Showing papers by "Pierre-and-Marie-Curie University published in 1996"

Life with 6000 Genes

Abstract: The genome of the yeast Saccharomyces cerevisiae has been completely sequenced through a worldwide collaboration. The sequence of 12,068 kilobases defines 5885 potential protein-encoding genes, approximately 140 genes specifying ribosomal RNA, 40 genes for small nuclear RNA molecules, and 275 transfer RNA genes. In addition, the complete sequence provides information about the higher order organization of yeast's 16 chromosomes and allows some insight into their evolutionary history. The genome shows a considerable amount of apparent genetic redundancy, and one of the major problems to be tackled during the next stage of the yeast genome project is to elucidate the biological functions of all of these genes.

Surgical resection of colorectal carcinoma metastases to the liver : A prognostic scoring system to improve case selection, based on 1568 patients

Abstract: BACKGROUND Five-year survival rates after resection of liver metastases from colorectal carcinoma are close to 25%. Recurrences occur in two-thirds of the patients after surgery. Selection of patients likely to benefit from surgery remains controversial and subjective. METHODS Data from 1568 patients with resected liver metastases from colorectal carcinoma were collected. The prognostic value of different factors was studied through uni- and multivariate analyses. A scoring system was developed including the most relevant factors. RESULTS Two- and 5-year survival rates were 64% and 28%, respectively, and were affected by: age; size of largest metastasis or CEA level; stage of the primary tumor; disease free interval; number of liver nodules; and resection margin. Giving one point to each factor, the population was divided into three risk groups with different 2-year survival rates: 0–2 (79%), 3–4 (60%), 5–7 (43%). CONCLUSIONS A simple prognostic scoring system was proposed to evaluate the chances for cure of patients after resection of liver metastases from colorectal carcinoma. The comparison between expected survival and estimated operative risk can help determine on an objective basis whether surgery is worthwhile. This system needs further prospective validation. Cancer 1996;77:1254-62.

NEUROPHENOMENOLOGY A Methodological Remedy for the Hard Problem

Abstract: This paper starts with one of Chalmers' basic points: first-hand experience is an irreducible field of phenomena. I claim there is no 'theoretical fix' or 'extra ingredient' in nature that can possibly bridge this gap. Instead, the field of conscious phenomena requires a rigorous method and an explicit pragmatics for its exploration and analysis. My proposed approach, inspired by the style of inquiry of phenomenology, I have called neurophenomenol- ogy. It seeks articulations by mutual constraints between phenomena present in experience and the correlative field of phenomena established by the cognitive sciences. It needs to expand into a widening research community in which the method is cultivated further. This paper responds to the issues raised by D.J. Chalmers (1995) by offering a research direction which is quite radical in the way in which some basic methodological principles are linked to the scientific studies of consciousness. Neuro-phenomenology is the name I am using here to designate a quest to marry modern cognitive science and a disciplined approach to human experience, thus placing myself in the lineage of the continental tradition of phenomenology. 1 My claim is that the so-called hard problem that animates these Special Issues of the Journal of Consciousness Studies can only be addressed productively by gathering a research community armed with new pragmatic tools ena- bling them to develop a science of consciousness. I will claim that no piecemeal empirical correlates, nor purely theoretical principles, will really help us at this stage. We need to turn to a systematic exploration of the only link between mind and consciousness that seems both obvious and natural: the structure of human experience itself. In what follows I open my proposal by briefly examining the current debate about consciousness in the light of Chalmers' hard problem. Next, I outline the (neuro)pheno- menological strategy. I conclude by discussing some of the main difficulties and conse- quences of this strategy.

Mapping of a susceptibility locus for Crohn's disease on chromosome 16

Abstract: Crohn's disease (CD) and ulcerative colitis are the major forms of chronic inflammatory bowel diseases in the western world, and occur in young adults with an estimated prevalence of more than one per thousand inhabitants. The causes of inflammatory bowel diseases remain unknown, but genetic epidemiology studies suggest that inherited factors may contribute in part to variation in individual susceptibility to Crohn's disease. A genome-wide search performed on two consecutive and independent panels of families with multiple affected members, using a non-parametric two-point sibling-pair linkage method, identified a putative CD-susceptibility locus on chromosome 16 (P less than 0.01 for each panel). The localization was centered around loci D16S409 and D16S419 by using multipoint sibpair analysis (P less than 1.5x10(-5)). This region of the genome contains candidate genes which may be relevant to the pathogenic mechanism of inflammatory bowel diseases.

