The tiny freshwater hydra is essentially an immortal creature. It can regenerate an entirely new animal from any fragment of its body with just a few thousands of cells. It also does this without sprouting multiple heads.

In a new study published in the journal Nature Communications on Jan. 19, researchers showed that it only takes one genetic tweak to create monstrous hydras with several functional heads.

What Prevents Regenerating Hydra From Sprouting Multiple Heads

Everytime a hydra regenerates, a process in its body ensures only the head ends up on top and just a foot sprouts on the bottom.

The researchers already have an idea that the gene Wnt3 is needed to prompt the growth of the head. The Wnt3 activates the receptor and genetic activator known as beta-catenin/TCF to initiate the process of growing the head. The researchers, however, still have to find the off switch that prevents the hydra from growing multiple heads.

The research team developed a gene-screening strategy to identify this inhibitor based on the results of a study conducted by the researchers in Germany on the planarian flatworm, a close relative of the hydra that also regenerates.

Study researcher Brigitte Galliot, from the University of Geneva, and colleagues eventually identified a gene that codes for a protein called Sp5.

The researchers found that when a hydra needs a new head, it releases Wnt3 that clings to beta-catenin/TCF, which then activates a bunch of genes that include more Wnt3 and Sp5.

In the absence of SP5, however, the Wnt3 continues the cycle, which results in many heads spouting all over a regenerating hydra.

Monsters With Multiple Heads

To check if their theory is correct, the researchers grew hydras that were engineered not to express the Sp5 gene. This produced monster-like creatures with multiple heads, which the researchers said are all totally functional.

"In 100 [percent] of these animals you get ectopic [extra] heads," Galliot said. "Which is really amazing."

Potential Application In Cancer Research

The study allowed the researchers to identify what keeps the hydra's head regeneration in check, which could be helpful in cancer research.

Sp5 could be a candidate treatment that can target human tumors that use the Wnt3 pathway to spread.

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