Showing papers by "Collège de France published in 1988"

Supramolecular Chemistry—Scope and Perspectives Molecules, Supermolecules, and Molecular Devices (Nobel Lecture)

Abstract: Supramolecular chemistry is the chemistry of the intermolecular bond, covering the structures and functions of the entities formed by association of two or more chemical species. Molecular recognition in the supermolecules formed by receptor-substrate binding rests on the principles of molecular complementarity, as found in spherical and tetrahedral recognition, linear recognition by coreceptors, metalloreceptors, amphiphilic receptors, and anion coordination. Supramolecular catalysis by receptors bearing reactive groups effects bond cleavage reactions as well as synthetic bond formation via cocatalysis. Lipophilic receptor molecules act as selective carriers for various substrates and make it possible to set up coupled transport processes linked to electron and proton gradients or to light. Whereas endoreceptors bind substrates in molecular cavities by convergent interactions, exoreceptors rely on interactions between the surfaces of the receptor and the substrate; thus new types of receptors, such as the metallonucleates, may be designed. In combination with polymolecular assemblies, receptors, carriers, and catalysts may lead to molecular and supramolecular devices, defined as structurally organized and functionally integrated chemical systems built on supramolecular architectures. Their recognition, transfer, and transformation features are analyzed specifically from the point of view of molecular devices that would operate via photons, electrons, or ions, thus defining fields of molecular photonics, electronics, and ionics. Introduction of photosensitive groups yields photoactive receptors for the design of light-conversion and charge-separation centers. Redox-active polyolefinic chains represent molecular wires for electron transfer through membranes. Tubular mesophases formed by stacking of suitable macrocyclic receptors may lead to ion channels. Molecular self-assembling occurs with acyclic ligands that form complexes of double-helical structure. Such developments in molecular and supramolecular design and engineering open perspectives towards the realization of molecular photonic, electronic, and ionic devices that would perform highly selective recognition, reaction, and transfer operations for signal and information processing at the molecular level.

Supramolekulare Chemie – Moleküle, Übermoleküle und molekulare Funktionseinheiten (Nobel-Vortrag)†

Abstract: Supramolekulare Chemie ist die Chemie der intermolekularen Bindung und beschaftigt sich mit Strukturen und Funktionen von Einheiten, die durch Assoziation von zwei oder mehr chemischen Spezies gebildet werden. Molekulare Erkennung in Ubermolekulen, die bei der Rezeptor/Substrat-Bindung entstehen, beruht auf dem Prinzip der molekularen Komplementaritat, wie es bei der Erkennung spharischer, tetraedrischer und linearer Substrate durch Rezeptoren, Corezeptoren, Metallorezeptoren und amphiphile Rezeptoren vorgefunden wird. Supramolekulare Katalyse mit Rezeptoren, die reaktive Gruppen tragen, bewirkt Bindungsspaltungen und -knupfungen durch Cokatalyse. Lipophile Rezeptoren konnen als selektive Carrier fur verschiedenartige Substrate verwendet werden, und sie ermoglichen den Aufbau von Transportsystemen, die mit einem Elektronen- oder Protonengradienten oder mit einem Photoprozes gekoppelt sind. Wahrend Endorezeptoren Substrate durch „konvergente Wechselwirkungen” in Molekulhohlraumen binden, werden bei Exorezeptoren die Substrate durch Wechselwirkungen zwischen den Ausenflachen von Rezeptor und Substrat gebunden. Demgemas lassen sich neue Typen von Rezeptoren, z. B. die Metallonucleate, entwickeln. In polymolekularen Aggregaten konnen Rezeptoren, Carrier und Katalysatoren zu molekularen und supramolekularen Funktionseinheiten fuhren, die strukturell organisierte und funktionell integrierte chemische Systeme sind („supramolekulare Architektur”). Erkennungs-, Translokations- und Transformationsprozesse mit molekularen Funktionseinheiten werden unter dem Gesichtspunkt analysiert, ob sie durch Photonen, Elektronen oder Ionen ausgelost werden konnen. Auf diese Weise lassen sich die Gebiete der molekularen Photonik, Elektronik und Ionik definieren. Fuhrt man photosensitive Gruppen ein, ergeben sich photoaktive Rezeptoren, die sich zur Lichtumwandlung und Ladungstrennung eignen. Redoxaktive, langkettige Polyolefine – „molekulare Drahte” – konnen Elektronen, z. B. durch Membranen, ubertragen. Tubulare Mesophasen, die durch Stapelung geeigneter makrocyclischer Rezeptoren entstehen, konnen Ionenkanale bilden. Bei acyclischen Liganden gibt es das Phanomen der molekularen Selbstorganisation, was zu Komplexen mit doppelt-helicaler Struktur fuhrt. Derartige Entwicklungen im Bereich des „molekularen und supramolekularen Designs und Engineerings” lassen auf photonische, elektronische und ionische molekulare Funktionseinheiten hoffen, die hochselektive Erkennungs-, Umwandlungs- und Ubertragungsprozesse – Verarbeitung von Signalen und Informationen auf molekularer Ebene – ausfuhren konnen.

