Ascidian Split Into Three Parts Regenerates Into Three Complete Animals

sea squirt title

Researchers from Israel's Tel Aviv University have discovered a species of sea squirt capable of regenerating all of its organs, even if it is chopped into three parts – thus creating three new animals.

Sea squirts – one of the common names given to a group of animals called ascidians – are found throughout the world's oceans. They mostly have a tube-like appearance and can be either solitary or gathered in clusters, and while they appear to be similar to soft coral growths or even sea-snails, they are in fact chordates – as in, they have a chord of nerves similar to humans and other vertebrates – which makes the discovery that they can regenerate so effectively all the more astonishing. 

The research, published in the journal Frontiers in Cell and Developmental Biology,  found that Polycarpa mytiligera, a solitary ascidian commonly found among the coral reefs in the Gulf of Eilat, was able to completely regenerate into three separate, functional individual animals after being dissected into separate fragments along two body axes – in other words, it was split from top-to-bottom and side-to-side, but still recovered. Three times.

Regeneration in animals that are capable of reproducing asexually – such as starfish, for example – is a well-known phenomenon. There are hundreds of different species of ascidian, some of which reproduce asexually and regenerate in order to do so, but the solitary P. mytiligera is not among them. The discovery, therefore, marks the first time that a sexually reproductive vertebrate was observed to be able to achieve 'bidirectional regeneration' of all its body structures and organs.

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'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 Professor Noa Shenkar, one of the study's co-authors. 'The ability to regenerate organs is common in the animal kingdom, and even among chordates you can find animals that regenerate organs, like the gecko who is 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 function of all its missing body systems within a short period of time.'

There are hundreds of species of ascidians, and they are found in all of the world’s oceans and seas. They are simple organisms with two body openings, sucking water in through one end, filtering out particles of food, and then squirting the leftovers out of the other end. Most scuba divers will have encountered many of them among tropical reefs around the world, quite naturally assuming that what they are looking at is a type of coral, or perhaps some form of tubeworm.

Previous studies by the researchers had shown that the species was able to recreate much of its digestive system within a few days, but they wanted to see if it was capable of further regenerations. They dissected some ascidians into two parts and these were also able to regenerate completely, but the team was unprepared for the result when they dissected specimens of P. mytiligera into three parts, leaving one of the pieces without a nerve centre, heart, or 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,' said co-author Tal Gordon. 'Instead of one ascidian, there were now three. This is very astonishing. Never before has such regenerative capacity been discovered among a solitary species that reproduces sexually, anywhere in the world.'

'Since the dawn of humanity, humans have been fascinated by the ability to regenerate damaged or missing organs,' said Professor Shenkar '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.'

 

The study 'And Then There Were Three…: Extreme Regeneration Ability of the Solitary Chordate Polycarpa mytiligera' by Tal Gordon et al of is available in Frontiers in Cell and Developmental Biology.

 

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