vincent fleury - Academia.edu (original) (raw)
Papers by vincent fleury
Physical Review Letters, 1992
%'e propose a model for the motion of the fluid How, for the electric field, and for the concentr... more %'e propose a model for the motion of the fluid How, for the electric field, and for the concentration map around the branches during electrodeposition of ramified metal clusters in two-dimensional cells. This model accounts for the observed distribution of ions in the solution around the metal tips.
Physical Review A, 1991
We report an extensive study of electrochemical deposition of copper with growth under galvanosta... more We report an extensive study of electrochemical deposition of copper with growth under galvanostatic conditions and parallel geometry. In such conditions a clear understanding of the origin of the ramified deposit and of its growth speed is possible, at least in the case of dense morphology. We confirm that this morphology belongs to a steady-state regime where growth can be modeled as the displacement of a Hat strip of nearly equipotential copper. The growth velocity is exactly the drift velocity of the anions, which is proportional to the current density. We also show that the mass of the deposit does not depend on the speed at which it was grown but only on the concentration of salt in the bulk of the electrolyte. We compute the modifications in concentration profiles and in the electric field due to pH changes during growth.
Physical Review A, 1991
We have studied the growth of electrodeposits from solutions of copper sulfate in thin cells, and... more We have studied the growth of electrodeposits from solutions of copper sulfate in thin cells, and focused our attention on the spectacular morphological transitions that occur in almost every experimental condition. We give experimental evidence and numerical and theoretical results showing that these transitions are due to the propagation of charged impurities leaving the dissolving anode at the beginning of the growth and hitting the deposit at later times. The arrival of the impurity front against the growing deposit modifies the growing conditions, thus leaving on the deposit the trace of an almost homothetical "ghost" image of the anode.
Cette Note présente un ensemble de preuves expérimentales démontrant que la formation du plan d’o... more Cette Note présente un ensemble de preuves expérimentales démontrant que la formation du plan d’organisation de l’embryon de poulet passe par un écoulement de tissu embryonnaire de nature hyperbolique. Il est suggéré que ce phénomène est général pour la formation des tétrapodes. A partir d’une configuration initialement 2D (« coque » ou « plaque » de tissu au sens mécanique), un écoulement visco-élastique de tissu, bidirectionnel dans le sens Antéro-Postérieur et bi-directionnel dans le sens Gauche–Droite forme l’embryon aviaire typique. Cet écoulement présente un point neutre, identifié comme un point de stagnation de l’écoulement. Ce point est rigoureusement situé à l’emplacement du pédicule vitellin présomptif des oiseaux (analogue du nombril des mammifères). Autour du point de stagnation, l’écoulement présente une brisure de symétrie se traduisant par une symétrie miroir Gauche-Droite et Haut-Bas. Cette brisure de symétrie est transmise à tous les stades ultérieurs de développem...
The European Physical Journal E, 2019
Current knowledge on limbs development lacks a physical description of the forces leading to form... more Current knowledge on limbs development lacks a physical description of the forces leading to formation of the limbs precursors or "buds". Earlier stages of development are driven by large scale morphogenetic movements, such as dipolar vortical flows and mechanical buckling, pulled by rings of cells. It is a natural hypothesis that similar phenomena occur during limb formation. However it is difficult to experiment on the developmental forces, in such a complex dynamic system. Here, we report a physical study of hindlimb bud formation in the chicken embryo. We use electrical stimulation to enhance the physical forces present in the tissue, prior to limb bud formation. By triggering the physical forces in a rapid and amplified pattern, we reveal the mechanism of formation of the hindlimbs : the early presumptive embryonic territory is composed of a set of rings encased like russian-dolls. Each ring constricts in an excitable pattern of force, and the limb buds are generated by folding at a pre-existing boundary between two rings, forming the dorsal and ventral ectoderms. The amniotic sac buckles at another boundary. Physiologically, the actuator of the excitable force is the tail bud pushing posteriorly along the median axis. The developmental dynamics suggests how animals may evolve by modification of the magnitude of these forces, within a common broken symmetry. On a practical level, localized electrical stimulation of morphogenetic forces opens the way to in vivo electrical engineering of tissues.
