bluuebunny/crossref_metadata_2025 huggingface dataset:
Randomly amplified polymorphic DNA markers are superior to somatic incompatibility tests for discriminating genotypes in natural populations of the ectomycorrhizal fungus Suillus granulatus.
Authors: Jacobson K M , Miller O K , Turner B J
Published: May 2006

Assessing genetic variation within populations and genetic exchange between populations requires an understanding of the distribution and abundance of individual genotypes within the population. Previous workers have used somatic incompatibility testing to distinguish clones or individuals in natural populations of ectomycorrhizal fungi. However, somatic incompatibility tests performed with isolates of Suillus granulatus from a natural population revealed a lack of transitiveness, which brought into question the validity of this method. Subsequent studies of genetic identity of these isolates, using randomly amplified polymorphic DNA (RAPD) markers, conclusively showed that somatically compatible isolates are not necessarily genetically identical. RAPD marker analysis is more reliable and provides higher resolution of genotype distribution in natural populations than does somatic incompatibility testing. This is of particular importance in populations of organisms such as ectomycorrhizal fungi in which the mating systems are incompletely known.
Selection of CUG and AUG initiator codons for Drosophila E74A translation depends on downstream sequences.
Authors: Boyd L , Thummel C S
Published: May 2006

Selection of a translation initiation site is thought to be determined by relative proximity to the 5' end and sequence context of a potential initiator codon. These guidelines seem insufficient to explain translation of the Drosophila E74A mRNA, whose 5' untranslated region is exceptionally long (1.8 kb) and contains many AUG triplets preceding the long open reading frame. In an effort to understand how the appropriate initiator codon is chosen, we have undertaken a study of E74A translation in transfected Drosophila cells. The results show that translation of the E74A protein utilizes at least three initiator codons: two minor forms of the protein are initiated at a CUG and an AUG, while the most abundant form initiates at a CUG. This main initiator CUG appears to be in a good context; however, it lies downstream of 17 AUG and 24 other CUG codons, several of which are also in good contexts. Unexpected results were obtained from sequence perturbations upstream and downstream of the main CUG initiator. Creating an AUG with a good context 72 bases 5' to the main CUG has only a modest inhibitory effect on initiation frequency at that CUG. Replacing sequences 44 bases 3' to the main CUG has an inhibitory effect on its use as an initiator as well as on the CUG 72 bases further upstream. These results indicate that factors other than context and relative proximity to the 5' end must be involved in initiator codon selection and may include elements such as secondary or tertiary structure of the RNA.
Altered synaptic plasticity and memory formation in nitric oxide synthase inhibitor-treated rats.
Authors: Böhme G A , Bon C , Lemaire M , Reibaud M , Piot O , Stutzmann J M , Doble A , Blanchard J C
Published: May 2006

Nitric oxide (NO) is a messenger molecule that is produced in the brain from the metabolism of L-arginine to L-citrulline. Growing evidence suggests a physiological role for NO in long-term potentiation (LTP). Since LTP is a form of synaptic plasticity thought to be involved in learning and memory, we have tested whether inhibition of endogenous NO production affects memory capacities of rats. We found that the NO synthase [L-arginine, NADPH:oxygen oxidoreductase (nitric oxide-forming), EC 1.14.13.39] inhibitor N omega-nitro-L-arginine, at doses blocking LTP in hippocampal slices, impairs spatial learning in a radial arm maze and olfactory memory in a social recognition test. In contrast, N omega-nitro-L-arginine left shock-avoidance learning unaffected. These results indicate that NO is involved in some but not all forms of memory and further support the existence of a causal link between LTP and spatial learning.
Stress-induced intrachromosomal recombination in plant somatic cells.
Authors: Lebel E G , Masson J , Bogucki A , Paszkowski J
Published: May 2006

Levels of induced homologous recombination between chromosomal repeats in plant somatic cells were examined. Transgenic plants of Nicotiana tabacum hemi- or homozygous for pairs of deletion derivatives of the neomycin phosphotransferase (nptII) marker gene integrated at a single genomic locus were produced. Homologous recombination within the overlapping parts of the nptII gene restored the function and the resulting kanamycin resistance was used for scoring recombination frequency. The recombination events were confirmed by the appearance of a characteristic 1245-base-pair EcoRV fragment detected in all kanamycin-resistant clones tested. The rate of spontaneous recombination was found to be related to the copy number of recombination substrates and was 9 x 10(-5) and 19 x 10(-5) for hemi- and homozygote strains, respectively. Ionizing radiation, mitomycin C, and heat shock markedly increased the frequency of intrachromosomal recombination. Low doses of x-rays (1.25 Gy) enhanced the relative recombination frequency to approximately twice the spontaneous value. The presence of mitomycin C increased the frequency of recombination 9-fold and exposure to an elevated temperature (50 degrees C) increased it 6.5-fold. The x-ray and heat shock treatments reduced cell viability to 53% and 8%, respectively. Mitomycin C treatment had no effect on cell survival.
Genomic structure and chromosomal localization of the human deoxycytidine kinase gene.
Authors: Song J J , Walker S , Chen E , Johnson E E , Spychala J , Gribbin T , Mitchell B S
Published: May 2006

