SELF-REPAIR is extremely important for living things. Get a cut on your finger and your skin can make new cells to heal the wound. Lose your tail--if you are a particular kind of lizard--and tissue regeneration may produce a new one. Researchers at the California Institute of Technology have discovered a previously unknown self-repair mechanism--the reorganization of existing anatomy to regain symmetry--in a certain species of jellyfish.
Many marine animals, including some jellyfish, can regenerate tissues rapidly in response to injury, and this trait is important for survival. If a sea turtle takes a bite out of a jellyfish, the injured animal can grow new cells quickly to replace the lost tissue. In fact, a jellyfish-like animal called the hydra is a very commonly used model organism in studies of regeneration.
However, assistant professor of biology Lea Goentoro, along with graduate student Michael Abrams and associate research technician Ty Basinger, were interested in another organism, the moon jellyfish (Amelia aurita). The trio wanted to know if the moon jellyfish would respond to injuries in the same manner as an injured hydra. The team focused its study on the jellyfish's juvenile (or ephyra) stage, because the ephyra's simple body plan--a disk-shaped body with eight symmetrical arms--would make any tissue regeneration clearly visible.
To simulate injury--like that caused by a predator in the wild--the team performed amputations on anesthetized ephyra, producing animals with two, three, four, five, six, or seven arms, rather than the usual eight. They then returned the jellyfish to their habitat of artificial seawater, and monitored the tissue response.
Although wounds healed up as expected, with the tissue around the cut closing in just a few hours, the researchers noticed something unexpected: the jellyfish were not regenerating tissues to replace the lost arms. Instead, within the first two days after the injury, the ephyra had reorganized its existing arms to be symmetrical and evenly spaced around the animal's disklike body. This so-called resymmetrization occurred whether the animal had as few as two limbs remaining or as many as seven, and the process was observed in three additional species of jellyfish ephyra.
"This is a different strategy of self-repair," says Goentoro. "Some animals just heal their wounds; other animals regenerate what is lost; but the moon jelly ephyrae don't regenerate their lost limbs. They heal the...