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  • Whitley Vistisen posted an update 4 months, 1 week ago

    Active and passive mechanical cell properties, cellcell adhesion, signaling, and genetic control are the principal factors acting in a coordinated manner in order to organize tissues from simple embryonic cell clusters to ligree structures and well organized tissues.Its transparency signicantly facilitates microscopic D and D observation. A further reason is its outstanding regenerative tissue plasticity raising many questions concerning tissue engineering and regeneration research. Both possess stem cell populations which proliferate slowly but without limitations. Zebrash is one of the most common model organisms for investigating embryogenesis, due to its advantage of producing transparent eggs in large numbers.As a vertebrate, it shows many features of the more complex Alizarin development of higher organisms.The development of an early embryo is quite rapid and consist of a very large yolk cell carrying the blastomere at the animal pole.The cleavage period shows a perfectly synchronous sequence of divisions up to cells.Subsequently, synchronization gets lost and the circular bastodisc, of which the cell number is not counted anymore, begins attening after little more than three hours after fertilization.Afterwards, yolk cells begin bulging toward the animal pole and epiboly begins.The spherical symmetry is broken leading to a sequence of complex rearrangements resulting in the sh embryo. This development is surprising with a discretecontinuous transition leading to spherical symmetry which nally is broken again to allow more complex structures.Holtfreter surprised by bringing denatured tissues into contact to a developing alive tissue observing that induction of differentiation still takes place.He showed that development can also be triggered by other factors and assumed chemical cues. It took a long time, however, before the molecular components and the corresponding mechanisms were identied.The question is how spatiotemporal patterns arise in a featureless medium. Mathematical models showing instable features lead to a description of patternformation by reactiondiffusion equations.The approach considers two crosscoupled, spatiotemporal elds, an activator and an inhibitor eld acting in opposite ways.Hydra was suggested as a model organism being sufciently simple for a mathematical description.Hydra shows a quite simple morphology presenting an advantage for modeling attempts.Its reproduction versatility is particularly remarkable.Besides sexual proliferation, it shows spore formation and complete regeneration from tissue fragments.Bud formation in the column, however, is the predominant way.The hollow gastric column is conned by an epithelial doublelayer separated by an ECM structure. Hydras contain about cell types and three different stem cell lineages able to proliferate without limitation. Within this process, rst a hollow sphere is formed.The gastric column cells proliferate constantly to renew the whole organism.Cells ow from the inner part toward the two opposite extremities and differentiate irreversibly. Hydra was, therefore, described as an eternal embryo which does not show a nal state with arrested cells as it is the case, for example, for zebrash or the human body.Hence, fate maps describing the functional and positional destination of cells during embryonic development do not fully cover the cellular dynamics.Cellular tissue invasion is studied by placing cells into different parts of a growing organism, which may serve as a model system for metastasis and wound healing.