Deoxycytidine kinase (NTP:deoxycytidine 5'-phosphotransferase, EC 2.7.1.74) is an enzyme that catalyzes phosphorylation of deoxyribonucleosides and a number of nucleoside analogs that are important in antiviral and cancer chemotherapy. Deficiency of this enzyme activity is associated with resistance to these agents, whereas increased enzyme activity is associated with increased activation of such compounds to cytotoxic nucleoside triphosphate derivatives. To characterize the regulation of expression of this gene, we have isolated genomic clones encompassing its entire coding and 5' flanking regions and delineated all the exon/intron boundaries. The gene extends over more than 34 kilobases on chromosome 4 and the coding region is composed of 7 exons ranging in size from 90 to 1544 base pairs (bp). The 5' flanking region is highly G+C-rich and contains four regions that are potential Sp1 binding sites. A 697-bp fragment encompassing 386 bp of 5' upstream region, the 250-bp first exon, and 61 bp of the first intron was demonstrated to promote chloramphenicol acetyltransferase activity in a T-lymphoblast cell line and to have > 6-fold greater activity in a Jurkat T-lymphoblast than in a Raji B-lymphoblast cell line. Our data suggest that these 5' sequences may contain elements that are important for the tissue-specific differences in deoxycytidine kinase expression.
Identification of a subunit-specific antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate receptor channels.
Authors: Keller B U , Blaschke M , Rivosecchi R , Hollmann M , Heinemann S F , Konnerth A
Published: May 2006

Excitatory synaptic transmission in the mammalian central nervous system is mediated predominantly by glutamate receptor (GluR) channels of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate/kainate (AMPA/KA) receptor type. A major improvement in our understanding of glutamatergic synaptic transmission has been achieved after the identification of quinoxalinediones (e.g., 6-cyano-7-nitroquinoxaline-2,3-dione) as specific antagonists of AMPA/KA receptors. In addition to their effects on neurons, quinoxalinediones were also shown to block glutamate-induced responses mediated by recombinant AMPA/KA receptor channels expressed in heterologous systems, irrespective of their particular subunit composition. Here we report the identification of an AMPA/KA receptor antagonist that selectively blocks a subset of AMPA/KA receptors. We found that Evans blue, a biphenyl derivative of naphthalene disulfonic acid, blocks at low concentrations (IC50 = 355 nM for the subunit combination GluR1,2) KA-mediated responses of the subunits GluR1, GluR1,2, GluR1,3, and GluR2,3 expressed in Xenopus oocytes but not responses of GluR3 or GluR6. The blocking action of Evans blue was partially reversible and did not compete with KA for the agonist binding site. These findings suggest not only that Evans blue is a potent tool for elucidating the functional role of specific AMPA/KA receptor subtypes for excitatory synaptic transmission but also that it may also represent a powerful starting point for clinically useful drugs that are able to reduce the excitatory drive in specific neuronal populations of the central nervous system.
Developmental regulation of a murine T-cell-specific tyrosine kinase gene, Tsk.
Authors: Heyeck S D , Berg L J
Published: May 2006

Protein-tyrosine kinases have been implicated in signal transduction in T lymphocytes after stimulation of many cell-surface molecules, including the T-cell antigen receptor, CD4, CD8, CD2, CD5, and CD28. Yet the identities of many of these tyrosine kinases remain unknown. We have isolated a murine tyrosine kinase gene, called Tsk for T-cell-specific kinase, that appears to be exclusively expressed in T lymphocytes. The Tsk cDNA clone encodes a polypeptide of 70 kDa, which is similar in sequence to both the src and abl families of tyrosine kinases. Sequence comparisons also indicate that Tsk contains one src-homology region 2 domain and one src-homology 3 domain but lacks the negative regulatory tyrosine (src Tyr-527) common to src-family kinases. In addition, Tsk expression is developmentally regulated. Steady-state Tsk mRNA levels are 5- to 10-fold higher in thymocytes than in peripheral T cells and increase in the thymus during mouse development from neonate to adult. Furthermore, Tsk is expressed in day 14 fetal thymus, suggesting a role for Tsk in early T-lymphocyte differentiation.
Rod photoreceptor cGMP-phosphodiesterase: analysis of alpha and beta subunits expressed in human kidney cells.
Authors: Piriev N I , Yamashita C , Samuel G , Farber D B
Published: May 2006

The bovine alpha and murine beta subunits of rod-photoreceptor cGMP-phosphodiesterase (PDE alpha and PDE beta) were expressed in adenovirus-transformed 293 human embryonic kidney cells. RNA blots from transfected cells showed transcripts of 3.0 and 2.8 kb corresponding to PDE alpha and PDE beta, respectively. Protein expression was analyzed by using affinity-purified antibodies against cGMP-PDE on immunoblots and by immunoprecipitation. PDE alpha and PDE beta exhibited the expected mobility (and thus apparent molecular size) and had cGMP hydrolytic activity. Reconstitution of the PDE alpha beta heterodimer with the expressed proteins increased by approximately 6-fold the activity of the individual alpha and beta subunits. Addition of expressed beta subunit to retinal extracts from 9- to 10-day-old rd/rd mice (which have only normal alpha and gamma subunits of rod cGMP-PDE and thus minimal activity) increased enzyme activity by approximately 3-fold. Our results therefore demonstrate that photoreceptor-specific cGMP-PDE can be synthesized in human kidney cells with consequent expression of enzymatic activity.
Tie-1 and tie-2 define another class of putative receptor tyrosine kinase genes expressed in early embryonic vascular system.
Authors: Sato T N , Qin Y , Kozak C A , Audus K L
Published: May 2006

