Showing papers by "Centre national de la recherche scientifique published in 1987"

A human retinoic acid receptor which belongs to the family of nuclear receptors

Abstract: A cDNA encoding a protein that binds retinoic acid with high affinity has been cloned. The protein is homologous to the receptors for steroid hormones, thyroid hormones and vitamin D3, and appears to be a retinoic acid-inducible trans-acting enhancer factor, suggesting that the molecular mechanisms of the effect of retinoids (vitamin A) on embryonic development, differentiation and tumour cell growth are similar to those described for other members of this nuclear receptor family.

A new member of the immunoglobulin superfamily--CTLA-4.

Abstract: The immunoglobulin superfamily is a group of proteins, each made of one or several domains sharing key structural features with either the variable (V) or the constant (C) immunoglobulin domains. It includes such functionally important members as the immunoglobulins themselves, major histocompatibility complex (MHC) class I and class II and T-cell receptor (TCR) molecules. Several members of this superfamily are expressed on lymphocytes where they are membrane-bound and capable of interactions with other members of the family, thus taking part in cell-cell recognition. In screening mouse cytolytic-T-cell-derived cDNA libraries, we came across cDNA clones defining a sequence, CTLA-4, which could encode a 223-amino-acid protein clearly belonging to the immunoglobulin superfamily. It consists of one V-like domain flanked by two hydrophobic regions, one of which has a structure suggestive of membrane anchoring. CTLA-4 is mainly expressed in activated lymphocytes and is coinduced with T-cell-mediated cytotoxicity in inducible models of this process. The mouse ctla-4 gene maps to band C of chromosome 1.

Vostok ice core: a continuous isotope temperature record over the last climatic cycle (160,000 years)

Abstract: A continuous deuterium profile along the 160,000-year Vostok ice core (Antarctica) is interpreted in terms of atmospheric temperature changes. This climatic record is the awaited terrestrial complement of the deep-sea records supporting the existence of a relation between the Pleistocene climate and orbital forcing.

Probing the structure of RNAs in solution

Abstract: During these last years, a powerful methodology has been developed to study the secondary and tertiary structure of RNA molecules either free or engaged in complex with proteins. This method allows to test the reactivity of every nucleotide towards chemical or enzymatic probes. The detection of the modified nucleotides and RNase cleavages can be conducted by two different paths which are oriented both by the length of the studied RNA and by the nature of the probes used. The first one uses end-labeled RNA molecule and allows to detect only scissions in the RNA chain. The second approach is based on primer extension by reverse transcriptase and detects stops of transcription at modified or cleaved nucleotides. The synthesized cDNA fragments are then sized by electrophoresis on polyacrylamide:urea gels. In this paper, the various structure probes used so far are described, and their utilization is discussed.

Constraints on human arm movement trajectories.

Abstract: AUSTKA< T The underlying pirn-esses in movement organization and control were studied by varying the conditions under which arm movements were made. The three-dimensional movement trajectories of the following conditions were contrasted: pointing to a target with the index linger versus grasping a disk the same size as the target, grasping a fragile object versus a soil resilient object, and grasping a disk either to throw into a large box or place into a light litting well. Results showed that the arm trajectories, as represented by the resultant velocity profile of the wrist, varied considerably in their shape with the main factor being when peak velocity was reached as a function of the total duration of the movement. It appeared that when task demands required greater precision, the main deceleration phase of the trajectory was increased in duration. These results do not support a movement production mechanism that has access to an abstract representation of a base velocity profile and that creates trajectories by a simple scaling procedure in the temporal domain. Rather, the results support a view of movement production as relatively specific to the past experience of the performer and the constraints of the task. Ix's processus a la base du controlc el de ('organisation du mouvement out etc etudies en variant les conditions sous lesquelles les mouvements du bras etaient executes. Les trajectoires de mouvemenl tridimcnsionncl des conditions suivantes etaient niises en contraste: pointer une cible avee l'index versus saisir un disque de la meme taille que la cible; saisir un objet fragile versus un object elastique. mou; ct, saisir un disque suit pour le lancer dans une grnnde boitc soit le placer dans un puits bien ajustc. Les resultats indiquent que les trajectoires du bras, lelles que represenlees par le prolil de velocite resultant du poignel, varicnt considerablement dans leur forme avec le facteur principal apparaissant au moment ou 1c pic de velocite etait atteinl en tant que function de la duiee tolale du mouvement. Lorsque la tache requiert line plus grande precision la phase de deceleration principale dc la trajecloire augmente en duree. Cos resultats n'appuient pas un mccanisme dc production du mouvemenl ayant acccs a line representation abslraitc d'un prolil dc velocite dc base et creant des trajectoires par un procedc d'echelonncment simple dans le domaine temporcl. Cos resultats supported! plulol I \"idee d'unc production de mouvement coiiunc relativement specilique ii lexperience passcc du …

