Biomedical subjects

J Xu

Publications and source records attributed to J Xu.

At least 1,009 records · Page 56Linked to original sources

PubMed1995

A YAC-, P1-, and cosmid-based physical map of the BRCA1 region on chromosome 17q21.

A familial early-onset breast cancer gene (BRCA1) has been localized to chromosome 17q21. To characterize this region and to aid in the identification of the BRCA1 gene, a physical map of a region of 1.0-1.5 Mb between the EDH17B1 and the PPY loci on chromosome 17q21 was generated. The physical map is composed of a yeast artificial chromosome (YAC) and P1 phage contig with one gap. The majority of the interval has also been converted to a cosmid contig. Twenty-three PCR-based sequence-tagged sites (STSs) were mapped to these contigs, thereby confirming the order and overlap of individual clones. This complex physical map of the BRCA1 region was used to isolate genes by a number of gene identification techniques and to generate transcript maps of the region, as presented in the three accompanying manuscripts of Brody et al. (1995), Osborne-Lawrence et al. (1995), and Friedman et al. (1995).

BRCA1 Protein↗

PubMed1995

Two-locus approach of segregation and linkage analysis in the study of complex traits.

A two-locus segregation and linkage-analysis approach was used to characterize the genetic control of a complex trait (Q1) and to localize the genes that have detectable effects. The results suggested that a two-locus Mendelian model fit the data significantly better than a one-locus model. The linkage results based on the most parsimonious two-locus model revealed linkage of Q1 to two areas (MG2 and MG3), while there was less evidence for linkage using one-locus models. Results also suggested that the subphenotypes (Q2 and Q3) provided useful information for further analysis of Q1 using two-locus models.

Alleles↗

PubMed1995

Vein-graft wrapping for the treatment of recurrent compression of the median nerve.

Recurrent compressive neuropathy of the median nerve due to cicatrix is an extremely challenging clinical problem. Available treatment techniques are difficult and results uncertain. Early experience with the autogenous vein graft wrapping technique has shown great promise for the treatment of chronic compressive neuropathy after other procedures have failed. We report on 3 patients with average follow-up of 2 years. Postoperatively, all the patients had significant improvement on electromyograms, and the findings of both subjective and objective assessments were excellent or good for 2 patients. The procedure is simple; the donor is readily available; no complications were noted in the donor area, and the graft tissue has good compatibility. This technique can also be applied for chronic compression of any peripheral nerve.

Adult↗

PubMed1995

Expression and characterization of type IV collagenases in rat lung cells during development.

Fetal type II epithelial cells rest on a basal lamina which separate them from the underlying connective tissue. At late fetal gestation, this basement membrane is occasionally disrupted, allowing epithelial cytoplasmic extensions to reach in close proximity of the interstitial fibroblast. The cellular source and enzymes responsible for the focal degradation of the basal membrane remains to be defined. In the present study, we examined the developmental expression of basement membrane associated type IV collagen and its degrading enzymes. Both fetal lung epithelial cells and fibroblasts expressed 72-kDa type IV collagenase and type IV (alpha 1) (alpha 2) collagen genes. Fibroblasts were enriched in the expression of 72-kDa type IV collagenase mRNA. Zymography showed that both cell types actively secrete 72- and 92-kDa type IV collagenases. Conditioned medium of fibroblasts contained more gelatin degrading activity than that of epithelial cells. At the time of appearance of basement membrane discontinuities (19-21 days, term = 22 days), 72-kDa type IV collagenase mRNA expression in fibroblasts increased while that of epithelial cells remained constant. Gelatinolytic activity of fibroblast conditioned medium also increased during this period. In contrast, type IV collagen gene expression decreased in both epithelial cells and fibroblasts. These data are compatible with a role for type IV collagenases in the genesis of basement membrane disruptions during late fetal lung development.

Animals↗

PubMed1995

Expression of the neurofibromatosis I gene product, neurofibromin, in blood vessel endothelial cells and smooth muscle.

