Animals that can regenerate limbs. Protective devices
Who in childhood did not listen with bated breath to the fairy tale about the Serpent Gorynych, who grew severed heads. No less amazing was his ability to spew fire from them. As adults, we stopped believing in miracles. However, such animals do exist in nature. They, of course, do not breathe fire, but their ability to restore lost body parts is unmatched among terrestrial vertebrates.
Nature has endowed newts with such abilities that people far from herpetology have a logical question: “Is this even possible?”
It is known that if you grab a lizard by the tail, it can throw it away. After some time, a new one will grow in place of the lost area. This ability is called regeneration.
Many tailed amphibians regenerate not only the tail, but also other parts of the body. For example - legs. If a newt's limb is amputated, then after a while a new one will grow in its place, which will be almost no different from the lost one.
Researchers were naturally interested in such unique qualities of these animals. What does regeneration depend on? Why can't other vertebrates regrow lost organs? Is it possible to achieve that people have the same ability to regenerate? To get an answer to these and other questions, we first tried to find out which systems in the body are responsible for regeneration.
In vertebrates, the work of almost all organs (digestion, circulatory system, muscles, etc.) controls nervous system. Maybe it is also responsible for regeneration in newts? Experiments have shown that the nervous system really has a role in the restoration of lost organs. For example, if the nerves that went to the leg of a newt were removed, and then this leg was amputated, then after the operation it did not grow back. If nerves from other parts of the body were brought to the amputated area, the leg was restored.
Soon new facts became known: the limbs of tailed amphibians, formed in embryos that were deprived of a nervous system and, therefore, never had innervation, are capable of regenerating after amputation.
Scientists decided to find out how a lost limb is restored, or more precisely, due to what tissues and cells. At first it was assumed that the tissues of the remaining (non-amputated) area produce similar cells. But when they compared the cells of the wound surface and the cells of the non-amputated area, it turned out that they were not at all similar to each other. Arose new question. If these new cells are dramatically different from the old ones, then where do they come from? Modern research methods have made it possible to solve this problem.
X-rays have been found to inhibit regeneration. When an animal's lower leg was irradiated and then amputated, the leg did not grow back. If the amputation line passed along the thigh, which was not irradiated, regeneration took place without any deviations. Scientists consider this fact to be proof that new cells of the regenerated organ are formed from the cells of the remaining, non-amputated area. Later, substances were found whose effects contributed to the restoration of lost limbs: solutions of table salt, glucose, some acids, bicarbonate of soda.
It would seem that along the tangled paths of evolution, mammals, including humans, have lost the ability to regenerate. Indeed, an amputated finger, leg or arm does not grow back. But it is known that red blood cells are replaced every four months. So, maybe it is still possible to restore lost tissue in humans, because blood is also tissue, only liquid.
And in the 50s, the Soviet scientists were the first began experiments on regeneration in mammals. Somewhat later, similar studies were carried out abroad. Experiments have shown that restoration of amputated limbs is possible, but so far only in newborns (experiments were carried out on rats and South American opossums). In 1972, American researcher R. Becker achieved limb regeneration in 21-day-old rats, using a weak stimulant electricity. Scientists are now able to restore skull bones and, most importantly, heart muscles in experimental animals.
Solving the problem of regeneration could bring humanity closer to relief from such a common illness as cardiovascular disease. Myocardial infarction, myocarditis and other heart diseases are one of the main causes of death in all industrialized countries.
When deciding on the protection of animals such as newts and salamanders, it is necessary to remember that any species is unique. In addition, many animals, including those discussed, are objects scientific research. And who knows what other surprises these unknown workers of science will present.
Recently, American ascolotls, relatives of our newts and salamanders, “proved” to scientists that it is possible to restore the brain. After the forebrain was removed, they were injected with crushed pieces of the brains of embryos from other animals. This not only stimulated brain regeneration, but also significantly increased the number of nerve cells.
E. M. Pisanets
Photo sources: herp.it, wikipedia.org
The axolotl, as scientists have established, is the larva of the Mexican ambystoma. Ambystomatidae, family of tailed amphibians. Ambystoma is a land animal, externally similar to a large salamander, but more modest in color.
The axolotl has the fantastic ability to regrow lost organs.
We, of course, know other animals that can grow new tails or paws, but all of them are very, very far from the axolotl: it can completely restore not only its limbs, but also its eyes, jaws, and heart. And finally, it is the only vertebrate that can regrow damaged parts of its brain.
How does this happen?
Researchers from the Broad Institute of MIT and Harvard found that the partially destroyed pallium (the part of the forebrain that forms the cortex in humans) cerebral hemispheres) the axolotl is able to form all the types of neurons that were in it before the damage. This means that the newly formed amphibian brain tissue can send all the same signals that were in its “arsenal” before injury. However, there are also limitations: axons (long processes of neurons), connecting the pallium with other parts of the brain during regeneration, are formed quite poorly in axolotls. The work was published in the journal eLife.
It was previously known that salamander larvae - axolotls - can regrow not only lost limbs, but also some more exotic parts of the body - for example, parts of the brain. However, it was not clear how correctly regeneration occurs. Indeed, for nervous tissue it is important not only the number and ratio of different types of cells, but also the order of their connections with each other. To determine it, American neuroscientists used electrophysiological methods, as well as dyes that change the color of neurons depending on how often they send signals of a certain intensity.
