bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lipophilic regulator of a developmental switch in Caenorhabditis elegans
Authors: Gill Matthew S. , Held Jason M. , Fisher Alfred L. , Gibson Bradford W. , Lithgow Gordon J. 
Published: November 2004

AbstractIn Caenorhabditis elegans, the decision to develop into a reproductive adult or arrest as a dauer larva is influenced by multiple pathways including insulin‐like and transforming growth factor β (TGFβ)‐like signalling pathways. It has been proposed that lipophilic hormones act downstream of these pathways to regulate dauer formation. One likely target for such a hormone is DAF‐12, an orphan nuclear hormone receptor that mediates these developmental decisions and also influences adult lifespan. In order to find lipophilic hormones we have generated lipophilic extracts from mass cultures of C. elegans and shown that they rescue the dauer constitutive phenotype of class 1 daf‐2 insulin signalling mutants and the TGFβ signalling mutant daf‐7. These extracts are also able to rescue the lethal dauer phenotype of daf‐9 mutants, which lack a P450 steroid hydroxylase thought to be involved in the synthesis of the DAF‐12 ligand; extracts, however, have no effect on a DAF‐12 ligand binding domain mutant that is predicted to be ligand insensitive. The production of this hormone appears to be DAF‐9 dependent as extracts from a daf‐9;daf‐12 double mutant do not exhibit this activity. Preliminary fractionation of the lipophilic extracts shows that the activity is hydrophobic with some polar properties, consistent with a small lipophilic hormone. We propose that the dauer rescuing activity is a hormone synthesized by DAF‐9 that acts through DAF‐12.
Aging activates adipogenic and suppresses osteogenic programs in mesenchymal marrow stroma/stem cells: the role of PPAR‐γ2 transcription factor and TGF‐β/BMP signaling pathways
Authors: Moerman Elena J. , Teng Kui , Lipschitz David A. , Lecka‐Czernik Beata 
Published: November 2004

SummaryOsteoblasts and adipocytes originate from a common progenitor, which arises from bone marrow mesenchymal stroma/stem cells (mMSC). Aging causes a decrease in the number of bone‐forming osteoblasts and an increase in the number of marrow adipocytes. Here, we demonstrate that, during aging, the status of mMSC changes with respect to both their intrinsic differentiation potential and production of signaling molecules, which contributes to the formation of a specific marrow microenvironment necessary for maintenance of bone homeostasis. Aging causes a decrease in the commitment of mMSC to the osteoblast lineage and an increase in the commitment to the adipocyte lineage. This is reflected by changes in the expression of phenotype‐specific gene markers. The expression of osteoblast‐specific transcription factors, Runx2 and Dlx5, and osteoblast markers, collagen and osteocalcin, is decreased in aged mMSC. Conversely, the expression of adipocyte‐specific transcription factor PPAR‐γ2, shown previously to regulate osteoblast development and bone formation negatively and to regulate marrow adipocyte differentiation positively, is increased, as is a gene marker of adipocyte phenotype, fatty acid binding protein aP2. Furthermore, production of an endogeneous PPAR‐γ activator(s) that stimulates adipocyte differentiation and production of autocrine/paracrine factor(s) that suppresses the osteoblastic phenotype are also increased. In addition, expression of different components of TGF‐β and BMP2/4 signaling pathways is altered, suggesting that activities of these two cytokines essential for bone homeostasis change with aging.
Accumulation of mutations and somatic selection in aging neural stem/progenitor cells
Authors: Bailey Kimberly J. , Maslov Alexander Y. , Pruitt Steven C. 
Published: November 2004

