bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of a Legionella pneumophila locus required for intracellular multiplication in human macrophages.
Authors: Marra A , Blander S J , Horwitz M A , Shuman H A
Published: May 2006

The legionnaires' disease bacterium, Legionella pneumophila, is a facultative intracellular parasite. Its interaction with phagocytes has characteristics in common with several other intracellular parasites. Critical aspects of L. pneumophila intracellular multiplication are evasion of lysosomal host cell defenses and the presence of a nutritionally appropriate environment. Following phagocytosis, wild-type L. pneumophila multiply within a specialized phagosome which does not fuse with secondary lysosomes. Mutants which have lost the ability to grow within phagocytes no longer cause disease in animals, indicating that the capacity to multiply intracellularly is important for pathogenesis. One such mutant, 25D, has been shown to be defective in inhibiting phagosome-lysosome fusion. This phagolysosomal environment is not conducive to Legionella growth. We report the isolation of a region of the L. pneumophila genome (icm, intracellular multiplication) which restores the capacity of 25D to multiply in human macrophages. The complemented mutants also regain the capacity to interfere with phagosome-lysosome fusion and to cause lethal pneumonia in guinea pigs.
Activation of expression of genes coding for extracellular matrix proteins in Tat-producing glioblastoma cells.
Authors: Taylor J P , Cupp C , Diaz A , Chowdhury M , Khalili K , Jimenez S A , Amini S
Published: May 2006

The Tat protein of human immunodeficiency virus type 1 has been increasingly implicated in directly contributing to the disease AIDS by altering the expression of strategic cellular genes. In this study we demonstrate that the presence of the human immunodeficiency virus type 1 regulatory protein Tat is associated with a significant induction in the expression of certain protein components of the extracellular matrix in glial-derived cells. Northern blot analysis reveals that in cells expressing Tat there is a marked elevation in the steady-state RNA levels for fibronectin and types I and III collagen. Metabolic labeling of the Tat-producing cells demonstrates that this induction is also reflected at the level of protein synthesis. Transient transfection experiments indicate that the presence of Tat results in increased transcription of fibronectin and alpha I type I collagen promoters. Possible mechanisms for this phenomenon and their significance with regard to AIDS are discussed.
Scanning tunneling microscopy imaging of Torpedo acetylcholine receptor.
Authors: Bertazzon A , Conti-Tronconi B M , Raftery M A
Published: May 2006

The synaptic surface of the acetylcholine receptor in membranes from Torpedo californica electric organ has been imaged by scanning tunneling microscopy. The molecule appears pentameric, with one major and four minor protrusions rising above the surface, and these protrusions encompass a large central cavity. The outer diameter of the molecule is 69 +/- 10 A, while the diameter of the cavity, measured at the widest complete contour line delimiting the opening, is 26 +/- 7 A. The images and dimensions obtained are consistent with the structure determined from hybrid density maps obtained by x-ray diffraction and electron microscopy. Thus, scanning tunneling microscopy can be used to obtain overall dimensions and low-resolution structural features of the surface of a membrane-embedded protein.
Metal-binding chimeric antibodies expressed in Escherichia coli.
Authors: Sawyer J R , Tucker P W , Blattner F R
Published: May 2006

Metallothionein, a well-characterized biological chelator of metals, has been genetically fused to the binding domain of an antibody and expressed in the periplasm of Escherichia coli. Specific delivery of 109Cd to immobilized hapten or to haptenated cells was demonstrated directly in periplasmic extracts. This approach is potentially useful for targeted radiotherapy and diagnostic imaging. We find six to seven atoms of metal per active antigen-combining site. Absence of the Fc portion of the immunoglobulin along with low immunogenicity of metallothionein-metal complexes should reduce immunologic reactions.
von Willebrand disease type B: a missense mutation selectively abolishes ristocetin-induced von Willebrand factor binding to platelet glycoprotein Ib.
Authors: Rabinowitz I , Tuley E A , Mancuso D J , Randi A M , Firkin B G , Howard M A , Sadler J E
Published: May 2006

von Willebrand factor (vWF) is a multimeric glycoprotein that mediates the adhesion of platelets to the subendothelium by binding to platelet glycoprotein Ib. For human vWF, this interaction can be induced in vitro by the antibiotic ristocetin or the snake venom protein botrocetin. A missense mutation, Gly-561-->Ser, was identified within the proposed glycoprotein Ib binding domain of vWF in the proband with von Willebrand disease type B, a unique variant characterized by no ristocetin-induced, but normal botrocetin-induced, binding to glycoprotein Ib. The corresponding mutant recombinant protein, rvWF(G561S), formed normal multimers and exhibited the same functional defect as the patient's plasma vWF, confirming that this mutation causes von Willebrand disease type B. These data show that botrocetin and ristocetin cofactor activities of vWF can be dissociated by a point mutation and confirm that these mediators promote vWF binding to platelets by different mechanisms. The normal botrocetin-induced binding and the defective ristocetin-induced binding of rvWF(G561S) suggest that the primary defect in von Willebrand disease type B may be a failure of normal allosteric regulation of the glycoprotein Ib binding function of vWF.
Membrane and synaptic properties of developing lateral geniculate nucleus neurons during retinogeniculate axon segregation.
Authors: White C A , Sur M
Published: May 2006

