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Ashley E.e. Bruce - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of zebrafish Epiboly: A current view
Current topics in developmental biology, 2019Co-Authors: Ashley E.e. Bruce, Carl-philipp HeisenbergAbstract:Abstract Epiboly is a conserved gastrulation movement describing the thinning and spreading of a sheet or multi-layer of cells. The zebrafish embryo has emerged as a vital model system to address the cellular and molecular mechanisms that drive Epiboly. In the zebrafish embryo, the blastoderm, consisting of a simple squamous epithelium (the enveloping layer) and an underlying mass of deep cells, as well as a yolk nuclear syncytium (the yolk syncytial layer) undergo Epiboly to internalize the yolk cell during gastrulation. The major events during zebrafish Epiboly are: expansion of the enveloping layer and the internal yolk syncytial layer, reduction and removal of the yolk membrane ahead of the advancing blastoderm margin and deep cell rearrangements between the enveloping layer and yolk syncytial layer to thin the blastoderm. Here, work addressing the cellular and molecular mechanisms as well as the sources of the mechanical forces that underlie these events is reviewed. The contribution of recent findings to the current model of Epiboly as well as open questions and future prospects are also discussed.
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Spatiotemporal characterization of dynamic epithelial filopodia during zebrafish Epiboly.
Developmental dynamics : an official publication of the American Association of Anatomists, 2019Co-Authors: Nathan E. Rutherford, Alex M. H. Wong, Ashley E.e. BruceAbstract:BACKGROUND During zebrafish Epiboly, the embryonic cell mass, or blastoderm, spreads to enclose the yolk cell. The blastoderm consists of an outer epithelial sheet, the enveloping layer (EVL), and the underlying deep cell layer (DEL). Studies have provided insights into the mechanisms of EVL and deep cell Epiboly, but little is known about the interactions between the two cell layers and what role they may play during Epiboly. RESULTS We used live imaging to examine EVL basal protrusions. We identified them as filopodia based on f-actin content and localization of fluorescently tagged filopodial markers. A spatiotemporal analysis revealed that the largest number of EVL filopodia were present during early Epiboly at the animal pole. In functional studies, expression of a constitutively active actin-bundling protein resulted in increased filopodial length and delayed gastrulation. CONCLUSIONS We identified protrusions on the basal surface of EVL cells as filopodia and showed that they are present throughout the EVL during Epiboly. The largest number of filopodia was at the animal pole during early Epiboly, which is when and where deep cell radial intercalations occur to the greatest extent. These findings suggest that EVL filopodia may function during Epiboly to promote deep cell rearrangements during Epiboly initiation.
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Zebrafish Epiboly: Spreading thin over the yolk.
Developmental dynamics : an official publication of the American Association of Anatomists, 2015Co-Authors: Ashley E.e. BruceAbstract:Tissue thinning and spreading, a morphogenetic movement termed Epiboly, is used widely during animal development. In zebrafish, Epiboly is a prominent cell movement during gastrulation, whereby a squamous epithelium (the enveloping layer), a multi-layer of loosely packed cells (the deep cells), and a yolk nuclear syncytium (the yolk syncytial layer) undergo coordinated expansion to engulf the yolk and close the blastopore. Elucidating the mechanisms that underlie Epiboly is important not only for understanding animal development in general, but also for providing insights into fundamental cell behaviors including cell intercalation, cell adhesion, cell signaling, and epithelial morphogenesis. Here, recent work is reviewed with a focus on findings that advance our understanding of (1) the role of actomyosin motors in the yolk cell to drive Epiboly, (2) the mechanisms that underlie the spreading of the epithelial enveloping layer, and (3) the regulation of deep cell movements by E-cadherin based adhesion. A discussion of how these new insights add to the current view of Epiboly and future prospects is also presented. Overall, the study of zebrafish Epiboly can provide general and broadly applicable insights into the genetic, molecular, and cellular control of morphogenesis.
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Dynamin-dependent maintenance of epithelial integrity is essential for zebrafish Epiboly.
