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Did you know salamanders can regrow tails after they are cut off? Did you know that zebrafish can replace entire limbs and replace their organs? On the other hand, complex animals like humans can only go to the extent of repairing a broken bone or regenerating a damaged liver. Why is it that humans can’t regrow their limbs?
Cells first exist as stem cells. This stem cell then undergoes certain structural and functional alterations that allows it to carry out a specific function efficiently. This process of changing is called cell differentiation. The stability of these differentiated cells to stay in their specialised state is a vital part of controlling the different essential life processes in complex organisms. For example, the red blood cell’s shape and organelles are important to allow it to transport blood around the body and the nerve cell’s structure allows our brain to send signals to different organs. The stability of cell growth is also important as too much cell division could lead to uncontrolled growth, which is cancer.
This high cell stability reduces the capacity of our cells to change into different specialised cells or revert back to their undifferentiated state (the stem cell). However, for a human to, say, regrow a limb, it would need a large amount of stem cells. And so the ability to regenerate shows a trend of increasing with reduced structural complexity. In other words, complex animals tend to be non-regenerative, whereas simple animals tend to be able to regenerate. The processes that control this regeneration are largely unknown and studying those organisms with the ability to regenerate can help us understand why others cannot.
Researchers studied a small tube-shaped sea creature related to simple organisms like sponges, jellyfish, and sea anemone. This organism is able to regrow an entire new body from only a fragment of tissue (its mouth). As the organism regenerated, scientists detected a molecular signature associated with the ageing process known as senescence.
Senescence is a process where cells reach a point in their growth where they stop dividing, but don’t die either. These cells can create chemicals that signal other cells around them to also enter senescence. Another response to the senescence signal has been observed. Cells around the senescent cells can be reprogrammed to undifferentiated cells capable of regeneration. In humans, senescent cells function in the process of ageing, however in the cells of regenerative animals senescence can lead to the reversion of these cells back to stem cells. This usually happens around the area of a wound or injury. This study demonstrated how senescence in this organism drove cell reprogramming for regeneration. The ability to respond to a senescence signal by reprogramming cells to stem cells has not been preserved across generations as organisms evolved to form more complex organisms. These results combined with other studies create a strong case that senescence is a process that existed in the past and allowed organisms’ cells to convey stress signals to surrounding cells, therefore leading to regeneration.
Similar phenomena have been observed in other animals but the extent to which senescence is seen across regenerative animals is unclear currently. This study can be taken forward by scientists to induce the ability to regenerate into complex, naturally non-regenerative organisms. It can also help us understand the processes of healing and ageing better, allowing a deeper understanding of human health and disease.
Works Cited
“Definition of CNIDARIAN.” Www.merriam-Webster.com, www.merriam-webster.com/dictionary/cnidarian. Accessed 24 Aug. 2023.
Institute, NIH/National Human Genome Research. “Scientists Discover Clues to Aging and Healing from a Squishy Sea Creature.” Phys.org, 30 June 2023, phys.org/news/2023-06-scientists-clues-aging-squishy-sea.html. Accessed 24 Aug. 2023.
Sinha Dutta, Sanchari. “The Role of Senescent Cells in Disease.” News-Medical.net, 4 May 2022, www.news-medical.net/health/The-Role-of-Senescent-Cells-in-Disease.aspx#:~:text=Cellular%20senescence%20is%20a%20process. Accessed 28 Aug. 2023.
“What Is Senescence? - Senescent Cells and Senescence in Plants.” BYJUS, byjus.com/biology/senescence/. Accessed 24 Aug. 2023.
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