Rajaa Boujemaa-Paterski | University of Grenoble (original) (raw)

Papers by Rajaa Boujemaa-Paterski

Research paper thumbnail of Network heterogeneity regulates steering in actin- based motility

The growth of branched actin networks powers cell-edge protrusions and motility. A heterogeneous ... more The growth of branched actin networks powers cell-edge protrusions and motility. A heterogeneous density of actin, which yields to a tunable cellular response, characterizes these dynamic structures. We study how actin organization controls both the rate and the steering during lamellipodium growth. We use a high-resolution surface structuration assay combined with mathematical modeling to describe the growth of a reconstituted lamellipo-dium. We demonstrate that local monomer depletion at the site of assembly negatively impacts the network growth rate. At the same time, network architecture tunes the pro-trusion efficiency, and regulates the rate of growth. One consequence of this interdependence between monomer depletion and network architecture effects is the ability of heterogeneous network to impose steering during motility. Therefore, we have established that the general principle, by which the cell can modulate the rate and the direction of a protrusion, is by varying both density and architecture of its actin network.

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Research paper thumbnail of Adaptive Response of Actin Bundles under Mechanical Stress

Actin is one of the main components of the architecture of cells. Actin filaments form different ... more Actin is one of the main components of the architecture of cells. Actin filaments form different polymer networks with versatile mechanical properties that depend on their spatial organization and the presence of cross-linkers. Here, we investigate the mechanical properties of actin bundles in the absence of cross-linkers. Bundles are polymerized from the surface of mDia1-coated latex beads, and deformed by manipulating both ends through attached beads held by optical tweezers, allowing us to record the applied force. Bundle properties are strikingly different from the ones of a homogeneous isotropic beam. Successive compression and extension leads to a decrease in the buckling force that we attribute to the bundle remaining slightly curved after the first deformation. Furthermore, we find that the bundle is solid, and stiff to bending, along the long axis, whereas it has a liquid and viscous behavior in the transverse direction. Interpretation of the force curves using a Maxwell visco-elastic model allows us to extract the bundle mechanical parameters and confirms that the bundle is composed of weakly coupled filaments. At short times, the bundle behaves as an elastic material, whereas at long times, filaments flow in the longitudinal direction, leading to bundle restructuring. Deviations from the model reveal a complex adaptive rheological behavior of bundles. Indeed, when allowed to anneal between phases of compression and extension, the bundle reinforces. Moreover, we find that the characteristic visco-elastic time is inversely proportional to the compression speed. Actin bundles are therefore not simple force transmitters, but instead, complex mechano-transducers that adjust their mechanics to external stimulation. In cells, where actin bundles are mechanical sensors, this property could contribute to their adaptability.

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Research paper thumbnail of Directed Actin Assembly and Motility

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Research paper thumbnail of Geometrical Control of Actin Assembly and Contractility

Methods in Cell Biology, 2014

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Research paper thumbnail of Actin Dynamics, Architecture, and Mechanics in Cell Motility

Physiological Reviews, 2014

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Research paper thumbnail of Devices and Methods for Controlling Actin Filaments Growth and Organization Using Micropatterned Nucleation Sites

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Research paper thumbnail of Actin Network Architecture Can Determine Myosin Motor Activity

Science, 2012

The organization of actin filaments into higher-ordered structures governs eukaryotic cell shape ... more The organization of actin filaments into higher-ordered structures governs eukaryotic cell shape and movement. Global actin network size and architecture are maintained in a dynamic steady state through regulated assembly and disassembly. Here, we used experimentally defined actin structures in vitro to investigate how the activity of myosin motors depends on network architecture. Direct visualization of filaments revealed myosin-induced actin network deformation. During this reorganization, myosins selectively contracted and disassembled antiparallel actin structures, while parallel actin bundles remained unaffected. The local distribution of nucleation sites and the resulting orientation of actin filaments appeared to regulate the scalability of the contraction process. This "orientation selection" mechanism for selective contraction and disassembly suggests how the dynamics of the cellular actin cytoskeleton can be spatially controlled by actomyosin contractility.

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Research paper thumbnail of Turnover of branched actin filament networks by stochastic fragmentation with ADF/cofilin.