We report the molecular cloning and characterization of two structurally related putative receptor tyrosine kinases, encoded by distinct genes (tie-1 and tie-2) on mouse chromosome 4. Both tie-1 and tie-2 encode receptor proteins possessing unique multiple extracellular domains: two immunoglobulin-like loop domains flanking three epidermal growth factor repeats followed by three fibronectin-type III repeats. Both genes are expressed in early embryonic vascular system and in maternal decidual vascular endothelial cells, where the vasculature undergoes an active angiogenesis. tie-2, but not tie-1, expression was also detected in extraembryonic mesoderm of the amnion. tie-1, but not tie-2, is expressed in an acute myelogenic cell line in vitro. tie-1 and tie-2 may form another class within the receptor tyrosine kinase gene family, and further characterization of these genes and identification of their putative ligands should define the nature of the signal-transduction cascades underlying early vascular system development, as well as their differential roles in mesodermal cells of the amniotic and myeloid lineages.
Identification of additional members of human G-protein-coupled receptor kinase multigene family.
Authors: Haribabu B , Snyderman R
Published: May 2006

Human neutrophils express several distinct guanine nucleotide binding (G)-protein-coupled receptors that mediate their responsiveness to chemoattractants. Phosphorylation by receptor-specific and second messenger-activated protein kinases is a common mechanism for regulation of G-protein-coupled receptors. To explore the possibility that chemoattractant receptors are regulated by unique receptor kinases, we utilized PCR to identify receptor kinases in human neutrophils. Here, we report the isolation of three G-protein-coupled-receptor-kinase (GPRK)-like sequences termed GPRK5, GPRK6, and GPRK7 in addition to the beta-adrenergic receptor kinase (beta ARK) 1 and 2 isoforms (beta ARK1 and beta ARK2). Two, GPRK5 and GPRK6, showed high homology at the amino acid level to the recently identified receptor-kinase-like sequence localized close to the Huntington disease locus. GPRK7 is of interest in that it contains a DLG (Asp-Leu-Gly) amino acid motif of receptor kinases preceded by a DFD (Asp-Phe-Asp) motif. We isolated cDNAs corresponding to GPRK6; the complete sequence shows > 66% identity and 81% similarity at the amino acid level to the GPRK from the Huntington disease locus. The GPRK6 cDNA probe hybridizes to two mRNAs of 2.9 and 2.1 kb that were expressed in all the tested human tissues including HL-60 cells and neutrophils. Genomic Southern blot analysis and chromosome mapping showed that GPRK6 hybridizes to two closely related genes located on chromosomes 5 and 13 and are, therefore, distinct from the GPRK located near the Huntington disease locus on chromosome 4. The identification herein of three putative receptor kinases indicates that in addition to beta ARK and rhodopsin kinase subfamilies, there are other receptor-kinase subfamilies that regulate the broad spectrum of G-protein-coupled receptors.
Molecular characterization of monoclonal CRIA-positive anti-arsonate antibodies derived from idiotype-negative mice bearing a light chain polymorphism.
Authors: Tassignon J , Brait M , Ismaili J , Urbain J , Gottlieb P , Brown A , Hasemann C A , Capra J D , Meek K
Published: May 2006

We have elicited anti-arsonate antibodies bearing the major cross-reactive idiotype (CRIA) in a double congenic idiotype-negative strain (C.C58.AL-20) bearing a light chain polymorphism that has previously been shown serologically not to complement idiotype-positive heavy chains. Using the idiotype cascade (Ab1-->Ab2-->Ab3-->-->Ab1'), CRIA-positive antibodies were raised and monoclonal antibodies were isolated and characterized serologically and by nucleotide sequence analysis. Two types of idiotype-positive anti-arsonate antibodies were generated in the C.C58.AL-20 strain. One group of hybridomas used the canonical VH1.8 heavy chain gene segment with V kappa 10 variant light chains. A second group used a VHGAM3.8 heavy chain with V kappa 10 variant light chains. This latter heavy-light pairing has been observed in CRIA-like responses previously in BALB/c mice after idiotypic manipulation (or rarely after antigen alone). These studies demonstrate the plasticity of the immune response when manipulated with idiotype reagents as well as its structural variability. Additionally, they provide important insights into the potentials of idiotype vaccines.
Cloning and expression of a Kv1.2 class delayed rectifier K+ channel from canine colonic smooth muscle.
Authors: Hart P J , Overturf K E , Russell S N , Carl A , Hume J R , Sanders K M , Horowitz B
Published: May 2006