The European Physical Journal E, 2016
We present a novel elastography method for soft materials (100 Pa-100 kPa) based on indentation b... more We present a novel elastography method for soft materials (100 Pa-100 kPa) based on indentation by a μm-sized water jet. We show that the jet creates a localized deformation ("cavity") of the material that can be easily visualized. We study experimentally how cavity width and depth depend on jet speed, height, incidence angle and sample elasticity. We describe how to calibrate the indenter using gels of known stiffness. We then demonstrate that the indenter yields quantitative elasticity values within 10% of those measured by shear rheometry. We corroborate our experimental findings with fluid-solid finite-element simulations that quantitatively predict the cavity profile and fluid flow lines. The water jet indenter permits in situ local stiffness measurements of 2D or 3D gels used for cell culture in physiological buffer, is able to assess stiffness heterogeneities with a lateral resolution in the range 50-500 μm (at the tissue scale) and can be assembled at low cost with standard material from a biology laboratory. We therefore believe it will become a valuable method to measure the stiffness of a wide range of soft, synthetic or biological materials.
Physical Review E, 2016
We present a detailed study of the formation of the amniotic sac in the avian embryo, and a compa... more We present a detailed study of the formation of the amniotic sac in the avian embryo, and a comparison with the crocodile amniotic sac. We show that the amniotic sac forms at a circular line of stiffness contrast, separating rings of cell domains. Cells align at this boundary, and this in turn orients and concentrates the tension forces. The tissue fold which forms the amniotic sac is locked exactly along this line due to the colocalization of the stiffness contrast and of the tensile force. In addition, the tensile force plays a regenerative role when the amniotic sac is cut. The fold forming the ventral side of the embryo displays the same characteristics. This work shows that amniote embryogenesis consists of a cascade of buckling events taking place at the boundaries between regions of differing mechanical properties. Hence, amniote embryogenesis relies on a simple and robust biomechanical scheme used repeatedly, and selected ancestrally.
In addition to a shared yolk sac, monochorionic chicken twins also have their circulatory systems... more In addition to a shared yolk sac, monochorionic chicken twins also have their circulatory systems intermingled, with both embryos perfusing each other. Of course, such unusual situations are not genetically encoded and are therefore valuable for understanding the contribution of epigenetic factors, such as hemodynamic shear or interstitial stress on the morphological evolution of the vascular system. We report on two serendipitous observations of the vascular pattern in eggs sheltering monochorionic twins. In both instances, the embryos were found head-to-head, but with different relative orientations and different vascular patterns. These difference in relative orientations of the embryos induces differences in : - relative positions of the localized high pressure sources (vitelline arteries rudiments in the presumptive navel areas of both embryos) and of the low pressure sinks (cranial and caudal vitelline veins rudiments) driving blood flow in the yolk sac area, - the shape of th...
Methods, 2016
Local mechanical properties play an important role in directing embryogenesis, both at the cell (... more Local mechanical properties play an important role in directing embryogenesis, both at the cell (differentiation, migration) and tissue level (force transmission, organ formation, morphogenesis). Measuring them is a challenge as embryonic tissues are small (lm to mm) and soft (0.1-10 kPa). We describe here how glass fiber cantilevers can be fabricated, calibrated and used to apply small forces (0.1-10 lN), measure contractile activity and assess the bulk tensile elasticity of embryonic tissue. We outline how pressure (hydrostatic or osmotic) can be applied to embryonic tissue to quantify stiffness anisotropy. These techniques can be assembled at low cost and with a minimal amount of equipment. We then present a protocol to prepare tissue sections for local elasticity and adhesion measurements using the atomic force microscope (AFM). We compare AFM nanoindentation maps of native and formaldehyde fixed embryonic tissue sections and discuss how the local elastic modulus obtained by AFM compares to that obtained with other bulk measurement methods. We illustrate all of the techniques presented on the specific example of the chick embryonic digestive tract, emphasizing technical issues and common pitfalls. The main purpose of this report is to make these micromechanical measurement techniques accessible to a wide community of biologists and biophysicists.
