Showing papers by "Collège de France published in 2004"

Maximal deformation of an impacting drop

Abstract: We first study the impact of a liquid drop of low viscosity on a super-hydrophobic surface. Denoting the drop size and speed as are the liquid density and surface tension). This law is also observed to hold on partially wettable surfaces, provided that liquids of low viscosity (such as water) are used. The law is interpreted as resulting from the effective acceleration experienced by the drop during its impact. Viscous drops are also analysed, allowing us to propose a criterion for predicting if the spreading is limited by capillarity, or by viscosity.

The netrin receptor UNC5B mediates guidance events controlling morphogenesis of the vascular system

Abstract: Blood vessels and nerves are complex, branched structures that share a high degree of anatomical similarity. Guidance of vessels and nerves has to be exquisitely regulated to ensure proper wiring of both systems. Several regulators of axon guidance have been identified and some of these are also expressed in endothelial cells; however, the extent to which their guidance functions are conserved in the vascular system is still incompletely understood. We show here that the repulsive netrin receptor UNC5B is expressed by endothelial tip cells of the vascular system. Disruption of the Unc5b gene in mice, or of Unc5b or netrin-1a in zebrafish, leads to aberrant extension of endothelial tip cell filopodia, excessive vessel branching and abnormal navigation. Netrin-1 causes endothelial filopodial retraction, but only when UNC5B is present. Thus, UNC5B functions as a repulsive netrin receptor in endothelial cells controlling morphogenesis of the vascular system.

High-energy particle acceleration in the shell of a supernova remnant.

Abstract: A significant fraction of the energy density of the interstellar medium is in the form of high-energy charged particles (cosmic rays)1. The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically2,3, unequivocal evidence for the production of high-energy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.7 - 3946 (G347.3 - 0.5), which was discovered by ROSAT4 in the X-ray spectrum and later claimed as a source of high-energy γ-rays5,6 of TeV energies (1 TeV = 1012 eV). We present a TeV γ-ray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in X-rays, which demonstrates that very-high-energy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks.

Neural crest cell plasticity and its limits

Abstract: The neural crest (NC) yields pluripotent cells endowed with migratory properties. They give rise to neurons, glia, melanocytes and endocrine cells, and to diverse 'mesenchymal' derivatives. Experiments in avian embryos have revealed that the differentiation of the NC 'neural' precursors is strongly influenced by environmental cues. The reversibility of differentiated cells (such as melanocytes or glia) to a pluripotent precursor state can even be induced in vitro by a cytokine, endothelin 3. The fate of 'mesenchymal' NC precursors is strongly restricted by Hox gene expression. In this context, however, facial skeleton morphogenesis is under the control of a multistep crosstalk between the epithelia (endoderm and ectoderm) and NC cells.

Flow regulates arterial-venous differentiation in the chick embryo yolk sac.

Abstract: Formation of the yolk sac vascular system and its connection to the embryonic circulation is crucial for embryo survival in both mammals and birds. Most mice with mutations in genes involved in vascular development die because of a failure to establish this circulatory loop. Surprisingly, formation of yolk sac arteries and veins has not been well described in the recent literature. Using time-lapse video-microscopy, we have studied arterial-venous differentiation in the yolk sac of chick embryos. Immediately after the onset of perfusion, the yolk sac exhibits a posterior arterial and an anterior venous pole, which are connected to each other by cis-cis endothelial interactions. To form the paired and interlaced arterial-venous pattern characteristic of mature yolk sac vessels, small caliber vessels of the arterial domain are selectively disconnected from the growing arterial tree and subsequently reconnected to the venous system, implying that endothelial plasticity is needed to fashion normal growth of veins. Arterial-venous differentiation and patterning are controlled by hemodynamic forces, as shown by flow manipulation and in situ hybridization with arterial markers ephrinB2 and neuropilin 1, which show that expression of both mRNAs is not genetically determined but plastic and regulated by flow. In vivo application of ephrinB2 or EphB4 in the developing yolk sac failed to produce any morphological effects. By contrast, ephrinB2 and EphB4 application in the allantois of older embryos resulted in the rapid formation of arterial-venous shunts. In conclusion, we show that flow shapes the global patterning of the arterial tree and regulates the activation of the arterial markers ephrinB2 and neuropilin 1.

