Biomedical subjects

X Fan

Publications and source records attributed to X Fan.

At least 163 records · Page 9Linked to original sources

PubMed1997

Molecular cloning of a cDNA encoding a potential water-borne pheromonal attractant released during Aplysia egg laying.

Recently deposited egg cordons are a source of water-borne pheromones that attract the marine mollusk Aplysia into breeding aggregations and coordinate male and female reproductive behavior within the aggregation. A potential pheromonal attractant has been isolated from egg cordon eluates and the peptide partially characterized [S.D. Painter, B. Clough, X. Fan, G.T. Nagle, Soc. Neurosci. Abstr., Vol. 22 (1996) 837]. Using this information, we have cloned an Aplysia albumen gland cDNA that encodes a precursor protein containing a single copy of the full-length peptide, and demonstrated that there are abundant levels of pheromone mRNA transcripts (0.8 and 2.5 kb) in the albumen gland. This is consistent with the reported function of the gland (i.e. packaging the eggs into a cordon for deposition), with behavioral studies showing that the albumen gland is a potential source of attractants, and more recent biochemical studies in which the full-length peptide has been isolated from the albumen gland. This is the first candidate peptide pheromone in mollusks and the first in invertebrates. The pheromonal regulatory system in Aplysia may provide a model system for examining the structural characteristics of peptide pheromones.

Amino Acid Sequence↗

PubMed1997

Upregulation of lymphoid and renal interferon-gamma mRNA in autoimmune MRL-Fas(lpr) mice with lupus nephritis.

MRL-Fas(lpr) mice develop an aggressive form of autoimmunity, characterized by immune complex-mediated glomerulonephritis and massive expansion of lymphoid tissues. Increased MHC class II expression by macrophages and renal parenchymal cells is a prominent feature of MRL-Fas(lpr) mice. Since interferon-gamma (IFN-gamma) is the major and the most potent inducer of MHC class II molecules it could play a pathogenic role in the disease process in MRL-Fas(lpr). We have analyzed IFN-gamma expression in normal and nephritic MRL-Fas(lpr) mice by examining renal and lymphoid IFN-gamma-specific mRNA production, using reverse transcription-polymerase chain reaction (RT-PCR) and Northern blotting. We detect abundant IFN-gamma mRNA expression in the kidney of nephritic MRL-Fas(lpr) by RT-PCR, whereas normal mice display absent or only very weak expression of this cytokine. By RT-PCR, IFN-gamma mRNA is detectable in normal spleen, but is overexpressed in the enlarged spleen and lymph nodes of MRL-Fas(lpr). Northern blotting using total RNA from tissues confirms abundant IFN-gamma expression in spleen and lymph node of MRL-Fas(lpr). We conclude that enhanced renal IFN-gamma mRNA expression is a prominent feature of MRL-Fas(lpr) lupus nephritis. Increased IFN-gamma produced by infiltrating T cells could lead to increased MHC class II expression by renal parenchymal cells, thereby promoting the nephritic process by augmentation of antigen presentation in the kidney of autoimmune MRL-Fas(lpr).

Animals↗

PubMed1997

Up-regulation of tubular epithelial interleukin-12 in autoimmune MRL-Fas(lpr) mice with renal injury.

Phagocyte-derived interleukin-12 (IL-12) is a key cytokine that induces the development of an effective Th1 type immune response in various inflammatory and infectious disorders. To determine the importance of IL-12 in the pathogenesis of autoimmune renal injury we examined the renal production of this heterodimeric cytokine in the MRL-Fas(lpr) lupus nephritis model. Compared with normal mice RT-PCR products encoding both the p35 and p40 subunits of IL-12 were markedly increased in the kidney of MRL-Fas(lpr). Immunofluorescence staining demonstrated expression of the IL-12 p75 heterodimer on isolated infiltrating mononuclear cells and also on proximal tubular epithelial cells in MRL-Fas(lpr) but less in normal mice kidneys. The enhanced expression of IL-12 correlated with an increased intrarenal transcription of IFN-gamma. The p35 and p40 transcripts and soluble IL-12 p75 protein were also produced by cultured TEC. In addition, membrane bound IL-12 was detected on Tec. We conclude that IL-12 production is significantly up-regulated in MRL-Fas(lpr) lupus nephritis. In addition to mononuclear cells, TEC are an important source of IL-12 and could thereby participate in the development of a Th1 type immune response in autoimmune renal injury.