The authors suggest that the axolotl's ability to regenerate different types of neurons is related to its larval state. Salamanders can live in axolotl form until death and are still capable of reproduction (reproduction during the larval stage is called neoteny). However, if certain conditions are met (for example, adding iodine to water), an axolotl at any age can turn into an adult salamander. This means that all the cells of his body are constantly ready for metamorphosis. Roughly speaking, their properties are quite close to stem cells.
As for the problems with the restoration of long processes, the researchers believe that this is not due to the inability of new neurons to form axons, but to the lack of appropriate signals from the surrounding nervous tissue. During embryonic development, the fate of each cell is determined by signaling substances released by its neighbors - other developing cells. Neurons in the brain of an adult axolotl do not produce such substances, so newly arrived cells “do not understand” where to direct their axons. However, if such substances are added to the tissue, new axons will certainly be able to grow.
The mechanism by which salamanders regenerate lost limbs has nothing to do with the action of stem cells, scientists have found.
Magical abilities of salamanders
The ability of these tailed amphibians to grow paws, lungs, and brains has worried humanity for thousands of years - it was studied by Aristotle, Voltaire, and Darwin.
When an animal loses a part of its body, the cells of the superficial layer of skin quickly cover the wound with the so-called epithelial cap, fibroblasts break bonds with the connective tissue and form a blastema at the site of the wound, from which a new limb is formed. For example, it only takes three weeks to get a new paw.
At the end of the 20th century, scientists assumed that salamander cells were similar to stem cells, that is, they could turn into any organ.
Martin Kragl from Germany's Max Planck Institute found that this is not the case. Together with American colleagues, he studied how the Mexican axolotl salamander Ambystoma mexicanum grows limbs and tissues. Kragl took advantage of the discoveries of the University of California, who proved that salamander blastema cells are similar to cells in the developing limbs of mammalian embryos, which are capable of renewing their limbs, but lose these skills before birth.
Ultraviolet experiment
Based on the idea that the development of limbs from the blastema practically repeats in in brief their natural development in growing creatures, German and American scientists divided animals into two groups. The first to inject was the GFP protein, derived from a fluorescent jellyfish. In ultraviolet light, this protein illuminates cells green, allowing scientists to trace the origins of various cells and their purpose. The second group included both adult axolotls and larvae. Scientists injected them with cells with protein taken from genetically modified individuals. The larvae were injected with the substance where, as biologists knew, various tissues and organs, in particular the nervous system, were supposed to grow. Adults were first injected with cells containing protein, and then pieces were cut off from the body.
After observing their patients for several weeks, biologists found that the cells behave very conservatively - they grow only into the organs and tissues from which they originated. " Main conclusion researchers: new muscle cells produce only old muscle cells, new skin cells produce only old skin cells, new neurons produce only old nerve cells,” writes Science Daily.
This process was most clearly observed in larvae: injected into the area from which the nervous system was to grow, green-lit cells spread throughout the growing axolotl exactly according to the pattern of the nervous system.
“In all likelihood, cells near the amputated organ are reprogrammed, allowing them to initiate embryonic tissue-forming programs without reverting to the original polypotential cell,” the researchers noted in a paper published in the prestigious journal Nature.
In other words, salamander cells behave in a fundamentally different way than stem cells. While the latter are capable of specialization and development into almost any organ, the cells of salamanders contain a mechanism of clear continuity.
From salamander to superman
The advantage of salamander cells is that they do not need to reach an embryonic state to begin the regeneration process - they work perfectly well as adults. Having revealed the secret of “active cells,” doctors will be able to grow a severed arm or leg for a person, following the example of a salamander.
“One day we will be able to regenerate human tissue,” believes one of the study’s authors, Malcolm Meaden. The hopes of American scientists are largely explained by the personality of those who ordered the study: it was sponsored by the US Department of Defense, whose representatives want to help amputated veterans of Iraq and Afghanistan.
Some sources even write that Axolotls can literally assemble themselves in parts - attaching to themselves the freed parts of other relatives - including their heads.
Roughly speaking, if you take pieces of axolotls, put them together and mix, then it is quite possible (we cannot say for sure) that this vinaigrette will soon grow together into something single, rise to its paws and go about its axolot business.
Thanks to their unique abilities, these animals are now found not only in Mexico - they can be found in scientific laboratories all over the world, where scientists continually cut them into pieces and then put them back together like a jigsaw puzzle, hoping to solve this hocus pocus.
What is regeneration and how does it happen? There are partial answers to these questions. For example, scientists already know what regeneration is. This process has been tested in every possible way in the laboratory, but they have not been able to fully determine how and why it occurs in some species. In this article we will understand this concept and try to determine whether regeneration is characteristic of humans.
Who mastered regeneration in the process of evolution
Regeneration is the process of restoration. Some creatures can regenerate lost limbs and some organs. For example, newts (they are considered one of the most ancient on our planet) can grow a new tail, paw and even jaw. This is a truly unique creature belonging to the tailed amphibians.
After a long study of newts in laboratories around the world, scientists determined that they regenerate not only lost limbs, but also vital organs: heart tissue, eyes, spinal cord. Due to their uniqueness, newts are in space more often than dogs and monkeys. They have a phenomenal ability to “adapt.”