A cDNA (CSMK1) encoding a delayed rectifier K+ channel of the Kv1.2 class was cloned from canine colonic circular smooth muscle and expressed in Xenopus oocytes. These channels appear to be uniquely expressed in gastrointestinal muscles and may participate in the electrical slow wave activity. Functional expression of CSMK1 in Xenopus oocytes demonstrated a K+ current that activated in a voltage-dependent manner upon depolarization. This current was highly sensitive to 4-aminopyridine (IC50, 74 microM). A low-conductance K+ channel was identified in inside-out patches from oocytes injected with CSMK1. This channel displayed a linear current-voltage relation with a slope conductance of 14 pS. The channels were blocked in a concentration-dependent manner by 4-aminopyridine. Northern blot analysis demonstrated that CSMK1 is expressed in a wide variety of gastrointestinal smooth muscles. Portal vein, renal artery, and uterus do not express CSMK1, suggesting that, among smooth muscles, expression of this K+ channel may be restricted to gastrointestinal smooth muscles. CSMK1 is 91% homologous to RAK, a delayed rectifier K+ channel cloned from rat heart, but displays unique pharmacological properties and tissue distribution.
The segment of invariant chain that is critical for association with major histocompatibility complex class II molecules contains the sequence of a peptide eluted from class II polypeptides.
Authors: Freisewinkel I M , Schenck K , Koch N
Published: May 2006

Major histocompatibility complex class II molecules present peptides from an extracellular source of antigens to CD4+ T lymphocytes. The class II-associated invariant chain affects this role of alpha and beta polypeptides by restriction of peptide loading to endocytic vesicles. Up to now no specific portion of the invariant chain has been defined as the class II binding site. We constructed recombinant invariant chain genes and inspected association of the mutant invariant chains with class II polypeptides. Here we demonstrate that an extracytoplasmic sequence of the invariant chain (aa 81-109) that is only 23 residues away from the transmembrane region is essential for contact with class II polypeptides, whereas the remaining C-terminal part is dispensable for binding. The sequence of invariant-chain-derived peptides that were eluted from class II molecules is contained in this segment and may define the class II binding site of the invariant chain. The membrane-proximal position of this region suggests that the invariant chain and invariant-chain-derived peptides isolated from class II molecules bind to a domain distinct from the class II pocket.
Ets oncogene-related gene Elg functions in Drosophila oogenesis.
Authors: Schulz R A , The S M , Hogue D A , Galewsky S , Guo Q
Published: May 2006

Members of the ets gene family encode transcription factors that regulate the expression of a variety of cellular and viral genes including several protooncogenes. We have utilized Drosophila to elucidate the in vivo function of one family member. We show by complementation rescue and sequence analysis that the female sterile mutant tiny eggs (tne) is an allele of the Drosophila Ets-related gene Elg (also called D-elg). The mutation of a highly conserved tyrosine residue in the ETS DNA-binding domain of the Elg gene product demonstrates that normal gene function is required for proper follicle cell migration, chorion formation, and nurse cell-chromosome decondensation during Drosophila oogenesis.
Allelic instability in mitosis: a unified model for dominant disorders.
Authors: Zheng C J , Byers B , Moolgavkar S H
Published: May 2006

Recent findings indicate that tandemly repeated triplet sequences in certain disease-causing human genes may render these genes highly unstable not only in meiosis but also in mitosis. Typically, a dominant mutation arises upon expansion in the number of these repeated elements. We have considered how mitotic instability of this sort might affect both phenotypic expression and allele transmission. A model based on these considerations leads to the following predictions: (i) Phenotypic severity among individuals who inherit an unstable allele should be highly variable due to stochastic variation in the stage of its earliest mutagenic expansion. (ii) Strikingly increased severity or decreased age of onset in some offspring should arise because of parental germ-line mosaicism for an expanded or mutant allele. (iii) The magnitude of genetic anticipation should be more strongly correlated with paternal than with maternal age at the time of conception. (iv) Given a child born with a severe phenotype, the recurrence risk for a second severely affected child should be significantly elevated. (v) The severity of phenotype in a child should be positively correlated with that in a parent. Available data on fragile X syndrome, Huntington disease, and myotonic dystrophy are shown to be consistent with the model, and implications for an understanding of achondroplasia and other dominant disorders are discussed.
Tissue- and stratum-specific expression of the human involucrin promoter in transgenic mice.
Authors: Carroll J M , Albers K M , Garlick J A , Harrington R , Taichman L B
Published: May 2006

Involucrin is a marker of keratinocyte terminal differentiation and is expressed only in the suprabasal layers of stratified squamous epithelium. In a previous study with various cell types in culture, we noted that expression of the putative human involucrin promoter was keratinocyte specific. To determine if this promoter is sufficient to direct expression to the suprabasal cells of stratified squamous epithelia in vivo, we have now generated transgenic mouse lines harboring the involucrin promoter sequences linked to a beta-galactosidase reporter gene. In the resulting lines, beta-galactosidase was expressed in the suprabasal compartment of stratified squamous epithelia and in hair follicles in a tissue-specific manner. In the palate, distinct vertical stacks of beta-galactosidase-expressing cells were present, suggesting movement of clonally derived cells through the epithelium. The involucrin gene has a single intron upstream of the translational start site, and removal of this intron did not affect tissue- or stratum-specific expression. These results show that the 3.7-kb involucrin upstream sequences contain all the information necessary for a high level of tissue- and stratum-specific expression.
Central oxytocin inhibition of salt appetite in rats: evidence for differential sensing of plasma sodium and osmolality.
Authors: Blackburn R E , Samson W K , Fulton R J , Stricker E M , Verbalis J G
Published: May 2006

