Using microstructures and composition to decipher the alterations of rodent teeth in modern regurgitation pellets—a good news-bad news story

Rodent accumulations are widely used for palaeoenvironmental reconstructions. But these accumulations are created through the activity of predators (carnivorous mammals, birds of prey), the predation and digestion of which modify the preservation of bones and teeth. The microstructures of dentine and enamel, as well as the mineralogy and composition of non-digested and digested Rodent teeth extracted from modern regurgitation pellets collected at Olduvai (Tanzania) from a bird of prey (Bubo sp.) are compared. Scanning electron microscopy (SEM), Electron Probe Micro Analysis (EPMA) and Raman spectrometry were used. The modifications induced by the digestion process are variable and depend on the tissue (enamel, dentine), tooth (incisor, molar) and the predator. For a given tissue of a tooth, the estimation of the intensity of the alteration varies according to the selected criteria. To classify the digested teeth in categories based on a single parameter to reconstruct environment is still subjective, even for modern accumulations. Moreover, to identify the interplay of diverse parameters to avoid biases in reconstructions is difficult

The Environment Recording Unit in coral skeletons – a synthesis of structural and chemical evidences for a biochemically driven, stepping-growth process in fibres

International audienceThis paper gathers a series of structural and biochemical in situ characterizations carried out to improve our knowledge of the fine scale growth patterns of fibres in coral skeletons. The resulting data show a clear correspondence between the mineral subunits of fibres and the spatial distribution of organic macromolecules. New observations using atomic force microscope confirm the close relationship between mineral and organic phases at the nanometre scale. Synthesis of these data results in a significant change in our concept of the mineralization process in coral skeletons. In contrast to the usual view of an aggregate of purely mineral units independently growing by simple chemical precipitation, coral fibres appear to be fully controlled structures. Their growth process is based on cyclic secretion of mineralizing compounds by the polyp basal ectoderm. These biochemical components of the coral fibres, in which sulfated acidic proteoglycans probably play a major role, are repeatedly produced (proteoglycans are those glycoproteins whose carbohydrate moieties consist of long unbranched chains of sulfated amino sugars). This results in a stepping growth mode of fibres and a layered global organization of coral skeletons. Therefore, in contrast to the widely accepted geochemical interpretation, we propose a fibre growth model that places coral skeletons among the typical ''matrix mediated'' structures. The crystal-like fibres are built by superimposition of few micron-thick growth layers. A biomineralization cycle starts by the secretion of a mineralizing matrix and the final step is the crystallization phase, during which mineral material grows onto the organic framework. Thus, each growth layer is the actual Environment Recording Unit. From a practical standpoint, these results may contribute to develop a new high resolution approach of the environment recording by coral skeletons

The environment recording unit in coral skeletons: structural and chemical evidences of a biochemically driven stepping-growth process in coral fibres

International audienceTo improve our understanding of the environment recording by scleractinian corals, a detailed study of the skeleton microstructure has been carried out. A series of physico-chemical in situ characterizations was made, an approach that provides us with structural and biochemical information at the micrometric and nanometric scales. Gathering of these data results in a significant change in our concept of the growth of coral skeletons. In contrast to the usual view of an aggregate of purely mineral units (the coral fibres) independently growing by a simple chemical precipitation, coral skeletons appear to be biochemically controlled structures. Both structural and biochemical data reveal the micron-scaled stepping growth-mode of fibres, and its global coordination. In this process, sulfated acidic proteoglycans probably play a major role, due to their ability to create polymeric frameworks. Atomic force microscopy confirms the close relationship of organic and mineral phases at the nanometric scale. A new microstructural model of coral skeleton formation is proposed, that places coral skeletons among the typical "matrix mediated structures". From a practical standpoint, these results may contribute to develop a new high resolution approach in the study of paleoenvironments

Oxygen isotope equilibrium in brachiopod shell fibres in the context of biological control

No abstract available

Generation and Applications of Human Pluripotent Stem Cells Induced into Neural Lineages and Neural Tissues

Human pluripotent stem cells (hPSCs) represent a new and exciting field in modern medicine, now the focus of many researchers and media outlets. The hype is well-earned because of the potential of stem cells to contribute to disease modeling, drug screening, and even therapeutic approaches. In this review, we focus first on neural differentiation of these cells. In a second part we compare the various cell types available and their advantages for in vitro modeling. Then we provide a “state-of-the-art” report about two major biomedical applications: (1) the drug and toxicity screening and (2) the neural tissue replacement. Finally, we made an overview about current biomedical research using differentiated hPSCs

The cuttlefish Sepia officinalis (Sepiidae, Cephalopoda) constructs cuttlebone from a liquid-crystal precursor

Cuttlebone, the sophisticated buoyancy device of cuttlefish, is made of extensive superposed chambers that have a complex internal arrangement of calcified pillars and organic membranes. It has not been clear how this structure is assembled. We find that the membranes result from a myriad of minor membranes initially filling the whole chamber, made of nanofibres evenly oriented within each membrane and slightly rotated with respect to those of adjacent membranes, producing a helical arrangement. We propose that the organism secretes a chitin-protein complex, which self-organizes layer-by-layer as a cholesteric liquid crystal, whereas the pillars are made by viscous fingering. The liquid crystallization mechanism permits us to homologize the elements of the cuttlebone with those of other coleoids and with the nacreous septa and the shells of nautiloids. These results challenge our view of this ultra-light natural material possessing desirable mechanical, structural and biological properties, suggesting that two self-organizing physical principles suffice to understand its formation.Spanish Ministerio de Ciencia e Innovacion [CGL2010-20748-CO2-01, CGL2013-48247-P, FIS2013-48444-C2-2-P]; Andalusian Consejeria de Innovacion Ciencia y Tecnologia [RNM6433]; (Sepiatech, PROMAR program) of the Portuguese Ministerio da Agricultura e do Mar, Portugal [31.03.05.FEP.002]; Junta de Andalucia [RNM363]; FP7 COST Action of the European Community. [TD0903]info:eu-repo/semantics/publishedVersio