Natural 13C abundance as a tracer for studies of soil organic matter dynamics

Abstract: A method for measuring the long- and medium-term turnover of soil organic matter is described. Its principle is based on the variations of 13C natural isotope abundance induced by the repeated cultivations of a plant with a high 13C/12C ratio (C4 photosynthetic pathway) on a soil which has never carried any such plant. The 13C/12C ratio in soil organic matter being about equal to the 13C/12C ratio of plant materials from which it is derived, changing the 13C content of the organic inputs to the soil (by altering vegetation from C3 type into C4 type) is equivalent to a true labelling in situ of the organic matter. Two cases of continuous corn cultivation (Zea mays: δ13C = −12%.) on soils whose initial organic matter average δ13C is −26%. were studied. The quantity of organic carbon originating from corn (that is the quantity which had turned-over since the beginning of continuous cultivation) was estimated using the 13C natural abundance data. After 13 yr, 22% of total organic carbon had turned-over, in the system studied. Particle size fractions coarser than 50μm on the one hand, and finer than 2μm on the other. contained the youngest organic matters. The turnover rate of silt-sized fractions was slower

Analysis of sound patterns through wavelet transforms

Abstract: This paper starts with a brief discussion of so-called wavelet transforms, i.e., decompositions of arbitrary signals into localized contributions labelled by a scale parameter. The main features of the method are first illustrated through simple mathematical examples. Then we present the first applications of the method to the recognition and visualisation of characteristic features of speech and of musical sounds.

Multiple Light Scattering from Disordered Media. The Effect of Brownian Motion of Scatterers

Abstract: We have measured the time autocorrelation function of the light intensity multiply scattered from turbid aqueous suspensions of submicron size polystyrene spheres in directions near backscattering. It is found strongly non-exponential at short times revealing the very fast decay of coherence in extended scattering loops due to the thermal motion of the many spheres involved; the longest living decay time is found remarkably close to the single particle backscattering relaxation time even under conditions of interparticle interactions. These features are only weakly affected by the particular interference effect between time-reversed pairs of loops giving rise to the coherent backscattering enhancement. A simple argument is presented which accounts for these observations.

Biological function of pathogenesis-related proteins: Four tobacco pathogenesis-related proteins are chitinases.

Abstract: Four endochitinases (poly[1,4-(N-acetyl-β-D-glucosaminide)] glycanohydrolase, EC 3.2.1.14) have been purified from leaves of Nicotiana tabacum cv. Samsun NN reacting hypersensitively to tobacco mosaic virus. Two of them are acidic proteins of molecular weights 27,500 and 28,500 and have been identified as 2 of the 10 pathogenesis-related proteins that are known to accumulate in tobacco in response to stress or pathogen attack. These two pathogenesis-related proteins, named “P” and “Q” when their biological function was unknown, account for one-third of tobacco mosaic virus-induced chitinase activity of tobacco leaves. They are serologically closely related to the two other chitinases, which can be considered as new basic pathogenesis-related proteins. These two basic chitinases exhibit higher molecular weights (32,000 and 34,000) and higher specific enzyme activity than the two acidic isoforms.