During the first postnatal month in the ferret (Mustela putorius furo), the projections from the retina to the lateral geniculate nucleus (LGN) become segregated into eye-specific layers and ON and OFF sublayers, a process that is thought to depend in part on neuronal activity. Remarkably, virtually nothing is known about the physiological features of LGN neurons during this period. We have recorded intracellularly from 46 A-layer neurons in slices of the ferret LGN between the ages of postnatal days 7 and 33. The passive membrane properties and current-voltage relationships of the developing neurons were similar in many, though not all, respects to those of adult LGN neurons. Action potentials in younger animals were smaller in amplitude and longer in duration than in older animals, but cells at all ages were capable of producing spike trains whose latency and spike number varied with stimulus intensity. In addition, cells at all ages responded with low-threshold potentials upon release from hyperpolarization. Slightly more than half of the LGN neurons responded to optic tract stimulation with excitatory postsynaptic potentials (EPSPs), inhibitory postsynaptic potentials (IPSPs), or EPSP-IPSP pairs, beginning with the youngest ages. Thus, as early as the second postnatal week, and much before the onset of pattern vision, LGN neurons have many of the membrane and synaptic properties of adult thalamic neurons. These data are consistent with LGN cells playing a significant role in activity-dependent reshaping of the retinogeniculate pathway.
Genetically engineered rice resistant to rice stripe virus, an insect-transmitted virus.
Authors: Hayakawa T , Zhu Y , Itoh K , Kimura Y , Izawa T , Shimamoto K , Toriyama S
Published: May 2006

The coat protein (CP) gene of rice stripe virus was introduced into two japonica varieties of rice by electroporation of protoplasts. The resultant transgenic plants expressed the CP at high levels (up to 0.5% of total soluble protein) and exhibited a significant level of resistance to virus infection. Plants derived from selfed progeny of the primary transformants also expressed the CP and showed viral resistance, indicating stable transmission of the CP gene and the trait of resistance to the next generation. Moreover, the virally encoded strip disease-specific protein was not detected in transgenic plants expressing CP 8 weeks after inoculation, indicating protection before viral multiplication. These studies demonstrated that CP-mediated resistance to virus infection can be extended to cereals and to the viruses transmitted by an insect vector (planthopper).
Selective disruption of growth hormone transcription machinery by viral infection.
Authors: de la Torre J C , Oldstone M B
Published: May 2006

Viruses that establish persistent infections may show selective and unique effects on the host's transcriptional machinery. Lymphocytic choriomeningitis virus (LCMV), a noncytolytic virus, can persistently infect a rat pituitary cell line. Although the infected cells remain free of structural damage, virus markedly interferes with growth hormone (GH) but only minimally interferes with prolactin transcription. The study of GH promoter-chloramphenicol acetyltransferase-transfected cells and GH promoter deletion mutants demonstrates that the viral effect is at the level of GH promoter and is due to interference with GH transactivator factor GHF1 (Pit1). Treatment of LCMV-infected cells with the antiviral agent ribavirin cures the infection and restores normal GH mRNA levels. These results illustrate a molecular mechanism by which a virus infection can disrupt synthesis of a cell's differentiated product without perturbing vital cellular functions.
Progesterone modulates a neuronal nicotinic acetylcholine receptor.
Authors: Valera S , Ballivet M , Bertrand D
Published: May 2006

The major brain nicotinic acetylcholine receptor is assembled from two subunits termed alpha 4 and n alpha 1. When expressed in Xenopus oocytes, these subunits reconstitute a functional acetylcholine receptor that is inhibited by progesterone levels similar to those found in serum. In this report, we show that the steroid interacts with a site located on the extracellular part of the protein, thus confirming that inhibition by progesterone is not due to a nonspecific perturbation of the membrane bilayer or to the activation of second messengers. Because inhibition by progesterone does not require the presence of agonist, is voltage-independent, and does not alter receptor desensitization, we conclude that the steroid is not an open channel blocker. In addition, we show that progesterone is not a competitive inhibitor but may interact with the acetylcholine binding site and that its effect is independent of the ionic permeability of the receptor.
Diagnosis of hepatitis C virus (HCV) infection using an immunodominant chimeric polyprotein to capture circulating antibodies: reevaluation of the role of HCV in liver disease.
Authors: Chien D Y , Choo Q L , Tabrizi A , Kuo C , McFarland J , Berger K , Lee C , Shuster J R , Nguyen T , Moyer D L
Published: May 2006

Structural and nonstructural regions of the HCV-encoded polyprotein have been expressed in recombinant yeast, bacteria, or insect cells and used to capture and measure reactive antibodies circulating in different individuals. The putative nucleocapsid protein (C) and nonstructural proteins 3-5 (NS3-NS5) were found to contain the most immunodominant epitopes. The NS3, NS4, and C regions were expressed in yeast in the form of a fused, chimeric polyprotein (C25) and a capture assay for reactive antibody was developed. This anti-C25 assay detects all previously identified HCV-seropositive cases and provides a substantially more sensitive diagnostic for both acute and chronic HCV infections than the current anti-C100-3 (NS4) assay. Anti-C25 was detected more frequently than anti-C100-3 in chronic, transfusion-associated non-A, non-B hepatitis patients from the United States (95% vs. 71%) and Japan (98% vs. 82%), in cryptogenic cirrhosis patients from the United States (62% vs. 28%), and in hepatitis B surface antigen-negative cases of hepatocellular carcinoma from Japan (83% vs. 63%). These data indicate that HCV has a greater role in these liver diseases than was previously thought. In volunteer United States blood donors sampled following the introduction of anti-C100-3 screening, the prevalence of anti-C25 and anti-C100-3 was 0.5% and 0.08%, respectively.
Isolation and characterization of allelic losses and gains in colorectal tumors by arbitrarily primed polymerase chain reaction.
Authors: Peinado M A , Malkhosyan S , Velazquez A , Perucho M
Published: May 2006

