Laboratoire Matière et Systèmes Complexes/ Université Paris-Diderot
Bâtiment Condorcet, Office 769A
tel: (+33)1 57 27 62 43
email: andrew.callan-jones AT univ-paris-diderot.fr
I am an assistant professor of theoretical biophysics. In addition to teaching at the undergraduate and Masters levels, I do research in the field of cell mechanics. My recent projects are described further below.
|Cell polarization and shape change|
| "Cortical Contractility
Triggers a Stochastic Switch to Fast Amoeboid Cell Motility" (Cell)
We found that elevated contractility spontaneously polarizes zebrafish cells, leading to cortical flows, migration, and cell deformation.
| "Cortical Flow-Driven Shapes of Nonadherent Cells
" (Phys. Rev. Lett.)
Using a minimal model that describes the cell cortex as a thin layer of contractile active gel, we show that the anisotropy of active stresses, controlled by cortical viscosity and filament ordering, can account for polarized zebrafish cell shapes.
| "Adaptive rheology and ordering of cell cytoskeleton govern matrix rigidity sensing" (Nat. Commun.)
Matrix rigidity sensing regulates a variety of cellular processes, with implications for tissue development. We find that increasing substrate stiffness triggers actin cytoskeletal remodelling: theory and experiment reveal an isotropic to nematic transition of actin stress fibers, and a transition from viscous to elastic rheology.
| "Viscous-Fingering-Like Instability of Cell Fragments" (Phys. Rev. Lett.)
We found a novel flow instability that can arise in thin films of cytoskeletal fluids if the friction with the substrate is sufficiently strong. This mechanism could be relevant to cell polarization preceding 2D migration.
|Cell motility under confinement|
| "Confinement and Low Adhesion Induce Fast Amoeboid Migration of Slow Mesenchymal Cells" (Cell)
We show that in low adhesion but high confinement conditions, mesenchymal cells spontaneously transform to an amoeboid migration mode.
| "Active gel model of amoeboid cell motility" (New J. Phys.)
Modeling a confined, motile cell as a layer of active gel permeated by a solvent, we obtain a contractile-type instability to a polarized moving state in which the rear is enriched in gel polymer, in agreement with experiments.
|Hydrodynamics of the cytoskeleton|
| "Hydrodynamics of active permeating gels" (New J. Phys.)
We developed a theory of active viscoelastic gels in which a polymer network is embedded in a background fluid. This is motivated by the cytoskeleton in which motor molecules generate elastic stresses in the network, driving permeation flows of the cytosol. Our approach differs from earlier ones by considering the elastic strain as a slowly relaxing dynamical variable.
|Intracellular trafficking and membrane mechanics|
| "IRSp53 senses negative membrane curvature and phase separates along membrane tubules" (Nat. Commun.)
The BAR protein IRSp53 is sorted non-monotonically by membrane curvature. At low tensions, protein-rich domains appear along the tube, possibly related to filopodium formation.
| "Hydrodynamics of bilayer membranes with diffusing transmembrane proteins" (Soft Matter)
We consider fluctuations of lipid bilayers containing transmembrane proteins of arbitrary shape, finding that proteins modify the intermonolayer friction coefficient. This could have implications for intracellular transport: at the junction between a large membrane body and a molecular motor-pulled tube, say, intermonolayer stress is high, which could exclude proteins that augment friction.
| "Nature of curvature coupling of amphiphysin with membranes depends on its bound density" (PNAS)
The BAR protein Amphiphysin1 spontaneously tubulates membrane vesicles, reflecting its preference for high curvature. Bound to pre-formed membrane tubes, it forms a rigid scaffold, with implications for endocytosis.
| "Curvature-driven lipid sorting needs proximity to a demixing point and is aided by proteins" (PNAS)
We test, model, and verify the hypothesis that lipid sorting - critical for transport and membrane homeostasis - can be driven by membrane curvature. Entropy usually outweighs this sorting, except for membrane mixtures susceptible to composition fluctuations.
|Malaria and membrane curling|
| "Red Blood Cell Membrane Dynamics during Malaria Parasite Egress" (Biophys. J.)
Parasite escape from red blood cells is preceded by a hole opening up in the membrane followed by membrane curling. We model this behavior with the idea that malaria modifies the membrane spontaneous curvature, provoking egress.
| "Self-Similar Curling of a Naturally Curved Elastica" (Phys. Rev. Lett.)
The curling of an elastica with intrinsic curvature - a useful model of curling in nature - is a surprisingly rich problem, owing to strong geometric nonlinearities. We found that at long times after release of a free end, the shape of the curl is invariant, but its size grows with the cube root of time. Self-similarity breaks down near the free end, where the curvature tends to the intrinsic one.