SummaryGenomic instability within somatic stem cells may lead to the accumulation of mutations and contribute to cancer or other age‐related phenotypes. However, determining the frequency of mutations that differ among individual stem cells is difficult from whole tissue samples because each event is diluted in the total population of both stem cells and differentiated tissue. Here the ability to expand neural stem/progenitor cells clonally permitted measurement of genomic alterations derived from a single initial cell. C57Bl/6 × DBA/2 hybrid mice were used and PCR analysis with strain‐specific primers was performed to detect loss of heterozygosity on nine different chromosomes for each neurosphere. The frequency with which changes occurred in neurospheres derived from 2‐month‐ and 2‐year‐old mice was compared. In 15 neurospheres derived from young animals both parental chromosomes were present for all nine chromosome pairs. In contrast, 16/17 neurospheres from old animals demonstrated loss of heterozygosity (LOH) on one or more chromosomes and seven exhibited a complete deletion of at least one chromosomal region. For chromosomes 9 and 19 there is a significant bias in the allele that is lost where in each case the C57Bl/6 allele is retained in 6/6 neurospheres exhibiting LOH. These data suggest that aging leads to a substantial mutational load within the neural stem cell compartment which can be expected to affect the normal function of these cells. Furthermore, the retention of specific alleles for chromosomes 9 and 19 suggests that a subset of mutational events lead to an allele‐specific survival advantage within the neural stem cell compartment.
The G/C915 polymorphism of transforming growth factor β1 is associated with human longevity: a study in Italian centenarians
Authors: Carrieri Giuseppina , Marzi Erika , Olivieri Fabiola , Marchegiani Francesca , Cavallone Luca , Cardelli Maurizio , Giovagnetti Simona , Stecconi Rosalia , Molendini Cinzia , Trapassi Chiara , De Benedictis Giovanna , Kletsas Dimitri , Franceschi Claudio 
Published: November 2004

SummarySequence variations in a variety of pro‐ or anti‐inflammatory cytokine genes have been found to influence successful aging and longevity. Because of the role played by the transforming growth factor β1 (TGF‐β1) cytokine in inflammation and regulation of immune responses, the variability of the TGF‐β1 gene may affect longevity by playing a role in inflamm‐aging. Two polymorphisms, G/A−800 and C/T−509, located in the 5′ region, and two missense polymorphisms, T/C869 and G/C915 which change (Leu > Pro)10 and (Arg > Pro)25, respectively, located in the signal peptide, were analysed in 419 subjects from Northern and Central Italy, including 172 centenarians and 247 younger controls. In addition, the effects of the TGF‐β1 genetic variability on plasma levels of the biologically active form (naturally processed) of this cytokine were studied in 143 randomly selected subjects, including 73 centenarians. Significant differences were found at the +915 site as far as the C allele and GC genotype were concerned, both of them being lower in centenarians than in young controls (P = 0.034 and 0.028, respectively), but none of the other tested genetic variants was significantly different between centenarians and controls. Moreover, a particular haplotype combination (G−800/C−509/C869/C915) was notably lower in centenarians than in younger individuals (P = 0.007). Finally, active TGF‐β1 plasma levels were significantly increased in the elderly group, but no relationship with TGF‐β1 genotypes was observed. These results suggest that, at least in this population, the variability of the TGF‐β1 gene influences longevity and that the age‐related increase in plasma levels of active TGF‐β1 seems not to be genetically regulated.
Age‐dependent expression of glucocorticoid‐ and mineralocorticoid receptors on neural precursor cell populations in the adult murine hippocampus
Authors: Garcia Ana , Steiner Barbara , Kronenberg Golo , Bick‐Sander Anika , Kempermann Gerd 
Published: November 2004

SummarySteroid hormones are regulators of adult hippocampal neurogenesis and are central to hypotheses regarding adult neurogenesis in age‐related and psychiatric disturbances associated with altered hippocampal plasticity – most notably dementias and major depression. Using immunohistochemistry, we examined the expression of glucocorticoid (GR) and mineralocorticoid (MR) receptors during adult hippocampal neurogenesis. In young mice only 27% of dividing cells in the subgranular zone expressed GR, whereas 4 weeks after division 87% had become positive for GR and MR. GR was expressed by 50% of the radial glia‐like type‐1 and type‐2a progenitor cells, whereas MR was expressed only by mature calbindin‐positive granule cells. Doublecortin‐positive neuronal progenitor cells (type‐2b) and early postmitotic calretinin‐positive neurons were devoid of GR and MR expression. Fifty per cent of the intermediate type‐3 cells showed GR expression, possibly reflecting cells terminating maturation. Thus, all subpopulations of dividing precursor cells showed an identical receptor profile (50% GR, no MR), except for type‐2b cells, which expressed neither receptor. There was also no overlap between calretinin and GR early postnatally (P8) or after physical activity or exposure to an enriched environment, both of which are potent neurogenic stimuli. In contrast, in old age calretinin‐positive young neurons became GR and MR positive, suggesting increased steroid sensitivity. Age also increased the expression of GR in type‐1 and type‐2a precursor cells. Other intermediates were so rare in old age that they could not be studied. This course and variability of receptor expression in aging might help to explain differential vulnerability of adult neural precursor cells to corticoid‐mediated influences.
Ischemia‐induced neurogenesis is preserved but reduced in the aged rodent brain
Authors: Jin Kunlin , Minami Manabu , Xie Lin , Sun Yunjuan , Mao Xiao Ou , Wang Yaoming , Simon Roger P. , Greenberg David A. 
Published: November 2004