The zebrafish, which we often keep in home aquariums, also mastered regeneration in the process of evolution. These beautiful small creatures can restore their hearts, fins, and eyes. The researchers specially cut out the above organs from the fish, after which they relatively quickly restored them. By the way, other types of fish can also do this, but often only their fins are quickly restored.
Classic examples of regeneration include:
- lizards and tadpoles that grow new tails (in childhood, almost everyone accidentally tore off a lizard’s tail, after which their parents convinced it that it would grow a new one);
- crabs and other crustaceans capable of restoring claws - their main “weapon”;
- snails that grow new “horns”;
- salamanders that can regenerate severed limbs;
- sea stars, growing new “rays” (peculiar limbs).
Champion of Regeneration
The champion in this case is considered to be the “flatfish” or “planaria” worm. If this creature is cut into two equal halves, then the missing tail is regenerated on one half, and the missing head is regenerated on the other. The worm's body somehow understands that it needs to grow. If small cuts are made on the front and rear ends of this creature, it will grow a second tail and head. The most interesting thing is that even from 1/280 of the body part of a “flat fish” you will get an independent, fully developed, healthy living creature.
History of the study of regeneration
Scientists have always been interested in how animals learned to regenerate lost body parts. A person would also benefit from such an opportunity. Specialists in various industries scientists conducted experiments to derive the laws of this supernatural skill.
The first person to come close to studying regeneration was the Frenchman R. A. Reaumur. It was he who coined the term “regeneration” and began to use it. In 1712, his first work was published on the regeneration of limbs in crustaceans. Colleagues were skeptical about Reaumur's works, which is why the scientist lost the desire to further study regeneration.
They became interested again in this phenomenal ability 30 years later. The experiments were continued by A. Trable. It was he who discovered the most mysterious creature, capable of regenerating, and conducted experiments on it ( we're talking about about the “flat plane” described above). For a long time the scientist could not determine who he was experimenting on. The creature looked like an empty stem with tentacles and a suction cup with which it was attached to the wall of the aquarium. Later it turned out that Abraham had a predator in his hands, and a very interesting one at that.
Individual fragments of the test subject's body quickly turned into a new full-fledged predator. New body parts grew at the site of the cuts, making the creature look like fantastic monster. Troblet called the creature a "hydra".
Trouble's experiments did not go unnoticed. Shocked scientists tried to repeat them on everything that moved. Soon the world appeared whole group living beings that can regenerate. For several decades, it included only the simplest organisms, but then scientists learned that birds can grow a new beak, and rats can grow a severed tail.
How can organisms regenerate?
Scientists have discovered that if a newt, for example, loses a limb, then in the damaged area the cells of various tissues lose their distinctive features. The newly born cells are now called “blastema”. Their feature is accelerated and enhanced division. These “blastemas” determine their purpose depending on which part of the body needs them most.
Regeneration can be influenced. Scientists have found that if, during the restoration of a frog's leg, the newborn cells are exposed to vitamin A acid, then instead of one limb the frog will grow several. By the way, experiments on cold-blooded animals are carried out because the skill described above is best developed in them. For some reason, warm-blooded animals have not learned to restore significant areas of the body.
Regeneration in humans
As you know, a person cannot grow new limb. But his body still knows how to regenerate. The simplest regeneration can be called wound healing and the like. A person cannot fully restore lost limbs for several reasons.
Doctor of Science in biology Petr Garyaev believes that our ability to regenerate has weakened during evolution, since humans have always been more protected from external influences than other living beings. We have enviable endurance, we can quickly find a way out of any situation, and we easily adapt to new conditions. Because of this, we do not need complete regeneration. We have partially preserved it, thanks to which nails and hair grow, wounds heal, burned or peeled skin is restored.
Is it possible to force the human body to regenerate?
Let's return to the "blastema". If a person had such cells, then theoretically he could regenerate his limbs and everything else that cold-blooded people can restore. IN human body There are two types of cells that can regenerate. These are blood and liver cells.
During embryonic development, some cells refrain from specialization. These cells are called stem cells. They are the ones who can replenish blood reserves and restore liver tissue, if necessary. Stem cells found in the bone marrow can develop into muscle, tissue, bone or cartilage. Due to this, they can be called a kind of “blastema”.
Scientists are already trying to experimentally test whether it is possible to develop in humans the ability to regenerate large areas of the body by programming stem cells. To do this, they take these cells and influence them in a certain way in the laboratory, trying to force them to change in the desired direction. Moreover, scientists are already able to grow organs from stem cells. All that remains is to learn how to grow full-sized organs that can function independently. This is where problems arise.
The fact is that what a tiny organism can achieve is very difficult for a large human organism to achieve. Theoretically, we could do like the newts: regenerate a small arm or leg, and then grow it. But newts don’t need to do this More than a month, and we are about 20 years old.