Variations in mode of formation and temperature of oceanic deep waters over the past 125,000 years

Abstract: Marked changes in the deep-water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the Norwegian Sea, and the Pacific, Atlantic and Southern oceans. The last interglacial deep-water temperatures were similar to the modern ones. At the 5e/5d transition, around 115 kyr BP, the deep-water temperatures dropped below approximately 0 °C in the Pacific and southern Indian oceans. In the Atlantic Ocean, the deep-water temperature dropped in 2 successive steps at ˜115 and 75ky BP. The global ocean deep-water temperatures were in the 0 to −1 °C range for the whole of the last ice age (isotope stages 4–2).

Sequence-specific recognition, photocrosslinking and cleavage of the DNA double helix by an oligo-(α]-thymidylate covalently linked to an azidoproflavine derivative

Abstract: A 3-azidoproflavine derivative was covalently linked to the 5'-end of an octathymidylate synthesized with the [alpha]-anomers of the nucleoside. Two target nucleic acids were used for this substituted oligo-[alpha]-thymidylate: a 27-mer single-stranded DNA fragment containing an octadeoxyadenylate sequence and a 27-mer duplex containing eight contiguous A.T base pairs with all adenines on the same strand. Upon visible light irradiation the octa-[alpha]-thymidylate was photocrosslinked to the single-stranded 27-mer. Chain breaks were induced at the crosslinked sites upon piperidine treatment. From the location of the cleavage sites on the 27-mer sequence it was concluded that a triple helix was formed by the azidoproflavine-substituted oligo-[alpha]-thymidylate with its complementary oligodeoxyadenylate sequence. When the 27-mer duplex was used as a substrate cleavage sites were observed on both strands after piperidine treatment of the irradiated sample. They were located at well defined positions which indicated that the octathymidylate was bound to the (dA)8.(dT)8 sequence in parallel orientation with respect to the (dA)8-containing strand. Specific binding of the [alpha]-octathymidylate involved local triple strand formation with the duplex (dA)8.(dT)8 sequence. This result shows that it is possible to synthesize sequence-specific molecules which specifically bind oligopurine-oligopyrimidine sequences in double-stranded DNA via recognition of the major groove hydrogen bonding sites of the purines.

Process for the preparation of dispersible colloidal systems of a substance in the form of nanoparticles

Abstract: The process according to the invention comprises: (1) the preparation of a liquid phase consisting essentially of a solution of a substance A in a solvent or in a mixture of solvents, and containing the substance B in solution or as a dispersion, (2) the preparation of a second liquid phase consisting essentially of a non-solvent or a mixture of non-solvents for the substances A and B, and supplemented with one or more surfactants, the solvent or mixture of solvents of the first phase being miscible in all proportions with the non-solvent or mixture of non-solvents of the second phase, (3) the addition of the first phase to the second phase with moderate agitation so as to produce a colloidal suspension of nanocapsules, the wall of which is constituted by the substance A and the core by the substance B, (4) if desired, the removal of all or part of the solvent or the mixture of solvents and of the non-solvent or the mixture of non-solvents so as to produce a colloidal suspension of nanocapsules of the desired concentration or to produce a powder of nanocapsules following the addition of stabilizing substances.