Supramolecular chemistry — Scope and perspectives: Molecules — Supermolecules — Molecular devices

Abstract: Supramolecular chemistry is the chemistry of the intermolecular bond, covering the structures and functions of the entities formed by association of two or more chemical species Molecular recognition in the supermolecules formed by receptor-substrate binding rests on the principles of molecular complementarity, as found in spherical and tetrahedral recognition, linear recognition by co-receptors, metallo-receptors, amphilic receptors and anion coordination Supramolecular catalysis by receptors bearing reactive groups effects bond cleavage reactions as well as synthetic bond formation via co-catalysis Lipophilic receptor molecules act as selective carriers for various substrates and allow the setting up of coupled transport processes linked to electron and proton gradients or to light Whereas endo-receptors bind substrates in molecular cavities by convergent interactions, exo-receptors rely on interactions between the surfaces of the receptor and the substrate; thus new types of receptors such as the metallonucleates may be designed In combination with polymolecular assemblies, receptors, carriers and catalysts may lead to molecular and supramolecular devices, defined as structurally organized and functionally integrated chemical systems built on supramolecular architectures Their recognition, transfer and transformation features are analyzed specifically from the point of view of molecular devices that would operate via photons, electrons or ions, thus defining the fields of molecular photonics, electronics and ionics Introduction of photosensitive groups yields photoactive receptors for the design of light conversion and charge separation centres Redox active polyolefinic chains represent molecular wires for electron transfer through membranes Tubular mesophases formed by stacking of suitable macrocyclic receptors may lead to ion channels Molecular self-assembling occurs with acyclic ligands that form complexes with a double helical structure Such developments in molecular and supramolecular design and engineering open perspectives towards the realization of molecular photonic, electronic and ionic devices, that would perform highly selective recognition, reaction and transfer operations for signal and information processing at the molecular level

Brain macrophages synthesize interleukin-1 and interleukin-1 mRNAs in vitro.

Abstract: Amoeboid microglial cells (brain macrophages) were purified from early post-natal mouse brain cultures. The percentage of cells stained with an anti-Mac-1 antibody was greater than 95%. Stimulation of these brain macrophages by lipopolysaccharides induced the synthesis of interleukin-1 (IL-1), which, in part, remained associated with the cell surface and, in part, was released into the culture medium. In contrast, pure primary astrocyte cultures and cell lines of transformed or immortalised astrocytes did not synthesise significant amounts of IL-1, demonstrating that amoeboid microglia and not astrocytes synthesise IL-1 in vitro. These physiological data were confirmed by RNA hybridisation studies showing that, on LPS treatment, brain macrophages synthesise significant amounts of IL-1 alpha and IL-1 beta mRNAs.

A molecular map of the chicken major histocompatibility complex: the class II beta genes are closely linked to the class I genes and the nucleolar organizer.

Abstract: We have cloned in a cosmid vector four DNA clusters covering 320 kb of the chicken MHC (B complex), including five class II (B-L) beta genes defining two related isotypic families. Additional B complex genes have been revealed using tissue-specific cDNA probes. A cosmid fragment has been used to isolate a cDNA for a class I (B-F) transcript. This transcript, that is by far the most divergent known member of the class I gene family, hybridized to six B-F genes present in the cosmids. One of the clusters was shown to contain two rRNA transcriptional units from the nucleolar organizer region (NOR), marking the telomeric boundary of the B complex. None of the other B complex genes hybridizes to, or has the transcriptional characteristics of mammalian MHC class II alpha or class III genes. The map we have obtained shows that the B complex does not contain well defined class I and class II regions since B-F and B-L beta genes are closely associated with unrelated genes. Moreover, class II beta genes are very closely linked to class I genes in two clusters, and to the NOR in a third one.