Branching in Nature, 2001
Physical Review E, 2008
The adult vasculature is comprised of three distinct compartments: the arteries, which carry bloo... more The adult vasculature is comprised of three distinct compartments: the arteries, which carry blood away from the heart and display a divergent flow pattern; the capillaries, where oxygen and nutrient delivery from blood to tissues, as well as metabolic waste removal, occurs; and the veins, which carry blood back to the heart and are characterized by a convergent flow pattern. These compartments are organized in series as regard to flow, which proceeds from the upstream arteries to the downstream veins through the capillaries. However, the spatial organization is more complex, as veins may often be found paralleling the arteries. The factors that control the morphogenesis of this hierarchically branched vascular network are not well characterized. Here, we explain how arteries exert a morphological control on the venous pattern. Indeed, during vertebrate development, the following transition may be observed in the spatial organization of the vascular system: veins first develop in series with the arteries, the arterial and venous territories being clearly distinct in space ͑cis-cis configuration͒. But after some time, new veins grow parallel to the existing arteries, and the arterial and venous territories become overlapped, with extensive and complex intercalation and interdigitation. Using physical arguments, backed up by experimental evidence ͑biological data from the literature and in situ optical and mechanical measurements of the chick embryo yolk-sac and midbrain developing vasculatures͒, we explain how such a transition is possible and why it may be expected with generality, as organisms grow. The origin of this transition lies in the remodeling of the capillary tissue in the vicinity of the growing arteries. This remodeling lays down a prepattern for further venous growth, parallel to the existing arterial pattern. Accounting for the influence of tissue growth, we show that this prepatterned path becomes favored as the body extends. As a consequence, a second flow route with veins paralleling the arteries ͑cis-trans configuration͒ emerges when the tissue extends. Between the cis-cis and cis-trans configurations, all configurations are in principle possible, and self-organization of the vessels contributes to determining their exact pattern. However, the global aspect depends on the size at which the growth stops and on the growth rate.
Physical Review E, 2006
Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upo... more Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upon perfusion, this lattice is remodeled into branched arteries and veins. Adaptation to mechanical forces is implied to play a major role in arterial patterning. However, numerical simulations of vessel adaptation to haemodynamics has so far failed to predict any realistic vascular pattern. We present in this article a theoretical modeling of vascular development in the yolk sac based on three features of vascular morphogenesis: the disconnection of side branches from main branches, the reconnection of dangling sprouts ͑"dead ends"͒, and the plastic extension of interstitial tissue, which we have observed in vascular morphogenesis. We show that the effect of Poiseuille flow in the vessels can be modeled by aggregation of random walkers. Solid tissue expansion can be modeled by a Poiseuille ͑parabolic͒ deformation, hence by deformation under hits of random walkers. Incorporation of these features, which are of a mechanical nature, leads to realistic modeling of vessels, with important biological consequences. The model also predicts the outcome of simple mechanical actions, such as clamping of vessels or deformation of tissue by the presence of obstacles. This study offers an explanation for flow-driven control of vascular branching morphogenesis.
Pediatric Research, 2005
The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal ... more The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal groove and subsequently early lung branching morphogenesis is mediated by finely regulated, interactive growth factor signaling mechanisms that determine the automaticity of branching, interbranch length, stereotypy of branching, left-right asymmetry, and finally gas diffusion surface area. The extracellular matrix is an important regulator as well as a target for growth factor signaling in lung branching morphogenesis and alveolarization. Coordination not only of epithelial but also endothelial branching morphogenesis determines bronchial branching and the eventual alveolar-capillary interface. Improved prospects for lung protection, repair, regeneration, and engineering will depend on more detailed understanding of these processes. Herein, we concisely review the functionally integrated morphogenetic signaling network comprising the critical bone morphogenetic protein, fibroblast growth factor, Sonic hedgehog, transforming growth factor-, vascular endothelial growth factor, and Wnt signaling pathways that specify and drive early embryonic lung morphogenesis. (Pediatr Res 57: 26R-37R, 2005) Abbreviations BMP, bone morphogenetic protein DKK, Dickkopf EGF (R), epidermal growth factor (receptor) ERK, extracellular regulated kinase FGF (R), fibroblast growth factor (receptor) FN, fibronectin LRP, lipoprotein receptor-related proteins MAP, membrane-associated protein PDGF, platelet-derived growth factor RAR, retinoic acid receptor sFRP, secreted Frizzled-related protein SHH, Sonic hedgehog Sp-C, surfactant protein C TGF-␣ (), transforming growth factor alpha (beta) VEGF (R), vascular endothelial growth factor (receptor)
Mechanisms of Development, 2008
Tracheal occlusion during lung development accelerates growth in response to increased intralumin... more Tracheal occlusion during lung development accelerates growth in response to increased intraluminal pressure. In order to investigate the role of internal pressure on murine early lung development, we cauterized the tip of the trachea, to occlude it, and thus to increase internal pressure. This method allowed us to evaluate the effect of tracheal occlusion on the first few branch generations and on gene expression. We observed that the elevation of internal pressure induced more than a doubling in branching, associated with increased proliferation, while branch elongation speed increased 3-fold. Analysis by RT-PCR showed that Fgf10, Vegf, Sprouty2 and Shh mRNA expressions were affected by the change of intraluminal pressure after 48 h of culture, suggesting mechanotransduction via internal pressure of these key developmental genes. Tracheal occlusion did not increase the number of branches of Fgfr2 À/À mice lungs nor of wild type lungs cultured with Fgfr2b antisense RNA. Tracheal occlusion of Fgf10 LacZ/À hypomorphic lungs led to the formation of fewer branches than in wild type. We conclude that internal pressure regulates the FGF10-FGFR2b-Sprouty2 pathway and thus the speed of the branching process. Therefore pressure levels, fixed both by epithelial secretion and boundary conditions, can control the branching process via FGF10-FGFR2b-Sprouty2.