Molecular Biology of the Cell, 2011

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Research paper thumbnail of Nucleation geometry governs ordered actin networks structures

Nature Materials, 2010

Actin filaments constitute one of the main components of cell cytoskeleton. Assembled into bundle... more Actin filaments constitute one of the main components of cell cytoskeleton. Assembled into bundles in filopodia or in stress fibres, they play a pivotal role in eukaryotes during cell morphogenesis, adhesion and motility. The bundle emergence has been extensively related to specific actin regulators in vivo. Such dynamic modulation was also highlighted by biochemical reconstitution of the actin-network assembly, in bulk solution or with biomimetic devices. However, the question of how geometrical boundaries, such as those encountered in cells, affect the dynamic formation of highly ordered actin structures remains poorly studied. Here we demonstrate that the nucleation geometry in itself can be the principal determinant of actin-network architecture. We developed a micropatterning method that enables the spatial control of actin nucleation sites for in vitro assays. Shape, orientation and distance between nucleation regions control filament orientation and length, filament-filament interactions and filopodium-like bundle formation. Modelling of filament growth and interactions demonstrates that basic mechanical and probabilistic laws govern actin assembly in higher-order structures.

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Research paper thumbnail of How actin network dynamics control the onset of actin-based motility

Proceedings of the National Academy of Sciences, 2012

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Research paper thumbnail of Autonomous and in trans functions for the two halves of Srv2/CAP in promoting actin turnover

Cytoskeleton, 2014

Recent evidence has suggested that Srv2/CAP (cyclase-associated protein) has two distinct functio... more Recent evidence has suggested that Srv2/CAP (cyclase-associated protein) has two distinct functional roles in regulating actin turnover, with its N-terminus enhancing cofilin-mediated severing of actin filaments and its C-terminus catalyzing actin monomer recycling. However, it has remained unclear to what degree these two activities are coordinated by being linked in one molecule, or whether they can function autonomously. To address this, we physically divided the protein into two separate halves, N-Srv2 and C-Srv2, and asked whether they are able to function in trans both in living cells and in reconstituted assays for F-actin turnover and actin-based motility. Remarkably, in F-actin turnover assays the stimulatory effects of N-Srv2 and C-Srv2 functioning in trans were quantitatively similar to those of intact full-length Srv2. Further, in bead motility assays and in vivo, the fragments again functioned in trans, although not with the full effectiveness of intact Srv2. From these data, we conclude that the functions of the two halves of Srv2/CAP are largely autonomous, although their linkage improves coordination of the two functions in specific settings, possibly explaining why the linkage is conserved across distant plant, animal, and fungal species.

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Research paper thumbnail of A “Primer”-Based Mechanism Underlies Branched Actin Filament Network Formation and Motility

Current Biology, 2010

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Research paper thumbnail of Actin-Filament Stochastic Dynamics Mediated by ADF/Cofilin

Current Biology, 2007

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Research paper thumbnail of Cofilin Tunes the Nucleotide State of Actin Filaments and Severs at Bare and Decorated Segment Boundaries

Current Biology, 2011

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Research paper thumbnail of Actin dynamics in plant cells: a team effort from multiple proteins orchestrates this very fast-paced game

Current Opinion in Plant Biology, 2010

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Research paper thumbnail of A Novel Mechanism for the Formation of Actin-Filament Bundles by a Nonprocessive Formin

Current Biology, 2006

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Research paper thumbnail of A Novel Mechanism for Actin Filament Bundle Formation by a Non-processive Formin

ABSTRACT

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Research paper thumbnail of Reconstitution of actin-based motility of Listeria and Shigella using pure proteins

Nature, Jan 7, 1999

Actin polymerization is essential for cell locomotion and is thought to generate the force respon... more Actin polymerization is essential for cell locomotion and is thought to generate the force responsible for cellular protrusions. The Arp2/3 complex is required to stimulate actin assembly at the leading edge in response to signalling. The bacteria Listeria and Shigella bypass the signalling pathway and harness the Arp2/3 complex to induce actin assembly and to propel themselves in living cells. However, the Arp2/3 complex alone is insufficient to promote movement. Here we have used pure components of the actin cytoskeleton to reconstitute sustained movement in Listeria and Shigella in vitro. Actin-based propulsion is driven by the free energy released by ATP hydrolysis linked to actin polymerization, and does not require myosin. In addition to actin and activated Arp2/3 complex, actin depolymerizing factor (ADF, or cofilin) and capping protein are also required for motility as they maintain a high steady-state level of G-actin, which controls the rate of unidirectional growth of act...

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Research paper thumbnail of 13 Actin-based Motility of Listeria monocytogenes and Shigella flexeneri

Methods in Microbiology, 2002

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Research paper thumbnail of The Arp2/3 complex branches filament barbed ends: functional antagonism with capping proteins.

Nature cell biology, 2000

The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling an... more The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling and generates a dendritic array of filaments in lamellipodia. Here we show that the activated Arp2/3 complex interacts with the barbed ends of filaments to initiate barbed-end branching. Barbed-end branching by Arp2/3 quantitatively accounts for polymerization kinetics and for the length correlation of the branches of filaments observed by electron microscopy. Filament branching is visualized at the surface of Listeria in a reconstituted motility assay. The functional antagonism between the Arp2/3 complex and capping proteins is essential in the maintenance of the steady state of actin assembly and actin-based motility.

