Public

Research at BF2I is focused on the comprehension of the functions managing the interaction of specific insect pests (aphids and weevils) with their direct biological partners (host plants and symbiotic microorganisms). Research approaches are multi-disciplinary thanks to the different expertise of the staff members.

The central theme of our research is to understand the relationships established between insects and their symbionts elucidating the molecular mechanisms that allow the establishment, maintenance and persistence of these complex interactions in multiple insect generations.

The final goal of research on these complex biological interactions, often involving multiple partners in interaction with the environment, is to identify tools and define new concepts for an integrated approach for plant protection against insect pests. Our research results are to be central for the development of agricultural practices that are sustainable, and respect both the environment and human health.

MicroRNAs ("miRNAs") are small post-transcriptional regulators. The function of these small RNAs in animals has been well characterized at a molecular level, but their role is less well known at the macroscopic scale: how could miRNAs have any biological function if they repress most of their targets less than 2-fold (while inter-individual gene expression fluctuation typically exceeds 2-fold, and is buffered by homeostatic mechanisms)?
According to the current dogma, each miRNA regulates tens or hundreds of targets, yet several observations suggest miRNAs have a much weaker impact on animal biology. We recently proposed an alternative hypothesis: most identified "targets" are not repressed enough by the miRNA to yield physiological consequences; these genes would rather act as competitive inhibitors, preventing the miRNA from interacting with its few, real targets. The only difference between real targets and competitive inhibitors would be the sensitivity of their biological activity to the modest repression guided by miRNAs. Hence the role of miRNAs in integrated phenomena should be assessed using a systems biology approach.
We are now testing directly the new hypothesis, assessing several of its predictions. We aim at providing the first quantitative analysis of miRNA action in vivo and an improvement in miRNA target identification (taking into account the extent of predicted repression and the robustness of affected biological pathways).
More generally, we are proposing a new vision of gene regulation: a regulatory target is not simply a gene that is affected by a regulatory pathway; it is a gene that is affected enough by the pathway - the extent of a measured regulation needs to be confronted to the robustness of biological systems to fluctuations.
 

Our objective is to develop a tool of modelling and simulation of nucleic acids (NA). The proposed approach consists in describing the conformation as a flexible beam, represented by a ribbon, by means of the theory of non-linear elasticity of beams.

The determination of the conformation of NA (DNA or RNA) is a challenge as great as that put by the conformation of proteins. Indeed, the current knowledge of the detailed conformations of NA is very low (5-10 % of the Protein Data Bank, PDB, the bank of all the known conformations of biological macromolecules). Nevertheless since 2000, we admit that the conformation of NA could be as rich and varied as that of the proteins, and that the part of the genome transcribed in ARN is of an order of magnitude greater than that of the proteins. Therefore, the conformational wealth of NA and the low level of current knowledge make difficult the bioinformatic approach, which consists in deducing a conformation from those already known. That is why the physical modelling of biomolecules is very important for NA and one of the major objectives of research in molecular modelling is the treatment of the various scales, atomic and mesoscopic (residues, several nucléotides) in a coherent and physical way.

We developed an approach of molecular modelling called Biopolymer Chain Elasticity (BCE). It is based on the observation that the sugar-phosphate chain of NA behaves at mesoscopic scales as a flexible beam. We recently finalized a protocol for the resolution of the conformation of DNA hairpins [1] (cf. banner above), with which we solved the structure of an aptamer anti-MUC1 [2] (cf. figure 1). The results are remarkable because the conformations correspond at the same time to a minimum at different scales : global, intermediate, and local, i.e. an energy minimum on the scale of the loop of several nucleotides, of the individual nucleotides in the loop, and atomic bonds [1, 2]. Our objective is to generalize this methodology for the hierarchical modelling of NA chains by using the theory of the non-linear elasticity of beams. We approach the problem on two scales: (I) that of the skeleton treated as a geometrical and mechanical object, and (II) that of the side chains, considered as stiff objects articulated around their attachment point onto the skeleton. From then on, a tool of simulation containing real active ribbons for the resolution of macromolecules is possible.