Bioarchitecture, 2014Co-Authors: Stephanie E. Lepage, Ashley E.e. BruceAbstract:Epiboly, the thinning and spreading of one tissue over another, is a widely employed morphogenetic movement that is essential for the development of many organisms. In the zebrafish embryo, Epiboly describes the coordinated vegetal movement of the deep cells, enveloping layer (EVL) and yolk syncytial layer (YSL) to engulf the yolk cell. Recently, we showed that the large GTPase Dynamin plays a fundamental role in Epiboly in the early zebrafish embryo. Because Dynamin plays a well-described role in vesicle scission during endocytosis, we predicted that Dynamin might regulate Epiboly through participating in bulk removal of the yolk cell membrane ahead of the advancing margin, a proposed part of the Epiboly motor. Unexpectedly, we found that Dynamin function was dispensable in the yolk cell and instead, it was required to maintain the epithelial integrity of the EVL during Epiboly. Here, we present a model describing the maintenance of EVL integrity, which is required for the proper generation and transmiss...
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Zebrafish Dynamin is required for maintenance of enveloping layer integrity and the progression of Epiboly.
Developmental biology, 2013Co-Authors: Stephanie E. Lepage, Masazumi Tada, Ashley E.e. BruceAbstract:Epiboly, the first morphogenetic cell movement that occurs in the zebrafish embryo, is the process by which the blastoderm thins and spreads to engulf the yolk cell. This process requires the concerted actions of the deep cells, the enveloping layer (EVL) and the extra-embryonic yolk syncytial layer (YSL). The EVL is mechanically coupled to the YSL which acts as an Epiboly motor, generating the force necessary to draw the blastoderm towards the vegetal pole though actomyosin flow and contraction of the actomyosin ring. However, it has been proposed that the endocytic removal of yolk cell membrane just ahead of the advancing blastoderm may also play a role. To assess the contribution of yolk cell endocytosis in driving Epiboly movements, we used a combination of drug- and dominant-negative-based approaches to inhibit Dynamin, a large GTPase with a well-characterized role in vesicle scission. We show that Dynamin-dependent endocytosis in the yolk cell is dispensable for Epiboly of the blastoderm. However, global inhibition of Dynamin function revealed that Dynamin plays a fundamental role within the blastoderm during Epiboly, where it maintains epithelial integrity and the transmission of tension across the EVL. The epithelial defects were associated with disrupted tight junctions and a striking reduction of cortically localized phosphorylated ezrin/radixin/moesin (P-ERM), key regulators of epithelial integrity in other systems. Furthermore, we show that Dynamin maintains EVL and promotes Epiboly progression by antagonizing Rho A activity.
Wolfgang Driever - One of the best experts on this subject based on the ideXlab platform.
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Progesterone modulates microtubule dynamics and Epiboly progression during zebrafish gastrulation.
Developmental biology, 2017Co-Authors: Stephanie Eckerle, Mario Ringler, Virginie Lecaudey, Roland Nitschke, Wolfgang DrieverAbstract:Control of microtubule dynamics is crucial for cell migration. We analyzed regulation of microtubule network dynamics in the zebrafish yolk cell during Epiboly, the earliest coordinated gastrulation movement. We labeled microtubules with EMTB-3GFP and EB3-mCherry to visualize and measure microtubule dynamics by TIRF microscopy live imaging. Yolk cell microtubules dynamics is temporally modulated during Epiboly progression. We used maternal zygotic Pou5f3 mutant (MZspg) embryos, which develop strong distortions of microtubule network organization and Epiboly retardation, to investigate genetic control of microtubule dynamics. In MZspg embryos, microtubule plus-end growth tracks move slower and are less straight compared to wild-type. MZspg embryos have altered steroidogenic enzyme expression, resulting in increased pregnenolone and reduced progesterone levels. We show that progesterone positively affects microtubule plus-end growth and track straightness. Progesterone may thus act as a non-cell-autonomous regulator of microtubule dynamics across the large yolk cell, and may adjust differing demands on microtubule dynamics and stability during initiation and progression phases of Epiboly.
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Non-directional radial intercalation dominates deep cell behavior during zebrafish Epiboly.