The European Physical Journal Applied Physics, 2011
There is increasing evidence that animal morphogenesis consists of a large scale tissue flow, whi... more There is increasing evidence that animal morphogenesis consists of a large scale tissue flow, which defines the gross characteristics of the animal body at a very early developmental stage. We have studied the vertebrate embryo cell trajectories between a moment when it is flat and formless, to a moment when the body plan is recognizable (chicken embryo days 2-3 of development). We find that a large vortex flow patterns the vertebrate bauplan, and especially the limb territories, both hindlimbs and forelimbs. In vivo velocity measurements show that the vortices are dragged by a localized shear oriented along the median axis. A simple hydrodynamic model accounts for the lenticular shape of the limb plates. On the hindlimb plate, the flow propagates in the form of a solid-body vortex on the limb plate, dragged by a Poiseuille flow along the backbone. In vivo tonometry measurements show that there exist stress gradients in the embryonic tissue, and that the flow pattern is congruent with the direction of decrease of stress magnitude.
The European Physical Journal Applied Physics, 2009
The origin of tetrapods is a complex question that webs together genetic, paleontological, develo... more The origin of tetrapods is a complex question that webs together genetic, paleontological, developmental and physical facts. Basically, the development of embryos is described by a complex mix of mechanical movements and biochemical inductions of genetic origin. It is difficult to sort out in this scientific question what are the fundamental features imposed by conservation laws of physics, and by force equilibria, and what can be ascribed to successive, very specific, stop-and-go inductions of genetic nature. A posteriori, evolution selects the parameters of this process as found in the observed species. Whether there is a general law to animal formation seems out of the question. However, several concepts developed in biology, like the concept of "organizer" seem questionable from a physics point of view, since the entire deformation and force field should be the "organizer" of development, and one can hardly ascribe such a role to a single small area of the embryo body. In the same spirit, the concept of "positional information" encapsulated in concentration of chemicals seems questionable since the deformation and force fields in embryonic tissues are tensors. Finally, the concept of a development organized in space along three orthogonal ("Cartesian") axes associated to chemical gradients seems also questionable, since early embryo development is driven by complex vortex fields, with hyperbolic trajectories which span the entire embryo. Such hyperbolic trajectories are best understood by a description in terms of dipolar components of the morphogenetic forces, whose projections along orthogonal axes have no specific meaning except as a mathematical tool. I review here the present state of description of several aspects of tetrapods morphogenesis and evolution, from the point of view of physics. It is getting clear that several basic features of tetrapods body are a direct consequences of fundamental laws of physics. Several lines of work reviewed here show that the topology of the tetrapods may be directly related to the structure of the earliest movements in embryos. The bio-mechanical approach leads to important consequences for the constraints on evolution of the craniates. Such consequences have received a controversial welcome in the last decade, although they may encapsulate the true origin of craniates, esp. simians, and eventually homo.
Development, 2003
Formation of the yolk sac vascular system and its connection to the embryonic circulation is cruc... more Formation of the yolk sac vascular system and its connection to the embryonic circulation is crucial for embryo survival in both mammals and birds. Most mice with mutations in genes involved in vascular development die because of a failure to establish this circulatory loop. Surprisingly,formation of yolk sac arteries and veins has not been well described in the recent literature. Using time-lapse video-microscopy, we have studied arterial-venous differentiation in the yolk sac of chick embryos. Immediately after the onset of perfusion, the yolk sac exhibits a posterior arterial and an anterior venous pole, which are connected to each other by cis-cis endothelial interactions. To form the paired and interlaced arterial-venous pattern characteristic of mature yolk sac vessels, small caliber vessels of the arterial domain are selectively disconnected from the growing arterial tree and subsequently reconnected to the venous system, implying that endothelial plasticity is needed to fash...
