Time ago

Humanity has always dreamed of finding a remedy that returning youth, but until recently, young apples, as well as potions and elixirs, turning back the time, existed only in fairy tales. In 2012, the Nobel Committee awarded the Physiology and Medicine Award to two scientists who came up with a method that allows not only to throw off for several years, but to return to the embryonic state. True, it does not work for an entire organism, but for individual cells, but this fact makes the discovery of Xinya Yamanak and John Gurdon much more significant than the invention of any anti -aging technologies.

Get in V childhood

The human body and any other multicellular creature consists of cells, markedly different from each other in appearance and in the functions that they perform. In addition, some types of “bricks”, of which a living fabric are built, have a much larger breadth of the profile than others. Part of the cells of our body is rigidly “sharpened” for the implementation of a particular task-and all the biochemistry and morphology of the cell are adjusted to this task. Others can choose what they would like to do: after the next division, the descendants of such cells can become, say, blood vessels, blood cells or something else.

Cells determined with their purpose are called differentiated or unipotent. For “oscillating” the term “undifferentiated” is used, and the degree of “potentiality” can vary significantly. The most undifferentiated (so to speak) body of the body is a fertilized egg, from which all tissues and organs develop. The egg, as well as its descendants of the first or second generation, is called totyotent cells, and each of them is able to give rise to the whole body. It is thanks to the totypotence of the “children” and “grandchildren” that the eggs are genetically identical, or single -eating twins.

Each next cell generation is more and more specialized. Although all the embryo cells in the early stages of development are able to share a huge number of times and generate various types of cells, they can no longer become the ancestors of the whole organism: some of the possible paths for them are closed (such, for example, all human stem cells). As the number of possible options for the future decreases, the cells become plural, then the multi-plot, and, finally, turn into rigidly determined “hard workers”, which no matter how much they share, they can never give rise to something other than copies of themselves. At least this was considered until recently.

The last proposal of the previous paragraph sins a little against the truth: the hypotheses that the “watch” of differentiated cells can be forced to go in the opposite direction in the first third of the 20th century. Nobel Prize laureate in physiology and medicine, the German embryologist Hans Spemann in 1935 suggested that the core of a specialized adult cell, which fell into the cytoplasm of a total of a total of a totytotent egg, could “change his mind” and begin to work as his genome had just formed during the merger of the motherland and the affordable Father's DNA. It was technically impossible to verify this prediction, which later turned out to be absolutely true, and Speman himself called the experiment “fantastic”.

The first attempt to “torture” the cells according to the meadow was made in the early 50s of the Americans Robert Briggs and Thomas King. They learned to remove the nucleus from fertilized eggs of the RANA leopard frog Pipiens And to plant undifferentiated and differentiated amphibious cells into the empty cytoplasm of the nucleus. In the first case, they managed to grow a tadpoles from such a hybrid egg, and then an adult frog, and in the second series of experiments, the eggs died. Moreover, scientists have shown that the farther the core-donor of the nucleus has advanced along the path of differentiation, the earlier the hybrid embryo died.

Despite the disappointing result, the colleagues of Briggs and King immediately appreciated the significance of the nucleus transplant methodology and began to use it with might and main for various experiments. One of those who became interested in a new area of ​​experiments was British biologist John Gurdon. He worked with a different type of amphibian - the famous curtain frog Xenopus Laevis , - and after several years of experiments in 1962, he managed to do what King and Briggs did not succeed. Gurdon slightly modified their methodology, and, in addition, he showed that if you transplant the nucleus of a differentiated cell in several stages (i.e., do not grow an egg with a transplanted nucleus to the stage of a thorough, but wait for the first divisions, take the nuclei of the newly formed cells and again plant them into a miraculous egg), the percentage of success is noticeably higher.

The scientific community reacted to the results of Gurdon wary: only a few years after the scientist was able to repeat the success of the scientist in other laboratories, his achievements were recognized from colleagues.

Remove the block

The experiments of Briggs, King, Gurdon and others showed the fundamental opportunity to turn the development of the cell. But the mechanism for removing the lock imposed by specialization remained unclear. In a fertilized egg, a whole cocktail of all kinds of factors acts on the nucleus of a differentiated cell, but it was not possible for a long time to highlight those that are really necessary for reprogramming adult cells.