The arbitrarily primed polymerase chain reaction (AP-PCR) [Welsh, J. & McClelland, M. (1990) Nucleic Acids Res. 18, 7213-7218] has been used to detect somatic genetic alterations in tumors of the colon and rectum. DNA fingerprints generated by single arbitrary primers were compared between normal and tumor tissue of the same individuals. AP-PCR bands showing decreased and increased intensities in tumor tissue DNA, relative to normal, have been cloned after reamplification with the same arbitrary primer. Standard restriction fragment length polymorphism and Southern blot analyses show that these DNA sequences have undergone allelic losses and gains, respectively, in the tumor cell genome. The deleted sequences have been assigned to the short arm of chromosome 17 by PCR of somatic hamster/human cell hybrids and linkage analysis. These results show the ability of the AP-PCR to detect and isolate, in a single step, DNA sequences representing two of the genetic alterations that underlie the aneuploidy of cancer cells: losses of heterozygosity and chromosomal gains. Altogether, they also show the quantitative nature of the amplification levels obtained in vitro by AP-PCR, which thus provides the basis for an alternative molecular approach to cancer cytogenetics.
Human spumaretrovirus-related sequences in the DNA of leukocytes from patients with Graves disease.
Authors: Lagaye S , Vexiau P , Morozov V , Guénebaut-Claudet V , Tobaly-Tapiero J , Canivet M , Cathelineau G , Périès J , Emanoil-Ravier R
Published: May 2006

Viruses, and more particularly retroviruses, have been postulated to play a role in the pathogenesis of autoimmune diseases. In a search for spumaretrovirus infection markers, we screened a group of 29 patients with Graves disease and a representative healthy population (23 subjects) as a control. Southern blot hybridization under stringent conditions, of patients' DNA extracted from peripheral blood lymphocytes, with a spumaretrovirus-specific genomic probe derived from the human spumaretrovirus (HSRV) prototype, gave a positive signal in 10 cases. Moreover, by PCR, HSRV-related sequences were detected in the DNA of 19 patients (66%). Positive DNA samples in Southern blots were also positive in PCR for all regions tested (gag, bel1, bel2, long terminal repeat). Amplified (gag and bel2) products were cloned and sequenced; they showed high homology with HSRV. On the other hand, all 23 control subjects were negative by both procedures. Sera from both populations were examined for the presence of antibodies reactive with antigens of the spumaretrovirus family. These sera were negative by several immunodetection techniques: ELISA, indirect immunofluorescence, serum neutralization, and Western blotting. These results strongly suggest the existence of an association between Graves disease and the presence of HSRV-related infection markers.
"7-tetrahydrobiopterin," a naturally occurring analogue of tetrahydrobiopterin, is a cofactor for and a potential inhibitor of the aromatic amino acid hydroxylases.
Authors: Davis M D , Ribeiro P , Tipper J , Kaufman S
Published: May 2006

The ability of 2-amino-4-hydroxy-7-[dihydroxylpropyl-(L-erythro)-5,6,7,8-tetrahyd ropterin] ("7-tetrahydrobiopterin" or 7-BH4) to substitute for the natural cofactor tetrahydrobiopterin (BH4) has been studied in vitro in the reactions of the three mammalian aromatic amino acid hydroxylases. With rat liver phenylalanine hydroxylase, the apparent Km for 7-BH4 is 160 microM, a value that is approximately 60-fold greater than that for the natural cofactor. In contrast, the hydroxylase reaction is severely inhibited by as little as 1 microM 7-BH4 when assayed in the presence of physiological concentrations of BH4. This inhibition can be overcome either by an increase in the concentration of BH4 or a decrease in the concentration of phenylalanine. With both rat brain tryptophan hydroxylase and rat pheochromocytoma tyrosine hydroxylase, the Km value for 7-BH4 is about one order of magnitude greater than the Km for BH4. Accordingly, 7-BH4 is a poor competitive inhibitor of both tryptophan and tyrosine hydroxylase. Thus, our results suggest that the observed hyperphenylalaninemia in patients who excrete 7-BH4 in their urine may arise directly from the inhibition of phenylalanine hydroxylase by low levels of this pterin. On the other hand, it is less likely that low levels of 7-BH4 would affect the activity of tyrosine or tryptophan hydroxylase in vivo.
Somatic recombination of heavy chain variable region transgenes with the endogenous immunoglobulin heavy chain locus in mice.
Authors: Giusti A M , Coffee R , Manser T
Published: May 2006