Physical Review Letters, 1992
%'e propose a model for the motion of the fluid How, for the electric field, and for the concentr... more %'e propose a model for the motion of the fluid How, for the electric field, and for the concentration map around the branches during electrodeposition of ramified metal clusters in two-dimensional cells. This model accounts for the observed distribution of ions in the solution around the metal tips.
Physical Review A, 1991
We report an extensive study of electrochemical deposition of copper with growth under galvanosta... more We report an extensive study of electrochemical deposition of copper with growth under galvanostatic conditions and parallel geometry. In such conditions a clear understanding of the origin of the ramified deposit and of its growth speed is possible, at least in the case of dense morphology. We confirm that this morphology belongs to a steady-state regime where growth can be modeled as the displacement of a Hat strip of nearly equipotential copper. The growth velocity is exactly the drift velocity of the anions, which is proportional to the current density. We also show that the mass of the deposit does not depend on the speed at which it was grown but only on the concentration of salt in the bulk of the electrolyte. We compute the modifications in concentration profiles and in the electric field due to pH changes during growth.
Physical Review A, 1991
We have studied the growth of electrodeposits from solutions of copper sulfate in thin cells, and... more We have studied the growth of electrodeposits from solutions of copper sulfate in thin cells, and focused our attention on the spectacular morphological transitions that occur in almost every experimental condition. We give experimental evidence and numerical and theoretical results showing that these transitions are due to the propagation of charged impurities leaving the dissolving anode at the beginning of the growth and hitting the deposit at later times. The arrival of the impurity front against the growing deposit modifies the growing conditions, thus leaving on the deposit the trace of an almost homothetical "ghost" image of the anode.
Cette Note présente un ensemble de preuves expérimentales démontrant que la formation du plan d’o... more Cette Note présente un ensemble de preuves expérimentales démontrant que la formation du plan d’organisation de l’embryon de poulet passe par un écoulement de tissu embryonnaire de nature hyperbolique. Il est suggéré que ce phénomène est général pour la formation des tétrapodes. A partir d’une configuration initialement 2D (« coque » ou « plaque » de tissu au sens mécanique), un écoulement visco-élastique de tissu, bidirectionnel dans le sens Antéro-Postérieur et bi-directionnel dans le sens Gauche–Droite forme l’embryon aviaire typique. Cet écoulement présente un point neutre, identifié comme un point de stagnation de l’écoulement. Ce point est rigoureusement situé à l’emplacement du pédicule vitellin présomptif des oiseaux (analogue du nombril des mammifères). Autour du point de stagnation, l’écoulement présente une brisure de symétrie se traduisant par une symétrie miroir Gauche-Droite et Haut-Bas. Cette brisure de symétrie est transmise à tous les stades ultérieurs de développem...
The European Physical Journal E, 2019
Current knowledge on limbs development lacks a physical description of the forces leading to form... more Current knowledge on limbs development lacks a physical description of the forces leading to formation of the limbs precursors or "buds". Earlier stages of development are driven by large scale morphogenetic movements, such as dipolar vortical flows and mechanical buckling, pulled by rings of cells. It is a natural hypothesis that similar phenomena occur during limb formation. However it is difficult to experiment on the developmental forces, in such a complex dynamic system. Here, we report a physical study of hindlimb bud formation in the chicken embryo. We use electrical stimulation to enhance the physical forces present in the tissue, prior to limb bud formation. By triggering the physical forces in a rapid and amplified pattern, we reveal the mechanism of formation of the hindlimbs : the early presumptive embryonic territory is composed of a set of rings encased like russian-dolls. Each ring constricts in an excitable pattern of force, and the limb buds are generated by folding at a pre-existing boundary between two rings, forming the dorsal and ventral ectoderms. The amniotic sac buckles at another boundary. Physiologically, the actuator of the excitable force is the tail bud pushing posteriorly along the median axis. The developmental dynamics suggests how animals may evolve by modification of the magnitude of these forces, within a common broken symmetry. On a practical level, localized electrical stimulation of morphogenetic forces opens the way to in vivo electrical engineering of tissues.