Very high-energy gamma rays from the direction of Sagittarius A*

Abstract: We report the detection of a point-like source of very high energy (VHE) gamma-rays coincident within 1' of Sgr A*, obtained with the H.E.S.S. array of Cherenkov telescopes. The gamma-rays exhibit a power-law energy spectrum with a spectral index of -2.2 +/- 0.09 +/- 0.15 and a flux above the 165 GeV threshold of (1.82 +/- 0.22) \times 10^{-7} m^{-2} s^{-1}. The measured flux and spectrum differ substantially from recent results reported in particular by the CANGAROO collaboration.

Historical phenology: Grape ripening as a past climate indicator

Abstract: Summer temperature variations are reconstructed from harvest dates since 1370. French records of grape-harvest dates in Burgundy were used to reconstruct spring–summer temperatures from 1370 to 2003 using a process-based phenology model developed for the Pinot Noir grape. Our results reveal that temperatures as high as those reached in the 1990s have occurred several times in Burgundy since 1370. However, the summer of 2003 appears to have been extraordinary, with temperatures that were probably higher than in any other year since 1370.

Between Michel Foucault and Erving Goffman: between discourse in the abstract and face-to-face interaction

Abstract: Michel Foucault's ‘archaeology’ and Erving Goffman's interpersonal sociology are complementary. Both are essential for understanding how classifications of people interact with the people classified, and hence for the author's studies of ‘making up people’. The paper begins by explaining how that project is rooted in an ‘existentialist’ conception of the person. It then uses Goffman's Asylums and Foucault's Folie et deraison - both published in 1961 - to illustrate how these methodologies reinforce each other.

Drops on a conical wire

Abstract: We study experimentally the behaviour of a drop deposited on a conical fibre. It is shown that for wetting liquids, such a drop spontaneously moves towards the region of lower curvature. The driving force is measured and shown to be a gradient of Laplace pressure, which allows us to characterize the dynamics of these self-propelling drops. We conclude by discussing the efficiency of this device for drying a solid initially coated with a liquid film.

Epithelial Bmpr1a regulates differentiation and proliferation in postnatal hair follicles and is essential for tooth development.

Abstract: Bone morphogenetic protein (BMP) signaling is thought to perform multiple functions in the regulation of skin appendage morphogenesis and the postnatal growth of hair follicles. However, definitive genetic evidence for these roles has been lacking. Here, we show that Cre-mediated mutation of the gene encoding BMP receptor 1A in the surface epithelium and its derivatives causes arrest of tooth morphogenesis and lack of external hair. The hair shaft and hair follicle inner root sheath (IRS) fail to differentiate, and expression of the known transcriptional regulators of follicular differentiation Msx1, Msx2, Foxn1 and Gata3 is markedly downregulated or absent in mutant follicles. Lef1 expression is maintained, but nuclear beta-catenin is absent from the epithelium of severely affected mutant follicles, indicating that activation of the WNT pathway lies downstream of BMPR1A signaling in postnatal follicles. Mutant hair follicles fail to undergo programmed regression, and instead continue to proliferate, producing follicular cysts and matricomas. These results provide definitive genetic evidence that epithelial Bmpr1a is required for completion of tooth morphogenesis, and regulates terminal differentiation and proliferation in postnatal hair follicles.

