TEAM

Physical and Molecular Principles Governing Cytoskeletal Organization

Group leader : A. Michelot

Our team has two main objectives. Our first aim is to understand some of the basic physical and biochemical principles governing cytoskeletal organization (principally actin) in eukaryotic cells. Our second aim is to understand how cells use different actin networks to perform a variety of cellular functions.

FOR BEGINNERS

The transition of a tumor to malignancy is associated with many genetic and epigenetic modifications of its cells. For some cancers, it is established that part of these modifications corresponds to changes in the expression level of some proteins implicated in the regulation of the actin cytoskeleton. The actin cytoskeleton is playing a major role in controlling cells’ structural integrity and in their dynamics within tissues. As a consequence, cancer cells have altered motile and biomechanical properties, but these properties are also well adapted for their propagation during the formation of metastases.

The actin cytoskeleton is composed of dense filamentous networks. These networks are essential for a large number of cellular processes implicating the generation of forces, or the resistance to mechanical constraints, such as cell motility, adhesion or division. The reason why actin-based structures, all composed of filaments assembled from identical subunits, are able to perform many different functions is due to the fact that cells are able to organize actin filaments in a wide variety of structures. Each of these structures has specific geometrical, dynamical and rheological properties that are adapted for a given cellular process. The properties of each individual networks are constantly remodeled by specific sets of actin binding proteins (ABPs), that are responsible for the nucleation, crosslinking, and/or disassembly of the filaments.

In this context, our objective is to determine how cells can generate a variety of structures of actin filaments with defined properties, and with appropriate protein composition, from a common pool of cytoplasmic components. This global understanding will enable us to predict how misbalancing the equilibrium of the cell affects actin networks organizational, dynamical and mechanical properties.

FOR SPECIALISTS

Self-organization of the actin cytoskeleton
To develop a working model, we are left with the complex question of what type of signaling may cells use to target precisely, spatially and temporally, multiple families of ABPs to the appropriate actin networks. Previously, we demonstrated that the local recruitment of specific actin nucleation promoting factor is sufficient to assemble from cell extracts actin networks of appropriate protein composition. This surprising observation indicates that recruitment of ABPs is not due to a specific signaling network, or as a local cellular context, such as pH or salt concentration, but on the contrary that the segregation of ABPs to appropriate structures is due to a fine-tuned biochemical regulation, although the underlying molecular mechanisms remain largely unknown.

Key regulators of actin filaments identity
Hence, what distinguishes different populations of actin filaments, although they are all assembled from identical actin subunits? In our projects, we are exploring several hypothesis to understand how identical actin filaments acquire a specific identity. In particular, recent research suggests that many proteins characterized previously as actin-filament bundling proteins may have an important function in giving actin filaments their identity. The decoration of actin filaments by subsets of actin binding protein may influence strongly the binding of others, through competitive or collaborative effects.
Inter-dependence of actin networks
More and more data indicate that actin networks in cells are in homeostasis. In other words, it means that actin networks compete for the same pool of ABPs, and that a perturbation of one actin network will disturb the whole equilibrium and affect also other actin networks. For example, the absence of an actin binding protein can not only affect the structural integrity of the actin structure where it normally binds to, but we also have evidences that it can modify the localization of other actin binding proteins, to trigger defects on other actin structures.

Our tools in the lab
To address detailed mechanistic questions, traditional biochemical, cell biological and genetic experiments need to be complemented by engineering-inspired reconstitution approaches. The use of simplified systems and the ability to modify individual components without the active contribution and complexity of the cell has proven beneficial in understanding emerging properties of a variety of biological systems.

equipe michelot IBDMWe usually use two complementary ways to reconstitute our biological processes of interest. With “bottom-up” reconstitutions, we purify the essential components, and assemble them in a test tube. Components are added one-by-one into the system, and it allows for testing the role of a molecule in the presence of a limited number of partners. However, for cellular processes involving the participation of large numbers of families of molecules, “bottom-up” approaches can be limited, because they require the identification of all essential components and their purification in an active form. In that situation, we use protein extracts, because they contain a mixture of all the proteins that are essential for the process. We are experts in genetic depletions in protein extracts, in order to experiment “top-down” approaches, where components are removed one-by-one from the extracts, in order to test for their functions in a near-physiological environment. Both “bottom-up” and “top-down” approaches are used in various experimental setups to bridge the gap between simple biochemistry and the complexity of a cell.


Main publications

PUBLICATION

Actin filament elongation in Arp2/3-derived networks is controlled by three distinct mechanisms

Michelot A, Grassart A, Okreglak V, Costanzo M, Boone C, Drubin DG.
Dev Cell. 2013 Jan 28;24(2):182-95. PMID: 23333351

PUBLICATION

Actin cytoskeleton: a team effort during actin assembly

Blanchoin L, Michelot A.
Curr Biol. 2012 Aug 21;22(16):R643-5. PMID: 22917514

PUBLICATION

Building distinct actin filament networks in a common cytoplasm

Michelot A, Drubin DG.
Curr Biol. 2011 Jul 26;21(14):R560-9. PMID: 21783039

PUBLICATION

Reconstitution and protein composition analysis of endocytic actin patches

Michelot A, Costanzo M, Sarkeshik A, Boone C, Yates JR 3rd, Drubin DG.
Curr Biol. 2010 Nov 9;20(21):1890-9. PMID: 21035341

PUBLICATION

Actin-filament stochastic dynamics mediated by ADF/cofilin.

