Why do Hydra end up with just a single head?

Often considered immortal, the freshwater Hydra can regenerate any part of its body, a trait discovered by the Geneva naturalist Abraham Trembley nearly 300 years ago.

Any fragment of its body containing a few thousands cells can regenerate the entire animal The one-centimeter polyp has a developmental organizer center located at the head level, and another located in the foot. The head organizer performs two opposite activities: activating, which causes the head to differentiate, and inhibiting, which prevents the formation of supernumerary heads.

Researchers at the University of Geneva (UNIGE), Switzerland, have discovered the identity of the inhibitor, a protein called Sp5, and deciphered the dialogue between these two antagonistic activities, which maintain a single-headed adult body and organize an appropriate regenerative response. Published in the journal Nature Communications, their study reports that this mechanism has been conserved throughout evolution, both in Hydra and in humans. Sp5 could therefore be an excellent candidate as an inhibitor of human tumors in which the activator pathway is the motor of proliferation.

"Regeneration of the head relies on the transformation of the stump into a tissue called the head organizing centre, which has developmental properties, and like an architect, it directs the construction of the future head," explains Brigitte Galliot, professor at the Department of Genetics and Evolution of the UNIGE Faculty of Science.