Object Affordances Tune Observers' Prior Expectations about Tool-Use Behaviors

Learning about the function and use of tools through observation requires the ability to exploit one's own knowledge derived from past experience. It also depends on the detection of low-level local cues that are rooted in the tool's perceptual properties. Best known as ‘affordances’, these cues generate biomechanical priors that constrain the number of possible motor acts that are likely to be performed on tools. The contribution of these biomechanical priors to the learning of tool-use behaviors is well supported. However, it is not yet clear if, and how, affordances interact with higher-order expectations that are generated from past experience – i.e. probabilistic exposure – to enable observational learning of tool use. To address this question we designed an action observation task in which participants were required to infer, under various conditions of visual uncertainty, the intentions of a demonstrator performing tool-use behaviors. Both the probability of observing the demonstrator achieving a particular tool function and the biomechanical optimality of the observed movement were varied. We demonstrate that biomechanical priors modulate the extent to which participants' predictions are influenced by probabilistically-induced prior expectations. Biomechanical and probabilistic priors have a cumulative effect when they ‘converge’ (in the case of a probabilistic bias assigned to optimal behaviors), or a mutually inhibitory effect when they actively ‘diverge’ (in the case of probabilistic bias assigned to suboptimal behaviors)

A High Throughput Genetic Screen Identifies New Early Meiotic Recombination Functions in Arabidopsis thaliana

Meiotic recombination is initiated by the formation of numerous DNA double-strand breaks (DSBs) catalysed by the widely conserved Spo11 protein. In Saccharomyces cerevisiae, Spo11 requires nine other proteins for meiotic DSB formation; however, unlike Spo11, few of these are conserved across kingdoms. In order to investigate this recombination step in higher eukaryotes, we took advantage of a high-throughput meiotic mutant screen carried out in the model plant Arabidopsis thaliana. A collection of 55,000 mutant lines was screened, and spo11-like mutations, characterised by a drastic decrease in chiasma formation at metaphase I associated with an absence of synapsis at prophase, were selected. This screen led to the identification of two populations of mutants classified according to their recombination defects: mutants that repair meiotic DSBs using the sister chromatid such as Atdmc1 or mutants that are unable to make DSBs like Atspo11-1. We found that in Arabidopsis thaliana at least four proteins are necessary for driving meiotic DSB repair via the homologous chromosomes. These include the previously characterised DMC1 and the Hop1-related ASY1 proteins, but also the meiotic specific cyclin SDS as well as the Hop2 Arabidopsis homologue AHP2. Analysing the mutants defective in DSB formation, we identified the previously characterised AtSPO11-1, AtSPO11-2, and AtPRD1 as well as two new genes, AtPRD2 and AtPRD3. Our data thus increase the number of proteins necessary for DSB formation in Arabidopsis thaliana to five. Unlike SPO11 and (to a minor extent) PRD1, these two new proteins are poorly conserved among species, suggesting that the DSB formation mechanism, but not its regulation, is conserved among eukaryotes

Genèse du nouveau master « Histoire des sciences et techniques, humanités numériques et médiations culturelles » : de l'articulation entre la recherche et la formation au Centre François Viète de l'Université de Bretagne Occidentale

L'objet de cet article est de montrer comment la dynamique de création simultanée, à Brest et depuis 2008, d'une nouvelle équipe de recherche et d'un nouveau master recherche à distance en 2012 s'est traduit par une proposition originale de formation par la recherche. Nous détaillons les spécificités de cette dernière. D'une part, elle prend fortement appui sur des axes de recherches et des nouvelles méthodologies en histoire des sciences et des techniques, qui s'inspirent des travaux sur la culture matérielle et la compréhension des systèmes complexes. En outre, nous montrons que des questions de recherche et de formation y sont intégrées concernant le développement ou l'usage des outils numériques (web sémantique, réalité virtuelle ou augmentée, etc.) pour la recherche en SHS et médiations culturelles. L'équipe de Brest s'inscrit de ce fait dans le champ des travaux de recherches en humanités numériques en très forte collaboration avec notamment des laboratoires d'informatique. Au travers des thématiques traitées, des méthodologies enseignées, d'une pédagogie universitaire basée sur une classe virtuelle ainsi que de la nature des différents partenaires qui y enseignent, nous montrons ainsi que le master en question constituent un laboratoire où il est possible d'expérimenter de nouvelles pratiques de formation par la recherche

Genèse du nouveau master « Histoire des sciences et techniques, humanités numériques et médiations culturelles » : de l'articulation entre la recherche et la formation au Centre François Viète de l'Université de Bretagne Occidentale