Animals↗

PubMed1997

Perinatal lethality with kidney and pancreas defects in mice with a targetted Pkd1 mutation.

PKD1 is the most common site for mutations in human autosomal dominant polycystic kidney disease (ADPKD). ADPKD is characterized by progressive replacement of kidney tissue by epithelial cysts and eventual renal failure. Hepatic and pancreatic cysts are also common. The PKD1 protein, polycystin, is a cell-surface protein of unknown function that is widely expressed in epithelia and in vascular smooth muscle and myocardium. None of the genetic forms of murine polycystic disease map to the murine Pkd1 locus. We introduced into mice by homologous recombination a Pkd1 truncation mutation, Pkd1-, that mimics a mutation found in ADPKD. Pkd1- heterozygotes have no discernible phenotype, whereas homozygotes die during the perinatal period with massively enlarged cystic kidneys, pancreatic ductal cysts and pulmonary hypoplasia. Renal cyst formation begins at embryonic day 15.5 (E15.5) in proximal tubules and progresses rapidly to replace the entire renal parenchyma. The timing of cyst formation indicates that full-length polycystin is required for normal morphogenesis during elongation and maturation of tubular structures in the kidney and pancreas.

Abnormalities, Multiple↗

PubMed1997

Coordinate regulation of G- and C strand length during new telomere synthesis.

We have used the ciliate Euplotes to study the role of DNA polymerase in telomeric C strand synthesis. Euplotes provides a unique opportunity to study C strand synthesis without the complication of simultaneous DNA replication because millions of new telomeres are made at a stage in the life cycle when no general DNA replication takes place. Previously we showed that the C-strands of newly synthesized telomeres have a precisely controlled length while the G-strands are more heterogeneous. This finding suggested that, although synthesis of the G-strand (by telomerase) is the first step in telomere addition, a major regulatory step occurs during subsequent C strand synthesis. We have now examined whether G- and C strand synthesis might be regulated coordinately rather than by two independent mechanisms. We accomplished this by determining what happens to G- and C strand length if C strand synthesis is partially inhibited by aphidicolin. Aphidicolin treatment caused a general lengthening of the G-strands and a large increase in C strand heterogeneity. This concomitant change in both the G- and C strand length indicates that synthesis of the two strands is coordinated. Since aphidicolin is a very specific inhibitor of DNA pol alpha and pol delta, our results suggest that this coordinate length regulation is mediated by DNA polymerase.

Animals↗

PubMed1997

Upregulated renal tubular CD44, hyaluronan, and osteopontin in kdkd mice with interstitial nephritis.

BACKGROUND: The hyaluronan (HA) receptor CD44 is upregulated on parenchymal cells in various inflammatory lesions and could play a role in immune injury. The purpose of the present study was to examine CD44 and its ligands HA and osteopontin (Opn) in a murine model of tubulointerstitial nephritis (TIN). METHODS: The expression of CD44 was investigated by immunofluorescence staining and RNA analysis in kidneys of kdkd mice with autoimmune TIN. The CD44 expression was then correlated with the location of its ligands HA and Opn. RESULTS: CD44 is expressed de novo by tubular epithelial cells (TEC) in areas of tubular injury in kdkd kidneys, but not in normal control kidneys. CD44 positive lymphocytes and macrophages also infiltrate the kidney to kdkd mice. RT-PCR and Southern blot analysis demonstrate that transcripts encoding standard and variant forms of CD44 are increased in kdkd mice with TIN. In parallel the CD44 ligand HA also accumulates in kdkd kidneys in the interstitial space, particularly in cortical areas of tubular injury. Furthermore, the expression of the chemotactic protein Open is enhanced in kdkd kidney, predominantly in areas of tubular injury. Opn mRNA expression also increases markedly in kdkd kidneys compared with normal kidneys, and correlates with disease severity. CONCLUSIONS: Prominent CD44 expression by TEC in areas of tubulointerstitial lesions is a characteristic feature of kdkd mice. The de novo appearance of CD44 on injured TEC might allow interaction with the ligands HA and Opn in vivo. Interaction of CD44 with these ligands could participate in the tubulointerstitial inflammatory response in kdkd mice.

Animals↗

PubMed1997

An investigation of penetration depth control using parallel opposed ultrasound arrays and a scanning reflector.

