This video says about itself:
8 February 2017
Regenerating pond animals called hydra inherit structural patterns from their original forms, researchers find. When researchers anchored rings of hydra tissue to a wire (right), they found that the added mechanical stability made hydra grow normally along one body axis, and thus grow one head. Without this stability, the actin scaffolding was more disrupted and animals grew two heads (left).
From Science News:
How hydras know where to regrow their heads
by Helen Thompson
10:00am, February 9, 2017
Hydras, petite pond polyps known for their seemingly eternal youth, exemplify the art of bouncing back. The animals’ cellular scaffolding, or cytoskeleton, can regrow from a slice of tissue that’s just 5 percent of its full body size. Researchers thought that molecular signals told cells where and how to rebuild, but new evidence suggests there are other forces at play.
Physicist Anton Livshits and colleagues at the Technion-Israel Institute of Technology genetically engineered Hydra vulgaris specimens so stretchy protein fibers called actins, which form the cytoskeleton, lit up under a microscope. Then, they sliced and diced to look for mechanical patterns in the regeneration process.
Beheaded hydras appear to inherit skeletal patterns from their past adult forms, the researchers found. Actin fibers in pieces of hydra exert mechanical force that lines up new cells and guides the growth of the animal’s head and tentacles. Manipulating the alignment of actin fibers results in hydras with multiple heads. Both mechanical and molecular forces may mold hydras in regeneration, the team reports February 7 in Cell Reports.
Hydra is able to regenerate any part of its body to rebuild an entire individual. The head organizer performs two opposite activities, one activating, which causes the head to differentiate, and the other inhibiting, which prevents the formation of supernumerary heads. Researchers have discovered the identity of the inhibitor, called Sp5, and deciphered the dialogue between these two antagonistic activities, which helps maintain a single-headed adult body and organize an appropriate regenerative response: here.