Biology open, 2013Co-Authors: Robert Bensch, Sungmin Song, Olaf Ronneberger, Wolfgang DrieverAbstract:Epiboly is the first coordinated cell movement in most vertebrates and marks the onset of gastrulation. During zebrafish Epiboly, enveloping layer (EVL) and deep cells spread over the vegetal yolk mass with a concomitant thinning of the deep cell layer. A prevailing model suggests that deep cell radial intercalations directed towards the EVL would drive deep cell Epiboly. To test this model, we have globally recorded 3D cell trajectories for zebrafish blastomeres between sphere and 50% Epiboly stages, and developed an image analysis framework to determine intercalation events, intercalation directionality, and migration speed for cells at specific positions within the embryo. This framework uses Voronoi diagrams to compute cell-to-cell contact areas, defines a feature-based spatio-temporal model for intercalation events and fits an anatomical coordinate system to the recorded datasets. We further investigate whether Epiboly defects in MZspg mutant embryos devoid of Pou5f1/Oct4 may be caused by changes in intercalation behavior. In wild-type and mutant embryos, intercalations orthogonal to the EVL occur with no directional bias towards or away from the EVL, suggesting that there are no directional cues that would direct intercalations towards the EVL. Further, we find that intercalation direction is independent of the previous intercalation history of individual deep cells, arguing against cues that would program specific intrinsic directed migration behaviors. Our data support a dynamic model in which deep cells during Epiboly migrate into space opening between the EVL and the yolk syncytial layer. Genetic programs determining cell motility may control deep cell dynamic behavior and Epiboly progress.
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alterations of the cytoskeleton in all three embryonic lineages contribute to the Epiboly defect of pou5f1 oct4 deficient mzspg zebrafish embryos
Developmental Biology, 2008Co-Authors: Martina Lachnit, Esther Kur, Wolfgang DrieverAbstract:Pou5f1/Oct4 is a transcription factor required for pluripotency of embryonic stem cells in mammals. Zebrafish pou5f1 deficient maternal and zygotic spiel ohne grenzen (MZspg) mutant embryos develop severe gastrulation defects, are dorsalized, and defective in endoderm formation. Here we analyze in detail gastrulation defects, which are manifested by a severe delay in Epiboly progression. All three embryonic lineages in MZspg embryos behave abnormally during Epiboly: the yolk cell forms an altered array of cortical microtubules and F-Actin, with large patches of microtubule free areas; the enveloping layer (EVL) is delayed in the coordinated cell shape changes of marginal cells, that may be mediated by F-Actin; the deep layer cells (DEL), forming the embryo proper, are non-autonomously affected in their motility and do not enter the space opening by Epiboly of the EVL. Analysis of adhesiveness as well as high resolution in vivo time lapse image analysis of DEL cells suggests changed adhesive properties and inability to migrate properly on EVL and yolk syncytial layer (YSL) surfaces. Our data further reveal that during Epiboly the EVL may actively probe the YSL by filopodia formation, rather than just being passively pulled vegetalwards. Our findings on the effect of Pou5f1 on cell behavior may be relevant to understand stem cell behavior and tumorigenesis involving Pou5f1.
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Alterations of the cytoskeleton in all three embryonic lineages contribute to the Epiboly defect of Pou5f1/Oct4 deficient MZspg zebrafish embryos.
Developmental biology, 2007Co-Authors: Martina Lachnit, Esther Kur, Wolfgang DrieverAbstract:Pou5f1/Oct4 is a transcription factor required for pluripotency of embryonic stem cells in mammals. Zebrafish pou5f1 deficient maternal and zygotic spiel ohne grenzen (MZspg) mutant embryos develop severe gastrulation defects, are dorsalized, and defective in endoderm formation. Here we analyze in detail gastrulation defects, which are manifested by a severe delay in Epiboly progression. All three embryonic lineages in MZspg embryos behave abnormally during Epiboly: the yolk cell forms an altered array of cortical microtubules and F-Actin, with large patches of microtubule free areas; the enveloping layer (EVL) is delayed in the coordinated cell shape changes of marginal cells, that may be mediated by F-Actin; the deep layer cells (DEL), forming the embryo proper, are non-autonomously affected in their motility and do not enter the space opening by Epiboly of the EVL. Analysis of adhesiveness as well as high resolution in vivo time lapse image analysis of DEL cells suggests changed adhesive properties and inability to migrate properly on EVL and yolk syncytial layer (YSL) surfaces. Our data further reveal that during Epiboly the EVL may actively probe the YSL by filopodia formation, rather than just being passively pulled vegetalwards. Our findings on the effect of Pou5f1 on cell behavior may be relevant to understand stem cell behavior and tumorigenesis involving Pou5f1.