Sodium chloride ingestion is stimulated during conditions of sodium deficiency to maintain body fluid and electrolyte balance. Recent studies have indicated that salt appetite in rats is often inversely related to peripheral and central secretion of the hormone oxytocin (OT). We studied the potential role of central OT on salt and water ingestion by treating rats intracerebroventricularly with OT conjugated to the A chain of the plant cytotoxin ricin (rAOT) to produce a chronic selective inactivation of brain cells containing OT-receptive elements. The rats treated with rAOT and control rats treated with the ricin A chain alone were given 5-hr two-bottle (water and 0.5 M NaCl) drinking tests 30 min after they were made hyperosmolar by injections of hypertonic (2M) mannitol solution, which elevated plasma osmolality but reduced plasma Na+ concentration. In the control rats only water intake was stimulated in response to the induced hyperosmolality, but in the rAOT-treated rats hypertonic mannitol caused a robust salt appetite as well as thirst. Analogous results were obtained in rats treated with two different OT-receptor antagonists prior to induction of hyperosmolality with mannitol. In contrast to these results, when hyperosmolality was induced by administration of equivalently hypertonic (1M) NaCl, which elevated both plasma osmolality and plasma Na+ concentration, only water intake but not salt intake was stimulated in both control and OT-receptor antagonist-treated rats. When salt appetite was stimulated by the physiological stimulus of polyethylene glycol-induced hypovolemia, hypertonic mannitol similarly inhibited salt ingestion in control animals but not in rAOT-treated rats, whereas hypertonic NaCl inhibited subsequent salt ingestion in both groups. These results suggest that salt appetite is regulated by both Na(+)- and osmolality-sensing mechanisms in rats. In addition, they indicate that central OT likely mediates a significant component of osmolality-related inhibition of salt appetite but does not appear to be essential for Na(+)-related inhibition of this important homeostatic behavior.
Structural characterization of the complete human perlecan gene and its promoter.
Authors: Cohen I R , Grässel S , Murdoch A D , Iozzo R V
Published: May 2006

The complete intron-exon organization of the gene encoding human perlecan (HSPG2), the major heparan sulfate proteoglycan of basement membranes, has been elucidated, and specific exons have been assigned to coding sequences for the modular domains of the protein core. The gene was composed of 94 exons, spanning > 120 kbp of genomic DNA. The exon arrangement was analyzed vis-à-vis the modular structure of the perlecan, which harbors protein domains homologous to the low density lipoprotein receptor, laminin, epidermal growth factor, and neural cell adhesion molecule. The exon size and the intron phases were highly conserved when compared to the corresponding domains of the homologous genes, suggesting that most of this modular proteoglycan has evolved from a common ancestor by gene duplication or exon shuffling. The 5' flanking region revealed a structural organization characteristic of housekeeping and growth control-related genes. It lacked canonical TATA or CAAT boxes, but it contained several GC boxes with binding sites for the transcription factors SP1 and ETF. Consistent with the lack of a TATA element, the perlecan gene contained multiple transcription initiation sites distributed over 80 bp of genomic DNA. These results offer insights into the evolution of this chimeric molecule and provide the molecular basis for understanding the transcriptional control of this important gene.
Image processing: some challenging problems.
Authors: Huang T S , Aizawa K
Published: May 2006

Image processing can be broadly defined as the manipulation of signals which are inherently multidimensional. The most common such signals are photographs and video sequences. The goals of processing or manipulation can be (i) compression for storage or transmission; (ii) enhancement or restoration; (iii) analysis, recognition, and understanding; or (iv) visualization for human observers. The use of image processing techniques has become almost ubiquitous; they find applications in such diverse areas as astronomy, archaeology, medicine, video communication, and electronic games. Nonetheless, many important problems in image processing remain unsolved. It is the goal of this paper to discuss some of these challenging problems. In Section I, we mention a number of outstanding problems. Then, in the remainder of this paper, we concentrate on one of them: very-low-bit-rate video compression. This is chosen because it involves almost all aspects of image processing.
Color appearance: the effects of illumination and spatial pattern.
Authors: Wandell B A
Published: May 2006

The color we perceive at each point in an image depends on information spread across the three spatial arrays of cone photoreceptors. I describe experiments aimed at clarifying how information is integrated across the spatial arrays to yield a color experience. We have found that changes of color appearance due to changes of the ambient illumination and the pattern's spatial frequency can be described by using a simple set of optical and neural transformations. Each transformation can be thought of as having two parts. First, the transformation converts the color representation into a new coordinate frame that is independent of the image contents. Second, the transformation scales the neural responses in the new coordinate frame by a gain factor that depends on the image contents.
Issues of imaging science for future consideration.
Authors: Beck R N
Published: May 2006

Acceleration of the emergence of imaging science as a new discipline will require the development of new organizational structures to foster research and educational programs that integrate components of the traditional disciplines, all of which stand to benefit. However, the greatest impact of imaging science will likely be from computer-based general educational programs that present both visual and verbal materials utilizing software that is not only interactive but also analytic, diagnostic, and adaptive in response to individual students. Ultimately, this powerful learning paradigm will have profound effects on all aspects of our culture. Imaging science will not have emerged fully until the conceptual, organizational, educational, cultural, and ethical issues it raises have been addressed.
Occurrence of fragmented 16S rRNA in an obligate bacterial endosymbiont of Paramecium caudatum.
Authors: Springer N , Ludwig W , Amann R , Schmidt H J , Görtz H D , Schleifer K H
Published: May 2006