By the way, obtaining the cells described above is very difficult and expensive. Such cells in maximum quantity are located in the bone marrow of the pelvic bones, but in an adult, stem cells lose their functionality. The most promising are stem cells obtained from umbilical cord blood. After birth, about 50 ml of such blood can be collected. Only 1 million stem cells can be obtained from each milliliter, and only 1% of them are suitable for regeneration. Therefore, in order to develop human regeneration, scientists will have to learn how to create stem cells in the laboratory or force other organs human body develop them. Fortunately, science does not stand still. Perhaps someday a person will learn to recover like a newt or even a “flatfish”.
restoration by the body of lost parts at one stage or another life cycle. Regeneration usually occurs in the event of damage or loss of an organ or part of the body. However, in addition to this, restoration and renewal processes constantly occur in every organism throughout its life. In humans, for example, the outer layer skin. Birds periodically shed their feathers and grow new ones, and mammals change their fur. Deciduous trees lose leaves every year and are replaced with fresh ones. Such regeneration is usually notassociated with damage or loss is called physiological. Regeneration that occurs after damage or loss of any part of the body is called reparative. Here we will consider only reparative regeneration.Reparative regeneration can be typical or atypical. In typical regeneration, the lost part is replaced by the development of exactly the same part. The cause of the loss may be an external force (for example, amputation), or the animal may deliberately tear off part of its body (autotomy), like a lizard breaking off part of its tail to escape an enemy. With atypical regeneration, the lost part is replaced by a structure that differs from the original quantitatively or qualitatively. The regenerated limb of a tadpole may have fewer fingers than the original one, and a shrimp may grow an antenna instead of an amputated eye.
REGENERATION IN ANIMALS The ability to regenerate is widespread among animals. Generally speaking, lower animals are more often capable of regeneration than more complex, highly organized forms. Thus, among invertebrates there is much more types, capable of restoring lost organs than among vertebrates, but only in some of them is it possible to regenerate a whole individual from a small fragment. Nevertheless general rule the decrease in the ability to regenerate with increasing complexity of the organism cannot be considered absolute. Such primitive animals as ctenophores and rotifers are practically incapable of regeneration, but in much more complex crustaceans and amphibians this ability is well expressed; Other exceptions are known. Some closely related animals differ greatly in this respect. Yes, y earthworm a new individual can completely regenerate from a small piece of the body, while leeches are unable to restore one lost organ. In tailed amphibians, a new limb is formed in place of the amputated limb, but in the frog, the stump simply heals and no new growth occurs.Many invertebrates are capable of regenerating large parts of their body. In sponges, hydroid polyps, flat, ribbon and annelids, bryozoans, echinoderms and tunicates, a whole organism can be regenerated from a small fragment of the body. Particularly noteworthy is the ability to regenerate in sponges. If the body of an adult sponge is pressed through the mesh tissue, then all the cells will separate from each other, as if sifted through a sieve. If you then place all these individual cells in water and carefully, thoroughly mix, completely destroying all the connections between them, then after some time they begin to gradually come closer together and reunite, forming a whole sponge, similar to the previous one. This involves a kind of “recognition” at the cellular level, as evidenced by the following experiment. Sponges of three different types separated into individual cells in the manner described and mixed thoroughly. It was discovered that cells of each type are able to “recognize” total mass cells of their own kind and reunite only with them, so that as a result not one, but three new sponges were formed, similar to the original three.
The tapeworm, which is many times longer than it is wide, can recreate an entire individual from any part of its body. It is theoretically possible, by cutting one worm into 200,000 pieces, to obtain 200,000 new worms from it as a result of regeneration. From one ray of a starfish, an entire star can regenerate.
Mollusks, arthropods and vertebrates are not able to regenerate a whole individual from one fragment, however, in many of them the lost organ is restored. Some resort to autotomy if necessary. Birds and mammals, as the most evolutionarily advanced animals, are less capable of regeneration than others. In birds, it is possible to replace feathers and some parts of the beak. Mammals can restore their integument, claws, and partly their liver; they are also capable of healing wounds, and deer are capable of growing new antlers to replace those shed.
Regeneration processes. Two processes are involved in regeneration in animals: epimorphosis and morphallaxis. In epimorphic regeneration, the lost part of the body is restored due to the activity of undifferentiated cells. These embryonic-like cells accumulate under the wounded epidermis at the cut surface, where they form the primordium, or blastema. Blastema cells gradually multiply and transform into the tissue of a new organ or body part. In morphallaxis, other tissues of the body or organ are directly transformed into the structures of the missing part. In hydroid polyps, regeneration occurs mainly through morphallaxis, while in planarians both epimorphosis and morphallaxis are simultaneously involved in it.Regeneration through blastema formation is widespread in invertebrates and plays a particularly important role important role in organ regeneration in amphibians. There are two theories of the origin of blastema cells: 1) blastema cells originate from “reserve cells”, i.e. cells that remained unused during embryonic development and were distributed among different organs of the body; 2) tissues, the integrity of which was damaged during amputation, “dedifferentiate” in the area of the incision, i.e. disintegrate and transform into individual blastema cells. Thus, according to the “reserve cell” theory, the blastema is formed from cells that remained embryonic, which migrate from different parts of the body and accumulate at the cut surface, and according to the “dedifferentiated tissue” theory, blastema cells originate from cells of damaged tissues.
There is enough data to support both one and the other theory. For example, in planarians, reserve cells are more sensitive to X-rays than cells of differentiated tissue; therefore, they can be destroyed by strictly dosing radiation so as not to damage normal planarian tissue. Individuals irradiated in this way survive, but lose their ability to regenerate. However, if only the anterior half of the planarian body is irradiated and then cut, then regeneration occurs, although with some delay. The delay indicates that the blastema is formed from reserve cells migrating to the cut surface from the non-irradiated half of the body. The migration of these reserve cells throughout the irradiated part of the body can be observed under a microscope.