Lipid-transfer proteins in plants

Abstract: Lipid-transfer proteins (LTP) are basic, 9-kDa proteins present in high amounts (as much as 4% of the total soluble proteinss) in higher plants. LTPs can enhance the in vitro transfer of phospholipids between membranes and can bind acyl chains. On the basis of these properties, LTPs were thought to participate in membrane biogenesis and regulation of the intracellular fatty acid pools. However, the isolation of several cDNAs and genes revealed the presence of a signal peptide indicating that LTPs could enter the secretory pathway. They were found to be secreted and located in the cell wall. Thus, novel roles were suggested for plant LTPs: participation in cutin formation, embryogenesis, defense reactions against phytopathogens, symbiosis, and the adaptation of plants to various environmental conditions. The validity of these suggestions needs to be determined, in the hope that they will elucidate the role of this puzzling family of plant proteins.

Highly stereoelective polymerization of rac-(D,L)-lactide with a chiral schiff's base/aluminium alkoxide initiator

Abstract: A chiral Schiff's base/aluminium alkoxide initiator bearing a ligand derived from R-(+)-1,1′-binaphthyl-2,2′-diamine was synthesized and used for the stereoelective polymerization of rac-(D,L)-lactide. Rather high stereoelectivity is observed: a polymer with 88% enantiomeric enrichment in D units is obtained at 19% conversion. At high conversions a stereocomplex between D- and L-enriched stereocopolymers is formed. The polymerization reaction shows living type features, and narrow molecular weight distributions (Mw/Mn = 1,05–1,30) are obtained up to very high conversions. This indicates that transesterification reactions do not occur significantly with this sterically hindered initiator.

Local Adaptation and Gene-For-Gene Coevolution in a Metapopulation Model

Abstract: In several reciprocal cross-infection experiments parasites were found to be significantly more adapted to their local host populations than to hosts from distant populations. We developed a metapopulation model, taking explicit account of both population densities and gene frequencies, to determine the influence of ecological and genetical parameters on the local adaptation of the parasites and on the spatial distribution of resistance and virulence genes. Our results point to the predominant effect of ecological parameters such as parasite growth rate and host and parasite migration rates on coevolutionary outcomes. In particular, the parasites are more likely to be adapted to their local host population than to allopatric hosts when the parasite migration rate is larger than the host migration rate. The opposite should be observed whenever hosts migrate more than parasites.

Bornes pour la torsion des courbes elliptiques sur les corps de nombres

Abstract: Corollaire. — Soit d un entier ≥ 1 . Il existe un nombre réel B(d) tel que pour toute courbe elliptique E , définie sur un corps de nombres K de degré d sur Q , tout point de torsion de E(K) soit d’ordre ≤ B(d) . Ou de façon équivalente, il n’existe qu’un nombre fini, à isomorphisme près, de groupes qui sont la partie de torsion du groupe de MordellWeil d’une courbe elliptique définie sur une extension de Q de degré d .

Immunocytochemical localization of serotonin1A receptors in the rat central nervous system.