Reference Frames for Spatial Cognition: Different Brain Areas are Involved in Viewer-, Object-, and Landmark-Centered Judgments About Object Location

Abstract: Functional magnetic resonance imaging was used to compare the neural correlates of three different types of spatial coding, which are implicated in crucial cognitive functions of our everyday life, such as visuomotor coordination and orientation in topographical space. By manipulating the requested spatial reference during a task of relative distance estimation, we directly compared viewer-centered, object-centered, and landmark-centered spatial coding of the same realistic 3-D information. Common activation was found in bilateral parietal, occipital, and right frontal premotor regions. The retrosplenial and ventromedial occipital–temporal cortex (and parts of the parietal and occipital cortex) were significantly more activated during the landmark-centered condition. The ventrolateral occipital–temporal cortex was particularly involved in object-centered coding. Results strongly demonstrate that viewer-centered (egocentric) coding is restricted to the dorsal stream and connected frontal regions, whereas a coding centered on external references requires both dorsal and ventral regions, depending on the reference being a movable object or a landmark.

First steps in the spreading of a liquid droplet.

Abstract: We describe the first steps of spreading of a liquid droplet brought in contact with a solid that it wets completely. Usually, it is assumed that the dynamics of the droplet results from a balance between the spreading forces and viscosity. But before this classical stage, inertia resists to the motion, which leads to a very different dynamic law. We study experimentally the nature of this law, compare our results with recent theoretical predictions, and determine the duration of this inertial regime.

Early Taming of the Cat in Cyprus

Abstract: It is generally accepted that cats were first domesticated in ancient Egypt ([ 1 ][1]–[ 3 ][2]), at the latest by the 20th to 19th century B.C. (Middle Kingdom, 12th dynasty) ([ 4 ][3]). However, several finds from Cyprus suggest that the origins of cat taming were earlier. A cat mandible at the

Wetting transitions on rough surfaces

Abstract: We consider microscopic contact states of a drop deposited on textured rough surfaces. The energies of three possible (meta)stable wetting states are compared and the lowest energy state is regarded as the "phase". We present the "phase diagrams" in the two-dimensional space of texture parameters, which suggests transitions between the wetting states. We propose a model which allows the description of transition states between (meta)stable contact states and quantify the energy barriers between them. Thereby, we theoretically suggest that the actually realized state is not always the lowest energy state.

In vivo activation of PPAR target genes by RXR homodimers

Abstract: The ability of a retinoid X receptor (RXR) to heterodimerize with many nuclear receptors, including LXR, PPAR, NGF1B and RAR, underscores its pivotal role within the nuclear receptor superfamily. Among these heterodimers, PPAR:RXR is considered an important signalling mediator of both PPAR ligands, such as fatty acids, and 9-cis retinoic acid (9-cis RA), an RXR ligand. In contrast, the existence of an RXR/9-cis RA signalling pathway independent of PPAR or any other dimerization partner remains disputed. Using in vivo chromatin immunoprecipitation, we now show that RXR homodimers can selectively bind to functional PPREs and induce transactivation. At the molecular level, this pathway requires stabilization of the homodimer–DNA complexes through ligand-dependent interaction with the coactivator SRC1 or TIF2. This pathway operates both in the absence and in the presence of PPAR, as assessed in cells carrying inactivating mutations in PPAR genes and in wild-type cells. In addition, this signalling pathway via PPREs is fully functional and can rescue the severe hypothermia phenotype observed in fasted PPARα−/− mice. These observations have important pharmacological implications for the development of new rexinoid-based treatments.

Inactivation of the glucocorticoid receptor in hepatocytes leads to fasting hypoglycemia and ameliorates hyperglycemia in streptozotocin-induced diabetes mellitus.

Abstract: Hepatic glucose production by gluconeogenesis is the main source of glucose during fasting and contributes significantly to hyperglycemia in diabetes mellitus. Accordingly, glucose metabolism is tightly controlled by a variety of hormones including insulin, epinephrine, glucagon, and glucocorticoids (GCs) acting on various cell types. GC effects are mediated by the GC receptor (GR), a ligand-dependent transcription factor, which in the liver and kidney controls gluconeogenesis by induction of gluconeogenic enzymes. To specifically study the contribution of GC on liver carbohydrate metabolism, we generated mice with an inactivation of the GR gene exclusively in hepatocytes using the Cre/loxP technology. Half of the mutant mice die within the first 2 d after birth most likely due to hypoglycemia. Adult mice have normal blood sugar under basal conditions but show hypoglycemia after prolonged starvation due to reduced expression of genes involved in gluconeogenesis. We further demonstrate that absence of GR in hepatocytes limits the development of hyperglycemia in streptozotocin-induced diabetes mellitus probably due to impaired induction of gluconeogenesis. These findings show the essential role of GR function in liver glucose metabolism during fasting and in diabetic mice and indicate that liver-specific GC antagonists could be beneficial in control of diabetic hyperglycemia.