Transgenic lines of mice were derived by using plasmid constructs containing DNA encoding an antibody heavy chain variable-diversity-joining region (VH-D-JH) and various amounts of 5' and 3' flanking DNA but lacking any repetitive isotype switch (S) or constant (C) region DNA. Unexpectedly, many of the antibody VH regions expressed by B-cell hybridomas generated from immunized transgenic mice were found to be of transgenic origin. Further analyses showed that somatic events had generated hybrid genomic loci in the mice containing the transgenic VH-D-JH gene and plasmid sequences 5' of endogenous heavy chain C region genes. Thus, VH-D-JH transgenes lacking S and C region DNA can recombine with endogenous Igh DNA, leading to the expression of transgene-encoded antibody.
DnaJ, DnaK, and GrpE heat shock proteins are required in oriP1 DNA replication solely at the RepA monomerization step.
Authors: Wickner S , Skowyra D , Hoskins J , McKenney K
Published: May 2006

We have found that three Escherichia coli heat shock proteins, DnaK (the hsp70 homolog), DnaJ, and GrpE, function in oriP1 DNA replication in vitro solely to activate DNA binding by the replication initiator protein RepA. Activation results from the conversion of P1 or P7 RepA dimers to monomers that bind with high affinity to the origin of replication of plasmid P1. Thus, the essential role of these three heat shock proteins in this replication system is to change the quaternary structure of a single protein, RepA.
IRS-1 activates phosphatidylinositol 3'-kinase by associating with src homology 2 domains of p85.
Authors: Myers M G , Backer J M , Sun X J , Shoelson S , Hu P , Schlessinger J , Yoakim M , Schaffhausen B , White M F
Published: May 2006

IRS-1 is an insulin receptor substrate that undergoes tyrosine phosphorylation and associates with the phosphatidylinositol (PtdIns) 3'-kinase immediately after insulin stimulation. Recombinant IRS-1 protein was tyrosine phosphorylated by the insulin receptor in vitro and associated with the PtdIns 3'-kinase from lysates of quiescent 3T3 fibroblasts. Bacterial fusion proteins containing the src homology 2 domains (SH2 domains) of the 85-kDa subunit (p85) of the PtdIns 3'-kinase bound quantitatively to tyrosine phosphorylated, but not unphosphorylated, IRS-1, and this association was blocked by phosphotyrosine-containing synthetic peptides. Moreover, the phosphorylated peptides and the SH2 domains each inhibited binding of PtdIns 3'-kinase to IRS-1. Phosphorylated IRS-1 activated PtdIns 3'-kinase in anti-p85 immunoprecipitates in vitro, and this activation was blocked by SH2 domain fusion proteins. These data suggest that the interaction between PtdIns 3'-kinase and IRS-1 is mediated by tyrosine phosphorylated motifs on IRS-1 and the SH2 domains of p85, and IRS-1 activates PtdIns 3'-kinase by binding to the SH2 domains of p85. Thus, IRS-1 likely serves to transmit the insulin signal by binding and regulating intracellular enzymes containing SH2 domains.
CDC46/MCM5, a yeast protein whose subcellular localization is cell cycle-regulated, is involved in DNA replication at autonomously replicating sequences.
Authors: Chen Y , Hennessy K M , Botstein D , Tye B K
Published: May 2006

Saccharomyces cerevisiae cells containing mutations in the cell-division-cycle gene CDC46 arrest with a large bud and a single nucleus with unreplicated DNA at the non-permissive temperature. This G1/S arrest, together with the increased rates of mitotic chromosome loss and recombination phenotype, suggests that these mutants are defective in DNA replication. The subcellular localization of the CDC46 protein changes with the cell cycle; it is nuclear between the end of M phase and the G1/S transition but is cytoplasmic in other phases of the cell cycle. Here we show that CDC46 is identical to MCM5, based on complementation analysis of the mcm5-1 and cdc46-1 alleles, complementation of the minichromosome maintenance defect of mcm5-1 by CDC46, and the genetic linkage of these two genes. Like mcm5-1, cdc46-1 and cdc46-5 also show a minichromosome maintenance defect thought to be associated with DNA replication initiation at autonomously replicating sequences. Taken together, these observations suggest that CDC46/MCM5 acts during a very narrow window at the G1/S transition or the beginning of S phase by virtue of its nuclear localization to effect the initiation of DNA replication at autonomously replicating sequences.
Function and evolution of a minimal plastid genome from a nonphotosynthetic parasitic plant.
Authors: Wolfe K H , Morden C W , Palmer J D
Published: May 2006

Complete nucleotide sequencing shows that the plastid genome of Epifagus virginiana, a nonphotosynthetic parasitic flowering plant, lacks all genes for photosynthesis and chlororespiration found in chloroplast genomes of green plants. The 70,028-base-pair genome contains only 42 genes, at least 38 of which specify components of the gene-expression apparatus of the plastid. Moreover, all chloroplast-encoded RNA polymerase genes and many tRNA and ribosomal protein genes have been lost. Since the genome is functional, nuclear gene products must compensate for some gene losses by means of previously unsuspected import mechanisms that may operate in all plastids. At least one of the four unassigned protein genes in Epifagus plastid DNA must have a nongenetic and nonbioenergetic function and, thereby, serve as the reason for the maintenance of an active genome. Many small insertions in the Epifagus plastid genome create tandem duplications and presumably arose by slippage mispairing during DNA replication. The extensive reduction in genome size in Epifagus reflects an intensification of the same processes of length mutation that govern the amount of noncoding DNA in chloroplast genomes. Remarkably, this massive pruning occurred with a virtual absence of gene order change.
On "genomenclature": a comprehensive (and respectful) taxonomy for pseudogenes and other "junk DNA".
Authors: Brosius J , Gould S J
Published: May 2006

