Laboratoire Matière et Systèmes Complexes

Séminaire interne du lundi 22 septembre 2014

Mechanics of neural crest cell migration

Nicolas Chevalier

Equipe Biofluidique

Neural crest cells are a population of multipotent cells that migrate extensively during vertebrate development to give rise to a wide range of vital structures such as the peripheral and enteric nervous system, melanocytes (skin pigment cells) and craniofacial cartilage and bones (e.g. the jaw). Failure of neural crest cell migration leads to severe birth-defects called neurocristopathies. While many essential signaling molecules responsible for guiding neural crest cells through their journey have been identified over the past decades, very little is known about the physical properties of the tissue through which (3D) they migrate. We have gathered such information from the gut of chick and mouse embryos using a tailor-made embryonic gut stretching device and the atomic force microscope (AFM). We investigated collagen distribution in the developing gut using second-harmonic generation imaging (SHG). Finally, we show in-vitro that crest cells are only able to migrate in sufficiently soft media. This study sheds light on our understanding of development, neurocristopathies and their potential treatment by neural crest stem cell injection.

Noise Propagation in a Population of Eukaryotic Cells

Valentina Peschetola

Equipe Physique du Vivant

A population of genetically identical cells in a homogeneous environment exhibits cell-to-cell variation in protein levels (noise). This ubiquitous phenomenon underlies the stochastic fluctuations in gene expression and has important functional roles, e.g. in development, and also in cancer. Understanding and characterizing the sources of noise at the single cell level and at the population level are key aims in this field. In the latter case, protein distribution analyzed in terms of mean and variance is usually considered as a steady distribution, and the contribution of different fractions of cells to the overall noise remains unclear. Here, we investigate, experimentally and with the help of stochastic simulations, the dynamics by which different cell subpopulations contribute to the heterogeneity of the whole population. Starting from a monoclonal cell line harboring a fluorescent marker, we isolated by sorting three different cell subpopulations that express the lowest, the mean and the highest fluorescence level and we follow their dynamics for several days. We found, experimentally and analytically, that two time steps characterize the reconstruction process and that this phenomenon is independent on the initial protein level of cell subpopulations.