The fate map of the cephalic neural primordium at the presomitic to the 3-somite stage in the avian embryo

Abstract: The fate map of the early neural plate and neural fold has been established at the cephalic level by using the quail–chick marker system (Le Douarin, 1969, 1973). The experimental design comprised the replacement of definite territories belonging to the neural plate and neural folds in the chick embryo by their counterparts from quail embryos at the same developmental stage. This technique is referred to as the isotopic and isochronic exchange of preneural tissues between these two species. The various types of experiments that were carried out are schematized in Fig. 2. The possibility of distinguishing quail from chick cells by the structure of their nuclei allowed the fate of the grafted territories to be recognized at later developmental stages ranging from 3 to 9 days of incubation (E3–E9). Fig. 1 illustrates the morphological changes in the anterior neural plate and neural ridges in the chick embryo at the early somitic stages.

Chern character for discrete groups

Abstract: Publisher Summary This chapter discusses the Chern character for discrete groups. H j (X;Q) is the j-th Cech cohomology group of X with coefficients the rational numbers Q. The key property of this classical Chern character is that it is a rational isomorphism. Cyclic cohomology can be used to define the delocalized equivariant cohomology of X. The traditional homotopy quotient Chern character gives a map, which is always surjective, for compact X. The chapter also discusses twisted homology and K homology. K homology is the homology theory associated to the Z × BU spectrum. A concrete realization of this theory is obtained by using the K-cycle definition.

Effects of muscle shortening on the responses of cat tendon organs to unfused contractions

Abstract: 1. The discharges from individual Golgi tendon organs of peroneus tertius and brevis muscles were recorded in anesthetized cats. Responses to unfused isometric contractions of single motor units and combinations of motor units were compared with responses to contractions eliciting muscle shortening (i.e., shortening contractions). 2. In 75% of the examined instances, the effect of muscle shortening during unfused contractions was a slight decrease in tendon organ activation, in keeping with the reduction of contractile tension recorded at the muscle tendon. In other instances there was either no change in tendon organ response or, in less than 10% of instances, a slight increase For two motor units eliciting similar activation of a given tendon organ under isometric conditions, the effect of shortening contraction was not necessarily the same. 3. The reductions observed in tendon organ discharges upon muscle shortening were less than proportional to the reductions of contractile tension and difficult to correlate with the properties of motor units, as determined under isometric conditions. The present observations suggest three main reasons for this lack of relation. 4. The first reason depended on the properties of motor units, in that the relation between length changes and tension changes was not the same for all units. Two motor units developing similar isometric tensions did not necessarily produce the same degree of muscle shortening. Some units produced relatively significant shortening without much loss of tension. 5. Second, the dynamic sensitivity of tendon organs is known to exert a major influence on their responses to isometric unfused contractions, accounting for 1:1 driving of discharge during tension oscillations and high frequency bursts upon abrupt increase of tension. Although less tension was produced and the rate of tension development was slower in shortening contractions, similar manifestations of the dynamic sensitivity of tendon organs were observed. In such cases, the responses of tendon organs were the same whether or not the muscle shortened during contraction. 6. Third, when several motor units were stimulated in combination, the unloading influences of in-parallel units were facilitated by muscle shortening so that unloading effects, which were hardly visible under isometric conditions became evident during shortening contractions.

Random Surface Model for the L3-Phase of Dilute Surfactant Solutions

Abstract: We present a simple model for the anomalous (flow-birefringent) isotropic phase, known as L3, that is seen in certain surfactant solutions at volume fractions of a few percent. The proposed structure consists of locally sheetlike sections of semi-flexible surfactant bilayer, connected up at larger distances into a multiply connected random surface, having a preferred structural length scale of order the persistence length of the bilayer. A first-order transition between this isotropic sheetlike phase and the nearby swollen lamellar phase is described.

Proportion of fatigue-resistant motor units in hindlimb muscles of cat and their relation to axonal conduction velocity.