At the beginning of the new millennium, as the technologies of mass genetic analysis are improved, the fundamental scheme of the experiment began to emerge, which would allow the key factors that control the cell “time machine”. Analyzing the activity of genes in embryonic and adult cells, scientists have found sequences that work only in an undifferentiated state. All these genes were encoded by regulatory proteins, called transcription factors (TF). Such proteins can contact DNA and activate or, conversely, block the work of specific genes. In the early stages of development, it is the TF that is launched by all the most difficult chains of reactions, which ultimately lead to the formation of the body. Having checked how exactly each of these factors and their all kinds of combinations affect the fate of differentiated cells, scientists could calculate from dozens of TF embryonic cells of those that launch a dispensing. Although the experimental algorithm is very simple, it demanded a colossal amount of work to overcome all combinations of TF - and the estimated amount of work, obviously, scared away many researchers.

The Japanese Signa Yamanaka (Shinya Yamanaka), who received a medical education, but later carried away by the problem of repaying to adult cells of pluripotence, was decided to take up the titanic project. The scientist chose 24 TF and inserted them into the genome of skin cells (fibroblasts) with the help of special viral “carriers”, able to embed their sequence in the DNA of the host cell. At the next stage of the experiment, Yamanaki planted modified fibroblasts on Petri's cups and selected those cells that lost their specialization and deducted. The scientist determined which TF genes work in “rejuvenated” cells, and then again inserted the genes of these TF into the DNA of fibroblasts, each time reducing their number each time. As a result, Yamanaka selected four from two and a half dozen genes, which launched fibroblasts. They are called C-Myc, Oct3/4, SOX2 and KLF4. Yamanaka called the Totipotent cells of Yamanaka in this way induced pluripotent stem cells (IPS). The work of a Japanese researcher was immediately called a breakthrough in molecular biology: the scheme invented by Yamanaka, unlike the laborious and demanding method of transplanting nuclei, made it possible to disiff with any cells easily and simple. After the release of the Japanese article in Cell magazine In 2006, the number of publications devoted to the Dedix cells began to grow at incredible speed. Yamanaka himself also continued to deal with this topic and completed several more iconic experiments. In particular, the next year, two groups of scientists (one of them worked under the leadership of Yamanaki) were able to get an IPS person. And in 2009, Chinese researchers were able to grow a relatively healthy mouse from the Yamanaki cells created by the Yamanaki method.

Difficulties

The technique developed by the Japanese had two significant drawbacks. Firstly, one of the Yamanaki TF genes included in the “magic four” is oncogen, which significantly increases the likelihood of developing tumors. And secondly, the IPS experiment itself is able to turn the normal cage into cancer: the supporting genes of TF viruses can be built into any place of the genome, and if the planting is unsuccessful, the cell begins to go crazy. The colossal enthusiasm of researchers who took up a promising topic allowed both these problems in several years to solve. The second difficulty was overcome, using first other viral “carriers” that are not able to integrate into DNA, and then completely “naked” DNA fragments that are lost during subsequent cell divisions. The problem with the MYC oncogen was solved by slightly changing the composition of the Deducting “cocktail”. As IPS studies, other difficulties were identified. In particular, a thorough analysis showed that IPS is still not an accurate analogue of total embryonic cells. IPS is active in a slightly different set of genes, and, in addition, the cells formed from them grow slower than the descendants of the “normal” egg. The reason for these differences most likely lies in epigenetic markers - the supra -mock "amendments", which can be introduced in the DNA as the cells exist and additionally regulate the function of the genome. In adult cells, epigenetic marks are on other DNA fragments compared to embryonic ones, and scientists do not yet know how to remove this “stigma” of age. It is believed that it was the epigenetics that led to the early death of the lobby of Dolly - the first mammal, cloned according to the same fundamental scheme used by Gurdon.

In 2008, the creators of the sheep Dolly Yang Wilmut and Kate Kempbell, along with Yamanaku, received the show award - an Asian analogue of the Nobel Prize. The scientific community was puzzled by the fact that Gurdon was left without this reward - all the more so since he worked with Wilmut and Kempbell for some time.

Work in the field of reprogramming of cells is very actively conducted in laboratories around the world. It is impossible to overestimate the meaning of these studies for fundamental science, but the prospects for using IPS are also huge in medicine. The re -created stem cells can be used to obtain specialized cells, which can be replaced by degraded cells for diseases such as Alzheimer's disease or lateral amyotrophic sclerosis (the disease from which Stephen Hawking suffers). In addition, on IPS, obtained from people with various ailments, you can study the mechanisms of the development of these pathologies and look for methods of combating them. However, today there are no ready -made clinical use techniques of induced stem cells, but if their study is promoted by the same pace as now, then their appearance can be counted already in the foreseeable future.

Irina Yakutenko