The phylogenetic position of Caedibacter caryophila, a so far noncultured killer symbiont of Paramecium caudatum, was elucidated by comparative sequence analysis of in vitro amplified 16S rRNA genes (rDNA). C. caryophila is a member of the alpha subclass of the Proteobacteria phylum. Within this subclass C. caryophila is moderately related to Holospora obtusa, which is another obligate endosymbiont of Paramecium caudatum, and to Rickettsia. A 16S rRNA targeted specific hybridization probe was designed and used for in situ detection of C. caryophila within its host cell. Comparison of the 16S rDNA primary structure of C. caryophila with homologous sequences from other bacteria revealed an unusual insertion of 194 base pairs within the 5'-terminal part of the corresponding gene. The intervening sequence is not present in mature 16S rRNA of C. caryophila. It was demonstrated that C. caryophila contained fragmented 16S rRNA.
Localized 1H NMR measurement of glucose consumption in the human brain during visual stimulation.
Authors: Chen W , Novotny E J , Zhu X H , Rothman D L , Shulman R G
Published: May 2006

Spatially localized 1H NMR spectroscopy has been applied to measure changes in brain glucose concentration during 8-Hz photic stimulation. NMR spectroscopic measurements were made in a 12-cm3 volume centered on the calcarine fissure and encompassing the primary visual cortex. The average maximum change in glucose levels was 0.34 mumol.g-1 (n = 5) at 15 min; glucose level had turned toward resting level at 25 min. The glucose change was used to calculate the increase of glucose cerebral metabolic rate in the visual cortex region for individual subjects by using the Michaelis-Menten model of glucose transport on the assumption of constant transport kinetics. The glucose cerebral metabolic rate was calculated to increase over the nonstimulated rate by 22% during the first 15 min of photic stimulation. A model in which the glucose metabolic rate gradually decreases during stimulation was proposed as a possible explanation for the recovery of brain glucose and previously measured lactate concentrations to prestimulus values after 15 min.
UDPglucose: fatty acid transglucosylation and transacylation in triacylglucose biosynthesis.
Authors: Ghangas G S , Steffens J C
Published: May 2006

Glandular trichomes of the wild tomato Lycopersicon pennellii Corr. (D'Arcy) secrete large amounts of 2,3,4-tri-O-acylglucoses possessing straight- and branched-chain fatty acids of short to medium chain length (C4-C12). Although previous biosynthetic studies suggested that glucose acylation proceeded via acyl CoA intermediates, repeated attempts to demonstrate isobutyryl-CoA-dependent glucose acylation were unsuccessful. When [14C]isobutyrate is administered to detached L. pennellii leaves, the label is readily converted to 1-O-isobutyryl-beta-D-glucose. This is immediately followed by the appearance of di- and triacylated glucose esters. L. pennellii extracts catalyzed the formation of 1-O-isobutyryl-beta-D-glucose from isobutyrate and UDPglucose, and detached L. pennellii trichomes catalyzed transfer of the isobutyryl moiety from synthetic 1-O-isobutyryl-beta-D-glucose to D-glucose. Detached L. pennellii trichomes also catalyzed the formation of diacylglucose and triacylglucose via transfer of the isobutyryl moiety from 1-O-[14C]isobutyryl-beta-D-glucose to mono- or diacylglucoses, respectively. These studies suggest a multistep mechanism in which activation of fatty acids to their respective high-energy 1-O-acyl-beta-D-glucopyranose derivatives is followed by transfer of the 1-O-acyl moiety to non-anomeric positions of other glucose and/or partially acylated glucose molecules. This appears to be the primary mechanism of activation and fatty acid esterification to glucose in L. pennellii trichomes. Cultivated tomato, L. esculentum Mill., also activates free fatty acids to their 1-O-acyl-beta-D-glucose derivatives but lacks the acyl transfer mechanism for synthesizing polyacylated sugars.
Spinons and holons for the one-dimensional three-band Hubbard models of high-temperature superconductors.
Authors: Tahir-Kheli J , Goddard W A
Published: May 2006

The one-dimensional three-band Hubbard Hamiltonian is shown to be equivalent to an effective Hamiltonian that has independent spinon and holon quasiparticle excitations plus a weak coupling of the two. The spinon description includes both copper sites and oxygen hole sites leading to a one-dimensional antiferromagnet incommensurate with the copper lattice. The holons are spinless noninteracting fermions in a simple cosine band. Because the oxygen sites are in the Hamiltonian, the quasiparticles are much simpler than in the exact solution of the t-J model for 2t = +/- J. If a similar description is correct for two dimensions, then the holons will attract in a p-wave potential.
Behavioral and magnetoencephalographic correlates of plasticity in the adult human brain
Authors: Ramachandran V. S.
Published: May 2006

Recent behavioral and physiological evidence suggests that even brief sensory deprivation can lead to the rapid emergence of new and functionally effective neural connections in the adult human brain.
Mitochondrial-genome-encoded RNAs: differential regulation by corticotropin in bovine adrenocortical cells.
Authors: Raikhinstein M , Hanukoglu I
Published: May 2006