Abstract: 1. A study of motor units to hindlimb muscles of cat has been made, with as complete a sample as possible of the motor axons to an individual muscle. In single experiments as much as 95% of the motor supply to a muscle has been examined. 2. The following muscles have been studied: peroneus brevis, peroneus tertius, peroneus longus, plantaris, gastrocnemius medialis, soleus, tenuissimus and lumbricalis superficialis. 3. Units were identified as slow resistant (S), fast resistant (FR), fast fatigable (FF) and fast intermediate (FI). The proportion of various motor unit types differs from one muscle to another. There is also some variation in the proportions to a given muscle from one animal to another. With the exceptions of soleus, which is entirely slow resistant, and gastrocnemius, which has relatively fewer resistant units, most muscles contain 60% or more of resistant (S and FR) units. 4. The conduction velocity ranges of FF, FR and FI units overlapped. There was little overlap between the conduction velocity ranges of these F units and of S units. 5. In individual experiments there was a strong and significant positive correlation between the logarithm of maximal tetanic tension and axonal conduction velocity in S and in S+FR units. In terms of contractile response the total fatigue-resistant population appeared to be a continuum. The correlation coefficient between maximal tetanic tension and conduction velocity was also high in the totality of units of all types, although within the FF group there appeared to be little or no correlation. In pooled data there was much more scatter and these relations were less clear. This resulted largely from differences in the ranges of axonal conduction velocity for a given motor unit type from one animal to another. 6. There was a highly significant negative correlation between isometric twitch contraction time and axonal conduction velocity in individual experiments. This relationship could also be seen, but less clearly, in pooled data. 7. The possible bases for these relationships are discussed.

The wall of the chick embryo aorta harbours M-CFC, G-CFC, GM-CFC and BFU-E

Abstract: In the 3- to 4-day avian embryo, after the first wave of haemopoiesis which derives in the yolk sac from haemopoietic stem cells formed in situ, haemopoietic cells emerge in an intraembryonic site, the wall of the aorta. In this paper, we demonstrate that this site harbours M-CFC, G-CFC, GM-CFC and late and early BFU-E. In serum-free medium, the growth of M-CFC and GM-CFC was strictly dependent on CSF present in fibroblast-conditioned medium (FCM). The growth of G-CFC was improved when FCM was replaced by a minute quantity of chicken and fetal calf serum. Like erythroid progenitors from bone marrow, BFU-E detected here required anaemic chicken serum to differentiate into haemoglobinized cells. The frequency of the different types of haemopoietic progenitors in the aortic population was very high: 80 M-CFC, 25 G-CFC, 4 GM-CFC and 70 BFU-E for 12,500 aorta cells, i.e. two to eight times more frequent than in the bone marrow population, depending on the type of progenitors.

Development of the peripheral nervous system from the neural crest.

Abstract: DEVELOPMENTAL FATE OF THE NEURAL RIDGES THAT DELIMIT THE EARLY PRIMORDIUM OF THE NERVOUS SYSTEM • • •• •.•.• 378 Methods to Study Migration and Fate of Neural Primordium Cells 378 Origin of the Constitutive Cells of the ANS 380 Fate of the Anterior Neural Ridge .... 385 DEVELOPMENTAL POTENTIALS OF NEURAL CREST ALONG THE NEURAXIS 387

On Lie groups with left-invariant symplectic or Kählerian structures

Abstract: Left-invariant symplectic structure on a group G; properties of the corresponding Lie algebra g. A unimodular symplectic Lie algebra has to be solvable (see [1]). Symplectic subgroups and left-invariant Poisson structures on a group. Affine Poisson structures: an affine Poisson structure associated to g and admitting g * as a unique leaf corresponds to a unimodular symplectic Lie algebra and the associate group is right-affine. If G is unimodular and endowed with a left-invariant metric g, harmonic theory for the left-invariant forms. Kahlerian group is metabelian and Riemannianly flat. Decomposition of a simply connected Kahlerian group. A symplectic group admitting a left-invariant metric with a nonnegative Ricci curvature is unimodular and admits a left-invariant flat Kahlerian structure.

