Morphomechanical rules of embryonic development.

We start by comparing two explicatory approaches, which we call law-centered and "instructivistic". Although the latter dominates in modern biology, we find it inappropriate for treating developmental problems, especially those related to morphogenesis. As an example of a law-centered approach we suggest a simple morphomechanical rule based upon the idea of the hyper-restoration of mechanical stresses.

Morphomechanical reactions and mechanically stressed structures in amphibian embryos, as related to gastrulation and axial organs formation.

Reactions of embryonic tissues to a distributed and concentrated stretching are described and compared with the mechanics of the normal gastrulation movements. A role of mechanically stressed dynamic cell structures in the gastrulation, demarcation of notochord borders and in providing proportionality of the axial rudiments is demonstrated. A morphomechanical scheme of amphibian gastrulation is presented.

Local and global dynamics in collective movements of embryonic cells.

Several important morphogenetic processes belong to the category of collective cell movements (CCM), by which we mean coordinated rearrangements of many neighboring cells. The causes of the dynamic order established during CCM are still unclear. We performed statistical studies of rates and angular orientations of cell rearrangements in two kinds of embryonic tissues, which we categorized as "committed" (in the sense of being capable of autonomous CCM) as opposed to "naïve" tissues, which are those that require external forces in order to exhibit full scale CCM.

Stress-generating tissue deformations in Xenopus embryos: Long-range gradients and local cell displacements.

Background: Although the role of endogenous mechanical stresses in regulating morphogenetic movements and cell differentiation is now well established, many aspects of mechanical stress generation and transmission in developing embryos remain unclear and require quantitative studies.

Results: By measuring stress-bearing linear deformations (caused by differences in cell movement rates) in the outer cell layer of blastula - early tail-bud Xenopus embryos, we revealed a set of long-term tension-generating gradients of cell movement rates, modulated by short-term cell-cell displacements much increasing the rates of local deformations. Experimental relaxation of tensions distorted the gradients but preserved and even enhanced local cell-cell displacements.

Two ways for interpreting Driesch's law: "Positional information" and morphogenetic fields.

The late Lev V. Beloussov wrote a 2005 textbook The Foundations of General Embryology which is available in Russian. In 2003 he prepared an excellent, annotated translation of the part of his manuscript for this book on distinguishing positional information models from morphogenetic field models of embryogenesis, which is reproduced here verbatim.