SummaryThe adult mammalian brain retains the capacity for neurogenesis, by which new neurons may be generated to replace those lost through physiological or pathological processes. However, neurogenesis diminishes with aging, and this casts doubt on its feasibility as a therapeutic target for cell replacement therapy in stroke and neurodegenerative disorders, which disproportionately affect the aged brain. In previous studies, neurogenesis was stimulated by cerebral ischemia in young rodents, and the neurogenesis response of the aged rodent brain to physiological stimuli, such as hormonal manipulation and growth factors, was preserved. To investigate the effect of aging on ischemia‐induced neurogenesis, transient (60 min) middle cerebral artery occlusion was induced in young adult (3‐month) and aged (24‐month) rats, who were also given bromodeoxyuridine to label newborn cells. As found in prior studies, basal neurogenesis in control, nonischemic rats was reduced with aging. Ischemia failed to stimulate neurogenesis in the dentate gyrus (DG) subgranular zone (SGZ), in contrast to results obtained previously after more prolonged (90–120 min) middle cerebral artery occlusion, but increased the number of BrdU‐labeled cells in the forebrain subventricular zone (SVZ). This effect was less prominent in aged than in young adult rats, with fold‐stimulation of BrdU incorporation reduced by ∼20% and the total number of cells generated diminished by ∼50%. BrdU‐labeled cells in SVZ coexpressed neuronal lineage markers, consistent with newborn neurons. We conclude that ischemia‐induced neurogenesis occurs in the aged brain, and that measures designed to augment this phenomenon might have therapeutic applications.
Neural stem cells as therapeutic agents for age‐related brain repair
Authors: Bernal Giovanna M. , Peterson Daniel A. 
Published: November 2004

SummaryNeurogenesis occurs in two germinal centres of the adult brain and persists with increasing age, although at a reduced level. This observation, that the mature brain can support neurogenesis, has given rise to the hope that neural stem cells could be used to repair the brain by repopulating regions suffering from neuronal loss as a result of injury or disease. The aging brain is vulnerable to mild cognitive impairment, increasing incidence of stroke, and a variety of neurodegenerative diseases. However, most studies to date have focused on the young adult brain, and relatively little information is available about the regulation of neurogenesis in the aged brain or the potential of using neural stem cells to repair the aged brain. This review summarizes the current state of knowledge on neurogenesis in the young adult brain and discusses the information available on age‐related changes in neurogenesis. Possible therapeutic strategies using neural stem cells for repair of the aging brain are considered.
Modulation of Swarming and Virulence by Fatty Acids through the RsbA Protein inProteus mirabilis
Authors: Liaw Shwu-Jen , Lai Hsin-Chih , Wang Won-Bo 
Published: November 2004

ABSTRACTAfter sensing external signals,Proteus mirabilisundergoes a multicellular behavior called swarming which is coordinately regulated with the expression of virulence factors. Here we report that exogenously added fatty acids could act as signals to regulate swarming inP. mirabilis. Specifically, while oleic acid enhanced swarming, some saturated fatty acids, such as lauric acid, myristic acid, palmitic acid, and stearic acid, inhibited swarming. We also found that expression of hemolysin, which has been shown to be coordinately regulated with swarming, was also inhibited by the above saturated fatty acids. Previously we identified a gene,rsbA, which may encode a histidine-containing phosphotransmitter of the bacterial two-component signaling system and act as a repressor of swarming and virulence factor expression inP. mirabilis. We found that while myristic acid, lauric acid, and palmitic acid exerted their inhibitory effect on swarming and hemolysin expression through an RsbA-dependent pathway, the inhibition by stearic acid was mediated through an RsbA-independent pathway. Biofilm formation and extracellular polysaccharide (EPS) production play an important role inP. mirabilisinfection. We found that RsbA may act as a positive regulator of biofilm formation and EPS production. Myristic acid was found to slightly stimulate biofilm formation and EPS production, and this stimulation was mediated through an RsbA-dependent pathway. Together, these data suggest that fatty acids may act as environmental cues to regulate swarming and virulence inP. mirabilisand that RsbA may play an important role in this process.
SOME APPLICATIONS OF LOW ENERGY ACCELERATORS
Authors: BUDNAR M. 
Published: November 2004

