Survival of the Gutless, Clues for regenerating human soft tissues in digestive tract
A recent Tel Aviv University study published in Scientific Reports explores the ability of the tropical ascidian Polycarpa mytiligera, a common coral reef organism, to eviscerate and regenerate its gut within 12 days and rebuild its filtration organ, the branchial sac, within 19 days.
Dr. Noa Shenkar and her student Tal Gordon from the Department of Zoology at TAU’s Faculty of Life Sciencesand the Steinhardt Museum of Natural History and National Research Center observed a recurrent pattern of evisceration, “death,” and finally rejuvenation in ascidians from the Gulf of Aqaba.
“Polycarpa are the most abundant ascidian species in the Gulf of Aqaba and one of the most abundant in the world,” said Dr. Shenkar. “In the process of studying their distribution and depths, we noticed they would throw something at us and then immediately shrink and remain highly contracted and camouflaged. I was sure they had died, but something told me not to discard them.
“Sure enough, four days later, the organisms regained their composition — as if they had been ‘reborn,’” Shenkar said. “This was very unexpected.”
The researchers conducted most of their study underwater, marking individual organisms then taking movies of the process. They watched how the specimens ejected the viscera and how they rebuilt their organs. They found that the polycarpa ruptured its branchial sac to eject its digestive tract. Using light mechanical pressure, it contracted, camouflaging itself as “dead.”
“In the underwater observatory, we observed fish — which had not fed for a day — circling, but none of them ate the ejected digestive tract,” said Shenkar.
Although the eviscerated guts were unpalatable to preying triggerfish and pufferfish, the researchers’ chemical analysis revealed no significant levels of toxic compounds in the expelled organs. It is possible that the digestive tract contains other compounds that are unpalatable to the fish, which are not detected in a regular chemical analysis.
The findings can be used to further study regeneration of the human digestive tract in its molecular, cellular, and developmental aspects.
“All signs point to evisceration as a defense mechanism, and this alone is interesting,” said Shenkar. “But this is also important and relevant to human research. Ascidians and vertebrates — and humans are vertebrates — share close affinities, so understanding ascidian regeneration pathways can point to promising new directions in human soft tissue regeneration research.”
The researchers say the human body and the ascidian body share many basic biochemical and cellular processes, as they are both chordates. Studying Polycarpa as a model organism provides insight into the workings of other organisms, as well as an in-vivo model for research of the human immune system and regeneration.
“This information can surely be used to study different biochemical pathways involved in soft-tissue regeneration,” Shenkar said.