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Microtubule arrays of the zebrafish yolk cell: organization and function during Epiboly.
Development, 1994Co-Authors: Lilianna Solnica-krezel, Wolfgang DrieverAbstract:In zebrafish (Danio rerio), meroblastic cleavages generate an embryo in which blastomeres cover the animal pole of a large yolk cell. At the 500-1000 cell stage, the marginal blastomeres fuse with the yolk cell forming the yolk syncytial layer. During Epiboly the blastoderm and the yolk syncytial layer spread toward the vegetal pole. We have studied developmental changes in organization and function during Epiboly of two distinct microtubule arrays located in the cortical cytoplasm of the yolk cell. In the anuclear yolk cytoplasmic layer, an array of microtubules extends along the animal-vegetal axis to the vegetal pole. In the early blastula the yolk cytoplasmic layer microtubules appear to originate from the marginal blastomeres. Once formed, the yolk syncytial layer exhibits its own network of intercrossing mitotic or interphase microtubules. The microtubules of the yolk cytoplasmic layer emanate from the microtubule network of the syncytial layer. At the onset of Epiboly, the external yolk syncytial layer narrows, the syncytial nuclei become tightly packed and the network of intercrossing microtubules surrounding them becomes denser. Soon after, there is a vegetal expansion of the blastoderm and of the yolk syncytial layer with its network of intercrossing microtubules. Concomitantly, the yolk cytoplasmic layer diminishes and its set of animal-vegetal microtubules becomes shorter. We investigated the involvement of microtubules in Epiboly using the microtubule depolymerizing agent nocodazole and a stabilizing agent taxol. In embryos treated with nocodazole, microtubules were absent and epibolic movements of the yolk syncytial nuclei were blocked. In contrast, the vegetal expansion of the enveloping layer and deep cells was only partially inhibited. The process of endocytosis, proposed to play a major role in Epiboly of the yolk syncytial layer (Betchaku, T. and Trinkaus, J. P. (1986) Am. Zool. 26, 193-199), was still observed in nocodazole-treated embryos. Treatment of embryos with taxol led to a delay in all epibolic movements. We propose that the yolk cell microtubules contribute either directly or indirectly to all epibolic movements. However, the epibolic movements of the yolk syncytial layer nuclei and of the blastoderm are not coupled, and only movements of the yolk syncytial nuclei are absolutely dependent on microtubules. We hypothesize that the microtubule network of the syncytial layer and the animal-vegetal set of the yolk cytoplasmic layer contribute differently to various aspects of Epiboly. Models that address the mechanisms by which the two microtubule arrays might function during Epiboly are discussed.
Carl-philipp Heisenberg - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of zebrafish Epiboly: A current view
Current topics in developmental biology, 2019Co-Authors: Ashley E.e. Bruce, Carl-philipp HeisenbergAbstract:Abstract Epiboly is a conserved gastrulation movement describing the thinning and spreading of a sheet or multi-layer of cells. The zebrafish embryo has emerged as a vital model system to address the cellular and molecular mechanisms that drive Epiboly. In the zebrafish embryo, the blastoderm, consisting of a simple squamous epithelium (the enveloping layer) and an underlying mass of deep cells, as well as a yolk nuclear syncytium (the yolk syncytial layer) undergo Epiboly to internalize the yolk cell during gastrulation. The major events during zebrafish Epiboly are: expansion of the enveloping layer and the internal yolk syncytial layer, reduction and removal of the yolk membrane ahead of the advancing blastoderm margin and deep cell rearrangements between the enveloping layer and yolk syncytial layer to thin the blastoderm. Here, work addressing the cellular and molecular mechanisms as well as the sources of the mechanical forces that underlie these events is reviewed. The contribution of recent findings to the current model of Epiboly as well as open questions and future prospects are also discussed.
