Primary Cilium Positioning – PrinciP

Fully differentiated cells stop dividing. When cells exit the cell cycle it becomes quiescent. The centrosome leaves the cell centre, moves to the cell periphery, plugs itself in the plasma membrane where it constitues the basal body on which the primary cilium grows. The cilium is a cellular outgrowth which functions as a cellular antenna. It collects extracellular biochemical signals and transduce mechanical constraints. It is present in most cells of our body. Its absence leads to severe embryonic defects and its malfunction induce numerous pathologies. The aim of our team is to study the genesis and functions of the primary cilium. We are interested in the mechanisms regulating primary cilium positioning at the cell surface. Indeed this position could play a key role in the way the cilium performs spatial integration of signals and the way it affects spatial arrangement of intracellular compartments. Early observations of cilia in electronic microscopy revealed that the basal body is a singular meeting point for the three cytoskeleton networks: intermediate filaments, actin filaments and microtubules. This suggests that primary cilium positioning results from the cooperation of the three networks. We plan to study the mechanical and functional links that could exist between cell architecture, definition of polarity and positioning of the primary cilium. We will focus on the role of cell-cell and cell-extra cellular matrix adhesions in the modulation of cell cytoskeleton architecture and the definition of cilium position. Our experimental strategy will be to use microfabrication techniques to manipulate cell micro-environment. We plan to use fully validated techniques to control individual cell adhesion patterns in 2D. We will also develop new fabrication methods to manipulate and monitor multicellular arrangements in 2D and 3D. These techniques allow automated and quantitative analyses of morphology and internal cell organisation. We will investigate the effect of cell microenvironment by measuring cilium position with respect to cell-cell and and cell-extracellular matrix adhesions. We will try to interpret these measures in the light of the three cytoskeletons structures. Our interpretation of cellular organisation will be coupled with the development of a theoretical model accounting for the effect of internal mechanical constraint on cilium position. Numerical simulations will be performed and compared to experimental data to help our progression. The back and forth movements between the fundamental bases of the model, numerical simulations and experimental data should help us to identify the mechanical parameters implicated in cilium positioning and bring to light some of the physical laws governing cell architecture.