The Hydra's Freaky Ability to Regrow Its Own Head Relies on This Incredible Mechanism

hydra have incredible powers, including the ability to regrow their own heads if they are decapitated.

These animals are one of the closest examples of beings with immortality. hydra stem cells can replicate indefinitely if they are destroyed by a predator or consumed by fire.
If at least five head-organizing cells remain intact, they'll ooze their way to each other, combine and start organizing the rest of the remaining mess of cells back into a body.

The PNAS, 2000 was written by Ulrich Technau.

Over time, pure hydra cells regain form with new head organizers.

These amazing qualities have held scientists' attention for a long time, but there's still a lot about how they work.

The 10-20mm hydra live in freshwater and temperate environments.

Their bodies are squishy and stinging at the same time, with a single foot at the base that excretes sticky stuff. Their body plan is symmetrical, unlike ours.

The hydra's hypostome is a dome-shaped structure that becomes their mouth when they rip themselves open to eat. The cells seal back together when not in use, and within this same structure is where the 50–300 head organizing cells usually reside.

The cells that dictate their neighbors should form the hypostome and the grabby tentacles by signaling which cell should form the hypostome and which should become part of the grabby tentacles.

If the hydra is chopped in two, anywhere along its top third, the remaining body bit will grow more organizer cells, which will then arrange a shiny new head for the animal.

When the hydra body is budding, the command cells appear along it.
A hydra has three budding clones.

The hydra's genetics were compared by Aide Macias-Muoz and colleagues to understand the mythical powers of the hydra. They mapped the areas of the genome that were open for expression of genes.

The epigenetics of multiple developmental pathways are thought to be involved. Messing with some of the regulatory genes can cause strange results, like multiple head organizers along the hydra's body.

Macias-Muoz says that the head regeneration and budding programs in Hydra are different.

The result is the same, but the expression of genes is different during regeneration. Gene expression is accompanied by chromatin remodeling at sites where transcription factors bind.

The cells can use the genes at these regions to make structure, because the scaffolding that DNA uses to make it is opened up at these regions.

enhancer genes, whose products help drive other developmental processes, are found in many of the 2,870 regions of the genome.

These findings show that the complex enhancers were present before Cnidaria split from the group of animals that were symmetrical.

The team found a family of genes that are involved in regeneration in other species, including fish, salamanders, and mice.

The genomes of cnidarians like hydra are very similar to ours, and the differences in our appearance are likely due to how the genes are regulated.

Regulatory enhancer genes have been shown to evolve more rapidly than other coding sequences in mammals, which may indicate an important mechanism that drives change and diversity over long evolutionary periods.

The team wrote that the study of cnidarians could provide opportunities to understand the formation of the bilaterian body plan and the nervous system.

The hydra's ability to regrowth its own head is a great example of the power of epigenetics.

This research was published in a journal.