The European Physical Journal E, 2016
We present a novel elastography method for soft materials (100 Pa-100 kPa) based on indentation b... more We present a novel elastography method for soft materials (100 Pa-100 kPa) based on indentation by a μm-sized water jet. We show that the jet creates a localized deformation ("cavity") of the material that can be easily visualized. We study experimentally how cavity width and depth depend on jet speed, height, incidence angle and sample elasticity. We describe how to calibrate the indenter using gels of known stiffness. We then demonstrate that the indenter yields quantitative elasticity values within 10% of those measured by shear rheometry. We corroborate our experimental findings with fluid-solid finite-element simulations that quantitatively predict the cavity profile and fluid flow lines. The water jet indenter permits in situ local stiffness measurements of 2D or 3D gels used for cell culture in physiological buffer, is able to assess stiffness heterogeneities with a lateral resolution in the range 50-500 μm (at the tissue scale) and can be assembled at low cost with standard material from a biology laboratory. We therefore believe it will become a valuable method to measure the stiffness of a wide range of soft, synthetic or biological materials.
Physical Review E, 2016
We present a detailed study of the formation of the amniotic sac in the avian embryo, and a compa... more We present a detailed study of the formation of the amniotic sac in the avian embryo, and a comparison with the crocodile amniotic sac. We show that the amniotic sac forms at a circular line of stiffness contrast, separating rings of cell domains. Cells align at this boundary, and this in turn orients and concentrates the tension forces. The tissue fold which forms the amniotic sac is locked exactly along this line due to the colocalization of the stiffness contrast and of the tensile force. In addition, the tensile force plays a regenerative role when the amniotic sac is cut. The fold forming the ventral side of the embryo displays the same characteristics. This work shows that amniote embryogenesis consists of a cascade of buckling events taking place at the boundaries between regions of differing mechanical properties. Hence, amniote embryogenesis relies on a simple and robust biomechanical scheme used repeatedly, and selected ancestrally.
In addition to a shared yolk sac, monochorionic chicken twins also have their circulatory systems... more In addition to a shared yolk sac, monochorionic chicken twins also have their circulatory systems intermingled, with both embryos perfusing each other. Of course, such unusual situations are not genetically encoded and are therefore valuable for understanding the contribution of epigenetic factors, such as hemodynamic shear or interstitial stress on the morphological evolution of the vascular system. We report on two serendipitous observations of the vascular pattern in eggs sheltering monochorionic twins. In both instances, the embryos were found head-to-head, but with different relative orientations and different vascular patterns. These difference in relative orientations of the embryos induces differences in : - relative positions of the localized high pressure sources (vitelline arteries rudiments in the presumptive navel areas of both embryos) and of the low pressure sinks (cranial and caudal vitelline veins rudiments) driving blood flow in the yolk sac area, - the shape of th...
Methods, 2016
Local mechanical properties play an important role in directing embryogenesis, both at the cell (... more Local mechanical properties play an important role in directing embryogenesis, both at the cell (differentiation, migration) and tissue level (force transmission, organ formation, morphogenesis). Measuring them is a challenge as embryonic tissues are small (lm to mm) and soft (0.1-10 kPa). We describe here how glass fiber cantilevers can be fabricated, calibrated and used to apply small forces (0.1-10 lN), measure contractile activity and assess the bulk tensile elasticity of embryonic tissue. We outline how pressure (hydrostatic or osmotic) can be applied to embryonic tissue to quantify stiffness anisotropy. These techniques can be assembled at low cost and with a minimal amount of equipment. We then present a protocol to prepare tissue sections for local elasticity and adhesion measurements using the atomic force microscope (AFM). We compare AFM nanoindentation maps of native and formaldehyde fixed embryonic tissue sections and discuss how the local elastic modulus obtained by AFM compares to that obtained with other bulk measurement methods. We illustrate all of the techniques presented on the specific example of the chick embryonic digestive tract, emphasizing technical issues and common pitfalls. The main purpose of this report is to make these micromechanical measurement techniques accessible to a wide community of biologists and biophysicists.
