It is well-known that the brain can be modified, or is plastic, through lifetime, even in adults. Brain and body injuries can result in life-changing, even devastating physical disability. Previous clinical and basic research studies have shown that the brain can undergo many self-organization processes following brain trauma or body injury, and lead to behavioral and perceptual impairments. However the mechanisms underlying brain plasticity remain largely unknown. There are very important questions that remain unclear in the field of brain plasticity. For example, how fast does plasticity occur' How does plasticity develop over time' Do different cortical layers express plasticity differently' What are the roles of cortical layers in shaping plasticity of other layers' What initiates these changes' What happens to perception and behavioral performance after plasticity occurs' And how can plasticity be regulated' Our research goal aims to address these important questions. A translational animal imaging model can help to bridge the gap between basic and clinical research. In this research proposal, we will utilize rodent MRI, in combination with different neuroscience approaches to study the activity (or experience) determinants of brain plasticity. Using an animal MRI model is critical because it allows investigating mechanistic questions using more invasive manipulations which are not feasible in human studies. Yet, since the same methodology is applied, knowledge obtained from animal fMRI experiments can be directly translated to human research. In addition, we will employ electrophysiology recordings to study neuronal properties, and use neuroanatomy to study neuronal connections because they have been considered the long-held, gold standard approaches to interpret brain functions. The aims of our research are to (1) understand how input activity contributes to cortical-layer specific brain plasticity, (2) investigate the development of brain plasticity, (3) evaluate the functional outcomes of brain plasticity, and (4) formulate strategies to regulate brain plasticity based on our understanding of these mechanisms. A better understanding of the mechanisms underlying brain plasticity is critical to formulate remedial therapy strategies in order to restore brain functions and to improve behavioral performance. To achieve these goals, we will first establish an animal model to study brain plasticity longitudinally. We will employ a multidisciplinary approach, including functional and anatomical MRI, electrophysiology, neuroanatomy and behavior to study altered brain functions and their accompanying perceptual and behavioral outcomes. We will study brain functions with functional MRI and electrophysiology. Particularly, we will examine whether different cortical layers express and maintain plasticity differently, and investigate the interactions between cortical layers and between cortical regions during the plasticity processes. Furthermore, to study the anatomical and cellular basis of these functional changes, we will employ a novel MRI visible tract-tracing compound and various histological staining methods to investigate whether these functional changes are accompanied by anatomical rewiring, and to examine the cellular mechanisms underlying these changes. After gaining a better understanding of the mechanisms underlying brain plasticity, we will perturb neuronal activity to understand the specific role of cortical layers and anatomical connections in mediating plasticity, and will formulate strategies for regulating cortical plasticity by 'turning-on' or 'silencing' the functions of anatomical pathways. Finally we will evaluate animals' behavioral performance after brain plasticity. The completion of this research proposal will yield a better understanding of the principles of brain dynamics, which is critical for developing therapeutic strategies to promote the recovery of cortical functions.

Because of the current and predicted environmental problems, the agronomic conditions for crop production are going to change in a near future. In particular, the yields of future crops must satisfy human needs, but with reduced supplies of fertilizers. Thus, the yields will have to be maintained although the adverse agronomic conditions resulting from reduced inputs of fertilizers. Based on our work with Arabidopsis, our view on the consequences of mineral starvation on plant growth has dramatically changed (Nature Genetics, 2007). The sensing of a low-mineral medium by the root tip seems to trigger a signaling pathway ending with an arrest of the primary root growth, before reduction of the metabolic the activity. Our knowledge about this pathway is very weak and only few mutants have been isolated so far. Until today, the power of classical genetics has been modestly exploited whereas chemical genetics has not been used yet for dissecting this biological process. We propose to dissect this transduction pathway by combining classical and chemical genetics. The effect of low-Pi on root architecture is known in crops since decades and in Arabidopsis since few years. In our lab, the working system since the last five years is the Arabidopsis thaliana primary root response to low-Pi. Our project contains two complementary and synergetic parts: the screening and study of mutants altered in this primary root response to low-Pi, and the screening of drugs (as well as their protein targets) interfering with this response. Part1) After an EMS (ethylmethane sulfonate) or gamma rays mutagenesis of WT seeds, we will isolate mutants insensitive to the primary root growth inhibition induced by low-Pi in vitro. The genetic and phenotypic analysis of these mutants will allow us to define complementation groups and to order the corresponding functions. The drugs identified in Part2 will help characterizing these mutants and functions. Two locus particularly interesting (i.e. mutations altering specifically the low-Pi response, several alleles, response altered by a drug, etc) will be chosen in order to identify the corresponding genes by positional cloning. The biological function of these genes will be analyzed. Part2) We will screen a library of several thousands of small organic and bioactive molecules (already available in our lab in 96-wells plates) in order to find those that trigger the low-Pi root response when seedlings are grown in high-Pi (screen 1) and those that repress the low-Pi root response (screen 2). These two primary screens are based on two criterions: a root-specific reporter gene of Pi starvation and the root growth. We have already started the screens and have identified several drugs (unpublished results). After these primary screens, we will test the drugs specificity toward the low-Pi response with additional assays. One crucial test for analyse the drugs effects will be their interference with mutations isolated in Part1. All these experiments will help to order functions altered by the mutations and/or by drugs (epistasis, suppression, etc). They will allow us also to identify hypersensitive or resistant mutants to these drugs. In case no such mutants are identified, we will screen specifically for them in our Arabidopsis EMS-mutagenesis. As in Part1, these last mutants will be analyzed in order to define complementation and phenotypic groups (in particular their response to low-Pi). Two locus will be chosen for positional cloning of the corresponding genes. Their function will be studied, in particular the effect of the corresponding drugs. This project is largely based on Arabidopsis genetics for which our lab has a long experience. It also relies on chemical genetics, a new methodology not yet used on plants, in France.