Accelerators producing ions with energies up to few MeV/amu have been extensively used in the past twenty years mainly in the atomic physics research and its several applications. The investigations first oriented towards the study of the inner-shell ionization through the Z1≪Z2 collisions, moved to the analysis of Z1~Z2 and Z1≫Z2 processes. Several mechanisms including direct Coubmb ionization (Dl), molecular orbital (MO) processes and transfer interaction (TE) excitations were studied this way. The observations of these phenomena stirred up possible explanations and gave deeper insight into the behaviour of the atomic electrons and their mutual correlations. Also several decay channels corresponding to the diagram processes and to the second order effects like satellites, hypersatellites, RAE, RER, etc. have been studied extensively for better understanding of the atomic physics phenomena. Based on the fundamental research, frequent applications using ions as the main research tool emerged. Here methods for the elemental concentrations determination as PIXE, µPIXE, RBS, PIGE and others are most known. Also the use of some of them for the profiling and the surface analysis is important. Above mentioned methods are now extensively and routinely used in several laboratories for environmental studies, material analysis, biomedical research and in other fields.
PRESENT STATUS OF NMCC AND SAMPLE PREPARATION METHOD FOR BIO-SAMPLES
Authors: FUTATSUGAWA S. , HATAKEYAMA S. , SAITOU S. , SERA K. 
Published: November 2004

In NMCC(Nishina Memorial Cyclotron Center) we are doing researches on PET of nuclear medicine (Positron Emission Computed Tomography) and PIXE analysis (Particle Induced X-ray Emission) using a small cyclotron of compactly designed. The NMCC facilities have been opened to researchers of other institutions since April 1993. The present status of NMCC is described. Bio-samples (medical samples, plants, animals and environmental samples) have mainly been analyzed by PIXE in NMCC. Small amounts of bio-samples for PIXE are decomposed quickly and easily in a sealed PTFE (polytetrafluoroethylene) vessel with a microwave oven . This sample preparation method of bio-samples also is described.
THE INVERSE OF A CR-HOMEOMORPHISM IS CR
Authors: DIEDERICH KLAS , PINCHUK SERGEY 
Published: November 2004

Let Ω, [Formula: see text] be domains and M ⊂ Ω, M′ ⊂ Ω′ be C2-smooth relatively closed real hyper-surfaces. The main result of the article is: Theorem. Let f: M → M′ be a homeomorphic CR-mapping. Then the inverse mapping f−1: M′ → M is also CR. As one of the main tools in the proof of this theorem the following removable singularity result for continuous CR-functions on real hypersurfaces is derived (it also might be useful for other applications): Theorem.Let [Formula: see text] be a family of closed complex hypersurfaces in M. Put [Formula: see text]. Suppose that h is a continuous function on M which is CR in a neighborhood of each point [Formula: see text] and such that the restriction h\Sα is holomorphic for all α ∈ A. Then h is CR on M.
A PARALLEL RAYCAST ALGORITHM OF CSG MODELS ON CM2
Authors: PILI PIERO 
Published: November 2004

One of the main problems for CSG models manipulators is the fast visualization of the results. The high computational cost on single-processor architectures makes the CSG scheme useless for the interactive creation of the model. This article deals with a parallel algorithm based on general purpose SIMD architecture, such as the Connection Machine 2, for the visualization of high quality shaded images of CSG models in nearly real time. The technique is based on a pixels parallelization of the Ray Casting algorithm. The Frame Buffer is divided into severals regions and for each of them we determine the CSG reduced model projected on it. Then a processor is assigned to each pixel in the sub-area; it determines the equation of the ray crossing the pixel and, using the Ray Casting technique, the nearest intersection point to the pixel on which it calculates the illumination model.
ISOTHERMAL MOLECULAR DYNAMICS: A PRACTICAL STUDY
Authors: FATTEBERT JEAN-LUC , BONOMI ERNESTO 
Published: November 2004