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Tension-oriented cell divisions limit anisotropic tissue tension in epithelial spreading during zebrafish Epiboly
Nature Cell Biology, 2013Co-Authors: Pedro Campinho, Martin Behrndt, Jonas Ranft, Thomas Risler, Nicolas Minc, Carl-philipp HeisenbergAbstract:As epithelial tissue spreads during development and wound healing, epithelial integrity needs to be maintained. Heisenberg and colleagues show that tension modulates cell division orientations during zebrafish Epiboly through cell elongation and control of myosin II activity to prevent cell fusion and epithelial disruption. Epithelial spreading is a common and fundamental aspect of various developmental and disease-related processes such as epithelial closure and wound healing. A key challenge for epithelial tissues undergoing spreading is to increase their surface area without disrupting epithelial integrity. Here we show that orienting cell divisions by tension constitutes an efficient mechanism by which the enveloping cell layer (EVL) releases anisotropic tension while undergoing spreading during zebrafish Epiboly. The control of EVL cell-division orientation by tension involves cell elongation and requires myosin II activity to align the mitotic spindle with the main tension axis. We also found that in the absence of tension-oriented cell divisions and in the presence of increased tissue tension, EVL cells undergo ectopic fusions, suggesting that the reduction of tension anisotropy by oriented cell divisions is required to prevent EVL cells from fusing. We conclude that cell-division orientation by tension constitutes a key mechanism for limiting tension anisotropy and thus promoting tissue spreading during EVL Epiboly.
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The zebrafish Epiboly mutants
Development (Cambridge England), 1996Co-Authors: D. A. Kane, Mary C. Mullins, Matthias Hammerschmidt, Hans-martin Maischein, Michael Brand, F. J. M. Van Eeden, Makoto Furutani-seiki, Michael Granato, Pascal Haffter, Carl-philipp HeisenbergAbstract:Epiboly, the enveloping of the yolk cell by the blastoderm, is the first zebrafish morphogenetic movement. We isolated four mutations that affect Epiboly: half baked, avalanche, lawine and weg. Homozygous mutant embryos arrest the vegetal progress of the deep cells of the blastoderm; only the yolk syncytial layer of the yolk cell and the enveloping layer of the blastoderm reach the vegetal pole of the embryo. The mutations half baked, avalanche and lawine produce a novel dominant effect, termed a zygotic-maternal dominant effect: heterozygous embryos produced from heterozygous females slow down Epiboly and accumulate detached cells over the neural tube; a small fraction of these mutant individuals are viable. Heterozygous embryos produced from heterozygous males crossed to homozygous wild-type females complete Epiboly normally and are completely viable. Additionally, embryos heterozygous for half baked have an enlarged hatching gland, a partial dominant phenotype. The phenotypes of these mutants demonstrate that, for the spreading of cells during Epiboly, the movement of the deep cells of the blastoderm require the function of genes that are not necessary for the movement of the enveloping layer or the yolk cell. Furthermore, the dominant zygotic-maternal effect phenotypes illustrate the maternal and zygotic interplay of genes that orchestrate the early cell movements of the zebrafish.
Enrique Martin-blanco - One of the best experts on this subject based on the ideXlab platform.