Similar experiments showed that in the newt, limb regeneration occurs due to blastema cells of local origin, i.e. due to dedifferentiation of damaged stump tissues. If, for example, you irradiate the entire newt larva except, say, the right forelimb, and then amputate that limb at the level of the forearm, the animal will grow a new forelimb. It is obvious that the blastema cells necessary for this come precisely from the stump of the forelimb, since the rest of the body has been irradiated. Moreover, regeneration occurs even if the entire larva is irradiated, with the exception of a 1 mm wide area on the right fore tarsus, and then the latter is amputated by making an incision through this non-irradiated area. In this case, it is quite clear that the blastema cells come from the cut surface, since the entire body, including the right foreleg, was deprived of the ability to regenerate.
The described processes were analyzed using modern methods. An electron microscope allows you to observe changes in damaged and regenerating tissues in all details. Dyes have been created that reveal certain chemicals contained in cells and tissues. Histochemical methods (using dyes) make it possible to judge the biochemical processes occurring during the regeneration of organs and tissues.
Polarity. One of the most mysterious problems in biology is the origin of polarity in organisms. From the spherical egg of a frog, a tadpole develops, which from the very beginning has a head with a brain, eyes and mouth at one end of the body, and a tail at the other. Similarly, if you cut the body of a planarian into individual fragments, a head develops at one end of each fragment and a tail at the other. In this case, the head is always formed at the anterior end of the fragment. Experiments clearly show that the planarian has a gradient of metabolic (biochemical) activity along the anterior-posterior axis of its body; wherein highest activity possesses the very anterior end of the body, and towards the posterior end the activity gradually decreases. In any animal, the head is always formed at the end of the fragment where metabolic activity is higher. If the direction of the gradient of metabolic activity in an isolated fragment of planaria is reversed, then the formation of the head will occur at the opposite end of the fragment. The gradient of metabolic activity in the body of planarians reflects the existence of some more important physicochemical gradient, the nature of which is still unknown.In the regenerating limb of a newt, the polarity of the newly formed structure appears to be determined by the preserved stump. For reasons that still remain unclear, only structures located distal to the wound surface are formed in the regenerating organ, and those located more proximally (closer to the body) never regenerate. So, if the hand of a newt is amputated, and the remaining part of the forelimb is inserted with the cut end into the body wall and this distal (distant from the body) end is allowed to take root in a new, unusual place for it, then the subsequent transection of this upper limb near the shoulder (freeing it from the connection with the shoulder) leads to the regeneration of the limb with a full set of distal structures. At the time of cutting, such a limb has the following parts (starting from the wrist, fused with the body wall): wrist, forearm, elbow and distal half of the shoulder; then, as a result of regeneration, the following appear: another distal half of the shoulder, elbow, forearm, wrist and hand. Thus, the inverted (upside down) limb regenerated all parts located distal to the wound surface. This striking phenomenon indicates that the tissues of the stump (in this case the limb stump) control the regeneration of the organ. The task of further research is to find out exactly what factors control this process, what stimulates regeneration and what causes the cells that ensure regeneration to accumulate on the wound surface. Some scientists believe that damaged tissue releases some kind of chemical “wound factor.” However, highlight Chemical substance, specific for wounds, has not yet been successful.
REGENERATION IN PLANTS The widespread occurrence of regeneration in the plant kingdom is due to the preservation of meristems (tissues consisting of dividing cells) and undifferentiated tissues. In most cases, regeneration in plants is, in essence, one of the forms of vegetative propagation. Thus, at the tip of a normal stem there is an apical bud, which ensures the continuous formation of new leaves and growth of the stem in length throughout life. of this plant. If this bud is cut off and kept moist, new roots often develop from the parenchyma cells present in it or from the callus formed on the surface of the cut; the bud continues to grow and gives rise to a new plant. The same thing happens in nature when a branch breaks off. The lashes and stolons are separated as a result of the death of old sections (internodes). In the same way, the rhizomes of iris, wolf's foot or ferns are divided, forming new plants. Typically, tubers, such as potato tubers, continue to live after the underground stem on which they grew has died; with the onset of a new growing season, they can give rise to their own roots and shoots. In bulbous plants, such as hyacinths or tulips, shoots form at the base of the bulb scales and can in turn form new bulbs, which eventually produce roots and flowering stems, i.e. become independent plants. In some lilies, aerial bulbs form in the axils of the leaves, and in a number of ferns, brood buds grow on the leaves; at some point they fall to the ground and resume growth.Roots are less capable of forming new parts than stems. For this, the dahlia tuber needs a bud that forms at the base of the stem; however, sweet potatoes can give rise to a new plant from a bud formed by a root cone.
Leaves are also capable of regeneration. In some species of ferns, for example, in crooked fern (
Camptosorus ), the leaves are highly elongated and have the appearance of long hair-like formations ending in a meristem. From this meristem the embryo develops with rudimentary stem, roots and leaves; if the tip of the parent plant's leaf bends down and touches the soil or moss, the bud begins to grow. The new plant separates from the parent after the depletion of this hair-like formation. Succulent leaves indoor plant Kalanchoe bears well-developed plants at the edges, which easily fall off. New shoots and roots form on the surface of begonia leaves. Special bodies called embryonic buds develop on the leaves of some club mosses ( Lycopodium ) and liverworts ( Marchantia ); falling to the ground, they take root and form new mature plants.Many algae reproduce successfully by breaking into fragments under the impact of waves.
see also PLANT SYSTEMATICS.LITERATURE Mattson P. Regeneration - present and future . M., 1982Gilbert S. Developmental biology , vol. 1-3. M., 1993-1995
Regeneration lost organs in animals is a mystery that has troubled scientists since ancient times. Until recently, it was believed that only lower species living creatures: a lizard grows back a severed tail, some worms can be cut into small pieces, and each will grow into a whole worm - there are many examples.
