Biological membranes

In-vitro reconstitution of focal-adhesions

Principal investigators: K. SENGUPTA & E. HELFER

PhD Student: M. Souissi (2019-2022)

Collaborations: C. Le Clainche (I2BC, Gif sur Yvette France)

Funding: ANR RECAMECA (2019-2022)

Cell biophysics and proteomics have revealed key links between force, integrin and the mechanical properties of the extra cellular matrix (ECM). However, in-cellulo, the existence of multiple isoforms of actin binding proteins, their embedding in a complex signaling network, and their associated with a complex membrane environment precludes extraction of even elementary molecular mechanisms. To reveal these force-dependent molecular mechanisms, we need to isolate actomyosin-integrin-ECM circuits. The global objective of our project is to decipher the molecular links between actomyosin force, integrin regulation and ECM properties through in vitro reconstitution of focal adhesions.

As a first step towards this goal, we have successfully integrated transmembrane integrins into giant unilamellar vesicles (GUVs) and demonstrated their functionality. We are also developing an alternative to fully in vitro reconstitution, namely cell derived giant plasma membrane vesicles (GPMVs). This alternative does not require elaborate biochemistry needed for integrin extraction and purification, yet offers many of the advantages of in vitro reconstitution.

Physics of membrane adhesion

Principal investigators: K. Sengupta; F. Thibaudau

PhD Student:  Ahmed Abdurahman (2019-)

Postdoc: Arnauld Hemmerlé (2016-2018), M. Arif Kamal (2014-2016)

Collaboration: Ana smith (Univ. Erlangen, Germany)

Funding: ANR-DGF MicroCJ (2019-2022), AMIDEX Affinity (2015-2019)

We have recently shown that from the spectrum of fluctuations recorded with the experimental techniques previously developed in the team, it is possible to measure the membrane interaction potential. We have also shown that transverse fluctuations can modulate the nucleation and growth of lateral adhesion domains. In addition, we have used soluble DNA oligomers to mimic binding between intracellular organelles and have shown that the physics of this system is very different from that of cell adhesion with ligands in the membrane. Currently, we are exploring the nucleation and growth of adhesion domains in the context of weak bonds where entropy can dominate the enthalpy generated by bond formation.

Shape and dynamics of vesicles in flow: theory and simulations

Principal investigator: M. Leonetti

Collaboration : P. G. Chen, M. Jaeger (M2P2, Marseille)

A vesicle is a droplet bounded by a lipid bilayer embedded in another liquid. This system knows a long standing interest due to its ability to mimic some properties of red blood cells. But it is also a fascinating system at a theoretical point of view, thanks to its original interfacial properties: resistance to bending and local surface incompressibility.  It is one of the ways to understand how soft matter flows. We study the shape and the spatiotemporal dynamics of vesicles in flow or in electric field by a methodology associating theory and numerical simulations.  We have developed our own code based on Finite Element Method and Boundary Element Method. The instabilities are characterized in the framework of nonlinear physics and soft matter. The results can highlight some behaviors of red blood cells in microcirculation.

Encapsulation

Principal investigator: M. Leonetti

A - Dynamics, shape, wrinkling and rupture of an elastic capsule

PhD Student: P. Regazzi

Funding: CNES

Encapsulation is a simple way of protecting, transporting and delivering internalized principles, but also of structuring space. This concerns very diverse fields such as food, cosmetics, new materials for construction or medicine. The capsules studied are droplets bounded by a thin polymer film (shell) and immersed in a liquid. The structural and mechanical properties of such objects are still poorly known: behaviour laws, elastic and viscous moduli, rupture, dynamics, etc. Indeed, there are few experimental results. The behavior of this closed elastic system is governed by the coupling at the interface between the viscous stress jump and the elastic response of the shell (also called skin or membrane depending on the domain).

We are interested in the rupture of capsules as a function of the nature of its membrane, the winkling/folding instabilities and the spatiotemporal dynamics of the shape by a multiscale analysis.

B – Interactions between capsules, collective behaviors

The strong deformation of capsules in flow induces more complex hydrodynamic interactions than between rigid particles. To this, it is necessary to add colloidal interactions as well as friction, key ingredients for the understanding of the rheology of rigid particle suspensions. We propose to study the implication of all these contributions to the case of binary interactions and more broadly in suspension.

Physics of (T) cell adhesion

Principal investigators: K. Sengupta

PhD Student:  Remy Torro (2019- ), Aya Nassereddine (2018-2021), Celine Dinet (2016-2019), Emmanuelle Benard (2015-2018), Pierre Dillard (2011-2016)

Postdocs: Zakaria Marmri (2022-), Fuwei Pi (2011-2013)

Collaboration : Laurent Limozin (LAI, Marseille France).

Funding: SATT (2019- ), CENTURI (2019 - ), ERC (SYNINTER 2013-2017), ATER AMU (2018), AMU ED 352 PhD grant (2014-2017), Region PACA (MadNano 2011-2013), PhD grant AMU (2011-2014)

We have developed innovative surface nano-patterning techniques to manipulate living cells to reveal aspects of cell adhesion. These surfaces feature regularly spaced islands of cell-activating proteins of nano- or submicron size with which cells can be induced to interact. They are imaged by advanced surface microscopy techniques that may not be applicable to traditional nano-patterning with metal nanoparticles. Using these surfaces, we have shown that the cell-scale behaviour of T cells is governed by the average protein density and not by their nanoscale organisation, which however has a strong impact on the local organisation of the membrane. Using a new AI analysis technique, we showed that actin organisation remains unaffected even locally.