L'objet de cet article est de montrer comment la dynamique de création simultanée, à Brest et depuis 2008, d'une nouvelle équipe de recherche et d'un nouveau master recherche à distance en 2012 s'est traduit par une proposition originale de formation par la recherche. Nous détaillons les spécificités de cette dernière. D'une part, elle prend fortement appui sur des axes de recherches et des nouvelles méthodologies en histoire des sciences et des techniques, qui s'inspirent des travaux sur la culture matérielle et la compréhension des systèmes complexes. En outre, nous montrons que des questions de recherche et de formation y sont intégrées concernant le développement ou l'usage des outils numériques (web sémantique, réalité virtuelle ou augmentée, etc.) pour la recherche en SHS et médiations culturelles. L'équipe de Brest s'inscrit de ce fait dans le champ des travaux de recherches en humanités numériques en très forte collaboration avec notamment des laboratoires d'informatique. Au travers des thématiques traitées, des méthodologies enseignées, d'une pédagogie universitaire basée sur une classe virtuelle ainsi que de la nature des différents partenaires qui y enseignent, nous montrons ainsi que le master en question constituent un laboratoire où il est possible d'expérimenter de nouvelles pratiques de formation par la recherche

Multi-method investigation of mass transfer mechanisms in a retrogressive clayey landslide (Harmalière, French Alps)

International audienceThe mass transfer mechanisms in landslides are complex to monitor because of their suddenness and spatial coverage. The active clayey Harmalière landslide, located 30 km south of Grenoble in the French Alps, exhibits two types of behavior: in its upper part, decameter-sized clay blocks slide along a listric slip surface, while a flow-like mechanism is observed in a clayey remolded material a few hundred meters below the headscarp. The landslide underwent a major retrogression affecting 45 ha in March 1981 and has experienced multiple reactivations since then. The last major event took place on the 26th of June 2016, and a large investigation survey was conducted to better understand the reactivation mechanism. A multi-method investigation was carried out at different temporal and spatial scales, including aerial photograph and light detection and ranging processing, correlation of optical satellite images, global navigation satellite system monitoring, continuous seismic monitoring, and passive seismic survey. The morphological evolution of the landslide was traced over the last 70 years, showing a headscarp retrogression of 700 m during multiple reactivations and a total mass transfer of more than 6 × 106 m3. The detailed study of the 2016 event allowed to track and understand the mechanism of a mass transfer of 1 × 106 m3 in 5 weeks, from a sliding mechanism at the headscarp to an earthflow at the toe

Xylan degradation by the human gut Bacteroides xylanisolvens XB1A(T) involves two distinct gene clusters that are linked at the transcriptional level

International audienceBackgroundPlant cell wall (PCW) polysaccharides and especially xylans constitute an important part of human diet. Xylans are not degraded by human digestive enzymes in the upper digestive tract and therefore reach the colon where they are subjected to extensive degradation by some members of the symbiotic microbiota. Xylanolytic bacteria are the first degraders of these complex polysaccharides and they release breakdown products that can have beneficial effects on human health. In order to understand better how these bacteria metabolize xylans in the colon, this study was undertaken to investigate xylan breakdown by the prominent human gut symbiont Bacteroides xylanisolvens XB1AT.ResultsTranscriptomic analyses of B. xylanisolvens XB1AT grown on insoluble oat-spelt xylan (OSX) at mid- and late-log phases highlighted genes in a polysaccharide utilization locus (PUL), hereafter called PUL 43, and genes in a fragmentary remnant of another PUL, hereafter referred to as rPUL 70, which were highly overexpressed on OSX relative to glucose. Proteomic analyses supported the up-regulation of several genes belonging to PUL 43 and showed the important over-production of a CBM4-containing GH10 endo-xylanase. We also show that PUL 43 is organized in two operons and that the knockout of the PUL 43 sensor/regulator HTCS gene blocked the growth of the mutant on insoluble OSX and soluble wheat arabinoxylan (WAX). The mutation not only repressed gene expression in the PUL 43 operons but also repressed gene expression in rPUL 70.ConclusionThis study shows that xylan degradation by B. xylanisolvens XB1AT is orchestrated by one PUL and one PUL remnant that are linked at the transcriptional level. Coupled to studies on other xylanolytic Bacteroides species, our data emphasize the importance of one peculiar CBM4-containing GH10 endo-xylanase in xylan breakdown and that this modular enzyme may be used as a functional marker of xylan degradation in the human gut. Our results also suggest that B. xylanisolvens XB1AT has specialized in the degradation of xylans of low complexity. This functional feature may provide a niche to all xylanolytic bacteria harboring similar PULs. Further functional and ecological studies on fibrolytic Bacteroides species are needed to better understand their role in dietary fiber degradation and their impact on intestinal health