Genomic nomenclature has not kept pace with the levels and depth of analyzing and understanding genomic structure, function, and evolution. We wish to propose a general terminology that might aid the integrated study of evolution and molecular biology. Here we designate as a "nuon" any stretch of nucleic acid sequence that may be identifiable by any criterion. We show how such a general term will facilitate contemplation of the structural and functional contributions of such elements to the genome in its past, current, or future state. We focus in this paper on pseudogenes and dispersed repetitive elements, since their current names reflect the prevalent view that they constitute dispensable genomic noise (trash), rather than a vast repertoire of sequences with the capacity to shape an organism during evolution. This potential to contribute sequences for future use is reflected in the suggested terms "potonuons" or "potogenes." If such a potonuon has been coopted into a variant or novel function, an evolutionary process termed "exaptation," we employ the term "xaptonuon." If a potonuon remains without function (nonaptive nuon), it is a "nonaptation" and we term it "naptonuon." A number of examples for potonuons and xaptonuons are given.
Phosphorylation/dephosphorylation of high-affinity IgE receptors: a mechanism for coupling/uncoupling a large signaling complex.
Authors: Paolini R , Numerof R , Kinet J P
Published: May 2006

Engagement of high-affinity IgE receptors leads to activation of tyrosine and serine/threonine kinases and the immediate phosphorylation of receptor beta (serine and tyrosine) and gamma (threonine and tyrosine) chains. Receptor disengagement leads to dephosphorylation of beta and gamma chains via the action of undefined phosphatases. Here we have identified five distinct polypeptides associated with the high-affinity IgE-receptor tetrameric complex, which apparently become phosphorylated and dephosphorylated in sequence with the beta and gamma chains. Like beta chain, polypeptides pp180, pp48, pp42, and pp28 are phosphorylated on serine and tyrosine, whereas pp125 is only phosphorylated on serine. The phosphorylation of each of these receptor-associated polypeptides is antigen-dose dependent and is restricted to activated receptor complexes. Furthermore the physical association between pp125 and the receptor is quantitatively affected by receptor phosphorylation and dephosphorylation, indicating a coupling-uncoupling mechanism. Finally, in vitro kinase experiments show that activated receptor complexes are also physically associated with tyrosine and serine/threonine kinases as part of a larger complex containing the phosphorylated polypeptides.
High-level expression in Escherichia coli of enzymatically active fusion proteins containing the domains of mammalian cytochromes P450 and NADPH-P450 reductase flavoprotein.
Authors: Fisher C W , Shet M S , Caudle D L , Martin-Wixtrom C A , Estabrook R W
Published: May 2006

This report describes the properties of two mammalian cytochromes P450 that have been expressed at high levels in Escherichia coli as enzymatically active fusion proteins containing the flavoprotein domain of rat NADPH-cytochrome P450 reductase (EC 1.6.2.4). Fusion proteins were prepared by engineering the cDNAs for the steroid-metabolizing bovine adrenal P450 17A with the cDNA for rat liver NADPH-P450 reductase with the introduction of a Ser-Thr linker to give a protein we have named rF450[mBov17A/mRatOR]L1. Similarly, the cDNA for the omega-hydroxylase of rat liver (P450 4A1) was linked with the cDNA for rat liver NADPH-P450 reductase to give rF450[mRat4A1/mRatOR]L1. A procedure involving disruption of transformed E. coli by sonication, isolation of membranes by differential centrifugation, solubilization with detergent, and affinity chromatography provided significant amounts of purified fusion proteins of approximately 118 kDa. The purified fusion proteins had turnover numbers for the metabolism of steroids (rF450[mBov17A/mRatOR]L1) or fatty acids (rF450[mRat4A1/mRatOR]L1) ranging from 10/min to 30/min in the absence of added phospholipid. Addition of purified rat liver cytochrome b5 stimulated the 17,20-lyase reaction for the conversion of 17-hydroxypregnenolone to dehydroepiandrosterone, and addition of purified rat NADPH-cytochrome P450 reductase enhanced the formation of omega--1 metabolites from lauric and arachidonic acids. NADPH oxidation was tightly coupled to substrate hydroxylation with the purified fusion proteins.
Deposition of beta/A4 immunoreactivity and neuronal pathology in transgenic mice expressing the carboxyl-terminal fragment of the Alzheimer amyloid precursor in the brain.
Authors: Kammesheidt A , Boyce F M , Spanoyannis A F , Cummings B J , Ortegón M , Cotman C , Vaught J L , Neve R L
Published: May 2006

The deposition of amyloid in senile plaques and along the walls of the cerebral vasculature is a characteristic feature of Alzheimer disease. The peptide comprising the carboxyl-terminal 100 amino acids of the beta-amyloid precursor protein (beta APP) has been shown to aggregate into amyloid-like fibrils in vitro and to be neurotoxic, suggesting that this fragment may play a role in the etiology of Alzheimer disease. To address this question, we expressed this carboxyl-terminal 100-amino acid peptide of beta APP in transgenic mice under the control of the brain dystrophin promoter. We used an antibody to the principal component of amyloid, beta/A4, to demonstrate cell-body and neuropil accumulation of beta/A4 immunoreactivity in the brains of 4- and 6-month-old transgenic mice. Only light cytoplasmic staining with this antibody was visible in control mice. In addition, immunocytochemical analysis of the brains with an antibody to the carboxyl terminus of beta APP revealed abnormal aggregation of this epitope of beta APP within vesicular structures in the cytoplasm and in abnormal-appearing neurites in the CA2/3 region of the hippocampus in transgenic mice, similar to its aggregation in the cells of Alzheimer disease brains. Thioflavin S histochemistry suggested accumulations of amyloid in the cerebrovasculature of transgenic mice with the highest expression of the beta APP-C100 transgene. These observations suggest that expression of abnormal carboxyl-terminal subfragments of beta APP in vivo may cause amyloidogenesis and specific neuropathology.
Amino acid residues required for fast Na(+)-channel inactivation: charge neutralizations and deletions in the III-IV linker.
Authors: Patton D E , West J W , Catterall W A , Goldin A L
Published: May 2006