Branching in Nature, 2001
Physical Review E, 2008
The adult vasculature is comprised of three distinct compartments: the arteries, which carry bloo... more The adult vasculature is comprised of three distinct compartments: the arteries, which carry blood away from the heart and display a divergent flow pattern; the capillaries, where oxygen and nutrient delivery from blood to tissues, as well as metabolic waste removal, occurs; and the veins, which carry blood back to the heart and are characterized by a convergent flow pattern. These compartments are organized in series as regard to flow, which proceeds from the upstream arteries to the downstream veins through the capillaries. However, the spatial organization is more complex, as veins may often be found paralleling the arteries. The factors that control the morphogenesis of this hierarchically branched vascular network are not well characterized. Here, we explain how arteries exert a morphological control on the venous pattern. Indeed, during vertebrate development, the following transition may be observed in the spatial organization of the vascular system: veins first develop in series with the arteries, the arterial and venous territories being clearly distinct in space ͑cis-cis configuration͒. But after some time, new veins grow parallel to the existing arteries, and the arterial and venous territories become overlapped, with extensive and complex intercalation and interdigitation. Using physical arguments, backed up by experimental evidence ͑biological data from the literature and in situ optical and mechanical measurements of the chick embryo yolk-sac and midbrain developing vasculatures͒, we explain how such a transition is possible and why it may be expected with generality, as organisms grow. The origin of this transition lies in the remodeling of the capillary tissue in the vicinity of the growing arteries. This remodeling lays down a prepattern for further venous growth, parallel to the existing arterial pattern. Accounting for the influence of tissue growth, we show that this prepatterned path becomes favored as the body extends. As a consequence, a second flow route with veins paralleling the arteries ͑cis-trans configuration͒ emerges when the tissue extends. Between the cis-cis and cis-trans configurations, all configurations are in principle possible, and self-organization of the vessels contributes to determining their exact pattern. However, the global aspect depends on the size at which the growth stops and on the growth rate.
Physical Review E, 2006
Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upo... more Vascularization of embryonic organs or tumors starts from a primitive lattice of capillaries. Upon perfusion, this lattice is remodeled into branched arteries and veins. Adaptation to mechanical forces is implied to play a major role in arterial patterning. However, numerical simulations of vessel adaptation to haemodynamics has so far failed to predict any realistic vascular pattern. We present in this article a theoretical modeling of vascular development in the yolk sac based on three features of vascular morphogenesis: the disconnection of side branches from main branches, the reconnection of dangling sprouts ͑"dead ends"͒, and the plastic extension of interstitial tissue, which we have observed in vascular morphogenesis. We show that the effect of Poiseuille flow in the vessels can be modeled by aggregation of random walkers. Solid tissue expansion can be modeled by a Poiseuille ͑parabolic͒ deformation, hence by deformation under hits of random walkers. Incorporation of these features, which are of a mechanical nature, leads to realistic modeling of vessels, with important biological consequences. The model also predicts the outcome of simple mechanical actions, such as clamping of vessels or deformation of tissue by the presence of obstacles. This study offers an explanation for flow-driven control of vascular branching morphogenesis.
Pediatric Research, 2005
The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal ... more The "hard wiring" encoded within the genome that determines the emergence of the laryngotracheal groove and subsequently early lung branching morphogenesis is mediated by finely regulated, interactive growth factor signaling mechanisms that determine the automaticity of branching, interbranch length, stereotypy of branching, left-right asymmetry, and finally gas diffusion surface area. The extracellular matrix is an important regulator as well as a target for growth factor signaling in lung branching morphogenesis and alveolarization. Coordination not only of epithelial but also endothelial branching morphogenesis determines bronchial branching and the eventual alveolar-capillary interface. Improved prospects for lung protection, repair, regeneration, and engineering will depend on more detailed understanding of these processes. Herein, we concisely review the functionally integrated morphogenetic signaling network comprising the critical bone morphogenetic protein, fibroblast growth factor, Sonic hedgehog, transforming growth factor-, vascular endothelial growth factor, and Wnt signaling pathways that specify and drive early embryonic lung morphogenesis. (Pediatr Res 57: 26R-37R, 2005) Abbreviations BMP, bone morphogenetic protein DKK, Dickkopf EGF (R), epidermal growth factor (receptor) ERK, extracellular regulated kinase FGF (R), fibroblast growth factor (receptor) FN, fibronectin LRP, lipoprotein receptor-related proteins MAP, membrane-associated protein PDGF, platelet-derived growth factor RAR, retinoic acid receptor sFRP, secreted Frizzled-related protein SHH, Sonic hedgehog Sp-C, surfactant protein C TGF-␣ (), transforming growth factor alpha (beta) VEGF (R), vascular endothelial growth factor (receptor)
Mechanisms of Development, 2008
Tracheal occlusion during lung development accelerates growth in response to increased intralumin... more Tracheal occlusion during lung development accelerates growth in response to increased intraluminal pressure. In order to investigate the role of internal pressure on murine early lung development, we cauterized the tip of the trachea, to occlude it, and thus to increase internal pressure. This method allowed us to evaluate the effect of tracheal occlusion on the first few branch generations and on gene expression. We observed that the elevation of internal pressure induced more than a doubling in branching, associated with increased proliferation, while branch elongation speed increased 3-fold. Analysis by RT-PCR showed that Fgf10, Vegf, Sprouty2 and Shh mRNA expressions were affected by the change of intraluminal pressure after 48 h of culture, suggesting mechanotransduction via internal pressure of these key developmental genes. Tracheal occlusion did not increase the number of branches of Fgfr2 À/À mice lungs nor of wild type lungs cultured with Fgfr2b antisense RNA. Tracheal occlusion of Fgf10 LacZ/À hypomorphic lungs led to the formation of fewer branches than in wild type. We conclude that internal pressure regulates the FGF10-FGFR2b-Sprouty2 pathway and thus the speed of the branching process. Therefore pressure levels, fixed both by epithelial secretion and boundary conditions, can control the branching process via FGF10-FGFR2b-Sprouty2.