Structure of the 100 K Superconductor Ba2YCu3O7 between (5 ÷ 300) K by Neutron Powder Diffraction

Abstract: Recently Siegrist et al. proposed a structure for a high-Tc superconductor Ba2YCu3O(9-∂) based on an orthorhombic (a = ap, b = ap, c = 3ap) perovskitelike model containing Ba and Y cations ordered over the A-sites of the ABO3 structure. This ordering is responsible for the tripling of the c-axis. Half of the oxygen vacancies (at z = 1/2) are ordered, while the other half (at z = 0) are disordered over two sites. Using profile refinement of high-resolution neutron powder data at six different temperatures between 5 K and 300 K, we have refined the structure of a pure and well-characterised powder sample with onset of superconductivity at 100 K. At all temperatures we confirmed the previous model except that in our structure, all oxygen vacancies are ordered. Two-thirds of the copper cations have a pyramidal coordination and one-third has a square coordination. In our structure all squares are parallel to the (b, c)-plane, while in the one reported by Siegrist et al. the squares are disorderedly parallel to either the (a, c)- or (b, c)-plane. The difference between the two models is probably due to the fact that the single crystal used in the earlier work was highly twinned. Empirical calculations of the copper valences show that the Cu+++ cations are almost equally distributed over the two sites. No structural change has been detected at the transition.

Actin polymerization and ATP hydrolysis.

Abstract: F-actin is the major component of muscle thin filaments and, more generally, of the microfilaments of the dynamic, multifunctional cytoskeletal systems of nonmuscle eukaryotic cells. Polymeric F-actin is formed by reversible noncovalent self-association of monomeric G-actin. To understand the dynamics of microfilament systems in cells, the dynamics of polymerization of pure actin must be understood. The following model has emerged from recent work. During the polymerization process, adenosine 5'-triphosphate (ATP) that is bound to G-actin is hydrolyzed to adenosine 5'-diphosphate (ADP) that is bound to F-actin. The hydrolysis reaction occurs on the F-actin subsequent to the polymerization reaction in two steps: cleavage of ATP followed by the slower release of inorganic phosphate (Pi). As a result, at high rates of filament growth a transient cap of ATP-actin subunits exists at the ends of elongating filaments, and at steady state a stabilizing cap of ADP.Pi-actin subunits exists at the barbed ends of filaments. Cleavage of ATP results in a highly stable filament with bound ADP.Pi, and release of Pi destabilizes the filament. Thus these two steps of the hydrolytic reaction provide potential mechanisms for regulating the monomer-polymer transition.

Basic fibroblast growth factor enters the nucleolus and stimulates the transcription of ribosomal genes in ABAE cells undergoing G0----G1 transition.

Abstract: The cellular action of growth factors, among them basic fibroblast growth factor (bFGF), is mediated by their interaction with a cell surface receptor, but the mechanism of transfer of mitogenic (or other) signals to the nucleus has not been identified. In this work, we show that bFGF is translocated to and accumulated in the nucleolus. Furthermore, the nucleolar localization of bFGF is correlated with a stimulation of transcription of ribosomal genes during G0----G1 transition induced by bFGF alone in adult bovine aortic endothelial cells (ABAE cells). Stimulation of ribosomal gene transcription is preceded by a significant increase of the major nonhistone nucleolar protein, nucleolin. In vitro, the growth factor has a direct effect on the enhancement of RNA polymerase I activity in isolated nuclei from quiescent sparse (G0) ABAE cells. The direct action of bFGF on the level of ribosomal gene transcription could correspond to an additional growth-signaling pathway, mediated by this growth factor.