But the evolution of the living world came from lower organisms to more and more highly organized people, so why did this property disappear at some stage? And was it lost?
The Lernaean Hydra, the Gorgon Medusa or our three-headed Serpent Gorynych, whose “self-repairing” heads Ivan tirelessly chopped off, are characters, although mythical, but clearly in a “family relationship” with very real creatures.
These include, for example, newts, a type of tailed amphibian that is rightfully considered one of the most ancient animals on Earth. Their amazing feature is the ability to regenerate - to regrow damaged or lost tails, paws, jaws.
Moreover, their damaged heart, eye tissue, and spinal cord are restored. For this reason, they are indispensable for laboratory research, and newts are sent into space no less often than dogs and monkeys. Many other creatures have these same properties.
Yes, zebrafish black and white color, only 2-3 cm long, tends to regenerate parts of fins, eyes, and even restore cells of its own heart, cut out by surgeons during regeneration experiments. This can be said about other types of fish.
Classic examples of regeneration are lizards and tadpoles that regenerate a lost tail; crayfish and crabs growing back their lost claws; snails that can grow new “horns” with eyes; salamanders, which naturally replace an amputated leg; starfish regenerating their severed rays.
By the way, from such a severed ray, like from a cutting, a new animal can develop. But the champion of regeneration was the flatworm, or planaria. If it is cut in half, then the missing head grows on one half of the body, and the tail grows on the other, that is, two completely independent viable individuals are formed.
And perhaps the appearance of a completely unusual, two-headed and two-tailed planaria. This will happen if longitudinal cuts are made at the front and rear ends and do not allow them to grow together. Even 1/280 of the body of this worm will make a new animal!
People watched our smaller brothers for a long time and, to be honest, secretly envied them. And scientists moved from fruitless observations to analysis and tried to identify the laws of this “self-healing” and “self-healing” of animals.
The first to try to bring scientific clarity to this phenomenon was the French naturalist Rene Antoine Reaumur. It was he who introduced into science the term “regeneration” - the restoration of a lost part of the body with its structure (from the Latin ge - “again” and generatio - “emergence”) - and conducted a series of experiments. His work on leg regeneration in cancer was published in 1712. Alas, her colleagues did not pay attention to her, and Reaumur abandoned this research.
Only 28 years later, the Swiss naturalist Abraham Tremblay continued his experiments on regeneration. The creature on which he experimented did not even have own name. Moreover, scientists did not yet know whether it was an animal or a plant. A hollow stalk with tentacles, with its rear end attached to the glass of an aquarium or to aquatic plants, turned out to be a predator, and a very surprising one at that.
In the researcher's experiments, individual fragments of the body of a small predator turned into independent individuals - a phenomenon known until then only in flora. And the animal continued to surprise the naturalist: in place of the longitudinal cuts at the front end of the body made by the scientist, it grew new tentacles, turning into a “multi-headed monster”, a miniature mythical hydra, with which, according to the ancient Greeks, Hercules fought.
It is not surprising that the laboratory animal received the same name. But the hydra under study had even more wonderful features than its Lernaean namesake. She grew to a whole even from 1/200 of her one-centimeter body!
Reality surpassed fairy tales! But the facts that are known to every schoolchild today, published in 1743 in the Proceedings of the Royal Society of London, seemed implausible to the scientific world. And then Tremblay was supported by the already authoritative Reaumur, confirming the authenticity of his research.
The “scandalous” topic immediately attracted the attention of many scientists. And soon the list of animals with regenerative abilities turned out to be quite impressive. Is it true, for a long time It was believed that only lower living organisms possess a self-renewal mechanism. Then scientists discovered that birds were able to grow beaks, and young mice and rats were able to grow tails.
Even mammals and humans have tissues with great capabilities in this area - many animals regularly change their fur, the scales of the human epidermis are renewed, cropped hair and shaved beards grow back.
Man is not only an extremely inquisitive creature, but also passionately desires to use any knowledge for his own benefit. Therefore, it is quite understandable that at a certain stage of research into the mysteries of regeneration, the question arose: why does this happen and is it possible to induce regeneration artificially? And why did higher mammals almost lose this ability?
Firstly, experts noted that regeneration is closely related to the age of the animal. The younger it is, the easier and faster the damage is corrected. A tadpole's missing tail easily grows back, but the loss of an old frog's leg makes it disabled.
Scientists have researched physiological differences, and the method used by amphibians for “self-repair” became clear: it turned out that in the early stages of development, the cells of the future creature are immature, and the direction of their development may well change. For example, experiments on frog embryos have shown that when the embryo has only a few hundred cells, part of the tissue destined to become skin can be cut out of it and placed in the brain area. And this tissue... will become part of the brain!
If a similar operation is performed on a more mature embryo, then skin still develops from skin cells - right in the middle of the brain. Therefore, scientists concluded that the fate of these cells is already predetermined. And if for the cells of most higher organisms there is no way back, then the cells of amphibians are able to turn back time and return to the moment when their purpose could have changed.