Influence of the hippocampus on interneurons of the rat prefrontal cortex.

Abstract: The hippocampus and prefrontal cortex (PFC), two structures implicated in learning and memory processes, are linked by a direct hippocampo-prefrontal pathway. It has been shown that PFC pyramidal cells receive monosynaptic excitatory inputs from the hippocampus and, in this study, we sought to determine the influence of the hippocampus on PFC interneurons in anesthetized rats. Extracellular recordings were coupled to juxtacellular injections of neurobiotin or biotinylated dextran amine to morphologically differentiate interneurons from pyramidal cells. In all cases, the action potentials of labeled interneurons were of shorter duration ( 0.70 ms). Single pulse stimulation of the hippocampal CA1/subiculum region induced an excitatory response in 70% of recorded interneurons in the prelimbic and medial-orbital areas of the PFC. In contrast to the one to two action potentials generated by pyramidal cells, an important group of interneurons fired a burst of action potentials in response to hippocampal stimulation. A large proportion of these excitatory responses was probably monosynaptic as their latency is consistent with the conduction time of the hippocampo-prefrontal pathway. In addition, when both a pyramidal cell and an interneuron were simultaneously recorded and both responded to stimulation, the interneuron consistently fired before the pyramidal cell. In conclusion, the hippocampus exerts a direct excitatory influence on PFC interneurons and is thus capable of feedforward inhibition of pyramidal cells. Hippocampal output is spatially and temporally focalized via this inhibitory process and consequently could facilitate the synchronization of a specific subset of PFC neurons with hippocampal activity.

Growth in small dinosaurs and pterosaurs: the evolution of archosaurian growth strategies

Abstract: Histological evidence of the bones of pterosaurs and dinosaurs indicates that the typically large forms of these groups grew at rates more comparable to those of birds and mammals than to those of other living reptiles. However, Scutellosaurus, a small, bipedal, basal thyreophoran ornithischian dinosaur of the Early Jurassic, shows histological features in its skeletal tissues that suggest relatively lower growth rates than in those of larger dinosaurs. In these respects Scutellosaurus, like other small dinosaurs such as Orodromeus and some basal birds, is more like young, rapidly growing crocodiles than larger, more derived ornithischians (hadrosaurs) and all saurischians (sauropods and theropods). Similar patterns can be seen in small, mostly basal pterosaurs such as Eudimorphodon and Rhamphorhynchus. However, superficial similarities to crocodile bone growth belie some important differences, which are most usefully interpreted in phylogenetic and ontogenetic contexts. Large size evolved second...

5‐HT2A and α1b‐adrenergic receptors entirely mediate dopamine release, locomotor response and behavioural sensitization to opiates and psychostimulants

Abstract: Addictive properties of drugs of misuse are generally considered to be mediated by an increased release of dopamine (DA) in the ventral striatum. However, recent experiments indicated an implication of alpha1b-adrenergic receptors in behavioural responses to psychostimulants and opiates. We show now that DA release induced in the ventral striatum by morphine (20 mg/kg) is completely blocked by prazosin (1 mg/kg), an alpha1-adrenergic antagonist. However, morphine-induced increases in DA release in the ventral striatum were found to be similar in mice deleted for the alpha1b-adrenergic receptor (alpha1b-AR KO) and in wild-type (WT) mice, suggesting the presence of a compensatory mechanism. This acute morphine-evoked DA release was completely blocked in alpha1b-AR KO mice by SR46349B (1 mg/kg), a 5-HT2A antagonist. SR46349B also completely blocked, in alpha1b-AR KO mice, the locomotor response and the development of behavioural sensitization to morphine (20 mg/kg) and D-amphetamine (2 mg/kg). Accordingly, the concomitant blockade of 5-HT2A and alpha1b-adrenergic receptors in WT mice entirely blocked acute locomotor responses but also the development of behavioural sensitization to morphine, D-amphetamine or cocaine (10 mg/kg). We observed, nevertheless, that inhibitory effects of each antagonist on locomotor responses to morphine or D-amphetamine were more than additive (160%) in naive WT mice but not in those sensitized to either drug. Because of these latter data and the possible compensation by 5-HT2A receptors for the genetic deletion of alpha1b-adrenergic receptors, we postulate the existence of a functional link between these receptors, which vanishes during the development of behavioural sensitization.