Abstract: Specific anti-rat 5-hydroxytryptamine1A (serotonin1A) receptor antibodies raised in a rabbit injected with a synthetic peptide corresponding to a highly selective portion of the third intracellular loop of the receptor protein (El Mestikawy et al. [1990] Neurosci. Lett. 118:189-192) were used for immunohistochemical mapping of serotonin1A receptors in the brain and spinal cord of adult rats. The highest density of immunostaining was found in limbic areas (lateral septum, CA1 area of Ammon's horn and dentate gyrus in the hippocampus, and frontal and entorhinal cortices), in the anterior raphe nuclei, and in the interpeduncular nucleus, in agreement with previous autoradiographic studies with selective radioligands showing the enrichment of these regions in serotonin1A receptor binding sites. Serotonin1A receptor-like immunoreactivity was also present, but at a moderate level, in the neocortex, in some thalamic and hypothalamic nuclei, in the nucleus of the solitary tract, in the dorsal tegmentum, in the nucleus of the spinal tract of the trigeminal nerve, and in the superficial layers of the dorsal horn in the spinal cord. In contrast, extrapyramidal areas, including the caudate putamen, the globus pallidus, and the substantia nigra as well as the cerebellum, exhibited very low to no immunostaining by antiserotonin1A receptor antibodies. At the cellular level, both the plasma membrane of neuronal perikarya and fine neuronal processes probably corresponding to dendritic fields were found to bind antiserotonin1A receptor antibodies. Regional differences were noted regarding these two types of immunostaining, because only dendrites bound antibodies within the hippocampus and the lateral septum, whereas both dendrites and neuronal cell bodies were immunoreactive in the medial septum, in the diagonal band of Broca, and in the dorsal and median raphe nuclei. Therefore, differential addressing of serotonin1A receptors could occur from one neuron to another. In general, the distribution and density of serotonin1A receptor-like immunoreactivity in the whole brain and in spinal cord were consistent with the mapping of serotonin1A receptor binding sites and serotonin1A receptor mRNA previously established by immunoautoradiographic and in situ hybridization procedures.

Essential role of beta-adrenergic receptor kinase 1 in cardiac development and function.

Abstract: The beta-adrenergic receptor kinase 1 (beta ARK1) is a member of the G protein-coupled receptor kinase (GRK) family that mediates the agonist-dependent phosphorylation and desensitization of G protein-coupled receptors. We have cloned and disrupted the beta ARK1 gene in mice by homologous recombination. No homozygote beta ARK1-/- embryos survive beyond gestational day 15.5. Prior to gestational day 15.5, beta ARK1-/- embryos display pronounced hypoplasia of the ventricular myocardium essentially identical to the "thin myocardium syndrome" observed upon gene inactivation of several transcription factors (RXR alpha, N-myc, TEF-1, WT-1). Lethality in beta ARK1-/- embryos is likely due to heart failure as they exhibit a > 70% decrease in cardiac ejection fraction determined by direct in utero intravital microscopy. These results along with the virtual absence of endogenous GRK activity in beta ARK1-/- embryos demonstrate that beta ARK1 appears to be the predominant GRK in early embryogenesis and that it plays a fundamental role in cardiac development.

Isotopic biogeochemistry ( 13 C, 18 O) of mammalian enamel from African Pleistocene hominid sites

Abstract: The carbon and oxygen isotope composition of carbonate in enamel hydroxylapatite can provide information on photosynthetic pathways of plants at the base of food webs, and on hydrological conditions. Retrieval ofpalaeoenvironmental information from isotopic composition of vertebrate fossils is complicated by potential diagenetic overprinting. In this study, alteration has been assessed by examining the extent to which expected biological carbon and oxygen isotope patterns are disrupted in fossils of species whose diets can be independently predicted by other criteria. The biological patterns used are 1) the differences in carbon isotope composition between grazers and browsers, and 2) the differences in oxygen isotope composition between hippopotamus and terrestrial herbivores. Results obtained on enamel samples from Tighenif (Algeria, =700,000 yr), Melka-Kunture (Ethiopia, 0.7-1.5 myr), and Anabo Koma (Djibouti, -1.6 myr) suggest that in vivo carbon and oxygen isotope compositions are preserved in most cases. Moreover, in all three regions, modern patterns of C3 versus C4 grass dominance were present within the Pleistocene.

Molecular Electronics Emerges from Molecular Magnetism

Abstract: Molecular electronics—the storage and processing of data on individual molecules—may be one path toward increased storage density and speed. In his Perspective, Verdaguer discusses work reported by Sato et al. (p. 704) in this issue on light-induced changes in the magnetic properties of various preparations of Prussian blue. This leads to switching of the long-range magnetic ordering of the compound and may point the way to molecular information processing.