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Contractility, differential tension and membrane removal lead zebrafish Epiboly biomechanics
Cell cycle (Georgetown Tex.), 2017Co-Authors: Maria Marsal, Amayra Hernández-vega, Enrique Martin-blancoAbstract:Precise tissue remodeling during development is essential for shaping embryos and optimal organ function. Epiboly is an early gastrulation event by which the blastoderm expands around the yolk to engulf it. Three different layers are involved in this process, an epithelial layer (the enveloping layer, EVL), the embryo proper, constituted by the deep cells (DCs), and the yolk cell. Although teleost Epiboly has been studied for many years, a clear understanding of its mechanics was still missing. Here we present new information on the cellular, molecular and mechanical elements involved in Epiboly that, together with some other recent data and upon comparison with previous biomechanical models, lets conclude that the expansion of the epithelia is passive and driven by active cortical contraction and membrane removal in the adjacent layer, the External Yolk Syncytial Layer (E-YSL). The isotropic actomyosin contraction of the E-YSL cortex generates an anisotropic stress pattern and a directional net movement consequence of the differences in the deformation response of the 2 opposites adjacent domains (EVL and the Yolk Cytoplasmic Layer - YCL). Contractility is accompanied by the local formation of membrane folds and its removal by Rab5ab dependent macropinocytosis. The increase in area of the epithelia during the expansion is achieved by cell-shape changes (flattening) responding to spherical geometrical cues. The counterbalance between the geometry of the embryo and forces dissipation among different elements is therefore essential for Epiboly global coordination.
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Contractility, Differential Tension and Membrane Removal direct zebrafish Epiboly Biomechanics
2017Co-Authors: Maria Marsal, Enrique Martin-blancoAbstract:Precise tissue remodeling during development is essential for shaping embryos and for optimal organ function. Epiboly is an early gastrulation event by which the blastoderm expands around the yolk to engulf it. Three different layers are involved, an epithelial layer (the enveloping layer, EVL), the embryo proper, constituted by the deep cells (DCs), and the yolk cell. Although teleost Epiboly has been studied for many years, a clear understanding of its mechanics was still missing. Here we present new information on the cellular, molecular and mechanical elements involved in Epiboly that, together with some other recent data and upon comparison with previous biomechanical models, lets conclude that the expansion of the epithelia is passive and driven by cortical contraction and membrane removal in the adjacent layer, the External Yolk Syncytial Layer (E-YSL). The isotropic actomyosin contraction of the E-YSL generates an anisotropic stress pattern and a directional net movement as a result of the differences in the deformation response of two opposites adjacent domains (the EVL and the Yolk Cytoplasmic Layer - YCL). Contractility is accompanied by the local formation of membrane folds and the membrane removal by Rab5ab dependent macropinocytosis. The increase in area of the epithelia during the expansion is achieved by cell-shape changes (flattening) responding to spherical geometrical cues. The counterbalance between the geometry of the embryo and forces dissipation is therefore essential for Epiboly global coordination.
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Rab5-mediated Yolk Cell Endocytosis modulates Zebrafish Epiboly Biomechanics and Tissue Movements
2016Co-Authors: Maria Marsal, Amayra Hernández-vega, Philippe-alexandre Pouille, Enrique Martin-blancoAbstract:Morphogenesis in early embryos demands the coordinated allocation of cells and tissues to their final end in a spatio-temporal controlled way. Topographical and scalar differences in adhesion and contractility are essential for these morphogenetic movements, while less clear are the roles that membrane remodeling (reviewed in [1]) may have. To determine how surface turnover may modulate tissue arrangements during embryogenesis we resorted to study Epiboly in the zebrafish. Experimental analyses and modeling have shown that the expansion of the blastoderm during Epiboly relies on an asymmetry of mechanical tension along the embryo surface [2]. In this scenario, we found that membrane turnover at the external yolk syncitial layer (E-YSL) in early zebrafish is mainly directed by the GTPase rab5ab. rab5ab was essential for endocytosis, and interference in its expression resulted in reduction of yolk acto-myosin contractility, disruption of cortical and internal flows, a disequilibrium in force balance and Epiboly impairment. We conclude that regulated membrane remodelling is crucial for directing cell and tissue mechanics and coordinating morphogenetic movements.