Vascular pathology is an underestimated complication of neurofibromatosis 1 (NF1). Manifestations include renovascular stenosis with associated hypertension, cerebrovascular occlusion, visceral ischaemia and aneurysms of smaller arteries. This is illustrated by a woman recently evaluated in our Neurofibromatosis Program who had multiple cerebrovascular and renovascular abnormalities. To determine the contribution of NF1 expression to NF1 vasculopathy, the expression of the NF1 gene product, neurofibromin, was examined in blood vessels. Neurofibromin was detected in the endothelial cell layer of rat cerebral vessels, renal arteries, and aorta by immunohistochemistry. Cultured bovine cerebral endothelial cells were found to express NF1 mRNA by RT-PCR and neurofibromin by Western immunoblotting and immunocytochemistry. Neurofibromin expression was also detected in the smooth muscle layer of the aorta but not of cerebral or renal vessels. The vascular abnormalities of NF1 are reviewed and possible pathogenesis with respect to neurofibromin expression is discussed.

Adult↗

PubMed1995

Computer-assisted assignment of peptides with non-standard amino acids.

A comprehensive peptide assignment program and its application to a cyclic peptide, cyclosporin A, are presented in this paper. A group of graph theoretical algorithms using fuzzy logic are discussed with the aid of examples from cyclosporin A. The algorithms deal with heavily overlapped peaks, recover disjointed and distorted spin coupling networks, and include strategies for sequence-specific assignment. A procedure to extend the Protein Knowledge Base for automatically assigning non-standard amino acid residues is also presented. The program is capable of completely automated assignment for small peptides (approximately 20 residues). For such molecules, it is insensitive to whether the peptide chain is cyclic or acyclic, and to whether amide protons are present or absent. For larger peptides/proteins, more user interaction is required and the sequence-specific assignment step usually must proceed through fragments smaller than the full length to avoid problems due to occurrence of a combinatorial explosion. The program can be applied as a rigorous tool to check manual assignments. The fuzzy graph theoretical concepts built in the program are illustrated with 2D proton spectra of a peptide, but may be extended to higher-dimensional spectra, other biopolymers, natural products and other organic structures.

Algorithms↗

PubMed1995

Dynamic changes in Rad51 distribution on chromatin during meiosis in male and female vertebrates.

Antibodies against human Rad51 protein were used to examine the distribution of Rad51 on meiotic chromatin in mouse spermatocytes and oocytes as well as chicken oocytes during sequential stages of meiosis. We observed the following dynamic changes in distribution of Rad51 during meiosis: (1) in early leptotene nuclei there are multiple, apparently randomly distributed, foci that by late leptonema become organized into tracks of foci. (2) These foci persist into zygonema, but most foci are now localized on Rad51-positive axes that correspond to lateral elements of the synaptonemal complex. As homologs synapse foci from homologous axes fuse. The distribution and involvement of Rad51 foci as contact points between homologs suggest that they may be components to early recombination nodules. (3) As pachynema progresses the number of foci drops dramatically; the temporal occurrence (mice) and physical and numerical distribution of foci on axes (chickens) suggest that they may be a component of late recombination nodules. (4) In early pachynema there are numerous Rad51 foci on the single axis of the X (mouse spermatocytes) or the Z (chicken oocytes) chromosomes that neither pair, nor recombine. (5) In late pachynema in mouse spermatocytes, but not oocytes, the Rad51 signal is preferentially enhanced at both ends of all the bivalents. As bivalents in spermatocytes, but not oocytes, begin to desynapse at diplonema they are often held together at these Rad51-positive termini. These observations parallel observations that recombination rates are exceptionally high near chromosome ends in male but not female eutherian mammals. (6) From diakinesis through metaphase I, Rad51 protein is detected as low-intensity fluorescent doublets that localize with CREST-specific antigens (kinetochores), suggesting that Rad51 participates, at least as a structural component of the materials involved, in sister kinetochore cohesiveness. Finally, the changes in Rad51 distribution during meiosis do not appear to be species specific, but intrinsic to the meiotic process.

Animals↗

PubMed1995

Effects of implicit memory on explicit recall: set size and word-frequency effects.

