Sea Ascidian. (Tel Aviv University/Tal Zaquin) (Tel Aviv University/Tal Zaquin)
Gulf of Eilat sea animal

The sea ascidian regenerates all of its organs, even after being dissected.

By Yakir Benzion, United With Israel

Israeli researchers have made an extraordinary discovery in the Gulf of Eilat, finding a species of ascidian – a small marine animal – that is capable of regenerating all of its organs even if it is dissected into three fragments.

The team from Tel Aviv University’s School of Zoology are hoping that understanding that process of how the ascidian does it will eventually lead to new ways of helping human health.

“It is an astounding discovery, as this is an animal that belongs to the Phylum Chordata – animals with a dorsal cord – which also includes us humans,” said Prof. Noa Shenkar who headed the research project.

“The ability to regenerate organs is common in the animal kingdom,” she said, pointing out creatures like geckos are able to grow a new tail, but not entire body systems.

“Here we found a chordate that can regenerate all of its organs even if it is separated into three pieces, with each piece knowing exactly how to regain functioning of all its missing body systems within a short period of time,” said Shenkar.

There are hundreds of species of ascidians, and they are found in all of the world’s oceans and seas. Anyone who has ever opened their eyes underwater has seen ascidians without knowing it, as they often camouflage themselves as lumps on rocks and are therefore difficult to discern. The animal that is the subject of this new study is an ascidian from the species Polycarpa mytiligera (see attached photo), which is very common in the coral reefs of Eilat.

“By all accounts, the ascidian is a simple organism, with two openings in its body: an entry and an exit,” said doctoral student Tal Gordon. “Inside the body there is a central organ that resembles a pasta strainer. The ascidian sucks in water through the body’s entry point, the strainer filters the food particles that remain in the body, and the clean water exits through the exit point.”

That sounds like a “fishy” lifestyle, but the amazing thing is that “among invertebrates, they are considered to be the closest to humans from an evolutionary point of view,” Gordon said.

Ascidians are actually know for their regenerative ability, but until now, these abilities have been identified mainly in asexual reproduction. Never before has such a high regenerative capacity been detected in a chordate animal that reproduces only by sexual reproduction.

“There are species of ascidians that perform simple regeneration in order to reproduce,” Gordon said. “These are species with a colonial lifestyle, with many identical individuals connected to one another. They replicate themselves in order to grow.”

“In previous studies, we showed that this species is able to regenerate its digestive system and its points of entrance and exit within a few days. But then we wanted to see if it is capable of renewing all of its body systems,” Gordon explained. “We took a few individual ascidians from Eilat and dissected them into two parts, which were able to replenish the removed sections without any problem.

In a subsequent experiment the team dissected several dozen ascidians into three fragments, leaving a part of the body without a nerve center, heart, and part of the digestive system.

“Contrary to our expectations, not only did each part survive the dissection on its own; all of the organs were regenerated in each of the three sections. Instead of one ascidian, there were now three,” Gordon said. “This is very astonishing. Never before has such regenerative capacity been discovered among a solitary species that reproduces sexually, anywhere in the world.”

Prof. Shenkar said the discovery will lead to more research that may hold the key to humans being able to regenerate limbs or organs in the future.

“Since the dawn of humanity, humans have been fascinated by the ability to regenerate damaged or missing organs,” Shenkar said. “Regeneration is a wonderful ability that we have, to a very limited extent, and we would like to understand how it works in order to try and apply it within our own bodies. Anyone snorkeling in the Gulf of Eilat can find this intriguing ascidian, who may be able to help us comprehend processes of tissue renewal that can help the human race.”

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