Canadian biologists have discovered that detached tentacles and tube feet of the Arctic sea cucumber Psolus fabricii can remain viable in regular seawater for over 3 years. During this extended period, these severed body parts not only survived but also healed their wounds, reorganized their internal structures, and began absorbing nutrients directly from their surroundings. Previously, it was believed that complex tissues separated from an organism would inevitably degrade and perish quickly. This refers to tissue containing nerves, muscles, skin, and connective fibers. While scientists have long been able to sustain individual cells in laboratory settings for extended durations, this requires sterile conditions, protection from microbes, and continuous feeding with specialized solutions. Maintaining such intricate multicellular tissue alive in a natural environment was previously considered impossible. Although sea stars and sea cucumbers possess regenerative capabilities to regrow lost body parts, detached fragments typically decompose within a few weeks. The authors of the study, published in Science Advances, sought to investigate the extent of regenerative capacity in the tissues of Psolus fabricii. To this end, zoologists severed the tube feet and tentacles from these animals and subsequently placed them in aquariums containing unfiltered, flowing seawater. No medical assistance or additional nourishment was provided to these tissues. For comparative purposes, fragments of sea stars and sea urchins were placed in adjacent aquariums. After 3 years, the control samples of sea stars and sea urchins, as anticipated, had perished. In contrast, the sea cucumber tissues remained alive. The wounds at the point of severance had closed in as little as 6 days. Using fluorescent markers, scientists observed ongoing active processes within the detached tube feet: new cells were developing, and older cells were undergoing programmed cell death. To ascertain the energy source for this separated tissue, lacking both a circulatory system and a digestive tract, biologists introduced amino acids labeled with a heavy nitrogen isotope into the aquariums. Analysis revealed that the detached tube feet indeed absorbed organic matter directly from the seawater. Following detachment from the main body, the tube foot essentially reconfigured itself to adapt to its new circumstances. Muscles became redundant, and immune cells within the tissue began to consume muscle fibers. The resulting substances were utilized for survival and restructuring. In place of the muscles, a more robust connective tissue gradually formed. Concurrently, the severed tentacles retained their nerve networks. Throughout the entire observation period, they continued to exhibit movement and contraction in response to tactile stimulation, demonstrating that the tissue maintained complex functions even after separation from the organism. Survival in the non-sterile water for these body parts was facilitated by immune defense mechanisms. Within the initial 48 hours post-amputation, immune cells known as coelomocytes migrated from the central regions of the tissue to the severed sites. There, they accumulated at the wound edges, engulfing pathogenic microorganisms and dead cells. Subsequently, these coelomocytes, along with their captured debris, were either expelled into the surrounding water or aggregated within the internal cavity of the tube foot. Once the wound edges had fully sealed, the concentration of these cells decreased to normal levels. Additionally, the tissue was protected by psolusosides, natural toxic compounds secreted by the sea cucumber that inhibit microbial growth. The researchers have coined a term for this remarkable phenomenon: “LiPfe.” They propose that this cellular autonomy observed in sea cucumbers could serve as a practical and accessible model for studying aging, wound healing, and combating infections, without the necessity of using laboratory mice.
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