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A vertically extended, isodiametric and horizontally extended cell. Shown are cell diameters measured along the direction of a cell row.

A vertically extended, isodiametric and horizontally extended cell. Shown are cell diameters measured along the direction of a cell row.

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Article
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Many important morphogenetic processes that take place in the development of an animal start from the segregation of a homogeneous layer of cells into a different number of the domains of columnar and flattened cells. In many cases, waves of cell shape transformation travel throughout embryonic tissues. A biomechanical model is presented which embr...

Citations

... In normal devel opment, this force is produced by tangential contrac tion of a dense cell group (cell domain) (Fig. 6a). By means of modeling, Beloussov and Grabovsky (2005) studied the morphogenetic role of the delay Δt of intercalation response to distension. Within the framework of this model it was shown that prolonged delays lead to the formation of a single extensive domain; if delays are shorter, a number of smaller domains are formed (Fig. 6b). ...
... Morphogenetic role of delays: (a) transition from passive extension of the right part of the cell layer by a domain of colum nar cells of the left part to active cell insertion in the right part; the second phase comes after the first by Δt; (b) modeling of domain organization of circular cell layer of constant length at different Δt ranging within 1 > Δt > 0. As Δt decreases, the number of columnar domains increases and the number of cells in each of them decreases (afterBeloussov and Grabovsky, 2005). ...
Article
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The presence and morphogenetic role of relatively autonomous pacemakers (“clocks”) during ontogeny is discussed. Although autonomous pacemakers in the strict sense seem nonexistent, the study of temporal processes is of great importance for recognizing the fundamental morphogenetic mechanisms. The most important and insufficiently understood questions in this field include the presence of hierarchies of characteristic times and their smoothing during critical developmental periods and also regulation of spatial processes via temporal delays.
... This problem was explored by assuming (Beloussov and Grabovsky 2005) that TIAE is switched on after exceeding certain tension threshold Tthr (normalized in the range 0 < Tthr < 1). ...
Chapter
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We start from reviewing several ubiquitous approaches to morphogenesis and argue that for a more adequate presentation of morphogenesis, they should be replaced by explanatory constructions based upon the self-organization theory (SOT). The first step on this way will be in describing morphogenetic events in terms of the symmetry theory, to distinguish the processes driven either toward increase or toward decrease of the symmetry order and to use Curie principle as a clue. We will show that the only way to combine this principle with experimental data is to conclude that morphogenesis passes via a number of instabilities. The latter, in their turn, point to the domination of nonlinear regimes. Accordingly, we come to the realm of SOT and give a survey of the dynamic modes which it provides. By discussing the physical basis of embryonic self-organization, we focus ourselves on the role of mechanical stresses. We suggest that many (although no all) morphogenetic events can be regarded as retarded relaxations of previously accumulated elastic stresses toward a restricted number of metastable energy wells.
... This problem was explored by assuming (Beloussov and Grabovsky 2005) that TIAE is switched on after exceeding certain tension threshold Tthr (normalized in the range 0 < Tthr < 1). ...
Chapter
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Regular patterns of mechanical stresses are perfectly expressed on the macromorphological level in the embryos of all taxonomic groups studied in this respect. Stress patterns are characterized by the topological invariability retained during prolonged time periods and drastically changing in between. After explanting small pieces of embryonic tissues, they are restored within several dozens minutes. Disturbance of stress patterns in developing embryos irreversibly breaks the long-range order of subsequent development. Morphogenetically important stress patterns are established by three geometrically different modes of cell alignment: parallel, perpendicular, and oblique. The first of them creates prolonged files of actively elongated cells. The second is responsible for segregation of an epithelial layer to the domains of columnar and flattened cells. The model of this process, demonstrating its scaling capacities, is described. The third mode which follows the previous one is responsible for making the curvatures. It is associated with formation of “cell fans,” the universal devices for shapes formation due to slow relaxation of the stored elastic energy.
... This problem was explored by assuming (Beloussov and Grabovsky 2005) that TIAE is switched on after exceeding certain tension threshold Tthr (normalized in the range 0 < Tthr < 1). ...
Book
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This book outlines a unified theory of embryonic development, assuming morphogenesis to be a multi-level process including self-organizing steps while also obeying general laws. It is shown how molecular mechanisms generate mechanical forces, which in the long run lead to morphological changes. Questions such as how stress-mediated feedback acts at the cellular and supra-cellular levels and how executive and regulatory mechanisms are mutually dependent are addressed, while aspects of collective cell behavior and the morphogenesis of plants are also discussed. The morphomechanical approach employed in the book is based on the general principles of self-organization theory.
... This problem was explored by assuming (Beloussov and Grabovsky 2005) that TIAE is switched on after exceeding certain tension threshold Tthr (normalized in the range 0 < Tthr < 1). ...
Chapter
An attempt is made to reconstruct the natural successions of the developmental events on the basis of a common mechanically based trend. It is formulated in terms of a hyper-restoration (HR) hypothesis claiming that embryonic tissue responds to any external deforming force by generating its own one, directed toward the restoration of the initial stress value, but as a rule overshooting it in the opposite side. We give a mathematical formulation of this model, present a number of supporting evidences, and describe several HR-driven feedbacks which may drive forth morphogenesis. We use this approach for reconstructing in greater detail the gastrulation of the embryos from different taxonomic groups. Also, we discuss the application of this model to cytotomy, ooplasmic segregation, and shape complication of tubular rudiments (taking hydroid polyps as examples). In addition, we review the perspectives for applying morphomechanical approach to the problem of cell differentiation.