Back Arc Extension in the Okinawa Trough

Abstract: The Okinawa Trough, lying to the east of China, is a back arc basin formed by extension within continental lithosphere behind the Ryukyu trench-arc system. Middle to late Miocene uplift, associated with normal faulting of the initially adjacent Ryukyu nonvolcanic arc and the Taiwan-Sinzi folded belt, corresponds to the first rifting phase. The timing of rifting is supported by the presence of marine sediments of corresponding age drilled in the northern Okinawa Trough. The rifting occurred after a major early Miocene change in the motion of the Philippine plate with respect to Eurasia and ceased during the Pliocene. A second rifting phase started about 2 m.y. ago, at the Plio-Pleistocene boundary and has continued until the present time. It has proceeded to a more advanced stage in the middle and southern Okinawa Trough than it has farther north. Detailed bathymetric (Sea Beam), seismic reflection, and magnetics data collected during the POP 1 cruise of the R/V Jean Charcot reveal the principal features of the extensional processes. The back arc spreading phase started very recently in the southern and middle Okinawa Trough, as exemplified by several en echelon and, in some cases, overlapping active, central graben oriented N70°E–N80°E. Some of these depressions are intruded by volcanic ridges of fresh back arc basalt with associated large magnetic anomalies. Transform faults between these en echelon active rifts are not obvious. We suggest that the major part of the southern Okinawa Trough is underlain by a thinned continental crust and that except for the system of en echelon rifts of the southern Okinawa Trough, the back arc basin oceanic domain is limited to a width of a few tens of kilometers or less in the axial portion of the trough. The system of axial back arc volcanic ridges that occur in the rifts ends at the latitude of Okinawa Island whereas active volcanoes in the Ryukyu arc occur only north of Okinawa Island. We refer to this transition between active arc and back arc volcanism as the volcanic arc-rift migration phenomenon (VAMP). Globally, back arc volcanism propagated from the southern Okinawa Trough to the Okinawa VAMP area. Rifting continues to occur in the northern Okinawa Trough but is not yet accompanied by associated volcanism. The Okinawa VAMP area is characterized by a series of parallel basaltic ridges oriented N75°E with associated linear magnetic anomalies characteristic of dyke intrusions. We suggest that the formation of the back arc oceanic domain took place along the axial back arc extensional zone trending N75°E and that this zone presently ends at the southern extremity of the active volcanic chain. The initial phase of formation of back arc basin oceanic crust is non-steady state and is characterized by the lack of a developed fracture zone pattern. The termination of the VAMP area in the direction of the volcanic zone of the arc is consistent with the suggestion of Molnar and Atwater that the volcanic arc is a fundamental line of weakness which determines where initial back arc spreading occurs. Apparently, back arc extension initially occurred within the continental lithosphere located westward of the Ryukyu arc, along its whole length, but the subsequent back arc volcanism was initiated in the southernmost portion of the region and then moved northward. This migration was accompanied by the shutting down of volcanic activity along the abandoned portions of the arc. It is this transfer of volcanism that we call the VAMP process. Thus arc and back arc basin volcanism seem to be associated in such a manner that spreading tends to migrate simultaneously with a cessation in volcanic activity along the arc. This interplay of arc and back arc activity is probably linked to changes in the parameters of plate convergence. Since the plate motion in the Phillippine sea is oblique to the trench at least in the southern part of the Okinawa Trough, we suggest that the oblique resisting force applied to the edge of the overriding plate engenders the development of en echelon extensional features within and behind the arc. The motion of the Ryukyu platelet with respect to Eurasia is consequently an extensional strike-slip motion trending roughly parallel to the Okinawa Trough.

Isotopic study of the Manaslu granite (Himalaya, Nepal): inferences on the age and source of Himalayan leucogranites

Abstract: A detailed isotopic study of the Manaslu leucogranite was carried out. A U-Pb age of 25 Ma and a whole rock Rb-Sr age isochron of 18 Ma were obtained, suggesting that the magmatic activity lasted at least 7 Ma. Initial Sr isotopic ratios are very high (0.740 to 0.760) and initial Nd isotopic ratios are low (ɛ Nd in : −13 to −16), and they show the existence of large isotopic variations even at the metre scale. These are not the result of perturbations by fluids but rather they reflect the initial isotopic heterogeneity of the source material which has not been obliterated by magmatic processes (e.g. fusion, mixing by convection). These results also support the crustal origin of this leucogranite. The Tibetan slab paragneisses, whose Sr and Nd isotopic ratios are very similar to those of the granite at an age of 20 Ma, are the most probable parental material. Nd model ages for both the leucogranite and the gneisses are in the range 1.5–2 Ga. A model of formation of the Manaslu granite by coalescence of different batches of magma is in agreement with the present data.