The European Physical Journal Applied Physics, 2011
There is increasing evidence that animal morphogenesis consists of a large scale tissue flow, whi... more There is increasing evidence that animal morphogenesis consists of a large scale tissue flow, which defines the gross characteristics of the animal body at a very early developmental stage. We have studied the vertebrate embryo cell trajectories between a moment when it is flat and formless, to a moment when the body plan is recognizable (chicken embryo days 2-3 of development). We find that a large vortex flow patterns the vertebrate bauplan, and especially the limb territories, both hindlimbs and forelimbs. In vivo velocity measurements show that the vortices are dragged by a localized shear oriented along the median axis. A simple hydrodynamic model accounts for the lenticular shape of the limb plates. On the hindlimb plate, the flow propagates in the form of a solid-body vortex on the limb plate, dragged by a Poiseuille flow along the backbone. In vivo tonometry measurements show that there exist stress gradients in the embryonic tissue, and that the flow pattern is congruent with the direction of decrease of stress magnitude.
The European Physical Journal Applied Physics, 2009
The origin of tetrapods is a complex question that webs together genetic, paleontological, develo... more The origin of tetrapods is a complex question that webs together genetic, paleontological, developmental and physical facts. Basically, the development of embryos is described by a complex mix of mechanical movements and biochemical inductions of genetic origin. It is difficult to sort out in this scientific question what are the fundamental features imposed by conservation laws of physics, and by force equilibria, and what can be ascribed to successive, very specific, stop-and-go inductions of genetic nature. A posteriori, evolution selects the parameters of this process as found in the observed species. Whether there is a general law to animal formation seems out of the question. However, several concepts developed in biology, like the concept of "organizer" seem questionable from a physics point of view, since the entire deformation and force field should be the "organizer" of development, and one can hardly ascribe such a role to a single small area of the embryo body. In the same spirit, the concept of "positional information" encapsulated in concentration of chemicals seems questionable since the deformation and force fields in embryonic tissues are tensors. Finally, the concept of a development organized in space along three orthogonal ("Cartesian") axes associated to chemical gradients seems also questionable, since early embryo development is driven by complex vortex fields, with hyperbolic trajectories which span the entire embryo. Such hyperbolic trajectories are best understood by a description in terms of dipolar components of the morphogenetic forces, whose projections along orthogonal axes have no specific meaning except as a mathematical tool. I review here the present state of description of several aspects of tetrapods morphogenesis and evolution, from the point of view of physics. It is getting clear that several basic features of tetrapods body are a direct consequences of fundamental laws of physics. Several lines of work reviewed here show that the topology of the tetrapods may be directly related to the structure of the earliest movements in embryos. The bio-mechanical approach leads to important consequences for the constraints on evolution of the craniates. Such consequences have received a controversial welcome in the last decade, although they may encapsulate the true origin of craniates, esp. simians, and eventually homo.
Development, 2003
Formation of the yolk sac vascular system and its connection to the embryonic circulation is cruc... more Formation of the yolk sac vascular system and its connection to the embryonic circulation is crucial for embryo survival in both mammals and birds. Most mice with mutations in genes involved in vascular development die because of a failure to establish this circulatory loop. Surprisingly,formation of yolk sac arteries and veins has not been well described in the recent literature. Using time-lapse video-microscopy, we have studied arterial-venous differentiation in the yolk sac of chick embryos. Immediately after the onset of perfusion, the yolk sac exhibits a posterior arterial and an anterior venous pole, which are connected to each other by cis-cis endothelial interactions. To form the paired and interlaced arterial-venous pattern characteristic of mature yolk sac vessels, small caliber vessels of the arterial domain are selectively disconnected from the growing arterial tree and subsequently reconnected to the venous system, implying that endothelial plasticity is needed to fash...