Functional dissociation of apelin receptor signaling and endocytosis: implications for the effects of apelin on arterial blood pressure

Abstract: Apelin is a novel neuropeptide involved in the regulation of body fluid homeostasis and cardiovascular functions. It acts through a G protein-coupled receptor, the APJ receptor. We studied the structure-activity relationships of apelin at the rat apelin receptor, tagged at its C-terminal end with enhanced green fluorescent protein and stably expressed in CHO cells. We evaluated the potency of N- and C-terminal deleted fragments of K17F to bind with high affinity to the apelin receptor, and to inhibit cAMP production and to induce apelin receptor internalization. We first characterized the internalization and trafficking of the rat apelin receptor. This receptor was internalized via a clathrin-dependent mechanism and our results suggest that receptor trafficking may follow a recycling pathway. We then tried to identify the amino acids of K17F required for apelin activity. The first five N-terminal and the last two C-terminal amino acids of K17F were not essential for apelin binding or the inhibition of cAMP production. However, the full-length sequence of K17F was the most potent inducer of apelin receptor internalization because successive N-terminal amino-acid deletions progressively reduced internalization and the removal of a single amino acid at the C-terminus abolished this process. Finally, the most novel observation of this work is that hypotensive actions of apelin peptides correlate best with the ability of those ligands to internalize. Thus, apelin receptor signaling and endocytosis are functionally dissociated, possibly reflecting the existence of several conformational states of this receptor, stabilized by the binding of different apelin fragments to the apelin receptor.

The First IBIS/ISGRI Soft Gamma-Ray Galactic Plane Survey Catalog*

Abstract: We report the first high-energy survey catalog obtained with the IBIS gamma-ray imager on board INTEGRAL. The analysis has been performed on the first-year Core Program ISGRI data comprising both Galactic Plane Scan and Galactic Centre Deep Exposure pointings for a total exposure time exceeding 5 Ms. This initial survey has revealed the presence of ~120 sources detected with the unprecedented sensitivity of ~1 mcrab in the energy range 20-100 keV. Each source is located to an accuracy between 1' and 3', depending on its brightness. The outstanding IBIS capability to locate soft γ-ray emitters has allowed us to identify most of the detected sources with already known Galactic X-ray binary systems, while 28 of the objects are of unknown nature.

External and Internal Morphology of the BAR 1002'00 Orrorin tugenensis Femur

Abstract: Late Miocene fossils from the Lukeino Formation in Kenya's Tugen Hills are assigned to Orrorin tugenensis. Of 20 fossils recovered there to date, 3 are proximal femurs. One of these, BAR 1002'00, preserves an intact head connected to the proximal shaft by an elongated neck. Although this fossil is comparable in size to Pan troglodytes, computerized tomography scans of the neck-shaft junction of BAR 1002'00 reveal that the cortex is markedly thinner superiorly than inferiorly, differing from the approximately equal cortical thicknesses observed in extant African apes, approaching the condition in later hominids, and indicating that O. tugenensis was bipedal.

Calibration of cameras of the H.E.S.S. detector.

