Biology subjects

Gaelle Letort

Publications and source records attributed to Gaelle Letort.

3 recordsLinked to original sources

bioRxiv2016

Microtubule stabilization drives centrosome migration to initiate primary ciliogenesis

Primary cilia are sensory organelles located at the cell surface. Their assembly is primed by centrosome migration to the apical surface. Yet surprisingly little is known about this initiating step. To gain insight into the mechanisms driving centrosome migration, we exploited the reproducibility of cell architecture on adhesive micropatterns to investigate the cytoskeletal remodeling supporting it. Microtubule network densification and bundling, with the transient formation of an array of cold-stable microtubules, and actin cytoskeleton asymmetric contraction participated in concert to destabilize basal centrosome position and drive apical centrosome migration. The distal appendage protein Cep164 appeared to be a key actor involved in the cytoskeleton remodeling and centrosome migration, whereas IFT88's role seemed to be restricted to axoneme elongation. Together our data elucidate the hitherto unexplored mechanism of centrosome migration and show that it is driven by the increase and clustering of mechanical forces to push the centrosome toward the cell apical pole.

Cell Biology↗

bioRxiv2016

Heterogeneity of single-cell mechanical responses to tumorigenic factors.

Tumor development progresses through a complex path of biomechanical changes leading first to cell growth and contraction followed by cell de-adhesion, scattering and invasion. Tumorigenic factors may act specifically on one of these steps or have wider spectrum of actions, leading to a variety of effects and thus sometimes to apparent contradictory outcomes. Here we used micropatterned lines of collagen type-I/fibronectin on deformable surfaces to standardize cell behavior and to measure simultaneously cell size, speed of motion and the magnitude of the associated contractile forces at the level of a single cell. We analyzed and compared normal human breast cell line MCF10A in control conditions and in response to various tumorigenic factors. In all conditions, distinct populations of cells with a wide range of biomechanical properties were identified. Despite this heterogeneity, normal and transformed motile cells followed a common trend whereby size and contractile forces were negatively correlated with cell speed. Some tumorigenic factors, such as activation of ErbB2 or the loss of the beta subunit of casein kinase 2 (CK2), shifted the whole population towards a faster speed and lower contractility state. Treatment with transforming growth factor beta (TGF-{beta}), induced some cells to adopt opposing behaviors such as extreme high contractility versus extreme low contractility. Thus, tumor transformation amplified the pre-existing population heterogeneity and led some cells to exhibit biomechanical properties that were more extreme than that observed with normal cells.

Cell Biology↗

bioRxiv2016

Centrosome centering and decentering by microtubule network rearrangement

The centrosome is positioned at the cell center by pushing and pulling forces transmitted by microtubules (MTs). Centrosome decentering is often considered to result from asymmetric, cortical pulling forces exerted in particular by molecular motors on MTs, and controlled by external cues affecting the cell cortex locally. Here we used numerical simulations to investigate the possibility that it could equally result from the redistribution of pushing forces due to a reorientation of MTs. We first showed that MT gliding along cell edges and pivoting around the centrosome regulate MT rearrangement and thereby direct the spatial distribution of pushing forces, while the number, dynamics and stiffness of MTs determine the magnitude of these forces. By modulating these parameters, we identified different regimes, involving both pushing and pulling forces, characterized either by robust centrosome centering, robust off-centering or \"reactive\" positioning. In those latter conditions weak asymmetric cues can induce a misbalance of pushing and pulling forces resulting in an abrupt transition from a centered to an off-centered position. Altogether these results point at the central role played by the configuration of the MTs on the distribution of pushing forces that position the centrosome. We suggest that asymmetric external cues should not be seen as direct driver of centrosome decentering and cell polarization, but rather as inducers of an effective reorganization of the MT network, fostering centrosome motion to the cell periphery.

Cell Biology↗