A theoretical study of penetration depth control in superficial hyperthermia utilizing parallel opposed linear ultrasound arrays and a double-faced (V-shaped) scanning reflector is presented. This is a dual array system (DAS), where one array operates at a low frequency and the other at a high frequency (1 and 5 MHz, respectively in this study). The arrays are positioned facing each other and both are aimed at a double-faced scanning reflector which distributes the energy over the scanned surface. Each reflecting surface is angled at 45 degrees with respect to the sound propagation direction so that both beams are deflected in the same direction toward the treatment volume. The system was designed to be compatible for combined operation with a medical linear accelerator for the delivery of simultaneous thermoradiotherapy. It is demonstrated that by varying the excitation magnitude of one array relative to the other, it is possible to control the magnitude of absorbed energy as a function of depth, and thus improved control of the heating pattern in all three spatial dimensions is obtained. This improvement is demonstrated with bio-heat transfer simulations which show how penetration depth control translates into control of temperature distributions. The simulations also show that the DAS is able to produce more uniform temperature distributions in highly perfused tissue.

Auditory Perception↗

PubMed1997

Acoustic field prediction for a single planar continuous-wave source using an equivalent phased array method.

Phased array theory is combined with the Rayleigh-Sommerfeld diffraction integral to predict measured acoustic fields generated by a single-source ultrasonic transducer. The idea is to treat a single-source as a "phased array," which is composed of many small elements. The goal is to find the excitation source for the phased array, that is, the amplitude and phase for each array element, which produces an acoustic field similar to the experimentally measured field generated by the single-source transducer. A pressure field measured at a given plane parallel and close to the face of the transducer in degased water was used to calculate the excitation source of the equivalent phased array using an inverse technique. The excitation source of the equivalent phased array was then used to calculate the acoustic field from this measurement plane to the far field. It was demonstrated that this phased array approach accurately predicted the location of major grating lobes and the general distributions of the near and far pressure fields for four different transducers. This equivalent phased array method (EPAM) used to model a single-source transducer should be useful in both diagnostic and therapeutic ultrasound applications.

Acoustics↗

PubMed1997

Structure and activity of uroguanylin and guanylin from the intestine and urine of rats.

Uroguanylin and guanylin are related peptides that activate common guanylate cyclase signaling molecules in the intestine and kidney. Uroguanylin was isolated from urine and duodenum but was not detected in extracts from the colon of rats. Guanylin was identified in extracts from small and large intestine but was not detected in urine. Uroguanylin and guanylin have distinct biochemical and chromatographic properties that facilitated the separation, purification, and identification of these peptides. Northern assays revealed that mRNA transcripts for uroguanylin were more abundant in small intestine compared with large intestine, whereas guanylin mRNA levels were greater in large intestine relative to small intestine. Synthetic rat uroguanylin and guanylin had similar potencies in the activation of receptors in T84 intestinal cells. Production of uroguanylin and guanylin in the mucosa of duodenum is consistent with the postulate that both peptides influence the activity of an intracellular guanosine 3',5'-cyclic monophosphate signaling pathway that regulates the transepithelial secretion of chloride and bicarbonate in the intestinal epithelium.

Amino Acid Sequence↗

PubMed1997

Signal transduction pathways via guanylin and uroguanylin in stomach and intestine.

Guanylin and uroguanylin are peptides that activate receptor guanylate cyclases (GCs) and elicit increased intestinal secretion. Bacteria that cause traveler's diarrhea produce heat-stable toxins (STs) that mimic this action. Investigation of the distribution and identity of receptor GCs in the gastrointestinal tract of rats revealed that receptors were localized to epithelial cells in stomach and intestine. Clusters of cells in gastric mucosa and enterocytes lining the intestine exhibited specific binding of 125I-labeled ST. Ligated loops of stomach and intestine treated with intraluminal ST had significant increases in guanosine 3',5'-cyclic monophosphate (cGMP), with duodenum exhibiting the greatest response. Expression of guanylate cyclase C (GCC) mRNA and a truncated, GCC-like mRNA was found in both stomach and intestine. Both mRNAs were isolated as cDNAs encoding the GC catalytic domain. The 0.9-kilobase (kb) cDNA is 99.8% identical to GCC, whereas the truncated, 0.75-kb GCC-like cDNA has a 159-nucleotide deletion and is 96.6% identical to GCC at the protein level. Uroguanylin and guanylin mRNAs were detected in stomach and intestine. Uroguanylin mRNA was most abundant in small intestine, whereas guanylin mRNA was highest in large intestine. Thus the stomach and intestine are targets for regulation of transport by guanylin and uroguanylin via cGMP.