... Such a regime may take place in reversible processes (typical for adult state) but it will not provide any kind of progressive irreversible morphological differentiation as the negative feedbacks do. As shown by modeling (Beloussov and Grabovsky, 2005 ...
... This may be the way for producing serial folding patterns, exemplified by scales, denticles , etc. Fig. 12B displays such a pattern emerged as a kind of a self-organization in explants of embryonic ectoderm. A role of several uniformly distributed morpho-mechanical parameters in regulating the folding has been modeled elsewhere (Beloussov and Grabovsky, 2005, 2007). A particular case of a fold is a lip, a widely spread bi-layered embryonic structure, characterized by unilateral connection of its commonly curved layers (Fig. 12C). ...
Article
We start from reviewing different epistemological constructions used for explaining morphogenesis. Among them, we explore the explanatory power of a law-centered approach which includes top-down causation and the basic concepts of a self-organization theory. Within such a framework, we discuss the morphomechanical models based upon the presumption of feedbacks between mechanical stresses imposed onto a given embryo part from outside and those generated within the latter as a kind of active response. A number of elementary morphogenetic events demonstrating that these feedbacks are directed towards hyper-restoration (restoration with an overshoot) of the initial state of mechanical stresses are described. Moreover, we show that these reactions are bound together into the larger scale feedbacks. That permits to suggest a reconstruction of morphogenetic successions in early Metazoan development concentrated around two main archetypes distinguished by the blastopores geometry. The perspectives of applying the same approach to cell differentiation are outlined. By discussing the problem of positional information we suggest that the developmental pathway of a given embryo part depends upon its preceded deformations and the corresponding mechanical stresses rather than upon its static position at any moment of development.
... Together with the Belintzev situation (taken as a limiting case) it plays a central role in patterning quite diverse embryonic samples (figures 10(A)-(C)). The CE feedback was a matter of modeling ( Beloussov and Grabovsky 2005), in which the D 3 )), which under further AET decrease will become non-stationary, transforming themselves into running waves. The introduction of the AET parameters deprives the model of absolute scale invariance, but retains it within biologically plausible limits. ...
Article
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A deep (although at the first glance naïve) question which may be addressed to embryonic development is why during this process quite definite and accurately reproduced successions of precise and complicated shapes are taking place, or why, in several cases, the result of development is highly precise in spite of an extensive variability of intermediate stages. This problem can be attacked in two different ways. One of them, up to now just slightly employed, is to formulate robust macroscopic generative laws from which the observed successions of shapes could be derived. Another one, which dominates in modern embryology, regards the development as a succession of highly precise 'micropatterns', each of them arising due to the action of specific factors, having, as a rule, nothing in common with each other. We argue that the latter view contradicts a great bulk of firmly established data and gives no satisfactory answers to the main problems of development. Therefore we intend to follow the first way. By doing this, we regard developing embryos as self-organized systems transpierced by feedbacks among which we pay special attention to those linked with mechanical stresses (MS). We formulate a hypothesis of so-called MS hyper-restoration as a common basis for the developmentally important feedback loops. We present a number of examples confirming this hypothesis and use it for reconstructing prolonged chains of developmental events. Finally, we discuss the application of the same set of assumptions to the first steps of egg development and to the internal differentiation of embryonic cells.
... To these belong, for example, the critical values of the externally applied stresses required for switching-on the active sample's responses, the rates and the values of the responses themselves and, as a special category , the temporal patterns of either passive or active stresses (see below). In this section two such models are briefly described (for more details see Beloussov and Grabovsky, 2003 Grabovsky, , 2005). ...
Article
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How a developing embryo becomes "informed" about its form?" This problem remains obscure and controversial. We argue that the "information about a form" is distributed throughout three main components: the dynamic laws, the parameters and the initial/boundary conditions. In the absence of a dynamic law two other components are "blind", that is, do not contain any unambiguous information. We present a version of a dynamic law of morphogenesis, based upon the presumption of a feedback between passive and active mechanical stresses. We explore several models of shape formation based upon this law and show that, as depending upon the parameters values, they generate a large set of realistic shapes. Genetic and epigenetic basis of the models parameters is discussed.
Article
The laboratory is engaged in morphomechanics—the study of self-organization of mechanical forces that create the shape and structure of the embryonic primordia. As part of its work, the laboratory described pulsating modes of mechanical stresses in hydroids, identified and mapped mechanical stresses in the tissues of amphibian embryos, and studied morphogenetic reorganization caused by the relaxation and reorientation of tensions. The role of mechanical stresses in maintaining the orderly architectonics of the embryo is shown. Mechano-dependent genes are detected. Microstrains of embryonic tissues and stress gradients associated with them are described. A model of hyper-recovery of mechanical stresses as a possible driving force of morphogenesis is proposed.
Article
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A fundamental problem of morphogenesis is whether it presents itself as a succession of links that are each driven by its own specific cause-effect relationship, or whether all of the links can be embraced by a common law that is possible to formulate in physical terms. We suggest that a common biophysical background for most, if not all, morphogenetic processes is based upon feedback between mechanical stresses (MS) that are imposed to a given part of a developing embryo by its other parts and MS that are actively generated within that part. The latter are directed toward hyper-restoration (restoration with an overshoot) of the initial MS values. We show that under mechanical constraints imposed by other parts, these tendencies drive forth development. To provide specificity for morphogenetic reactions, this feedback should be modulated by long-term parameters and/or initial conditions that are set up by genetic factors. The experimental and model data related to this concept are reviewed. Graphical abstract