Motor nuclei of peroneal muscles in the cat spinal cord

Abstract: The cat peroneal muscles have been used in numerous investigations dealing with the physiological properties of motor units, muscle spindles, and Golgi tendon organs. This report presents a study of the organization of peroneal motor pools in the cat spinal cord by means of retrograde axonal transport of horseradish peroxidase from individual muscles to the corresponding motoneurons. The motor nuclei of peroneus longus (PL), peroneus brevis (PB), and peroneus tertius (PT) muscles formed thin columns in the lateral part of the ventral horn in spinal segments L6-S1. In the transverse plane, the PT and PL nuclei occupied, respectively, dorsolateral and ventromedial positions, with PB nucleus in an intermediate position overlapping with the other two nuclei. Measurements of cell body diameters allowed identification of alpha and gamma subgroups in peroneal motoneuron populations. The average numbers of motoneurons were about 96 alpha and 60 gamma in PL, 75 alpha and 54 gamma in PB, and 34 alpha and 23 gamma in PT. Comparison with data from electrophysiological studies indicated that whole populations of motoneurons were labeled in each motor nucleus. The proportions of gamma motoneurons were the same, and cell bodies of gamma motoneurons had similar sizes in the three peroneal populations. In contrast, alpha motoneurons were significantly smaller in PB than in the two other pools, in keeping with the fact that PB contains a proportion of slow motor units larger than the two other muscles. In large samples of homonymous motoneurons, the numbers of first-order dendrites correlated linearly with motoneuron sizes.

Isolation of chicken major histocompatibility complex class II (B-L) beta chain sequences: comparison with mammalian beta chains and expression in lymphoid organs.

Abstract: By cross-hybridization in low stringency conditions, using a probe derived from an HLA-DQ beta cDNA clone, we have isolated several chicken genomic DNA clones. These clones were mapped to the major histocompatibility complex (MHC) of the chick (B complex) by virtue of their ability to detect restriction enzyme length polymorphisms between congenic lines of chicken. Evidence was obtained for the presence of at least three B-L beta genes in the chicken genome. The B-L beta genes are transcribed specifically in tissues containing cells of the B lymphocyte and myeloid lineages and expressing the B-L antigens. Exons encoding the beta 1, beta 2 and transmembrane domains of a B-L beta chain have been identified with 63, 66 and 62% similarity with the HLA-DQ beta sequence. This first isolation of an MHC class II gene outside of the mammalian class provides insight into the evolution of MHC genes based on the comparison of avian and mammalian class II beta chain amino acid and nucleotide sequences.

Myoblast migration specifically inhibited in the chick embryo by grafted CSAT hybridoma cells secreting an anti-integrin antibody

Abstract: We report a teratological method in which mouse hybridoma cells are grafted into a chick host. CSAT (Cell Substratum ATtachment) hybridoma was used. It produces an antibody directed against the avian integrin complex. The grafts were performed during the second and third days of incubation either at the level of the somites or in the coelom of the chick embryo. The anomalies were revealed by means of a monoclonal antibody that recognizes myogenic cells as soon as they become committed in the myotome. When embryos were grafted at the level of the somites, body wall muscles failed to develop on the side of the graft only. After coelomic grafting, total agenesis of abdominal muscles was induced. The anomalies were specific since the engraftment of three control hybridoma clones induced no change in muscle formation. These control hybridomas produce antibodies directed against the same molecular complex but not against the same epitope as CSAT. The injection of hybridoma cells in an embryo appears as a method of general interest to determine the long-term consequences of perturbing a specific developmental process.

Brain astrocytes express region‐specific surface glycoproteins in culture

Abstract: Astrocytes derived from the mouse brain mesencephalon and striatum regulate neuronal morphogenesis in a region-specific manner in vitro. To begin defining molecular mechanisms that may underlie this functional heterogeneity, lectin probes were used to compare surface glycoproteins expressed by astrocytes from different brain regions. These experiments demonstrated marked differences in surface glycoproteins depending on the anatomic origin of the astrocytes. In particular, mesencephalic and cerebellar astrocytes express a fucosylated glycoprotein with an apparent molecular weight of 190 kD that is absent or rarely expressed by striatal or cortical astrocytes. These findings raise the possibility that carbohydrate diversity of astrocyte surface molecules may play a role in the heterogeneity of region-specific neuron-glial interactions.