Amino Acid Sequence↗

PubMed1997

Structural equation modeling: basic concepts and applications in personality assessment research.

Structural equation modeling (SEM) has become an increasingly used methodological strategy in psychology. Nevertheless, many psychologists continue to be unclear about how to apply this analytic tool in their research. This article reviews SEM from a conceptual perspective, particularly focusing on confirmatory factor analysis. Additionally, the relation between SEM and other analytic techniques (e.g., exploratory factor analysis) are addressed. A confirmatory factor analytic example is presented and reviewed in detail. Finally, limitations of SEM and other considerations are discussed.

Humans↗

PubMed1997

Induction of carbonic anhydrase II expression in osteoclast progenitors requires physical contact with stromal cells.

Carbonic anhydrase II (CA II) expression is vital to normal osteoclast function. We and others have previously reported induction of CA II messenger RNA (mRNA) expression by 1,25(OH)2D3 in myelomonocytic cells and marrow culture. However, since 1,25(OH)2D3 stimulates osteoclast differentiation as well, we wished to separate direct effects of 1,25(OH)2D3 on the CA II gene from the differentiating effects of the hormone. Using primary murine mixed marrow cultures, we measured CA II mRNA expression by RT-PCR. 10 nM 1,25(OH)2D3 dose dependently induced expression of CA II mRNA (4.12 +/- 0.68-fold) at day 4 in culture compared with control with an ED50 of 0.25 nM. When nonadherent marrow cells containing osteoclast progenitors were depleted of stromal cells and exposed to 10 nM 1,25(OH)2D3, CA II mRNA expression was decreased by more than 60%. Coculture of progenitors with ST-2 stromal cells for 3 days with 10 nM 1,25(OH)2D3 stimulated CA II expression by 22 +/- 3.6-fold. 1,25(OH)2D3 stimulated CA II mRNA expression in progenitors separated from ST-2 cells by transwells was insignificant demonstrating that the two cell types must be in physical contact. PTH also stimulated CA II mRNA expression (4.91 +/- 0.01-fold) to a similar degree as seen with 1,25(OH)2D3 treatment. These results demonstrate that induction of CA II in osteoclast progenitors requires their physical communication with stromal cells and is inseparable from the osteoclast differentiation process.

Animals↗

PubMed1997

Signaling pathways for guanylin and uroguanylin in the digestive, renal, central nervous, reproductive, and lymphoid systems.

Guanylin and uroguanylin are peptides that stimulate membrane guanylate cyclases (GC) and regulate intestinal and renal function via cGMP. Complementary DNAs were isolated encoding opossum preproguanylin and a 279-amino acid portion of a receptor-guanylate cyclase expressed in opossum kidney (OK) cells (GC-OK). The tissue expression of messenger RNA transcripts for these signaling molecules were then compared. Northern and/or reverse transcription-PCR assays revealed that guanylin, uroguanylin, and GC-OK messenger RNAs are expressed in tissues within the digestive, renal, central nervous, reproductive, and lymphoid organ systems. Receptor autoradiography localized the receptors for uroguanylin and guanylin to renal proximal tubules and seminiferous tubules of testis. Synthetic guanylin and uroguanylin peptides activated the receptor-GCs in opossum kidney cortex and in cultured OK cells eliciting increased intracellular cGMP. Expression of agonist and receptor-GC signaling molecules provides a pathway for paracrine and/or autocrine regulation of cellular functions via cGMP in the digestive, renal, central nervous, reproductive, and lymphoid/immune organ systems. Uroguanylin also links the intestine and kidney in a potential endocrine axis that activates tubular receptor-GCs and influences renal function.

Amino Acid Sequence↗

PubMed1997

Macrophage colony stimulating factor down-regulates MCSF-receptor expression and entry of progenitors into the osteoclast lineage.