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Polarized cortical tension drives zebrafish Epiboly movements
The EMBO journal, 2016Co-Authors: Amayra Hernández-vega, Maria Marsal, Philippe-alexandre Pouille, Sébastien Tosi, Julien Colombelli, Tomás Luque, Daniel Navajas, Ignacio Pagonabarraga, Enrique Martin-blancoAbstract:Abstract The principles underlying the biomechanics of morphogenesis are largely unknown. Epiboly is an essential embryonic event in which three tissues coordinate to direct the expansion of the blastoderm. How and where forces are generated during Epiboly, and how these are globally coupled remains elusive. Here we developed a method, hydrodynamic regression (HR), to infer 3D pressure fields, mechanical power, and cortical surface tension profiles. HR is based on velocity measurements retrieved from 2D+T microscopy and their hydrodynamic modeling. We applied HR to identify biomechanically active structures and changes in cortex local tension during Epiboly in zebrafish. Based on our results, we propose a novel physical description for Epiboly, where tissue movements are directed by a polarized gradient of cortical tension. We found that this gradient relies on local contractile forces at the cortex, differences in elastic properties between cortex components and the passive transmission of forces within the yolk cell. All in all, our work identifies a novel way to physically regulate concerted cellular movements that might be instrumental for the mechanical control of many morphogenetic processes.
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Polarized Cortical Tension drives Zebrafish Epiboly Movements
2015Co-Authors: Amayra Hernández-vega, Maria Marsal, Philippe-alexandre Pouille, Sébastien Tosi, Julien Colombelli, Tomás Luque, Daniel Navajas, Ignacio Pagonabarraga, Enrique Martin-blancoAbstract:The physical principles underlying the biomechanics of morphogenetic processes are largely unknown. Epiboly is an essential embryonic event in which three distinct tissues coordinate to direct the expansion of the blastoderm. How and where forces are generated during Epiboly and how these are globally coupled remains elusive. Here we first develop a method, Hydrodynamic Regression (HR), to infer 3D dynamic pressure fields, mechanical power densities and cortical surface tension profiles within living organisms. HR is based on velocity measurements retrieved from 2D+T microscopy time-lapses and their hydrodynamic modeling. We then applied this method to identify biomechanically active structures during Epiboly in the zebrafish and the changes in the distribution of cortex local tension as Epiboly progresses. Based on these results, we propose a novel simple physical description for Epiboly, where tissue movements are directed by a polarized gradient of cortical tension. We found that this tensional gradient relies on local contractile forces at the cortex, differences in the elastic properties of cortex components and force passive transmission within the incompressible yolk cell. All in all, our work identifies a novel way to physically regulate concerted cellular movements that will be fundamental for the mechanical control of many morphogenetic processes.
Michael Lardelli - One of the best experts on this subject based on the ideXlab platform.
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zebrafish aplnra functions in Epiboly
BMC Research Notes, 2009Co-Authors: Svanhild Nornes, Ben Tucker, Michael LardelliAbstract:Background The zebrafish, Danio rerio, possesses the paralogous genes aplnra and aplnrb that are duplicates of an ancestral orthologue of the human APLNR gene encoding a G-protein coupled receptor that binds the peptide ligand APELIN and is required for normal cardiovascular function. aplnrb is required for migration of cells contributing to heart development in zebrafish embryos. aplnra is transcribed in a complex pattern during early development but its function in embryogenesis is largely unknown.
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zebrafish angiotensin ii receptor like 1a agtrl1a is expressed in migrating hypoblast vasculature and in multiple embryonic epithelia
Gene Expression Patterns, 2007Co-Authors: Ben Tucker, C Hepperle, D Kortschak, B Rainbird, Simon Wells, Andrew C Oates, Michael LardelliAbstract:Abstract The human gene AGTRL1 is an angiotensin II receptor-like gene expressed in vasculature, which acts as the receptor for the small peptide APELIN, and a co-receptor for Human Immunodeficiency Virus. Mammalian AGTRL1 has been shown to modulate cardiac contractility, venous and arterial dilation, and endothelial cell migration in vitro , but no role in the development of the vasculature, or other tissues, has been described. We report the identification and expression of the zebrafish ortholog of the human gene AGTRL1 . Zebrafish agtrl1a is first expressed before Epiboly in dorsal precursors. During Epiboly it is expressed in the enveloping layer, yolk syncytial layer and migrating mesendoderm. During segmentation stages, expression is observed in epithelial structures such as adaxial cells, border cells of the newly formed somites, developing lens, otic vesicles and venous vasculature.