What is it about?
How do organisms manage to shape their stereotypic body-forms so reliably during development or regeneration while facing unpredictable environmental conditions and internal fluctuations? This property, coined canalization, remains one of nature's great mysteries. Traditionally, canalization in morphogenesis has been attributed to highly organized, deterministic underlying processes - a "program" refined over millions of years of evolution. However, in this article, we shed light on the prominent role of stochasticity in morphogenesis, by investigating Hydra – an organism renowned for its extraordinary regeneration capabilities. Hydra is a tiny freshwater organism that can regenerate its entire body from just a small tissue fragment. Such a tissue segment, excised from the middle region of a mature animal and containing a few hundred cells, first folds into a hollow sphere. Remarkably, within approximately 48 hours—and without significant cell divisions—this tissue undergoes a complete transformation and regenerates into a fully functional mature Hydra. A particularly striking stage in this process is a rapid morphological transition from a spherical shape to a long, tube-like form, followed by the development of a head, a foot, and tentacles thus completing the regeneration process. Using an external electric field, we were able to slow down the internal developmental processes leading to this morphological transition. To our surprise, this intervention led to an extended phase during which the tissue displayed stochastic, multiple morphological swings back-and-forth between spherical and tube-like shapes, before ultimately completing the normal regeneration process. This observation implies that stochastic processes within the tissue are not merely background noise, but, in fact, play a key role in guiding the regeneration process itself. We further harnessed our ability to influence morphogenesis by an electric field to quantify the level of noise within the tissue. By introducing a small periodic modulation of the electric field’s amplitude, we observed a phenomenon known as stochastic resonance, where the interplay of noise and periodic signals enhanced the tissue's response. This resonance demonstrates the tissue's inherent ability to self-regulate noise levels, effectively utilizing it as a powerful driving force of morphogenesis.
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Photo by Yaniv Knobel on Unsplash
Why is it important?
This study highlights the unexpected and significant role of stochasticity in the seemingly precise process of morphogenesis. It offers fresh insights into how biological systems overcome unpredictability and complexity to ensure canalized morphogenesis. The widely recognized universality of the molecular and cellular processes in development across diverse organisms, suggests that our conclusion about the key role of noise in morphogenesis may extend beyond Hydra regeneration. It also holds significant promise for applications in regenerative medicine and tissue engineering, opening the door to innovative approaches in these important fields.
Perspectives
This manuscript is an important step in our program to construct a physics framework for morphogenesis. It follows three previous publications along this line: The first is focused on the calcium activity in the tissue, the second discusses the nature of the major morphological transition during Hydra regeneration and the third, introduces a toy model that reproduces the experimental results.
Erez Braun
Technion Israel Institute of Technology
Read the Original
This page is a summary of: Stochastic morphological swings in
Hydra
regeneration: A manifestation of noisy canalized morphogenesis, Proceedings of the National Academy of Sciences, December 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2415736121.
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