Macrophage colony-stimulating factor (MCSF), although necessary for entry of precursors into the early preosteoclast pathway, inhibits osteoclastogenesis at high doses. To clarify the relationship between MCSF and osteoclast formation, we investigated the effect of exogenous MCSF in murine bone marrow culture. Precursor proliferation and the expression of MCSF-receptor were examined after 4 days of culture in the presence or absence of accessory stromal cells. In both mixed marrow and destromalized cell cultures, exogenous MCSF dose-dependently decreased 125I-MCSF binding (by 65 +/- 5.0% at 3500 and 87 +/- 16.7% at-7000 U/ml, respectively) while enhancing mononuclear cell proliferation after 3 days of exposure (by 2.8- and 6.3-fold, respectively). These effects were maintained 24 h after removal of exogenous MCSF and, as such, likely represented an MCSF-induced change in MCSF receptor-bearing cells. Exposure to exogenous MCSF (3500 U/ml) days 2-4 dose-dependently inhibited tartrate resistant acid phosphatase positive multinuclear cell (TRAP+ MNC) formation counted at the end of day 7, by 64.3 +/- 4.1%. This inhibition of TRAP+ MNC formation was preceded by a 92 +/- 9% decrease in the expression of carbonic anhydrase II mRNA measurable at 4 days. These results indicate that MCSF promotes proliferation of a population of cells expressing lower cognate receptor sites. Changes in MCSF-receptor expression appear to modulate the final lineage selection of the pluripotent monoblastic progenitor.

Animals↗

PubMed1997

[Molecular cloning of the imipenem resistant gene in bacteroides fragilis].

Imipenem, as a representative of-cabapenem, is one of the most effective beta-Lactam agents against Bacteroides, but recently there have been a few reports on the resistant strains of Bacteroides. To explore the mechanism of imipenem resistance (IMPr) at the molecular level, we extracted chromosome DNA of the resistant strains and acquired a 1.7 kb fragment of resistant gene of imipenem. Recombinant plasmid was stably reserved in generation after generation in E. coli DH5. Resistant gene of imipenem was labeled with Dig-11-dUTP by way of random prime, and 40 strains of clinically isolated Bacteroides were detected by the prepared DNA probe. Two IMPr strains showed hybridization signal, whereas 38 IMPr strains did not show such a signal. The result suggests that the Dig-labeled IMPr gene probe can be used in molecular epidemiology for investigating IMPr strains.

Bacteroides fragilis↗

PubMed1997

[Distribution of leucine-enkephalin like immunoreactive nerve fibers in feline temporomandibular joint: an immunohistochemical PAP method].

In this paper, the immunohistochemical PAP method has been used for the investigation of the distribution of leucine-enkephalin (L-ENK) like immunoreactive fibers in feline temporomandibular joint (TMJ). The results demonstrated as follows: the TMJ capsule, anterior and posterior disc attachments all contained L-ENK immunoreactive nerve fibers which appeared largely as the fine plexi fibers. The density of the distribution of L-ENK positive nerve fibers was the highest in the subsynovium of TMJ capsule, and the plexi structures proceeding to the synovial membrane were observed. The density of the distribution in the lateral joint capsule was the same as the density of distribution in the anterior and posterior discs attachments. No L-ENK positive fibers were detected in the central portion of joint disc. These results indicate that there is the material basis of endogenous analgesic mechanism in TMJ and provide the neuroanatomical basis for exploring physiological functions such as analgesic, immunological and anti-inflammatory effects of ENK nerve fibers in TMJ.

Animals↗

PubMed1997

[The measurement of ST-T segment parameters in ambulatory ECG].

The measure methods of ECG parameters in the repolarization process were studied experimently. The conception of adaptive adjustment in ST segment level measurement was proposed, and a scheme for the adjustment was established with clinical experiences. With the progress of ambulatory ECG, the sectioned and equivalent areas of ST-T segments were extracted.

Electrocardiography, Ambulatory↗

PubMed1996

Monocytes can phagocytose Gram-negative bacteria by a CD14-dependent mechanism.

Phagocytosis of bacteria by monocytes and neutrophil granulocytes provides an important first line of defense against bacterial infections. Opsonization of bacteria with complement and phagocytosis by neutrophils is dependent on divalent cations and does not take place in blood that has been anticoagulated with EDTA. Monocytes, however, do carry out phagocytosis even in the presence of EDTA. We show here that this divalent cation-independent phagocytosis pathway requires the presence of the LPS receptor CD14 on the cell surface. This pathway is dependent on the availability of LPS binding protein, can be blocked by anti-CD14 Abs, by an excess of soluble CD14, by excess free LPS, or by an excess of unlabeled Gram-negative bacteria. In contrast, intact Gram-positive bacteria fail to inhibit this process. These experiments define a CD14-dependent phagocytosis pathway for Gram-negative bacteria that operates in monocytes in human whole blood. This pathway may be able to deal with bacterial pathogens that have developed resistance to complement-dependent opsonization and phagocytosis by neutrophils.

Acute-Phase Proteins↗