Differential screening of an adrenal cortex cDNA library for corticotropin (ACTH)-inducible genes led to the isolation of a group of cDNAs representing mitochondrial genes that encode subunits of cytochrome oxidase, ATPase, and NADH dehydrogenase. Northern blot analysis of RNA from cells stimulated by ACTH confirmed the induction of these genes by ACTH yet revealed major differences in the relative responses of the respective mRNAs. The levels of mRNAs for cytochrome oxidase subunit I and ATPase increased 2- to 4-fold and for NADH dehydrogenase subunit 3 increased 20-fold, whereas the levels of the mitochondrial 16S rRNA showed no change within 6 h of ACTH stimulation. These effects of ACTH on mitochondrial mRNA levels probably result from both activation of the H2 transcription unit that encodes mitochondrial mRNAs and alteration of mRNA stability. ACTH also increased the activity of cytochrome oxidase after 12 h of stimulation. Examination of the tissue specificity of expression of five mitochondrial genes showed a wide range of RNA levels among 11 tissues but high correlations between individual RNA levels, consistent with a coordinated expression of the mitochondrial genes, although at different levels in each cell type. Proportionately high levels of mitochondrial mRNAs were found in adrenal cortex, probably reflecting a stimulatory effect of ACTH in vivo. Overall, the results indicate that ACTH enhances the energy-producing capacity of adrenocortical cells.
Ion channels induced in lipid bilayers by subvirion particles of the nonenveloped mammalian reoviruses.
Authors: Tosteson M T , Nibert M L , Fields B N
Published: May 2006

Mechanisms by which nonenveloped viruses penetrate cell membranes as an early step in infection are not well understood. Current ideas about the mode for cytosolic penetration by nonenveloped viruses include (i) formation of a membrane-spanning pore through which viral components enter the cell and (ii) local breakdown of the cellular membrane to provide direct access of infecting virus to the cell's interior. Here we report that of the three viral particles of nonenveloped mammalian reoviruses: virions, infectious subvirion particles, and cores (the last two forms generated from intact reovirus virions by proteolysis), only the infectious subvirion particles induced the formation of anion-selective, multisized channels in planar lipid bilayers under the experimental conditions used in this study. The value for the smallest size conductance varied depending on the lipid composition of the bilayer between 90 pS (Asolectin) and 300 pS (phosphatidylethanolamine:phosphatidylserine) and was found to be voltage independent. These findings are consistent with a proposal that the proteolytically activated infectious subviral particles mediate the interaction between virus and the lipid bilayer of a cell membrane during penetration. In addition, the findings indicate that the "penetration proteins" of some enveloped and nonenveloped viruses share similarities in the way they interact with bilayers.
Expression of the human beta-amyloid precursor protein gene from a yeast artificial chromosome in transgenic mice.
Authors: Pearson B E , Choi T K
Published: May 2006

One hallmark of Alzheimer disease is the formation in the brain of amyloid plaques containing a small peptide derived from the beta-amyloid precursor protein (APP). The APP gene exhibits a complex pattern of expression in peripheral tissues and in the brain. The entire human APP gene was introduced into embryonic stem (ES) cells by co-lipofection of a 650-kb yeast artificial chromosome (YAC). Three ES lines containing an essentially intact YAC were isolated, and expression of human APP mRNAs at levels comparable to those of endogenous mouse APP transcripts was obtained. A transgenic mouse line was established by germ-line transmission of the APP YAC. RNase protection analysis of human APP mRNAs demonstrated appropriate splicing of the primary APP transcript in ES cells and in the brain of a transgenic animal. These mice may be useful for elucidating the function of the various APP isoforms in vivo.
Chromatin structure and regulation of the eukaryotic regulatory gene GAL80.
Authors: Lohr D
Published: May 2006

The chromatin structure around the 5' end of the yeast regulatory gene GAL80 has been determined. The chromatin organization is very similar to that on the 5' regions of the GAL1-10 structural genes: a constitutive hypersensitive region containing the upstream activating sequence (UAS) element, and nucleosomes around this hypersensitive region. The downstream nucleosome, which is a positioned nucleosome, covers the TATA and transcription start sites. The nucleosome upstream of the hypersensitive region undergoes significant change when cells are grown in galactose, where GAL80 gene expression is induced to maximal levels. The change may be related to the induction process. GAL4 protein binds strongly to the GAL80 UAS in galactose-grown cells, less strongly in glycerol-grown cells, and not at all in glucose-grown cells. These data and published gene expression data are used to develop a model for the regulation of the GAL80 regulatory gene.
cDNA cloning, characterization, and tissue-specific expression of human xanthine dehydrogenase/xanthine oxidase.
Authors: Wright R M , Vaitaitis G M , Wilson C M , Repine T B , Terada L S , Repine J E
Published: May 2006

We isolated cDNAs encoding xanthine dehydrogenase (XD; xanthine:NAD+ oxidoreductase, EC 1.1.1.204) from a human liver cDNA library. The complete nucleotide sequence of human XD was determined; the deduced amino acid sequence encoded a protein of 1336 amino acid residues of M(r) 147,782. Human XD possessed many of the signature sequences typical of XDs from flies and rodents, including an unusual cysteine distribution, a potential 2Fe/2S binding site, and a putative molybdopterin cofactor binding domain. Analysis of potential NAD binding sites suggested a simple hypothesis for the conversion of human XD into the oxygen metabolite forming xanthine oxidase (XO; xanthine:oxygen oxidoreductase, EC 1.1.3.22). Using a human XD complementary RNA hybridization probe, we found a 5100-base RNA in human liver by RNA blot-hybridization analysis. This RNA exhibited tissue-specific distribution that may be pertinent to XD- and XO-mediated oxygen radical injury in ischemia/reperfusion and inflammation. A second 4500-base RNA was detected in some tissues and may arise through differential transcription termination.
Yeast precursor mRNA processing protein PRP19 associates with the spliceosome concomitant with or just after dissociation of U4 small nuclear RNA.
Authors: Tarn W Y , Lee K R , Cheng S C
Published: May 2006

