Last updated March 27th 2017

Hydra, a small freshwater animal, knows exactly where to regenerate lost body parts, and that “trick” could someday be used to regenerate human muscles, a new Israeli study suggests. And, if the hydra can infinitely regenerate itself, perhaps it knows the secret to immortality.

Until recently, it was thought that hydras – small, tentacled animals that can literally be shredded into pieces and regrow into healthy animals – use chemical signals to regenerate body parts, but researchers at the Technion-Israel Institute of Technology now suggest that hydras have structural memory that guides the regeneration of cells in the right direction.

Recently published in the scientific journal Cell Reports, the study suggests that pieces of hydras have structural memory that helps them shape their new body plan according to the pattern inherited by the animal’s “skeleton.” Previously, scientists thought that only chemical signals told a hydra where its heads or feet should form.

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Hydras use a network of tough, stringy protein fibers to align their cells. When pieces are cut or torn from hydras, this pattern (called “cytoskeleton”) survives and becomes part of the new animal. The pattern generates a small but potent amount of mechanical force that shows cells where to line up.

This force can serve as a form of “memory” that stores information about the layout of animal bodies. When pieces of hydra begin the regeneration process, the scraps of hydra fold into little balls, and the cytoskeleton has to find a balance between maintaining its old shape and adapting to the new conditions.

Hydra attached to a substrate

“If you take a strip or a square fragment and turn it into a sphere, the fibers have to change or stretch a lot to do that,” the study’s senior author, biophysicist Kinneret Keren of the Technion, said in a statement.


However, some portions retain their pattern. As the little hydra tissue ball stretches into a tube and grows a tentacle-ringed mouth, the new body parts follow the template set by the cytoskeleton in fragments from the original hydra. The main cytoskeletal structure in adult hydra is an array of aligned fibers that span the entire organism. Tampering with the cytoskeleton is enough to disrupt the formation of new hydras, the researchers found. In many ways, the cytoskeleton is like a system of taut wires that helps the hydra keep its shape and function.

Regenerating human muscles?

In one experiment, the researchers cut the original hydra into rings which folded into balls that contained multiple domains of aligned fibers. Those ring-shaped pieces grew into two-headed hydras. However, anchoring the hydra rings to stiff wires resulted in healthy one-headed hydras, suggesting that mechanical feedbacks promote order in the developing animal.

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Hydras are much simpler than most of their cousins in the animal kingdom, but the basic pattern of aligned cytoskeletal fibers is common in many organs, including human muscles, heart, and guts. Studying hydra regeneration may lead to a better understanding of how mechanics integrate with biochemical signals to shape tissues and organs in other species.

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Photos and video: Technion, Frank Fox


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