Important scientific news: biologists from Tufts University (USA) managed to restore the ability to regenerate the tail tissue in tadpoles.
Such work could be considered ordinary, if not for one circumstance: the result was achieved in a non-trivial way, using optogenetics, which is based on the control of cell activity with the help of light.
The ultimate goal of all such studies is to discover the natural mechanisms that control the repair of body parts and learn how to turn them on in humans. Tadpoles are perfect for this task, since at an early stage of development they retain the ability to replace lost limbs, but then they suddenly lose it. If you cut off the tail of individuals that have entered the so-called refractory period, they will no longer be able to regrow it.
Internal systems that control regeneration are still present in their bodies, but for some reason they are stopped. Michael Levin and his colleagues made them work again, effectively turning physiological time back.
The way they did it is great. One group of tailless tadpoles was raised in a container illuminated with short flashes of light for two days; the other lived in complete darkness. As a result, the tadpoles of the first group recovered full-fledged tail tissue, including the structures of the spine, muscles, nerve endings, and skin. The second tadpoles could not overcome the consequences of amputation, as it should be at their age.
If it sounds like a trick, it is only partly. To understand why this happened, you need to explain the principle underlying the experiment. Indeed, all animals at the same stage of the life cycle were subjected to identical manipulations. The only thing that distinguished the two groups was the presence or absence of lighting. However, light was not the true cause of the change. It served as a remote switch, activating a factor that (not entirely clear) triggered the regeneration process. Such a factor was the hyperpolarization of the transmembrane cell potentials; or, more simply, bioelectricity.
Optogenetics makes it relatively easy to design an experiment. The mRNA molecules of the photosensitive protein archerhodopsin were injected into tadpoles. This led to the fact that after a while on the surface of ordinary cells located in the thickness of the tissue, “pump proteins” appeared. Under the condition of stimulation with light (and only in this case), they induced the current of ions through the membrane, thereby changing its electrical potential.
In fact, apart from light-activated membrane pumps, scientists have offered nothing to help tadpoles. However, just one effect on the electrical properties of cells was enough to trigger a complex cascade of regeneration processes in the body. In turn, thanks to optogenetics, it is as easy as shelling pears to cause these changes from the outside, you just need to shine light on the tadpole.
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Regeneration remains one of the main mysteries of biology. In 2005, Science magazine included the following question among the 25 most important problems facing science: What Controls Organ Regeneration? Unfortunately, scientists have not yet been able to fully understand why some animals at any stage of their lives freely restore the lost parts of the body, while others lose this ability forever. Once upon a time, your body knew how to grow an eye or an arm.
It was a long time ago, at the very beginning of life as an embryo. Experts are interested in where this knowledge disappears and whether it is possible to revive it again in an adult. At the moment, the search for most biologists is focused mainly on the expression of genes or chemical signals. In the laboratory of Michael Levin, they hope to find the answer to the riddle of regeneration in another phenomenon, bioelectricity, and these hopes, apparently, are not without foundation.
The fact that electric currents are present in a living organism has been known since the time of Galvani's experiments. However, few have studied their impact on development as closely as Lewin does. Bioelectricity has long had a chance to become a worthy topic of experiments, but the molecular revolution in biology in the second half of the 20th century pushed research interest in this issue to the margins of science.
Levin, coming from the field of computer modeling and genetics, employing the most modern methods that were absent from his predecessors, in fact returns this direction to the biological mainstream. His enthusiasm is based on the belief that electricity is a basic physical phenomenon, and evolution could not help but use it in fundamental processes, such as the development of the organism.
By changing the transmembrane potential of cells, the scientist can instruct the tissues of the tadpole to grow an eye in a predetermined area of the body. A photograph of a six-legged frog hangs on the wall of his laboratory. Additional limbs appeared in her solely as a result of exposure to electrical biocurrents. Unlike neurons, ordinary cells are incapable of firing, but they can consistently transmit signals throughout the body through gap junctions. If a planarian, a tiny worm that can regenerate, has the tail cut off, a request is sent to the head from the cut area to make sure it is in place. Block the transmission of this information, and a head will grow instead of the intended tail.
By manipulating various ion channels that determine the electrical properties of cells, scientists in their experiments produced worms with two heads, two tails, and even worms of an unusual design with four heads. According to Levin, he was almost always told that his ideas should not work. He relied on his intuition, and in most cases it did not fail.
These attempts are still very far from complete knowledge of how to restore a limb in a person. While disabled people can only count on the improvement of prostheses. However, the unique laboratory at Tufts University is looking for something even more fundamental: like the genetic code, Levin believes, there must be a bioelectrical code linking gradients and dynamics of membrane tension with anatomical structures.
Having understood it, it will be possible not only to control regeneration, but also to influence the growth of tumors. Levin sees them as a consequence of the loss of information about the shape of the organism by cells, and the study of the problem of cancer is among the tasks of his laboratory. As is often the case, seemingly different processes can have a single nature.
If the bioelectric code really is behind the construction of various organs of the body, its solution could shed light on two of the most important problems facing humanity at once.