Somatic cell nucleus transfer: a new round of developments?
Embryonic stem cells obtained by cloning
Kirill Stasevich, Compulenta
Embryonic stem cells (ESCs) could become a truly magical tool for modern medicine, if their production were not associated with significant technical and insurmountable ethical problems. You can grow any tissue from such cells, but you can't get them from human embryos! In 2006, the way out seemed to have been found: with the help of molecular genetic manipulations, scientists managed to obtain so-called induced pluripotent stem cells. They, too, could give any kind of tissue, and they could be obtained from adult cells. But later it turned out that despite all the similarities with real ESCs, induced ones have some significant differences in development, which calls into question their applicability in medicine.
Another possible way to obtain stem cells was to clone them using eggs. After 1996, when Dolly the sheep was born, a real "clone attack" began in molecular biology, but attempts to get a stable line of human ESCs ended unsuccessfully. Only in a few experiments on animal eggs it was possible to obtain the necessary cell cultures. In addition, the researchers were limited in research material to conduct sufficiently thorough and verified experiments: after all, we were talking about human eggs.
The essence of the usual cloning technique is that its DNA is removed from the egg, instead of which a double chromosome set from an adult cell is inserted. Ideally, the egg feels fertilized and triggers the mechanisms of embryogenesis by executing those programs that are recorded in the DNA injected into it. But in practice, such eggs stopped multiplying after only a few divisions. Researchers from the New York Stem Cell Foundation (USA) have tried to overcome this obstacle. They took 270 eggs from 16 donors and processed them according to various modern modifications of cloning techniques. Paradoxical as it may sound, but the reason for the early failures was the removal of their own DNA from eggs.
When the cell's own cellular DNA was not removed from the cell, it continued to divide, reaching the blastocyst stage and forming up to a hundred daughter cells. Despite the fact that they contained a triple set of chromosomes, the cells did not feel any concern about this. Stem cells obtained in this way were no different from ESCs, they had "omnipotence" genes that determine the ability of such cells to turn into anything. The scientists presented their results in the journal Nature (Noggle et al., Human oocytes reprogram somatic cells to a pluripotent state; a short retelling in Nature News – Cloned human embryo makes working stem cells – VM).
Researchers believe that removing the egg's own DNA at the same time removes from it the molecular factors that support division. These may be, for example, protein transcription factors. Anyway, the authors of the work managed to get a completely accessible and ethically acceptable source of real ESCs. At the same time, other scientists, paying tribute to the phenomenal results, ask what to do with the extra set of chromosomes that are present in such stem cells. Will they really behave well once they get into the human body? However, the researchers are convinced that it is much easier to solve this problem than to deal with the differences between natural stem cells and their ersatz in the form of induced pluripotent stem cells.
Prepared based on the materials of the New York Foundation for the Study of Stem Cells:
Scientists at New York Stem Cell Foundation, Columbia U.
Make Advance in Development of Patient-Specific Stem Cells.
Portal "Eternal youth" http://vechnayamolodost.ru06.10.2011