The cytoplasmic linker connecting domains III and IV of the voltage-gated Na+ channel is thought to be involved in fast inactivation. This linker is highly conserved among the various Na+ channels that have been cloned. In the rat brain IIA Na+ channel, it consists of 53 amino acids of which 15 are charged. To investigate the role of this linker in inactivation, we mutated all 15 of the charged residues in various combinations. All but one of these mutants expressed functional channels, and all of these inactivated with kinetics similar to the wild-type channel. We then constructed a series of deletion mutations that span the III-IV linker to determine if any region of the linker is essential for fast inactivation. Deletion of the first 10 amino acids completely eliminated fast inactivation in the channel, whereas deletion of the last 10 amino acids had no substantial effect on inactivation. These results demonstrate that some residues in the amino end of the III-IV linker are critical for fast Na(+)-channel inactivation, but that the highly conserved positively charged and paired negatively charged residues are not essential.
Gene family for an elicitor-induced sesquiterpene cyclase in tobacco.
Authors: Facchini P J , Chappell J
Published: May 2006

The initial step in the conversion of the isoprenoid intermediate farnesyl diphosphate to the sesquiterpenoid phytoalexin capsidiol in elicitor-treated tobacco tissues is catalyzed by an inducible sesquiterpene cyclase [5-epi-aristolochene synthase (EAS)]. Two independent cDNA clones (cEAS1 and cEAS2) encoding EAS were isolated from an elicitor-induced tobacco cDNA library by differential hybridization and subsequently were characterized by hybrid selection--in vitro translation. Insertion of cEAS1, a partial cDNA clone encoding 175 C-terminal amino acids, into an Escherichia coli expression vector resulted in accumulation of a fusion protein immunodetectable with EAS-specific polyclonal antibodies. The cDNA clones were used to isolate two full-length EAS genes that mapped 5 kilobases (kb) apart on one 15-kb genomic clone. The nucleotide sequences of the structural gene components were identical from 388 base pairs (bp) upstream of the transcription initiation site to 40 bp downstream of the translation termination codon, suggesting a relatively recent duplication event. The genes consist of 1479-bp open reading frames, each containing five introns and specifying 56,828-Da proteins. The N-terminal amino acid sequence deduced from the genomic clones was identical to the first 16 amino acids of the EAS protein identifiable by Edman degradation. RNA blot hybridization with cEAS1 demonstrated a mRNA induction time course consistent with the induction of the EAS mRNA translational activity with maximum levels 4-6 h after elicitation. EAS mRNA was not detected in control cells. DNA blot-hybridization analysis of genomic DNA revealed a copy number of approximately 12-15 for EAS-like genes in the tetraploid tobacco genome. The conservation of a putative allelic prenyl diphosphate binding motif is also discussed.
Requirement for coenzyme Q in plasma membrane electron transport.
Authors: Sun I L , Sun E E , Crane F L , Morré D J , Lindgren A , Löw H
Published: May 2006

Coenzyme Q is required in the electron transport system of rat hepatocyte and human erythrocyte plasma membranes. Extraction of coenzyme Q from the membrane decreases NADH dehydrogenase and NADH:oxygen oxidoreductase activity. Addition of coenzyme Q to the extracted membrane restores the activity. Partial restoration of activity is also found with alpha-tocopherylquinone, but not with vitamin K1. Analogs of coenzyme Q inhibit NADH dehydrogenase and oxidase activity and the inhibition is reversed by added coenzyme Q. Ferricyanide reduction by transmembrane electron transport from HeLa cells is inhibited by coenzyme Q analogs and restored with added coenzyme Q10. Reduction of external ferricyanide and diferric transferrin by HeLa cells is accompanied by proton release from the cells. Inhibition of the reduction by coenzyme Q analogs also inhibits the proton release, and coenzyme Q10 restores the proton release activity. Trans-plasma membrane electron transport stimulates growth of serum-deficient cells, and added coenzyme Q10 increases growth of HeLa (human adenocarcinoma) and BALB/3T3 (mouse fibroblast) cells. The evidence is consistent with a function for coenzyme Q in a trans-plasma membrane electron transport system which influences cell growth.
High density of Ca(2+)-dependent K+ and Cl- channels on the luminal membrane of lacrimal acinar cells.
Authors: Tan Y P , Marty A , Trautmann A
Published: May 2006