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Research paper thumbnail of Network heterogeneity regulates steering in actin- based motility

The growth of branched actin networks powers cell-edge protrusions and motility. A heterogeneous ... more The growth of branched actin networks powers cell-edge protrusions and motility. A heterogeneous density of actin, which yields to a tunable cellular response, characterizes these dynamic structures. We study how actin organization controls both the rate and the steering during lamellipodium growth. We use a high-resolution surface structuration assay combined with mathematical modeling to describe the growth of a reconstituted lamellipo-dium. We demonstrate that local monomer depletion at the site of assembly negatively impacts the network growth rate. At the same time, network architecture tunes the pro-trusion efficiency, and regulates the rate of growth. One consequence of this interdependence between monomer depletion and network architecture effects is the ability of heterogeneous network to impose steering during motility. Therefore, we have established that the general principle, by which the cell can modulate the rate and the direction of a protrusion, is by varying both density and architecture of its actin network.

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Research paper thumbnail of Adaptive Response of Actin Bundles under Mechanical Stress

Actin is one of the main components of the architecture of cells. Actin filaments form different ... more Actin is one of the main components of the architecture of cells. Actin filaments form different polymer networks with versatile mechanical properties that depend on their spatial organization and the presence of cross-linkers. Here, we investigate the mechanical properties of actin bundles in the absence of cross-linkers. Bundles are polymerized from the surface of mDia1-coated latex beads, and deformed by manipulating both ends through attached beads held by optical tweezers, allowing us to record the applied force. Bundle properties are strikingly different from the ones of a homogeneous isotropic beam. Successive compression and extension leads to a decrease in the buckling force that we attribute to the bundle remaining slightly curved after the first deformation. Furthermore, we find that the bundle is solid, and stiff to bending, along the long axis, whereas it has a liquid and viscous behavior in the transverse direction. Interpretation of the force curves using a Maxwell visco-elastic model allows us to extract the bundle mechanical parameters and confirms that the bundle is composed of weakly coupled filaments. At short times, the bundle behaves as an elastic material, whereas at long times, filaments flow in the longitudinal direction, leading to bundle restructuring. Deviations from the model reveal a complex adaptive rheological behavior of bundles. Indeed, when allowed to anneal between phases of compression and extension, the bundle reinforces. Moreover, we find that the characteristic visco-elastic time is inversely proportional to the compression speed. Actin bundles are therefore not simple force transmitters, but instead, complex mechano-transducers that adjust their mechanics to external stimulation. In cells, where actin bundles are mechanical sensors, this property could contribute to their adaptability.

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Research paper thumbnail of Directed Actin Assembly and Motility

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Research paper thumbnail of Geometrical Control of Actin Assembly and Contractility

Methods in Cell Biology, 2014

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Research paper thumbnail of Actin Dynamics, Architecture, and Mechanics in Cell Motility

Physiological Reviews, 2014

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Devices and Methods for Controlling Actin Filaments Growth and Organization Using Micropatterned Nucleation Sites

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Actin Network Architecture Can Determine Myosin Motor Activity

Science, 2012

The organization of actin filaments into higher-ordered structures governs eukaryotic cell shape ... more The organization of actin filaments into higher-ordered structures governs eukaryotic cell shape and movement. Global actin network size and architecture are maintained in a dynamic steady state through regulated assembly and disassembly. Here, we used experimentally defined actin structures in vitro to investigate how the activity of myosin motors depends on network architecture. Direct visualization of filaments revealed myosin-induced actin network deformation. During this reorganization, myosins selectively contracted and disassembled antiparallel actin structures, while parallel actin bundles remained unaffected. The local distribution of nucleation sites and the resulting orientation of actin filaments appeared to regulate the scalability of the contraction process. This "orientation selection" mechanism for selective contraction and disassembly suggests how the dynamics of the cellular actin cytoskeleton can be spatially controlled by actomyosin contractility.

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Research paper thumbnail of Turnover of branched actin filament networks by stochastic fragmentation with ADF/cofilin.

Molecular Biology of the Cell, 2011

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Research paper thumbnail of Nucleation geometry governs ordered actin networks structures

Nature Materials, 2010

Actin filaments constitute one of the main components of cell cytoskeleton. Assembled into bundle... more Actin filaments constitute one of the main components of cell cytoskeleton. Assembled into bundles in filopodia or in stress fibres, they play a pivotal role in eukaryotes during cell morphogenesis, adhesion and motility. The bundle emergence has been extensively related to specific actin regulators in vivo. Such dynamic modulation was also highlighted by biochemical reconstitution of the actin-network assembly, in bulk solution or with biomimetic devices. However, the question of how geometrical boundaries, such as those encountered in cells, affect the dynamic formation of highly ordered actin structures remains poorly studied. Here we demonstrate that the nucleation geometry in itself can be the principal determinant of actin-network architecture. We developed a micropatterning method that enables the spatial control of actin nucleation sites for in vitro assays. Shape, orientation and distance between nucleation regions control filament orientation and length, filament-filament interactions and filopodium-like bundle formation. Modelling of filament growth and interactions demonstrates that basic mechanical and probabilistic laws govern actin assembly in higher-order structures.