Abstract: H.E.S.S.—the high energy stereoscopic system—is a new system of large atmospheric Cherenkov telescopes for GeV/TeV astronomy. Each of the four telescopes of 107 m2 mirror area is equipped with a 960-pixel photomultiplier-tube camera. This paper describes the methods used to convert the photomultiplier signals into the quantities needed for Cherenkov image analysis. Two independent calibration techniques have been applied in parallel to provide an estimation of uncertainties. Results on the long-term stability of the H.E.S.S. cameras are also presented.

Capturing drops with a thin fiber

Abstract: We study experimentally the dynamics of drops impacting horizontal fibers and characterize the ability of these objects to capture the drops. We first show that a drop larger than a critical radius cannot be trapped by a fiber whatever its velocity. We determine this critical size as a function of the fiber radius. Then we show that for smaller drops, different situations can occur: at a low impact velocity, the drop is entirely captured by the fiber, whereas some liquid is ejected when arriving faster. We quantify the threshold velocity of capture.

Renin and angiotensinogen expression and functions in growth and apoptosis of human glioblastoma

Abstract: The expression and function in growth and apoptosis of the renin–angiotensin system (RAS) was evaluated in human glioblastoma. Renin and angiotensinogen (AGT) mRNAs and proteins were found by in situ hybridisation and immunohistochemistry in glioblastoma cells. Angiotensinogen was present in glioblastoma cystic fluids. Thus, human glioblastoma cells produce renin and AGT and secrete AGT. Human glioblastoma and glioblastoma cells expressed renin, AGT, renin receptor, AT2 and/or AT1 mRNAs and proteins determined by RT–PCR and/or Western blotting, respectively. The function of the RAS in glioblastoma was studied using human glioblastoma cells in culture. Angiotensinogen, des(Ang I)AGT, tetradecapaptide renin substrate (AGT1–14), Ang I, Ang II or Ang III, added to glioblastoma cells in culture, did not modulate their proliferation, survival or death. Angiotensin-converting enzyme inhibitors did not diminish glioblastoma cell proliferation. However, the addition of selective synthetic renin inhibitors to glioblastoma cells decreased DNA synthesis and viable tumour cell number, and induced apoptosis. This effect was not counterbalanced by concomitant addition of Ang II. In conclusion, the complete RAS is expressed by human glioblastomas and glioblastoma cells in culture. Inhibition of renin in glioblastoma cells may be a potential approach to control glioblastoma cell proliferation and survival, and glioblastoma progression in combination therapy.

CYCLIC COHOMOLOGY, QUANTUM GROUP SYMMETRIES AND THE LOCAL INDEX FORMULA FOR SU q (2)

Abstract: We analyse the non-commutative space underlying the quantum group -symmetry. We shall explain how this naturally leads to the general concept of invariant cyclic cohomology in the framework of quantum group symmetries.AMS 2000 Mathematics subject classification: Primary 81R50; 19K33; 46L; 58B34

First detection of polarization of the submillimetre diffuse galactic dust emission by Archeops

Abstract: We present the first determination of the Galactic polarized emission at 353 GHz by Archeops. The data were taken during the Arctic night of February 7, 2002 after the balloon--borne instrument was launched by CNES from the Swedish Esrange base near Kiruna. In addition to the 143 GHz and 217 GHz frequency bands dedicated to CMB studies, Archeops had one 545 GHz and six 353 GHz bolometers mounted in three polarization sensitive pairs that were used for Galactic foreground studies. We present maps of the I, Q, U Stokes parameters over 17% of the sky and with a 13 arcmin resolution at 353 GHz (850 microns). They show a significant Galactic large scale polarized emission coherent on the longitude ranges [100, 120] and [180, 200] deg. with a degree of polarization at the level of 4-5%, in agreement with expectations from starlight polarization measurements. Some regions in the Galactic plane (Gem OB1, Cassiopeia) show an even stronger degree of polarization in the range 10-20%. Those findings provide strong evidence for a powerful grain alignment mechanism throughout the interstellar medium and a coherent magnetic field coplanar to the Galactic plane. This magnetic field pervades even some dense clouds. Extrapolated to high Galactic latitude, these results indicate that interstellar dust polarized emission is the major foreground for PLANCK-HFI CMB polarization measurement.