Tight-seal whole-cell recording and Ca2+ imaging were simultaneously performed on cell clusters or individual acinar cells of rat lacrimal glands during application of the secretagogue acetylcholine. Activation of Ca(2+)-dependent K+ and Cl- currents was selectively followed as a function of time by placing the cell potential near the equilibrium potential for Cl- or for K+ ion, respectively. Upon acetylcholine application to cell clusters, K(+)- and Cl(-)-selective currents displayed a distinctive initial rise ("hump"). At this time, there was only a small elevation of Ca2+ concentration, [Ca2+]i, that was restricted to the luminal end of acinar cells. A quantitative analysis of Ca2+ and current signals during the hump suggested that the luminal membrane contained high densities of K(+)- and Cl(-)-selective channels, roughly 10 times higher than those found in the basolateral domain. Distinct luminal and basolateral membrane domains were preserved in isolated cells, but with less contrasted densities than in cell clusters. The results suggest that Ca(2+)-dependent K+ channels are implicated not only in the transfer of salt from the blood compartment to the interior of acinar cells, as commonly accepted, but also in the electrolyte secretion from the cell interior to the acinar lumen.
Epidermal growth factor stimulates mouse placental lactogen I but inhibits mouse placental lactogen II secretion in vitro.
Authors: Yamaguchi M , Ogren L , Endo H , Thordarson G , Kensinger R , Talamantes F
Published: May 2006

This study was undertaken to determine whether epidermal growth factor (EGF) regulates the secretion of mouse placental lactogen (mPL)-I and mPL-II. Primary cell cultures were prepared from placentas from days 7, 9, and 11 of pregnancy and cultured for up to 5 days. Addition of EGF (20 ng/ml) to the medium resulted in significant stimulation of mPL-I secretion by the second day of culture in cells from days 7 and 9 of pregnancy and significant inhibition of mPL-II secretion by the third or fourth day of culture in cells from days 7, 9, and 11. Dose-response studies carried out with cells from day 7 of pregnancy demonstrated that the minimum concentration of EGF that stimulated mPL-I secretion and inhibited mPL-II secretion was 1.0 ng/ml. EGF did not affect the DNA content of the cells or cell viability, assessed by trypan blue exclusion, nor did it have a general effect on protein synthesis. There are three types of PL-containing giant cells in mouse placental cell cultures: cells that contain either mPL-I or mPL-II and cells that contain both hormones. Immunocytochemical analysis and the reverse hemolytic plaque assay indicated that EGF treatment was accompanied by a significant increase in the number of cells that produce mPL-I, but among the PL cells that contained mPL-I, there was no change in the fraction of cells that contained only mPL-I or the fraction that contained both mPL-I and mPL-II. In contrast, EGF treatment did affect the distribution of mPL-II among PL cells. In control cultures, about 75% of the cells that contained mPL-II also contained mPL-I, but in EGF-treated cultures, all of the cells that contained mPL-II also contained mPL-I. These data suggest that EGF regulates mPL-I and mPL-II secretion at least partly by regulating PL cell differentiation.
Tyrosine phosphorylation is required for activation of an alpha interferon-stimulated transcription factor.
Authors: Gutch M J , Daly C , Reich N C
Published: May 2006

The signal transduction pathway of alpha interferon utilizes tyrosine phosphorylation to transmit a signal generated at the cell surface to the transcriptional machinery in the nucleus. Activation of the interferon pathway initiates with the binding of alpha interferon to its cell surface receptor. The ligand-receptor complex signals the activation of a latent cytoplasmic transcription factor. The active form of the interferon-stimulated gene factor (ISGF3) is phosphorylated on tyrosine residues. ISGF3 subsequently translocates to the nucleus and binds to a DNA sequence, the interferon-stimulated response element, found within the promoter of inducible genes. ISGF3 is a multicomponent factor consisting of four proteins of 113 kDa, 91 kDa, 84 kDa, and 48 kDa. Three proteins consistent with sizes of 113 kDa, 91 kDa, and 84 kDa copurify with ISGF3 and are phosphorylated on tyrosine residues after stimulation by alpha interferon. Tyrosine phosphorylation is essential for activation of ISGF3. Genistein, a tyrosine kinase inhibitor, blocks the appearance of ISGF3 and blocks the transcriptional stimulation of interferon-induced genes. This study shows that tyrosine phosphorylation provides a link between the interferon-receptor complex at the plasma membrane and specific activation of gene expression in the nucleus.
Reproductive biology of the Permian Glossopteridales and their suggested relationship to flowering plants.
Authors: Taylor E L , Taylor T N
Published: May 2006

The discovery of permineralized glossopterid reproduction organs from Late Permian deposits in the Beard-more Glacier region (central Transantarctic Mountains) of Antarctica provides anatomical evidence for the adaxial attachment of the seeds to the megaasporophyll in this important group of Late Paleozoic seed plants. The position of the seeds is in direct contradiction to many earlier descriptions, based predominatly on impression/compression remains. The attachement of the ovules on the adaxial surface of a leaf-like megasporophyll, combined with other features, such as megaga-reproductive biology in this group than has previously been hypothesized. The findings confirm the classification of the Glossopteridales as seed ferns and are important considerations in disscussion of the phylogeny of group, including their suggested role as close relatives or possible ancestors of the angiosperms.
Identification and genetic mapping of a homeobox gene to the 4p16.1 region of human chromosome 4.
Authors: Stadler H S , Padanilam B J , Buetow K , Murray J C , Solursh M
Published: May 2006

