Some Jellyfish Are Immortal

While most creatures in the animal kingdom follow a linear path from birth to death, a tiny jellyfish defies this fundamental rule of life. Found in temperate and tropic waters, *Turritopsis dohrnii* possesses the remarkable ability to reverse its life cycle, earning it the nickname "the immortal jellyfish." This unique characteristic was discovered by accident in the 1980s by scientists who were studying hydrozoans. They observed that when the mature jellyfish, or medusa, faced environmental stress, physical harm, or starvation, it could revert to its earliest stage of life, a polyp colony. This process is akin to a butterfly turning back into a caterpillar. The jellyfish can, in theory, repeat this cycle indefinitely, making it biologically immortal.

The secret to this incredible feat lies in a cellular process known as transdifferentiation. This is when a mature, specialized cell transforms into a different type of specialized cell. For instance, a skin cell could become a nerve cell. In the case of *Turritopsis dohrnii*, when it is under duress, its cells can essentially reprogram themselves, reverting to a blob-like cyst that then develops into a new polyp colony. From this new colony, genetically identical medusae bud off, effectively rebooting the jellyfish's life. This process has been observed to happen multiple times, with one Japanese researcher, Dr. Shin Kubota, successfully inducing a single colony to renew itself ten times within a two-year period.

Despite its potential for eternal life, the immortal jellyfish is not invincible (Review). It can still fall prey to predators or succumb to diseases in its medusa stage before it has the chance to transform. However, its unique ability has captured the interest of scientists studying aging and cellular regeneration. The study of *Turritopsis dohrnii* offers a fascinating glimpse into the plasticity of life and the potential for cellular reprogramming, a field with significant implications for regenerative medicine.