PIER was designed to explain findings related to tasks involving an encoding phase and a testing phase in which retrieval cues prime the recovery of what has been encoded. The model assumes that retrieval cues initiate the sampling of associated memories linked to the encoded information and that sampled memories are subjected to a recognition check to determine whether they meet criteria specified by the purpose of the retrieval. The model explains how the number of implicitly activated associates linked to a studied word affects its later recovery and predicts that words infrequently experienced will be recovered with greater likelihood than words frequently experienced. This prediction was tested and confirmed in two experiments in which the associative set size and the frequency of the studied words were manipulated. Implications for the study of implicit memory are considered.

Attention↗

PubMed1995

Digoxin-induced ventricular arrhythmias in the guinea pig heart in vivo: evidence for a role of endogenous catecholamines in the genesis of delayed afterdepolarizations and triggered activity.

The mechanisms of digoxin-induced ventricular arrhythmias were studied in vivo using a novel experimental model. Anesthetized guinea pigs were instrumented with custom-made electrode catheters which enabled the monitoring and recording of right atrial, right ventricular, and His bundle electrograms, midmyocardial monophasic action potentials (MAP), and systemic arterial blood pressure. Intravenous digoxin induced ventricular arrhythmias ranging from ventricular premature contractions (VPCs) to ventricular fibrillation (VF). These were associated with delayed afterdepolarizations (DADs) observed on the MAP recordings. The severity of the arrhythmias depended on the dose of digoxin. Short bursts of ventricular pacing neither terminated nor suppressed episodes of ventricular tachycardias (VTs). A direct relationship existed between the paced ventricular cycle length and the coupling interval between the last paced beat and the first ectopic beat (r = 0.913, P < 0.001, n = 10) and between the amplitude of the DADs and the pacing rate (r = 0.972, P < 0.05, n = 7). The increased contractility (LV dp/dt) and heart rate evoked by isoproterenol (0.1 microgram/kg) did not induce DADs in the absence of digoxin. Verapamil terminated the digoxin-induced VTs in 15 of 16 animals and abolished the associated DADs in 7 of 7 animals. Adenosine terminated the VTs in 15 of 19 animals and abolished the DADs in 8 of 10 animals. Digoxin induced VT in only 1 of 6 animals treated with reserpine (5 + 5 mg/kg) 24 and 48h prior to experimentation. However, subsequent intravenous isoproterenol (0.2 micrograms/kg) induced VT and DADs, both of which were abolished by verapamil, in all 6 animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗

PubMed1995

The effect of mechanical strain on fetal rat lung cell proliferation: comparison of two- and three-dimensional culture systems.

Normal growth of the fetal lung is dependent on fetal breathing movements. We have previously reported that an intermittent strain, which simulates normal fetal breathing movements, stimulates DNA synthesis and cell division of mixed fetal rat lung cells maintained in organotypic culture. To examine which cell type is responding to mechanical strain and to investigate whether the effects of strain on cell proliferation and mechanotransduction are affected by tissue architecture, we isolated fetal lung cells and subjected them to intermittent strain either as two-dimensional monolayer cultures or as three-dimensional organotypic cultures. Strain enhanced DNA synthesis of mixed cells, epithelial cells, and fibroblasts when cultured in a three-dimensional configuration. In contrast, no stimulatory effect on cell proliferation was observed when cells were strained as monolayer cultures. Intracellular signals, induced by strain, and cell morphology also varied depending on the culture conditions. These results suggest that mechanical strain stimulates the proliferation of both epithelial cells and fibroblasts and that the response of fetal lung cells to mechanical strain in vitro depends on cellular architecture.

Animals↗

PubMed1995

Prevention of carbon tetrachloride-induced rat liver injury by soluble tumor necrosis factor receptor.