Secondary instability of a temporally growing mixing layer

Abstract: The three-dimensional stability of two-dimensional vortical states of planar mixing layers is studied by direct numerical integration of the Navier-Stokes equations. Small-scale instabilities are shown to exist for spanwise scales at which classical linear modes are stable. These modes grow on convective timescales, extract their energy from the mean flow and exist at moderately low Reynolds numbers. Their growth rates are comparable with the most rapidly growing inviscid instability and with the growth rates of two-dimensional subharmonic (pairing) modes. At high amplitudes, they can evolve into pairs of counter-rotating, streamwise vortices, connecting the primary spanwise vortices, which are very similar to the structures observed in laboratory experiments. The three-dimensional modes do not appear to saturate in quasi-steady states as do the purely two-dimensional fundamental and subharmonic modes in the absence of pairing. The subsequent evolution of the flow depends on the relative amplitudes of the pairing modes. Persistent pairings can inhibit threedimensional instability and, hence, keep the flow predominantly two-dimensional. Conversely, suppression of the pairing process can drive the three-dimensional modes to more chaotic, turbulent-like states. An analysis of high-resolution simulations of fully turbulent mixing layers confirms the existence of rib-like structures and that their coherence depends strongly on the presence of the two-dimensional pairing modes.

Fluoride complexes of aluminium or beryllium act on G-proteins as reversibly bound analogues of the gamma phosphate of GTP.

Abstract: Fluoride activation of G proteins requires the presence of aluminium or beryllium and it has been suggested that AIF4- acts as an analogue of the gamma-phosphate of GTP in the nucleotide site. We have investigated the action of AIF4- or of BeF3- on transducin (T), the G protein of the retinal rods, either indirectly through the activation of cGMP phosphodiesterase, or more directly through their effects on the conformation of transducin itself. In the presence of AIF4- or BeF3-, purified T alpha subunit of transducin activates purified cyclic GMP phosphodiesterase (PDE) in the absence of photoactivated rhodopsin. Activation is totally reversed by elution of fluoride or partially reversed by addition of excess T beta gamma. Activation requires that GDP or a suitable analogue be bound to T alpha: T alpha-GDP and T alpha-GDP alpha S are activable by fluorides, but not T alpha-GDP beta S, nor T alpha that has released its nucleotide upon binding to photoexcited rhodopsin. Analysis of previous works on other G proteins and with other nucleotide analogues confirm that in all cases fluoride activation requires that a GDP unsubstituted at its beta phosphate be bound in T alpha. By contrast with alumino-fluoride complexes, which can adopt various coordination geometries, all beryllium fluoride complexes are tetracoordinated, with a Be-F bond length of 1.55 A, and strictly isomorphous to a phosphate group. Our study confirms that fluoride activation of transducin results from a reversible binding of the metal-fluoride complex in the nucleotide site of T alpha, next to the beta phosphate of GDP, as an analogue of the gamma phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)

A single human gene encoding multiple tyrosine hydroxylases with different predicted functional characteristics

Abstract: Catecholaminergic systems in discrete regions of the brain are thought to be important in affective psychoses, learning and memory, reinforcement and sleep-wake cycle regulation. Tyrosine hydroxylase (TH) is the first enzyme in the pathway of catecholamine synthesis. Its importance is reflected in the diversity of the mechanisms that have been described which control its activity; TH levels vary both during development and as a function of the activity of the nervous system. Recently, we deduced the complete amino-acid sequence of rat TH from a complementary DNA clone encoding a functional enzyme. Here we demonstrate that, in man, TH molecules are encoded by at least three distinct messenger RNAs. The expression of these mRNAs varies in different parts of the nervous system. The sequence differences observed are confined to the 5' termini of the messengers and involve alternative splicing events. This variation has clear functional consequences for each putative form of the enzyme and could represent a novel means of regulating catecholamine levels in normal and pathological neurons.