In a molecular dynamics simulation, trapping of the phase space trajectory can occur at low energy for long time intervals. To untrap that evolution and recover the canonical ensemble description, at regular clock hits, all particle velocities are randomly redistributed according to the Maxwell statistics. The organization of this hybrid evolution mixing molecular dynamics and random number generation leads to a fully parallel and synchronous algorithm. An illustration of this approach on the one-dimensional jellium is presented. For large values of the coupling λ for which the evolution at constant energy is trapped, the hybrid method allows to reproduce the exact Boltzmann statistical description. Computer simulations show that the Nosé-Hoover method does not really improve the pure molecular dynamics for the one dimensional jellium.
CHANNEL CLASSES: A NEW CONCEPT FOR DEADLOCK AVOIDANCE IN WORMHOLE NETWORKS
Authors: DUATO JOSÉ 
Published: November 2004

In previous papers, we have developed the theoretical background for the design of deadlock-free adaptive routing algorithms for store-and-forward and wormhole networks. Some definitions and theorems have been proposed, developing conditions to verify that an adaptive algorithm is deadlock-free, even when there are cyclic dependencies between channels. Also, two design methodologies have been proposed. In this paper, we propose a partial order between channels as well as an equivalence relation. This relation splits the set of channels into equivalence classes. Then, we extend our previous theory by considering equivalence classes (channel classes) instead of channels. This extension drastically simplifies the verification of deadlock freedom for adaptive routing algorithms with cyclic dependencies between channels. Finally, we present an example.
FAULT TOLERANT ROUTING IN THE SUPERCUBE
Authors: AULETTA VINCENZO , RESCIGNO ADELE ANNA , SCARANO VITTORIO 
Published: November 2004

In this paper we study the fault-tolerant properties of the Supercube, a new inter-connection network recently introduced by Sen [15]. The Supercube is a generalization of the Hypercube that can be realized for any number of nodes and not only for powers of 2. Moreover, it has the same diameter and connectivity of the Hypercube. We shall prove that the diameter of the surviving route graph of the N-node Supercube SN, if less than [ log 2 N] nodes or edges fail, is at most 4 for any minimal routing, and exhibit a minimal routing for which the surviving route graph has diameter 2. Then, we will show that, when 2s+2s−1≤N<2s+1 the failures are [log2 N], the diameter of the surviving route graph is at most 5 for any minimal routing. We will also prove that the fault diameter of SN is exactly [ log 2 N]+1 when N∉{2s+1−1, 2s+1−2, 2s+2s−1+1} and [ log 2 N]+2 otherwise.
SIMULTANEOUS CREATION OF ELECTRON–POSITRON PAIRS AND PHOTONS IN ROBERTSON–WALKER UNIVERSES WITH STATICALLY BOUNDED EXPANSION
Authors: LOTZE K.-H. 
Published: November 2004

We present, based upon quantum electrodynamics in Robertson–Walker flat universes, a thorough analysis of the creation of mutually interacting electron–positron pairs and photons from vacuum. Therefore we discuss at least qualitatively all processes contributing to the number densities of created particles up to the second order in the coupling constant. For two particular expansion laws with Minkowskian in respectively in and out regions, we obtain exact solutions to the Dirac equation and investigate in detail the process of simultaneous creation of electron–positron pairs and photons and the related attenuation effect for fermionic particles. This is done for electrons and positrons which have nonrelativistic momenta at Compton time in rapidly expanding universes. The results are compared with the zeroth-order creation of electron–positron pairs. Despite being smaller by a factor of roughly [Formula: see text], the interacting-particle creation is important mainly as a source of photons even in conformally flat universes.
AN INVESTIGATION OF THE ${\mathscr R}^2$ GRAVITY, WITH RESPECT TO THE SYMMETRY OF A MASSLESS POINTLIKE PARTICLE
Authors: TOLKSDORF JÜRGEN 
Published: November 2004

We show that the vacuum [Formula: see text] theory has no nontrivial solution admitting the same symmetry as the massless pointlike particle in flat space–time. This is interpreted as a special kind of "gravitational anomaly." The "conformal" part of the theory, however, is anomaly-free and admits an entire class of these vacuum solutions. If we use an electromagnetic field as the source of these solutions it has to be unpolarized.