During assembly of the spliceosome, the U4 small nuclear RNA (snRNA) interacts with the spliceosome as a preformed U4/U6-U5 triple small nuclear ribonucleoprotein (snRNP) complex. Subsequently, U4 becomes loosely associated with the spliceosome, whereas U5 and U6 remain tightly associated, suggesting unwinding of the U4/U6 duplex. We show that this step of the assembly process can be blocked by limiting the ATP concentration in the splicing reaction. We also show that the yeast precursor mRNA processing protein PRP19 becomes associated with the spliceosome during this transition. Thus, PRP19 may function in this step of spliceosome assembly.
Cell growth and lambda phage development controlled by the same essential Escherichia coli gene, ftsH/hflB.
Authors: Herman C , Ogura T , Tomoyasu T , Hiraga S , Akiyama Y , Ito K , Thomas R , D'Ari R , Bouloc P
Published: May 2006

The lambda phage choice between lysis and lysogeny is influenced by certain host functions in Escherichia coli. We found that the frequency of lambda lysogenization is markedly increased in the ftsH1 temperature-sensitive mutant. The ftsH gene, previously shown to code for an essential inner membrane protein with putative ATPase activity, is identical to hflB, a gene involved in the stability of the phage cII activator protein. The lysogenic decision controlled by FtsH/HflB is independent of that controlled by the protease HflA. Overproduction of FtsH/HflB suppresses the high frequency of lysogenization in an hflA null mutant. The FtsH/HflB protein, which stimulates cII degradation, may be a component of an HflA-independent proteolytic pathway, or it may act as a chaperone, maintaining cII in a conformation subject to proteolysis via such a pathway. Suppressor mutations of ftsH1 temperature-sensitive lethality, located in the fur gene (coding for the ferric uptake regulator), did not restore FtsH/HflB activity with respect to lambda lysogenization.
TAP1 alleles in insulin-dependent diabetes mellitus: a newly defined centromeric boundary of disease susceptibility.
Authors: Jackson D G , Capra J D
Published: May 2006

It has been previously demonstrated that individuals with certain DR alleles have an increased relative risk of developing insulin-dependent diabetes mellitus (IDDM). The disease association is even stronger with certain DQ alleles but there is little association with DP providing a boundary of disease association to the 430 kb between DQ and DP. The recently described TAP (transporter associated with antigen processing) genes have been mapped approximately midway between DP and DQ. Therefore, it was of interest to determine if any TAP alleles were associated with IDDM. In addition to the alleles of TAP1 that have been described, others were identified during this study. Diabetics and normal controls were screened for TAP1 using single-stranded conformational polymorphism and relative risk was determined. In the same population group we have studied extensively in the past, we found a higher association of a TAP1 allele with IDDM than with any single HLA-DP allele but the risk was lower than with HLA-DQB1*0302. These data provide new limits for IDDM susceptibility to the 190-kb interval between TAP1 and HLA-DQB1.
Nitric oxide is a mediator of the decrease in cytochrome P450-dependent metabolism caused by immunostimulants.
Authors: Khatsenko O G , Gross S S , Rifkind A B , Vane J R
Published: May 2006

Bacterial lipopolysaccharide (LPS) and a diverse array of other immunostimulants and cytokines suppress the metabolism of endogenous and exogenous substances by reducing activity of the hepatic cytochrome P450 mixed-function oxidase system. Although this effect of immunostimulants was first described almost 40 yr ago, the mechanism is obscure. Immunostimulants are now known to cause NO overproduction by cells via induction of nitric oxide synthase. We have investigated whether NO overproduction is involved in suppressing hepatic metabolism by LPS. In vitro treatment of hepatic microsomes with NO, produced by chemical decomposition of 3-morpholinosydnonimine or by nitric oxide synthase, substantially suppressed cytochrome P450-dependent oxygenation reactions. This effect of NO was seen with hepatic microsomes prepared from two species (rat and chicken) and after exposure to chemicals that induce distinct molecular isoforms of cytochromes P450 (beta-naphthoflavone, 3-methylcholanthrene, and phenobarbital). Spectral studies indicate that NO reacts in vitro with both Fe(2+)- and Fe(3+)-hemes in microsomal cytochromes P450. In vivo, LPS diminished the phenobarbital-induced dealkylation of 7-pentoxyresorufin by rat liver microsomes and reduced the apparent P450 content as measured by CO binding. These LPS effects were associated with induction of NO synthesis; LPS-induced NO synthesis showed a strong positive correlation with the severity of cytochrome P450 inhibition. The decrease in both hepatic microsomal P450 activity and CO binding caused by LPS was largely prevented by the selective NO synthase inhibitor N omega-nitro-L-arginine methyl ester. Our findings implicate NO over-production as a major factor mediating the suppression of hepatic metabolism by immunostimulants such as LPS.