What is this amazing substance that allows amphibians to “self-heal”? Scientists have discovered that if a newt or salamander loses a leg, then the bone, skin and blood cells in the damaged area of the body lose their distinctive features.
All secondarily “newborn” cells, which are called blastema, begin to rapidly divide. And in accordance with the needs of the body, they become cells of bones, skin, blood... to eventually become a new paw. And if at the moment of “self-repair” you add tretinoinic acid (vitamin A acid), then this boosts the regenerative abilities of frogs so much that they grow three legs instead of the one lost.
For a long time it remained a mystery why the regeneration program was suppressed in warm-blooded animals. There may be several explanations. The first comes down to the fact that warm-blooded animals have slightly different priorities for survival than cold-blooded animals. Scarring of wounds became more important than total regeneration, since it reduced the chances of fatal bleeding when wounded and the introduction of a deadly infection.
But there may be another explanation, a much darker one - cancer, that is, the rapid restoration of a large area of damaged tissue implies the emergence of identical rapidly dividing cells in certain place. This is exactly what is observed during the emergence and growth of a malignant tumor. Therefore, scientists believe that it has become vital for the body to destroy rapidly dividing cells, and therefore, the ability to quickly regenerate has been suppressed.
Doctor of Biological Sciences Petr Garyaev, academician Russian Academy medical and technical sciences, states: “It (regeneration) did not disappear, it’s just that higher animals, including humans, turned out to be more protected from external influences and complete regeneration became not so necessary.”
To some extent, it has been preserved: wounds and cuts heal, torn skin is restored, hair grows, and the liver partially regenerates. But our severed arm no longer grows back, just as our internal organs do not grow back to replace those that have ceased to function. Nature simply forgot how to do this. Perhaps I need to remind her of this.
As always, His Majesty Chance helped. Immunologist Helen Heber-Katz of Philadelphia once gave her laboratory assistant a routine task: piercing the ears of laboratory mice to attach tags to them. A couple of weeks later, Heber-Katz came to the mice with ready-made tags, but... did not find holes in the ears.
We did it again and got the same result: no hint of a healed wound. The mice's bodies regenerated tissue and cartilage, filling in unnecessary holes. Herber-Katz drew the only correct conclusion from this: in the damaged areas of the ears there is a blastema - the same unspecialized cells as in amphibians.
But mice are mammals, they should not have such abilities. Experiments on the unfortunate rodents continued. Scientists cut off pieces of mice's tails and... got 75 percent regeneration! True, no one even tried to cut off the “patients’” paws for an obvious reason: without cauterization, the mouse would simply die from massive blood loss long before regeneration of the lost limb began (if at all). And cauterization eliminates the appearance of blastema. So full list The regenerative abilities of mice could not be determined. However, we have already learned a lot.
True, there was one “but”. These were not ordinary house mice, but special pets with a damaged immune system. Heber-Katz made the first conclusion from her experiments: regeneration is inherent only in animals with destroyed T-cells - cells of the immune system.
Here's the main problem: amphibians don't have it. This means that the answer to this phenomenon lies precisely in the immune system. Conclusion two: mammals have the same genes necessary for tissue regeneration as amphibians, but T cells do not allow these genes to work.
Conclusion three: organisms originally had two ways of healing from wounds - the immune system and regeneration. But over the course of evolution, the two systems became incompatible with each other - and mammals chose T cells because they were more important, since they were the body's main weapon against tumors.
What is the use of being able to regrow a lost arm if at the same time cancer cells are rapidly developing in the body? It turns out that the immune system, while protecting us from infections and cancer, at the same time suppresses our ability to “self-repair”.
But is it really impossible to think of anything, because you really want not just rejuvenation, but restoration of the life-supporting functions of the body? And scientists have found, if not a panacea for all ills, then an opportunity to become a little closer to nature, however, thanks not to the blastema, but to stem cells. It turned out that humans have a different principle of regeneration.
For a long time it was known that only two types of our cells can regenerate - blood cells and liver cells. When the embryo of any mammal develops, some cells remain aside from the process of specialization.
These are stem cells. They have the ability to replenish blood or dying liver cells. Bone marrow also contains stem cells, which can become muscle tissue, fat, bone or cartilage - depending on what nutrients they are given in laboratory conditions.
Now scientists had to test experimentally whether there was a chance to “launch” the “instructions” written in the DNA of each of our cells for growing new organs. Experts were convinced that you just need to force the body to “turn on” its ability, and then the process will take care of itself. True, the ability to grow limbs immediately runs into a temporary problem.
What a tiny body can easily do is beyond the power of an adult: the volumes and dimensions are much larger. We can't do like newts: form a very small limb and then grow it. For this, amphibians need only a couple of months, for humans to grow new leg to reach normal size, according to the calculations of the English scientist Jeremy Brox, it takes at least 18 years...
But scientists have found a lot of work for stem cells. However, first it is necessary to say how and where they are obtained from. Scientists know what is most a large number of stem cells are located in the bone marrow of the pelvis, but in any adult they have already lost their original properties. The most promising resource is considered to be stem cells obtained from umbilical cord blood.
But after birth, researchers can only collect 50 to 120 ml of such blood. From every 1 ml, 1 million cells are released, but only 1% of them are progenitor cells. This personal reserve of the body’s recovery reserve is extremely small and therefore priceless. Therefore, stem cells are obtained from the brain (or other tissues) of embryos - abortive material, no matter how sad it is to talk about it.
