusion process. Polymorphonuclear neutrophil-specific myeloperoxidase activity in the area at risk was elevated comparably in groups 2 and 3 (group 2: 2.9 +/- 0.5 units/gm tissue, p = 0.06 vs group 1; group 3: 3.9 +/- 1.0 units/gm tissue, p < 0.05 vs group 1) compared with that in the standard blood cardioplegia group (1.7 +/- 0.3 units/gm tissue), suggesting polymorphonuclear neutrophil accumulation occurs primarily during reperfusion. Polymorphonuclear neutrophil adherence in ischemic-reperfused left anterior descending artery segments was comparably greater in group 2 (L-nitro-arginine as an additive to blood cardioplegic solution and at reperfusion: 195 +/- 21 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) and group 3 (L-nitro-arginine only at reperfusion: 224 +/- 20 polymorphonuclear neutrophils/mm2 of artery, p < 0.05 vs group 1) relative to that in group 1 (108 +/- 19 polymorphonuclear neutrophils/mm2 of artery). There was no significant adherence to nonischemic circumflex arteries. We conclude that blockade of endogenous nitric oxide augments postischemic injury mediated by polymorphonuclear neutrophils, and this damage is expressed primarily during the reperfusion phase.

Animals↗

PubMed1997

Cytogenetic study of twenty-three primary squamous cell carcinomas of the lung.

Fifty-seven primary squamous cell carcinomas of the lung were analyzed cytogenetically. Karyotyping was possible in seven cases, and chromosome counting without detailed analysis was possible in 16 other cases. The results suggested that structural chromosome rearrangements related to the short arms of chromosomes 1(5/7), 9(3/7), and 11(6/7), and the long arms of chromosomes 6(4/7) and 7(6/7) may be the primary and non-random chromosome defects which are closely associated with human lung squamous cell carcinoma. These primary and non-random chromosome defects are believed to confer a proliferative advantage to cells carrying them, and to be involved in the pathogenesis of human lung squamous cell carcinoma.

Adult↗

PubMed1997

Chronic estrogen treatment in female transgenic (mRen2)27 hypertensive rats augments endothelium-derived nitric oxide release.

Postmenopausal estrogen replacement therapy is associated with a reduction in cardiovascular events in women, but the mechanisms for this protection are unclear, especially in hypertensive subjects. In this study we investigated the effects of 17beta-estradiol (E2) treatment on blood pressure and endothelial function of transgenic [(mRen2)27] hypertensive and normotensive rats. Thirty female transgenic negative [Tg(-)] and hypertensive positive [Tg(+)] rats were ovariectomized and received either E2 (1.5 mg/rat, subcutaneously, for 3 weeks) or placebo. Chronic 17beta-estradiol treatment lowered mean blood pressure in both Tg hypertensive (159 +/- 4 v 145 +/- 4 mm Hg, P < .05, placebo v E2) and normotensive rats (119 +/- 4 v 108 +/- 2 mm Hg, P < .05, placebo v E2). Pressor responses to intravenous injection of phenylephrine were augmented in the Tg(+) as compared with Tg(-) rats. With chronic E2 treatment the pressor responses to phenylephrine were attenuated in both groups. Isometric tension of aortic rings was measured in vitro in organ chambers. The acetylcholine (Ach)-induced endothelium-dependent vascular relaxation was less potent in Tg(+) versus Tg(-) rats. E2 treatment significantly enhanced the Ach-induced relaxation of both Tg(+) and Tg(-) groups (ED50: 55.5 +/- 11.7 v 10.3 +/- 2.6; 23.8 +/- 6.5 v 5.1 +/- 1.2 nmol/L, placebo v E2 in Tg(+) and Tg(-), respectively). After E2 treatment the ED50 response in Tg(+) rats was no different from Tg(-) rats. However, the maximum vasodilation elicited by Ach was attenuated in Tg(+) as compared with Tg(-) rats. The calcium ionophore (A23187)-induced endothelium-dependent relaxation was less potent in Tg(+) as compared to Tg(-) rats and was enhanced by E2 treatment only in Tg(+) animals. There were no differences in the vasodilator responses elicited by sodium nitroprusside. Removal of endothelium and blockade of NO production abolished the endothelium-dependent vasodilation. The selective NO synthase inhibitor, N(G)-monomethyl-L-arginine (LMMNA), was used to evaluate indirectly the basal contribution of NO in vascular rings. The response to LMMNA was attenuated in untreated Tg(+) as compared to Tg(-) rats. E2 treatment augmented the contraction response to NOS inhibition in both Tg(+) and Tg(-) rats, resulting in a response in Tg(+) rats that was no different from Tg(-) rats. These results indicate that untreated, surgically ovariectomized hypertensive rats show deficiencies in endothelial function, which can be improved by estrogen replacement.

Animals↗