Effets de la collision "ride des Loyauté - arc des Nouvelles-Hébrides" sur la terminaison sud de l'ensemble "Nouvelle Calédonie - Loyauté"

Les données de bathymétrie multifaisceaux et de géophysique de la campagne ZoNéCo 1 révèlent, au niveau du prolongement sud des rides de Nouvelle-Calédonie et des Loyauté, la présence de trois directions structurales et de deux phases volcaniques majeures. La direction WSW-ENE se retrouve sur l'ensemble de la zone "ride de Norfolk-bassin et ride des Loyauté" sous la forme de décrochements sénestres. La direction NNW-SSE est caractérisée par un réseau de failles normales. La direction SSW-NNE est présente au Sud de 24°40'S le long de la ride de Norfolk et s'exprime, sur la ride des Loyauté, par des failles normales et des décrochements dextres localisés. La première phase volcanique, ayant généré les guyots qui forment le substratum des deux rides, est vraisemblablement d'âge Oligocène-Miocène inférieur. La seconde phase, qui s'exprime par des volcans non érodés, pourrait être postérieure à la surrection Miocène supérieur-Pliocène. Les décrochements sénestres WSW-ENE qui découpent la plaque australienne sont interprétés comme résultant de la collision active "Loyauté - Nouvelles-Hébrides", l'arc des Nouvelles-Hébrides se comportant comme un poinçon rigide. (Résumé d'auteur

Jean Charcot Seabeam Survey along ODP Leg 112 Northern Transect

A marine geophysical survey that used Seabeam, multi- and single-channel seismic reflection, gravity, and magnetic profiling was conducted in two locations along the landward slope of the Peru Trench. This survey was conducted during the SeaPERC cruise of the Jean Charcot in July 1986 (Bourgois et al., 1986a; Bourgois et al., 1986b; Bourgois et al., 1987; Bourgois et al., in press). These areas were two possible drilling locations for ODP Leg 112, which was scheduled to begin in November 1986. The drilling transects center around latitudes of 5°30'S and 9°30'S, along multichannel seismic lines CDP-3 and CDP-2, respectively. The northern transect is located in the Paita Zone (Fig. 1, Box 2), and the southern transect is in the Chimbote Zone (Fig. 1, Box 6). During Leg 112, we drilled two sites (683 and 685) in the Chimbote area. This became the northern transect of Leg 112. Here, we report the Seabeam data acquired during the SeaPERC cruise. Drilling results from Sites 683 and 685, the CDP-2 multichannel seismic record, and the Seabeam data provide a threedimensional view of this region

Seabeam and seismic reflection imaging of the tectonic regime of the Andean continental margin off Peru (4°S to 10°S)

Suite à une campagne géophysique réalisée au large de la côte du Perou (croisière Seaperc du R/V "Jean Charcot", juillet 1986), les auteurs proposent une nouvelle interprétation des structures caractérisant la pente continentale de la région étudiée. D'autre part, ils considèrent que cette marge active est une marge active en extension ou bien une marge d'effondrement qui développe un complexe d'accrétion induit par les effondrements de la partie médiane de la pente

Etude morphostructurale de la zone sud des rides Nouvelle-Calédonie et Loyauté (Zone Economique Exclusive de Nouvelle-Calédonie, Pacifique Sud-Ouest)

Les données de la campagne ZoNéCo 1 permettent de préciser la morphostructure du Sud des rides calédonienne et Loyauté qui s'avèrent plus complexes que les cartes précédentes ne le montraient, mais on retrouve les principales structures de la région Calédonie-Loyauté. L'imagerie met en évidence les zones de roches nues ou encroûtées, la présence d'écoulements gravitaires du Sud du bassin des Loyauté vers le bassin Sud-Fidjien. (Résumé d'auteur

Colloids as Mobile Substrates for the Implantation and Integration of Differentiated Neurons into the Mammalian Brain

Neuronal degeneration and the deterioration of neuronal communication lie at the origin of many neuronal disorders, and there have been major efforts to develop cell replacement therapies for treating such diseases. One challenge, however, is that differentiated cells are challenging to transplant due to their sensitivity both to being uprooted from their cell culture growth support and to shear forces inherent in the implantation process. Here, we describe an approach to address these problems. We demonstrate that rat hippocampal neurons can be grown on colloidal particles or beads, matured and even transfected in vitro, and subsequently transplanted while adhered to the beads into the young adult rat hippocampus. The transplanted cells have a 76% cell survival rate one week post-surgery. At this time, most transplanted neurons have left their beads and elaborated long processes, similar to the host neurons. Additionally, the transplanted cells distribute uniformly across the host hippocampus. Expression of a fluorescent protein and the light-gated glutamate receptor in the transplanted neurons enabled them to be driven to fire by remote optical control. At 1-2 weeks after transplantation, calcium imaging of host brain slice shows that optical excitation of the transplanted neurons elicits activity in nearby host neurons, indicating the formation of functional transplant-host synaptic connections. After 6 months, the transplanted cell survival and overall cell distribution remained unchanged, suggesting that cells are functionally integrated. This approach, which could be extended to other cell classes such as neural stem cells and other regions of the brain, offers promising prospects for neuronal circuit repair via transplantation of in vitro differentiated, genetically engineered neurons