They can be isolated, placed in tissue culture, where reproduction begins. These cells can live in culture for more than a year and can be used for any patient. Stem cells can be isolated from umbilical cord blood and from the brain of adults (for example, during neurosurgery).
Or it can be isolated from the brains of recently deceased people, since these cells are resistant (compared to other cells of the nervous tissue); they are preserved when the neurons have already degenerated. Stem cells extracted from other organs, such as the nasopharynx, are not as versatile in their use.
Needless to say, this direction is fantastically promising, but has not yet been fully explored. In medicine, it is necessary to measure seven times, and then recheck for ten years to make sure that the panacea does not lead to any disaster, for example, an immune shift. Oncologists also did not say their strong “yes”. But nevertheless, there have already been successes, although only at the level of laboratory developments and experiments on higher animals.
Let's take dentistry as an example. Japanese scientists have developed a treatment system based on genes that are responsible for the growth of fibroblasts - the very tissues that grow around teeth and hold them. They tested their method on a dog that had previously developed a severe form of periodontal disease.
When all the teeth fell out, the affected areas were treated with a substance that included these same genes and agar-agar, an acidic mixture that provides a nutrient medium for cell reproduction. Six weeks later, the dog's fangs erupted.
The same effect was observed in a monkey with teeth cut down to the base. According to scientists, their method is much cheaper than prosthetics and for the first time allows a huge number of people to literally return their teeth. Especially when you consider that after 40 years of age, a tendency to periodontal disease occurs in 80% of the world's population.
In another series of experiments, the tooth chamber was filled with dentinal filings (playing the role of an inductor) with gingival connective tissue (amphodont) as a reacting material. And the amphodont also turned into dentin. In the near future, English dentists hope to successful experiences on mice, proceed to further laboratory studies. Conservative estimates suggest that stem implants will cost the same as conventional prosthetics in England - between £1,500 and £2,000.
Research has shown that people with kidney failure only need to have 10% of their kidney cells revived to stop being dependent on a dialysis machine.
And research in this direction has been ongoing for many years. How important it is - not to sew it on, but to grow it again, not to sit on pills, but to restore healthy function using the hidden capabilities of the body.
In particular, a way has been found to grow new pancreatic beta cells that produce insulin, which promises millions of diabetics relief from daily injections. And experiments on the possibility of using stem cells in the fight against diabetes are already in the completion phase.
Work is also underway to create products that include regeneration. Ontogeny has developed a growth factor called OP1, which will soon be approved for sale in Europe, the US and Australia. It stimulates the growth of new bone tissue. OP1 will help in the treatment of complex fractures, when the two parts of the broken bone are very misaligned with each other and therefore cannot heal.
Often in such cases the limb is amputated. But OP1 stimulates bone tissue so that it begins to grow and fill the gap between the parts of the broken bone. At the Russian Institute of Traumatology and Orthopedics, researchers obtain stem cells from bone marrow. After 4-6 weeks of propagation in culture, they are transplanted into the joint, where they reconstruct the cartilaginous surfaces.
And a few years ago a group of English geneticists made sensational statement: They begin work on cloning the heart. If the experiment is successful, there will be no need for transplants, which could lead to tissue rejection. But it is unlikely that wave genetics will be limited to the regeneration of only internal organs, and scientists hope that they will learn to “grow” limbs for patients.
In the field of gynecology, stem cells also great prospects. Unfortunately, many young women today are doomed to infertility: their ovaries have stopped producing eggs.
This often means that the pool of cells from which follicles arise has been exhausted. Therefore, it is necessary to look for mechanisms that replenish them. The first encouraging results in this area have appeared recently.
Scientists are already seeing how to save people who have been given a terrible diagnosis - cirrhosis of the liver. They believe that at some stages of the development of the disease, transplantation of an entire organ can be replaced by the introduction of only stem cells (through the arterial bed, direct punctures, direct cell transplantations into liver tissue). Specialists from the Center for Surgery of the Russian Academy of Medical Sciences have begun a pilot study, and the first results are encouraging.
Ukrainian scientists are conducting very interesting preliminary developments in the field of cardiovascular diseases. Already today they have accumulated experimental evidence that the introduction of stem cells to patients with myocardial infarction or severe ischemia is a promising treatment method.
The first clinical experiments with stem cell transplantation, which began at the University of Pittsburgh in the USA, also yielded good results in severely ill patients who had suffered an ischemic or hemorrhagic stroke. After cell therapy, their neurological rehabilitation is clearly noticeable.
Unfortunately, the frightening statistics of the number of children with intrauterine brain damage, including those with cerebral palsy. It has already been proven that if such children begin stem cell transplantation (or therapy aimed at stimulating them, i.e., localizing their own, endogenous cells in the affected area), then after the first year of life it is often observed that even with preservation of anatomical Children with brain defects have minimal neurological symptoms.
Effectively developed stem cell transplantation technologies can completely change our lives. But this is the future, and today this field of knowledge does not even have its own name, only options: “cell therapy”, “stem cell transplantation”, “regeneration medicine”, even “tissue engineering” and “organ engineering”.
But it is already possible to list all the possibilities of this new direction. No wonder they say that XXI a century will pass under the sign of biology, and perhaps the experience of regeneration, preserved over millions of years by amphibians and protozoa, will help humanity.