Nicolas Desprat

Nicolas Desprat's picture
Status
Assistant Professor (MC)
Email
nicolas.desprat@lps.ens.fr
Scientific interests

"Social interactions inside bacterial colonies."

Teaching University Paris 7

 

 

Curriculum

► 2007-2005 Post-doctoral fellow - Institut Curie. (advisor: Emmanuel Farge)
 

"Mecanotransduction during embryogenesis."

Gastrulation, the first steps of morphogenetic movements in a drosophila embryo, leads to the formation of three embryonic sheets: mesoderm, endoderm and ectoderm. This process involves active deformations of the initial cell layer such as the invagination of the ventral furrow and the germ band extension. These active deformations are triggered by gene expression. Since the initial cell layer is mechanically cohesive, the active deformations can be transmitted through the whole tissue. Hence, even far away from the place where these movements occur, cells are passively deformed.  By using femtosecond microscopy and magnetic nanoparticles, we were able i) to perturb morphogenetic movements by laser-ablation of the most dorsal cells, ii) to mimic morphogenetic movements with ferrofluids injection in the antero-dorsal cells. Injected cells were directly manipulated via a magnetic field gradient produced by magnetic tweezers. Thus, we highlighted that the deformations caused by germ band extension up-regulate Twist expression in the stomodeal primordium and that stomodeal compression triggers Src42A-dependent nuclear translocation of Armadillo/β-catenin, which is required for Twist mechanical induction in the stomodeum. Finally, we observed that stomodeal-specific RNAi-mediated silencing of Twist during compression impairs the differentiation of midgut cells. Hence, we showed that mechanically induced levels of Twist expression in stomodeal cells are necessary for subsequent mid-gut differentiation. This experiments furhter confirms that the logic of embryonic development involves mechanosensitivity.
 

 

► 2001-2004 PhD - University Paris VII . (advisor: Atef Asnacios)
 

"Rheology of a single living cell."
As mecanotransduction appears to be part of cell physiology, mechanical properties of cells play a central role in the development and the survival of organisms. To determine the mechanical properties of isolated living cells, we built a single cell rheometer. Individual cells, of various types, were strained under constant stress (creep experiment). Their creep function always scaled with a power law of time (J(t)=Atß). The exponent gave a normal distribution around 0.25, whereas the distribution of the prefactor was log-normal. As the mechanical response was linear, we could compare our creep parameters to those observed previously by dynamical rheology (magnetocytometry, AFM). Thus we confirmed, qualitatively as well as quantitatively, results obtained with local and oscillating perturbations. In order to identify the contribution of cytoskeletal elements to the mechanical properties, we compared wild-type and vimentin-deficient fibroblasts. We found that vimentin had no effect on the form of the creep function, but was necessary to maintain mechanical integrity at high strain. In addition, we measured the force generated by a cell upon spreading between two glass microplates. Preliminary results indicated that myoblasts adapted the force they applied to the stiffness of the microplates.