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Research paper thumbnail of How actin network dynamics control the onset of actin-based motility

Proceedings of the National Academy of Sciences, 2012

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Research paper thumbnail of Autonomous and in trans functions for the two halves of Srv2/CAP in promoting actin turnover

Cytoskeleton, 2014

Recent evidence has suggested that Srv2/CAP (cyclase-associated protein) has two distinct functio... more Recent evidence has suggested that Srv2/CAP (cyclase-associated protein) has two distinct functional roles in regulating actin turnover, with its N-terminus enhancing cofilin-mediated severing of actin filaments and its C-terminus catalyzing actin monomer recycling. However, it has remained unclear to what degree these two activities are coordinated by being linked in one molecule, or whether they can function autonomously. To address this, we physically divided the protein into two separate halves, N-Srv2 and C-Srv2, and asked whether they are able to function in trans both in living cells and in reconstituted assays for F-actin turnover and actin-based motility. Remarkably, in F-actin turnover assays the stimulatory effects of N-Srv2 and C-Srv2 functioning in trans were quantitatively similar to those of intact full-length Srv2. Further, in bead motility assays and in vivo, the fragments again functioned in trans, although not with the full effectiveness of intact Srv2. From these data, we conclude that the functions of the two halves of Srv2/CAP are largely autonomous, although their linkage improves coordination of the two functions in specific settings, possibly explaining why the linkage is conserved across distant plant, animal, and fungal species.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A “Primer”-Based Mechanism Underlies Branched Actin Filament Network Formation and Motility

Current Biology, 2010

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Research paper thumbnail of Actin-Filament Stochastic Dynamics Mediated by ADF/Cofilin

Current Biology, 2007

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Research paper thumbnail of Cofilin Tunes the Nucleotide State of Actin Filaments and Severs at Bare and Decorated Segment Boundaries

Current Biology, 2011

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Research paper thumbnail of Actin dynamics in plant cells: a team effort from multiple proteins orchestrates this very fast-paced game

Current Opinion in Plant Biology, 2010

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Research paper thumbnail of A Novel Mechanism for the Formation of Actin-Filament Bundles by a Nonprocessive Formin

Current Biology, 2006

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A Novel Mechanism for Actin Filament Bundle Formation by a Non-processive Formin

ABSTRACT

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Reconstitution of actin-based motility of Listeria and Shigella using pure proteins

Nature, Jan 7, 1999

Actin polymerization is essential for cell locomotion and is thought to generate the force respon... more Actin polymerization is essential for cell locomotion and is thought to generate the force responsible for cellular protrusions. The Arp2/3 complex is required to stimulate actin assembly at the leading edge in response to signalling. The bacteria Listeria and Shigella bypass the signalling pathway and harness the Arp2/3 complex to induce actin assembly and to propel themselves in living cells. However, the Arp2/3 complex alone is insufficient to promote movement. Here we have used pure components of the actin cytoskeleton to reconstitute sustained movement in Listeria and Shigella in vitro. Actin-based propulsion is driven by the free energy released by ATP hydrolysis linked to actin polymerization, and does not require myosin. In addition to actin and activated Arp2/3 complex, actin depolymerizing factor (ADF, or cofilin) and capping protein are also required for motility as they maintain a high steady-state level of G-actin, which controls the rate of unidirectional growth of act...

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Research paper thumbnail of 13 Actin-based Motility of Listeria monocytogenes and Shigella flexeneri

Methods in Microbiology, 2002

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Research paper thumbnail of The Arp2/3 complex branches filament barbed ends: functional antagonism with capping proteins.

Nature cell biology, 2000

The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling an... more The Arp2/3 complex is an essential regulator of actin polymerization in response to signalling and generates a dendritic array of filaments in lamellipodia. Here we show that the activated Arp2/3 complex interacts with the barbed ends of filaments to initiate barbed-end branching. Barbed-end branching by Arp2/3 quantitatively accounts for polymerization kinetics and for the length correlation of the branches of filaments observed by electron microscopy. Filament branching is visualized at the surface of Listeria in a reconstituted motility assay. The functional antagonism between the Arp2/3 complex and capping proteins is essential in the maintenance of the steady state of actin assembly and actin-based motility.

Bookmarks Related papers MentionsView impact