Biology subjects

Shani-Zerbib, L.

Publications and source records attributed to Shani-Zerbib, L..

3 recordsLinked to original sources

bioRxiv2021

Canalized morphogenesis driven by inherited tissue asymmetries in Hydra regeneration

The emergence and stabilization of a body axis is a major step in animal morphogenesis, determining the symmetry of the body plan as well as its polarity. To advance our understanding of the emergence of body-axis polarity we study regenerating Hydra. Axis polarity is strongly memorized in Hydra regeneration even in small tissue segments. What type of processes confer this memory? To gain insight into the emerging polarity, we utilize frustrating initial conditions by studying regenerating tissue strips which fold into hollow spheroids by adhering their distal ends, of opposite original polarities. Despite the convoluted folding process and the tissue rearrangements during regeneration, these tissue strips develop a new organizer in a reproducible location preserving the original polarity and yielding an ordered body plan. These observations suggest that the integration of mechanical and biochemical processes supported by their mutual feedback attracts the tissue dynamics towards a well-defined developmental trajectory biased by weak inherited cues from the parent animal. Hydra thus provide an example of dynamic canalization in which the dynamic rules themselves are inherited, in contrast to the classical picture where a detailed developmental trajectory is pre-determined.

biophysics↗

bioRxiv2021

Plasticity of body axis polarity in Hydra regeneration under constraints

One of the major events in animal morphogenesis is the emergence of a polar body axis. Here, we combine classic grafting techniques with live imaging to study the emergence of body axis polarity during whole body regeneration in Hydra. Composite tissues are made by fusing two rings, excised from separate animals, in different configurations that vary in the polarity and original positions of the rings along the body axes of the parent animals. Under frustrating initial configurations, body axis polarity that is otherwise stably inherited from the parent animal, can become labile and even be reversed. Importantly, the site of head regeneration exhibits a strong bias toward the edges of the tissue, even when this involves polarity reversal. In particular, we observe head formation at an originally aboral tissue edge, which is not compatible with models of Hydra regeneration based only on preexisting morphogen gradients or an injury response. Rather, we suggest that the structural bias toward head formation at the doublets edge is reinforced by the presence of a defect in the organization of the supra-cellular actin fibers, which invariably forms at the edge as the tissue heals. In this scenario, the defect supports head formation at the edge, even though a defect is neither required nor sufficient for head formation. Altogether, our results suggest that body axis determination is an integrated process that arises from the dynamic interplay between mechanical feedback and signaling processes.

biophysics↗

bioRxiv2020

Topological defects in the nematic order of actin fibers as organization centers of Hydra morphogenesis

Animal morphogenesis arises from the complex interplay between multiple mechanical and biochemical processes with mutual feedback. Developing an effective, coarse-grained description of morphogenesis is essential for understanding how these processes are coordinated across scales to form robust, functional outcomes. Here we show that the nematic order of the supra-cellular actin fibers in regenerating Hydra defines a slowly-varying field, whose dynamics provide an effective description of the morphogenesis process. We show that topological defects in this field, which are long-lived yet display rich dynamics, act as organization centers with morphological features developing at defect sites. These observations suggest that the nematic orientation field can be considered a "mechanical morphogen" whose dynamics, in conjugation with various biochemical and mechanical signaling processes, result in the robust emergence of functional patterns during morphogenesis.

biophysics↗