Scientists are trying to mimic salamanders' ability to regrow limbs

Researchers believe that tissue regeneration by the body is better than transplantation or the use of stem cells

Andrew Pollack, New York Times

Irvine, California. In a small room at the University of California, transparent plastic cups are placed, and salamanders stare from them. The place is called the "foot laboratory", because most of the animals there have had their feet cut off, or will be cut off. But the damage to the salamanders will only be temporary: They heal and grow new, healthy limbs within a few weeks.

Salamanders are the "superstars" of the regeneration process - the regrowth of tissues and organs. They can regrow not only limbs but also tails, parts of the heart and even the retinas and lenses of their eyes. Humans can regrow parts of certain organs - including the liver, muscles and bones - but the process is usually limited to a limited number of tissues. In contrast, salamanders can regrow diverse types of tissue to form complete structures such as limbs. The scientists at the lab hope that one day the salamanders' abilities can be applied to grow human organs.

Regenerative medicine - whose goal is the regrowth or repair of damaged tissues - is currently at the center of the scientific discourse. Attention in this field has so far focused on stem cells, but some scientists argue that a better approach is to regrow organs in humans, as occurs in salamanders and other animals. According to them, naturally regenerated growth, which can perhaps be achieved with drugs or genes, will be easier than transplantation. In addition, the tissue will come from the patient himself, and this will solve the problem of transplant rejection.

In the past, natural regeneration did not receive much attention. This may be because, although the field has been studied for 200 years, it is still not sufficiently understood. However, genetic techniques are beginning to allow scientists to delve deeper into the mechanisms of regrowth.

The only example of multi-tissue organ regrowth in humans is the fact that small children can regrow fingertips above the upper joint, including the bone, skin, and bones. This ability was discovered by chance in England in 1974. A child who lost the tip of his finger in an accident was then taken to the hospital, but the doctor was too busy to sew up the injury. When she came to treat him the next day, she found that the finger had started to regrow.

Scientists say that animals that regenerate organs and tissues do not do so with the method that scientists hope to apply in humans, which is based on finding stem cells in the body that can be made to become a certain type of tissue. "We think they can do that, not because they're full of stem cells waiting to burst after an injury," says Professor Jeremy Brooks of University College London.
According to him, the explanation is different: cells close to the injured area, which already have unique characteristics (like muscle cells), lose their special properties and return to their initial state. In this process, known as "dedifferentiation", the animal actually produces stem cells when needed. These cells then multiply, redifferentiate and form the tissue needed to build the organ.

"It seems that the higher you go up the evolutionary ladder," Tsiplidis says, "the less regenerative capacity you have." However, there are hints that multi-tissue organ growth can also occur in animals at higher levels. It was found that it is possible to renew the stock of neurons in the retina of chickens, because other nerve cells dedifferentiate. In the distant future, the researchers hope, it will be possible to use these cells to cure blindness caused by retinal diseases.

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