Curve Crossing Formulation for Proton Transfer Reactions in Solution

Abstract: A Landau−Zener curve crossing formulation is developed for proton transfer rate constants over the range of proton coupling. This approach spans the weak coupling regime, where the transfer is a nonadiabatic proton tunneling, to the strong coupling regime, where at the reaction transition state the proton motion is a quantized vibration lying above the barrier in the proton coordinate. The theory requires that there is strong coupling of the proton transfer solute to the surrounding polar solvent and includes the influence of the vibrational motion of the heavy particles between which the proton transfers. Analytic formulas are given for the rate constants in various limits of the proton coupling strength and the vibrational frequency of the heavy particle motion.

Tuning and test of fragmentation models based on identified particles and precision event shape data

Abstract: Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.

Atomic shell structure and electron numbers

Abstract: rn The electron localization function (ELF) was calculated for the atoms Li to Sr The ELF maxima reveal the atomic shell structure for all these atoms The shells are separated from each other by ELF minima The integration of the electron density in a shell gives electron numbers For the valence shell those are in good agreement with the ones expected from the Periodic Table of Elements 0 1996 John Wiley & Sons, Inc

An Analytical Method for Performance Evaluation of Kanban Controlled Production Systems

Abstract: The aim of this paper is to develop a general purpose analytical method for performance evaluation of multistage kanban controlled production systems. We consider a single-part type production system decomposed into stages in series. Each stage consists of a manufacturing cell and an output buffer. With each stage is associated a given number of kanbans. The kanban controlled production system is modeled as a queueing network with synchronization mechanisms. The basic principle of the proposed approximation method is to decompose the original kanban system into a set of subsystems, each subsystem being associated with a particular stage. Each subsystem is analyzed in isolation using a product-form approximation technique. An iterative procedure is then used to determine the unknown parameters of each subsystem. Numerical results show that the method is fairly accurate.

Possible role of atmosphere-biosphere interactions in triggering the last glaciation

Abstract: We coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system, at the time of glacial inception 115,000 years ago. Orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present (atmospheric composition, oceans, biosphere and cryosphere). Summers were however cold enough to induce major vegetation shifts in high northern latitudes. Southward migration of the boreal forest/tundra limit helped to create favourable conditions for continental ice-sheet growth, with increasing snow depth and duration in Labrador, Arctic Canada and northern/western Fennoscandia. These results support a role for biogeophysical feedback in initiating glaciations.

The membrane shell model in nonlinear elasticity: A variational asymptotic derivation

Abstract: We consider a shell-like three-dimensional nonlinearly hyperelastic body and we let its thickness go to zero We show, under appropriate hypotheses on the applied loads, that the deformations that minimize the total energy weakly converge in a Sobolev space toward deformations that minimize a nonlinear shell membrane energy The nonlinear shell membrane energy is obtained by computing the Γ-limit of the sequence of three-dimensional energies

Phase dependence of (N+1)-color (N>1) ir-uv photoionization of atoms with higher harmonics.

Abstract: We discuss, via a numerical calculation, the main properties of atomic photoelectron spectra, as they would be obtained by using a radiation pulse containing N+1 frequencies associated with a ``Dirac comb'' of N higher harmonics together with the laser which has been used to generate them. We address more precisely the physically relevant situation in which the harmonics have much weaker intensities than the one of the laser. In such (N+1)-color photoionization processes, the atom can simultaneously absorb harmonic uv photons and exchange, i.e., absorb and/or emit, (via stimulated emission) laser ir photons. We have simulated the photoelectron spectra by numerically solving the time-dependent Schr\"odinger equation for a three-dimensional hydrogen atom in the presence of the radiation pulse. Our results show that, everything else being kept fixed, the magnitudes of the photoelectron peaks are strongly dependent on the difference of phase between successive harmonics. This strong dependence results from interference effects taking place between competing quantum paths leading to a given final state. An interesting feature is that these interferences involve transitions in the continuum states of the atom and do not depend on resonances in the discrete spectrum. Another interesting outcome of our study is to show that such effects should be observable with currently developed harmonic sources. \textcopyright{} 1996 The American Physical Society.