Michelot A, Berro J, Guérin C, Boujemaa-Paterski R, Staiger CJ, Martiel JL, Blanchoin L.
Curr Biol. 2007 May 15;17(10):825-33. PMID: 17493813

PUBLICATION

A novel mechanism for the formation of actin-filament bundles by a nonprocessive formin.

Michelot A, Derivery E, Paterski-Boujemaa R, Guérin C, Huang S, Parcy F, Staiger CJ, Blanchoin L.
Curr Biol. 2006 Oct 10;16(19):1924-30. PMID: 17027489

PUBLICATION

The formin homology 1 domain modulates the actin nucleation and bundling activity of Arabidopsis FORMIN1.

Michelot A, Guérin C, Huang S, Ingouff M, Richard S, Rodiuc N, Staiger CJ, Blanchoin L.
Plant Cell. 2005 Aug;17(8):2296-313 PMID: 15994911
Other publications

PUBLICATION

Lsb1 is a negative regulator of las17 dependent actin polymerization involved in endocytosis.

Spiess M, de Craene JO, Michelot A, Rinaldi B, Huber A, Drubin DG, Winsor B, Friant S.
PLoS One. 2013;8(4):e61147 PMID: 23577202

PUBLICATION

Mechanism and cellular function of Bud6 as an actin nucleation-promoting factor.

Graziano BR, DuPage AG, Michelot A, Breitsprecher D, Moseley JB, Sagot I, Blanchoin L, Goode BL.
Mol Biol Cell. 2011 Nov;22(21):4016-28. PMID: 21880892

PUBLICATION

Determinants of endocytic membrane geometry, stability, and scission

Kishimoto T, Sun Y, Buser C, Liu J, Michelot A, Drubin DG.
Proc Natl Acad Sci U S A. 2011 Nov 1;108(44):E979-88. PMID: 22006337

PUBLICATION

The formin DAD domain plays dual roles in autoinhibition and actin nucleation.

Gould CJ1, Maiti S, Michelot A, Graziano BR, Blanchoin L, Goode BL.
Curr Biol. 2011 Mar 8;21(5):384-90. PMID: 21333540

PUBLICATION

A "primer"-based mechanism underlies branched actin filament network formation and motility.

Achard V, Martiel JL, Michelot A, Guérin C, Reymann AC, Blanchoin L, Boujemaa-Paterski R.
Curr Biol. 2010 Mar 9;20(5):423-8. PMID: 20188562

PUBLICATION

Stochastic severing of actin filaments by actin depolymerizing factor/cofilin controls the emergence of a steady dynamical regime.

Roland J, Berro J, Michelot A, Blanchoin L, Martiel JL.
Biophys J. 2008 Mar 15;94(6):2082-94. PMID: 18065447

PUBLICATION

Attachment conditions control actin filament buckling and the production of forces.

Berro J, Michelot A, Blanchoin L, Kovar DR, Martiel JL.
Biophys J. 2007 Apr 1;92(7):2546-58. PMID: 17208983

PUBLICATION

Villin Severing Activity Enhances Actin-Based Motility in vivo

Revenu C, Courtois M, Michelot A, Sykes C, Louvard D, Robine S.
Mol Biol Cell. 2007 Mar;18(3):827-38. PMID: 17182858

Interactions

NATIONAL
  • O. du Roure and J. Heuvingh, ESPCI ParisTech
  • C. Campillo, Université d’Evry
INTERNATIONAL
  • D. Kovar, University of Chicago
  • R. Robinson, IMCB, Singapore

Announcement

Funding

ERC

ANR

Labex

Members more

  Adrien Antkowiak   Micaela Boiero Sanders Jessica Colombo Audrey Guillotin
Alphée Michelot
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Alphée Michelot

Researcher

Alphée Michelot studied physics and chemistry at the Ecole Normale Supérieure de Lyon, France. After a PhD in biophysics and biochemistry at the University of Grenoble, France, he worked as a post-doc in the department of Molecular and Cell Biology at the University of California, Berkeley, USA. He joined the CNRS as a research scientist at the Institut de Recherches en Technologies et Sciences pour le Vivant, Grenoble, France, in 2012. Group leader at the Institute for Developmental Biology of Marseille since 2015,his research is focused on the molecular and physical principles of actin assembly.

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Thomas Le Goff

Researcher

Adrien Antkowiak
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Adrien Antkowiak

Postdoctoral fellow

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Mohamed reda Belbahri

PhD student

Micaela Boiero Sanders
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Micaela Boiero Sanders

PhD student

Jessica Colombo
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Jessica Colombo

PhD student

Audrey Guillotin
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Audrey Guillotin

Technical staff