PHYSICS OF THE CYTOSKELETON AND MORPHOGENESIS

Our aim is to unravel the physical processes directing cytoskeleton self-organization. In particular we investigate the production and balance of mechanical forces in the networks of actin filaments and microtubules. We further analyze how the control of symmetry in these architectures regulate cell polarity. To that end we use microfabrication tools to impose spatial boundary conditions to individual cells or purified cytoskeleton filaments.

Actin filaments and microtubules form such complex intricate networks in cells that it is difficult to identify the principles of their self-organization. Our rationale is that these principles can manifest themselves in a reproducible, and therefore understandable, way only in response to defined geometrical cues. Thus, to study the geometrical and mechanical rules underlying cytoskeleton self-organization we used microfabrication tools in order to control and manipulate the spatial boundary conditions the cytoskeleton networks are sensitive to.

These tools allow us to analyze and quantify actin and microtubule networks in cells of controled and regular shapes. Considering that the complexity of the intra-cellular biochemical conditions may partially hinder the physical rules we want to investigate, we are also developing alternative methods to analyze cytoskeleton self-organization in controlled biochemical conditions in vitro by mixing, in defined proportions, the individual cytoskeleton components. Cells extracts and cytoplastes allow us to bridge the gap between these two approaches. The simplification of the cellular approach, the top-down way, and the complexification of the biochemical approach, the bottom-up way, should eventually encounter and provide us a continuous experimental platform to analyze the physics of cytoskeleton networks and morphogenesis from molecules to cells.

PROJECTS

AAA, adaptive actin networks

ERC Advanced Grant to Laurent Blanchoin

Although we have extensive knowledge of many important processes in cell
biology, including information on many of the molecules involved and the physical interactions among them, we still do not understand most of the dynamical features that are the essence of living systems. This is particularly true for the actin cytoskeleton, a major component of the internal architecture of eukaryotic cells. In living cells, actin networks constantly assemble and disassemble filaments while maintaining an apparent stable structure, suggesting a perfect balance between the two processes. Such behaviors are called “dynamic steady states”. They confer upon actin networks a high degree of plasticity allowing them to adapt in response to external changes and enable cells to adjust to their environments. Despite their fundamental importance in the regulation of cell physiology, the basic mechanisms that control the coordinated dynamics of co-existing actin networks are poorly understood. In the AAA project, first, we will characterize the parameters that allow the coupling among co-existing actin networks at steady state. In vitro reconstituted systems will be used to control the actin nucleation patterns, the closed volume of the reaction chamber and the physical interaction of the networks. We hope to unravel the mechanism allowing the global coherence of a dynamic actin cytoskeleton. Second, we will use our unique capacity to perform dynamic micropatterning, to add or remove actin nucleation sites in real time, in order to investigate the ability of dynamic networks to adapt to changes and the role of coupled network dynamics in this emergent property. In this part, in vitro experiments will be complemented by the analysis of actin network remodeling in living cells. In the end, our project will provide a comprehensive understanding of how the adaptive response of the cytoskeleton derives from the complex interplay between its biochemical, structural and mechanical properties.

https://cordis.europa.eu/project/id/741773

ICEBERG, exploration below the tip of the microtubule

ERC Consolidator to Manuel Théry

Microtubules (MTs) are dynamic cytoskeleton filaments. They permanently transit between growth and shrinkage. This famous “dynamic instability” is governed by the addition and loss of tubulin dimers at their tips. In contrast to the tip, the MT lattice was considered to be a passive structure supporting intracellular transport. However, we recently found that MT lattice is dynamic and active! Actually, tubulin dimers can be exchanged with the cytoplasmic pool along the entire length of the MT. These incorporations can repair sites on the lattice that have been mechanically damaged. These repair sites protect the MTs from depolymerisation and increase the MT’s life span. This discovery opens up a new vista for understanding MT biology.

First, we will investigate the biochemical consequences of MT-lattice turnover. We hypothesise that tubulin turnover affects the recruitment of MAPs, motors and tubulin-modifying enzymes. These recruitments may feedback on lattice turnover and further regulate MT life span and functions.

Second, we will investigate the mechanical impact of the MT-lattice plasticity. Tubulin removal is likely to be associated with a local reduction of MT stiffness that can impact MT shape and the propagation of forces along the lattice. We anticipate that such effects will require us to reformulate the biophysical rules directing network architecture.

To achieve this, we will use reconstituted MT networks in vitro to investigate the molecular mechanism regulating MT-lattice plasticity, and cultured cells to test the physiological relevance of these mechanisms. In both approaches, microfabricated devices will be used to control the spatial boundary conditions directing MT self-organisation.

By exploring the hidden 90% of MT iceberg we aim to show that the MT lattice is a dynamic mechano-sensory structure which regulates interphase MT-network architectures and possibly confers them unexpected functions.

https://cordis.europa.eu/project/id/771599/fr

Matador

ERC Proof of Concept to Manuel Théry

MATADOR project is developing a cell-based test that could help discover new drugs capable of curing breast cancer.

Breast cancer is the most common cancer in women worldwide, with nearly 1.7 million new cases diagnosed in 2012. Fortunately, the availability of diagnosis tools to detect mammary neoplastic tissues, as well as transcriptomic biomarkers helping for prognosis, and the diversity of treatment options for primary tumors allows a 90% 5-year survival rate. However the metastatic grade of breast cancer is still not curable mainly due to chemo-resistance.

Advances from basic research in the last decade outline the epithelial-to-mesenchymal transition (EMT) as a key program of molecular events triggering metastatic dissemination from a stationary state [Nieto MA, Cell, 2016]. More recently, EMT was shown to confer chemo-resistance in breast and pancreatic cancer models [Fischer KR, Nature, 2015; Zheng X, Nature, 2015]. The EMT reversion strategy, named mesenchymal-to-epithelial transition (MET) subsequently appears as a very seductive way to impair the metastasis potential of breast carcinoma as well as it chemo-resistance [Yoshida T, Br. J. Cancer, 2014].

Based on preliminary results obtained from “SPICY” ERC Frontier Research Starting Grant, in which we successfully develop an assay dedicated to characterize the EMT state of breast carcinoma cells [Thery M, EP 2180042 A1, 2008 ; Burute M, Dev. Cell, 2016], MATADOR is an ERC proof-of-concept project which proposes a genuine innovative strategy to (1) develop marketable cell based assays allowing the discovery of new drugs promoting the MET process in breast carcinoma cells to (2) initiate drug discovery programs to efficiently slaughtering mammary tumors by targeting the whole population of cancer cells, and (3) create a CRO-type biotechnology company exploiting the pre-existing and newly created intellectual property: including marketable assays, therapeutics and drug cocktails defined in MATADOR. Patented services and compounds will ultimately be proposed to pharmaceutical companies to initiate pre-clinical developments.

https://cordis.europa.eu/article/id/386916-developing-the-cancer-fighting-drugs-of-tomorrow