A human craniofacial cDNA library was screened with a degenerate oligonucleotide probe based on the conserved third helix of homeobox genes. From this screening, we identified a homeobox gene, H6, which shared only 57-65% amino acid identity to previously reported homeodomains. H6 was physically mapped to the 4p16.1 region by using somatic cell hybrids containing specific deletions of human chromosome 4. Linkage data from a single-stranded conformational polymorphism derived from the 3' untranslated region of the H6 cDNA placed this homeobox gene more than 20 centimorgans proximal of the previously mapped HOX7 gene on chromosome 4. Identity comparisons of the H6 homeodomain with previously reported homeodomains reveal the highest identities to be with the Nk class of homeobox genes in Drosophila melanogaster.
Metabolic engineering of medicinal plants: transgenic Atropa belladonna with an improved alkaloid composition.
Authors: Yun D J , Hashimoto T , Yamada Y
Published: May 2006

The tropane alkaloid scopolamine is a medicinally important anticholinergic drug present in several solanaceous plants. Hyoscyamine 6 beta-hydroxylase (EC 1.14.11.11) catalyzes the oxidative reactions in the biosynthetic pathway leading from hyoscyamine to scopolamine. We introduced the hydroxylase gene from Hyoscyamus niger under the control of the cauliflower mosaic virus 35S promoter into hyoscyamine-rich Atropa belladonna by the use of an Agrobacterium-mediated transformation system. A transgenic plant that constitutively and strongly expressed the transgene was selected, first by screening for kanamycin resistance and then by immunoscreening leaf samples with an antibody specific for the hydroxylase. In the primary transformant and its selfed progeny that inherited the transgene, the alkaloid contents of the leaf and stem were almost exclusively scopolamine. Such metabolically engineered plants should prove useful as breeding materials for obtaining improved medicinal components.
Axon substitution in the reorganization of developing neural connections.
Authors: Bhide P G , Frost D O
Published: May 2006

Insights into the mechanisms of normal and pathological neural development may be gained by studying the reorganization of developing neural connections, caused experimentally or by disease. Many reorganized connections are assumed to arise by the anomalous stabilization of transient connections that occur during normal development. We report that, although the retina projects transiently to the somatosensory system in normal developing hamsters, the permanent retinal projections to the somatosensory system that arise as a consequence of early brain lesions are not formed by the stabilization of the normally transient projection. Instead, the transient retinal axons are replaced by retinal axons that do not normally project to the somatosensory system. The distinction between anomalous stabilization and substitution is significant for determining the cellular mechanisms underlying the development of neural connectivity.
Cantharidin-binding protein: identification as protein phosphatase 2A.
Authors: Li Y M , Casida J E
Published: May 2006

The toxic effects of cantharidin from blister beetles and its analogs, including the herbicide endothall, are attributable to their high affinity and specificity for a cantharidin-binding protein (CBP). An ammonium sulfate precipitate of mouse liver cytosol was purified by five chromatographic steps to isolate CBP in 14% yield and > 99% purity as monitored by [3H]cantharidin-binding activity. The purification factor of 2230-fold corresponds to a CBP content of 0.045% of the liver cytosolic protein. CBP is a heterodimer consisting of a 61-kDa alpha subunit and a 39-kDa beta subunit. Amino acid sequences of four peptides from CBP-alpha and three peptides from CBP-beta are identical with deduced amino acid sequences for the A alpha regulatory and C beta catalytic subunits, respectively, of protein phosphatase 2A (PP2A). This assignment of CBP as PP2A-AC from structural evidence is supported by biochemical studies with selective substrates and inhibitors. CBP dephosphorylation of phosphorylase alpha is sensitive not only to okadaic acid, as with PP2A, but also to cantharidin and its analogs, consistent with their potency in blocking the radioligand binding site of CBP. Okadaic acid is a potent inhibitor of [3H]cantharidin binding to CBP. PP2A is present in many mammalian tissues and in plants and is involved in regulatory phosphorylation-dephosphorylation events which modulate multiple cellular functions. Inhibition of PP2A activity may account for the diverse effects and toxicity of cantharidin and its analogs, including the herbicide endothall, in mammals and possibly plants.
Major histocompatibility complex class I-restricted T cells are required for resistance to Mycobacterium tuberculosis infection.
Authors: Flynn J L , Goldstein M M , Triebold K J , Koller B , Bloom B R
Published: May 2006

Mice with a targeted disruption in the beta 2-microglobulin (beta 2m) gene, which lack major histocompatibility complex class I molecules and consequently fail to develop functional CD8 T cells, provided a useful model for assessing the role of class I-restricted T cells in resistance to infection with virulent Mycobacterium tuberculosis. Of mutant beta 2m-/-mice infected with virulent 10(6) M. tuberculosis, 70% were dead or moribund after 6 weeks, while all control mice expressing the beta 2m gene remained alive for > 20 weeks. Granuloma formation occurred in mutant and control mice, but far greater numbers of tubercle bacilli were present in the lungs of mutant mice than in controls, and caseating necrosis was seen only in beta 2m-/-lungs. In contrast, no differences were seen in the course of infection of mutant and control mice with an avirulent vaccine strain, bacille Calmette-Guérin (BCG). Immunization with BCG vaccine prolonged survival of beta 2m-/-mice after challenge with M. tuberculosis for 4 weeks but did not protect them from death. These data indicate that functional CD8 T cells, and possibly T cells bearing gamma delta antigen receptor, are a necessary component of a protective immune response to M. tuberculosis in mice.