A Strawberry KNOX Gene Regulates Leaf, Flower and Meristem Architecture

The KNOTTED-LIKE HOMEODOMAIN (KNOX) genes play a central role in maintenance of the shoot apical meristem. They also contribute to the morphology of simple and compound leaves. In this report we characterize the FaKNOX1 gene from strawberry (Fragaria spp.) and demonstrate its function in trasgenic plants. The FaKNOX1 cDNA was isolated from a cultivated strawberry (F.×ananassa) flower EST library. The sequence is most similar to Class I KNOX genes, and was mapped to linkage group VI of the diploid strawberry genome. Unlike most KNOX genes studied, steady-state transcript levels were highest in flowers and fruits. Transcripts were also detected in emerging leaf primordia and the apical dome. Transgenic strawberry plants suppressing or overexpressing FaKNOX1 exhibited conspicuous changes in plant form. The FaKNOX1 RNAi plants presented a dwarfed phenotype with deeply serrated leaflets and exaggerated petiolules. They also exhibited a high level of cellular disorganization of the shoot apical meristem and leaves. Overexpression of FaKNOX1 caused dwarfed stature with wrinkled leaves. These gain- and loss-of-function assays in strawberry functionally demonstrate the contributions of a KNOX domain protein in a rosaceous species

From 2D to 3D: novel nanostructured scaffolds to investigate signalling in reconstructed neuronal networks

To recreate in vitro 3D neuronal circuits will ultimately increase the relevance of results from cultured to whole-brain networks and will promote enabling technologies for neuro-engineering applications. Here we fabricate novel elastomeric scaffolds able to instruct 3D growth of living primary neurons. Such systems allow investigating the emerging activity, in terms of calcium signals, of small clusters of neurons as a function of the interplay between the 2D or 3D architectures and network dynamics. We report the ability of 3D geometry to improve functional organization and synchronization in small neuronal assemblies. We propose a mathematical modelling of network dynamics that supports such a result. Entrapping carbon nanotubes in the scaffolds remarkably boosted synaptic activity, thus allowing for the first time to exploit nanomaterial/cell interfacing in 3D growth support. Our 3D system represents a simple and reliable construct, able to improve the complexity of current tissue culture models

Self-Organizing Circuit Assembly through Spatiotemporally Coordinated Neuronal Migration within Geometric Constraints

Neurons are dynamically coupled with each other through neurite-mediated adhesion during development. Understanding the collective behavior of neurons in circuits is important for understanding neural development. While a number of genetic and activity-dependent factors regulating neuronal migration have been discovered on single cell level, systematic study of collective neuronal migration has been lacking. Various biological systems are shown to be self-organized, and it is not known if neural circuit assembly is self-organized. Besides, many of the molecular factors take effect through spatial patterns, and coupled biological systems exhibit emergent property in response to geometric constraints. How geometric constraints of the patterns regulate neuronal migration and circuit assembly of neurons within the patterns remains unexplored.We established a two-dimensional model for studying collective neuronal migration of a circuit, with hippocampal neurons from embryonic rats on Matrigel-coated self-assembled monolayers (SAMs). When the neural circuit is subject to geometric constraints of a critical scale, we found that the collective behavior of neuronal migration is spatiotemporally coordinated. Neuronal somata that are evenly distributed upon adhesion tend to aggregate at the geometric center of the circuit, forming mono-clusters. Clustering formation is geometry-dependent, within a critical scale from 200 µm to approximately 500 µm. Finally, somata clustering is neuron-type specific, and glutamatergic and GABAergic neurons tend to aggregate homo-philically.We demonstrate self-organization of neural circuits in response to geometric constraints through spatiotemporally coordinated neuronal migration, possibly via mechanical coupling. We found that such collective neuronal migration leads to somata clustering, and mono-cluster appears when the geometric constraints fall within a critical scale. The discovery of geometry-dependent collective neuronal migration and the formation of somata clustering in vitro shed light on neural development in vivo