BACKGROUND/AIMS: Considerable indirect evidence suggests that cytokine tumor necrosis factor alpha contributes to the hepatocellular damage caused by toxic liver injury. The effects of tumor necrosis factor alpha neutralization on liver cell injury were determined in an in vivo model of toxic liver injury. METHODS: The in vivo effects of tumor necrosis factor alpha were examined in carbon tetrachloride liver injury through the administration of a soluble tumor necrosis factor receptor to neutralize the effects of this cytokine. RESULTS: Soluble tumor necrosis factor receptor treatment decreased the degree of liver injury as measured by reduced levels of serum liver enzymes and improved histology. Soluble tumor necrosis factor receptor administration also lowered the mortality from a lethal dose of carbon tetrachloride from 60% to 16%. Tumor necrosis factor alpha neutralization had no detrimental effect on liver regeneration as determined by the timing of histone gene expression and postinjury liver weight. CONCLUSIONS: These data provide direct evidence for a role of tumor necrosis factor alpha in toxin-induced liver cell injury. In addition, these investigations suggest that soluble tumor necrosis factor receptor therapy may be of benefit in the treatment of human liver disease.

Animals↗

PubMed1995

The characterization of chromosomal rearrangements by a combined micro-FISH approach in a patient with myelodysplastic syndrome.

We report the application of a combined strategy: chromosome microdissection, degenerate oligonucleotide primed-PCR, and reverse chromosome painting (micro-FISH), as well as forward chromosome painting, for the characterization of chromosomal rearrangements in a MDS patient with the karyotype 46,XX, -11, +r analyzed by G-banding. The karyotype was refined as 46,XX,der(2)t(2;11) (q35;?p13),der(11)dic r(11)(:p13-->q13::p13-->q13:). Our study demonstrated that the chromosome composition of a neoplasia can be identified more systematically and accurately using these combined molecular cytogenetic approaches. The DOP-PCR methodology modified is suitable for the practical application of micro-FISH on specimens prepared for routine banding analysis.

Aged↗

PubMed1995

Characterization of a Bombyx mori cDNA encoding a novel member of the attacin family of insect antibacterial proteins.

A Bombyx mori cDNA was cloned that hybridized with Hyalophora cecropia attacin probe and its nucleotide sequence was determined. This cDNA consisted of 846 nucleotides and the deduced amino acid sequence showed that the cDNA encodes an attacin precursor protein. The putative mature protein of B. mori attacin had 70.4, 68.3 and 18.8% identity in amino acid sequences with that of H. cecropia acidic and basic attacins and Sarcophaga peregrina sarcotoxin IIA, respectively. B. mori and H. cecropia attacins and S. peregrina sarcotoxin IIA had two subdomains in each G domain, suggesting that common amino acid residues in the subdomains are conserved during evolution and plays an important role in the activity of the antibacterial proteins. Expression of B. mori attacin gene was rapidly induced by the injection of Escherichia coli cells into B. mori larvae and continued at least for 48 h mainly in fat bodies and hemocytes.

Amino Acid Sequence↗

PubMed1995

Direct physical interaction involving CD40 ligand on T cells and CD40 on B cells is required to propagate MMTV.

The propagation of mouse mammary tumor virus (MMTV) has been analyzed in mice defective for expression of CD40 ligand (CD40L). Mice with endogenous viral superantigen (SAG) delete T cells with cognate V beta independent of CD40L expression. Nevertheless, CD40L-mice do not show deletion of cognate T cells after being exposed to infectious MMTV and have greatly diminished viral replication. The response of CD40L- T cells to SAG in vitro is also impaired, but can be reconstituted by adding B cells activated by recombinant CD40L to express costimulatory molecules. Thus, direct CD40L-dependent B cell activation appears to be a critical step in the life cycle of MMTV. The initial step in SAG-dependent T cell activation, and hence the MMTV life cycle, may be mediated by non-B cells, because splenocytes from B cell-deficient SAG-transgenic mice are able to activate cognate T cells.

Animals↗

PubMed1995

The developmental pattern of Brca1 expression implies a role in differentiation of the breast and other tissues.

We have examined the developmental expression of the murine breast and ovarian cancer susceptibility gene, Brca1, to investigate its role in the control of cell growth and differentiation. Specifically, we have analysed Brca1 expression during embryonic development, in adult tissues, and during postnatal mammary gland development, particularly in response to ovarian hormones. Our results suggest that Brca1 is expressed in rapidly proliferating cell types undergoing differentiation. In the mammary gland, Brca1 expression is induced during puberty, pregnancy, and following treatment of ovariectomized animals with 17 beta-estradiol and progesterone. These observations imply that Brca1 is involved in the processes of proliferation and differentiation in multiple tissues, notably in the mammary gland in response to ovarian hormones.

Animals↗

PubMed1995

Structure of a single-cytidine hairpin loop formed by the DNA triplet GCA.

In certain contexts the DNA triplet GGA, when juxtaposed on opposite strands of a DNA duplex, shows the unusual property of pairing with itself in an antiparallel orientation to form the (GGA)2 motif. In this motif the central guanines do not pair but intercalate and stack between sheared G.A pairs. Similar studies with GCA triplets reveal that they do not form analogous paired (GCA)2 motifs but instead strongly promote formation of a hairpin, the structure of which is now reported here. The GCA hairpin loop consists of a single cytidine residue closed by a sheared G.A pair and this structure is discussed in the context of triplet expansions in triplet-repeat diseases.

Base Sequence↗

PubMed1995

Synthesis and characterization of covalent adducts derived from the binding of benzo[a]pyrene diol expoxide to a -GGG- sequence in a deoxyoligonucleotide.

Direct synthesis and purification procedures are described for the preparation of adducts derived from the covalent binding of 7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydro-benzo[a]pyrene [(+)-anti-BPDE or (+)-BPDE 2] to each of the three guanine residues (trans-N2-dG lesions) in the oligodeoxyribonucleotide d(CTATG1G2G3TATC). The positions of the modified Gs are defined by Maxam-Gilbert sequencing techniques. Six different oligonucleotides with one or two precisely positioned (+)-anti-BPDE residues are identified. The absorbance, circular dichroism and fluorescence characteristics are changed upon formation of duplexes with the complementary strands d(GATACCCATAG). In the doubly-modified oligonucleotides, a broad, excimer-like long wavelength fluorescence emission band is observed with a maximum near 455 nm only if the two (+)-anti-BPDE-modified Gs are adjacent to one another. The covalently attached (+)-anti-BPDE residues decrease the thermodynamic stabilities of the duplexes; their melting points are markedly dependent on the position of the lesions, being highest with the (+)-anti-BPDE residue at G1 (Tm = 40 degrees C, only 2 degrees C lower than in the case of the unmodified oligonucleotide) and lowest when it is situated at G3 (Tm = 29 degrees C). The implications of these and other physical characteristics are discussed. The facile synthesis of these or similar site-specific and stereochemically defined (+)-trans-anti-BPDE-N2-dG lesions in runs of contiguous guanines in oligodeoxyribonucleotides of specified base sequence should be useful for the design of site-directed mutagenesis studies in vitro and in vivo.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗

PubMed1995

Analysis of inbreeding depression in Agaricus bisporus.

Inbreeding depression was observed in the commercial button mushroom, Agaricus bisporus, by examining two laboratory populations. The outbred population consisted of 20 compatible pairings, 10 homokaryons with each of the homokaryons Ag1-1 and Ag89-65. The inbred population consisted of 104 backcrosses (among which 52 were expected to be sexually compatible) obtained from the pairings of two progenitor homokaryons, Ag1-1 and Ag89-65, with 52 progeny homokaryons derived from the mating between Ag1-1 and Ag89-65. The eight fitness components examined for these two populations were successful matings as identified by the analysis of restriction fragment length polymorphisms, positive mycelial interaction in these successful matings, heterokaryon growth rate, primordium formation by the successful matings, fertile fruiting body formation, time to first break, average number of fruiting bodies per square foot, and average weight per fruiting body. The outcrossed population showed a significant advantage over the inbred population in three of eight fitness components. Two pairs of traits were significantly correlated. The multiplicative fitness ratio of the inbred to the outcrossed population was 0.18. The relevance of inbreeding depression to the evolution of fungal mating systems and to mushroom breeding is discussed.

Agaricus↗