Yuka won't help clone a mammoth
Scientists failed to fully "revive" the DNA of the Yakut mammoth
Russian and Japanese molecular biologists have successfully extracted nuclei from the cells of the Yakut mammoth Yuki and transplanted them into the eggs of mice, but could not fully "revive" them. The results of experiments on the "resurrection" of the genetic heritage of mammoths were presented in the journal Scientific Reports (Yamagata et al., Signs of biological activities of 28,000-year-old mammoth nuclei in mouse oocytes visualized by live-cell imaging).
"The five cells we received showed signs of activity that are characteristic of dividing cells. On the other hand, none of them was able to start dividing, which is necessary for the revival of mammoths. It seems to me that we are still extremely far from solving this problem," said Kei Miyamoto from Kindai University in Wakayama (in an interview with AFP Mammoth moves: frozen cells come to life, but only just–.
The mummy of the famous mammoth Yuki was found in the summer of 2010 on the shore of the Laptev Sea by residents of the village of Yukagir. As scientists suggest, it belonged to a young female who died at the age of 8 to 10 years about 29 thousand years ago. The remains of the animal have never been thawed, so they are very well preserved.
This discovery immediately attracted the attention of geneticists and biologists from Russia, South Korea, Japan and other countries who hoped to find an almost intact genome in frozen mammoth cells. Legends immediately formed around Yuki that there are "living" cells in the mammoth's body, with the help of which scientists will be able to "resurrect" the giants of the glaciation era.
Miyamoto and his colleagues, including Albert Protopopov and Valery Plotnikov from the Academy of Sciences of Yakutia, have been working for several years to solve this ambitious task, extracting all genetic material from mammoth cells and transplanting it into the eggs of mice whose DNA was previously removed.
The first such experiment, which Japanese geneticists conducted in 2009, ended unsuccessfully. Mammoth cell nuclei that have lain in permafrost for about 15 thousand years have not "taken root" in donor bodies and have not shown any signs of vital activity. These failures have forced many other geneticists to look for alternatives.
For example, the group of George Church from Harvard University goes a completely different way – they extract individual genes from mammoth DNA and "transplant" them into the genome of ordinary modern elephants. Such an approach does not require obtaining perfectly intact cell samples, but has another disadvantage – the final "product" of such manipulations will be an elephant, similar to the giants of the Ice Age, but not a real mammoth.
The discovery of Yuki's remains, as noted by Miyamoto and his colleagues, gave them new hope that their approach could still bring success. Studying the DNA of cells in different mammoth tissues, scientists noticed that in the muscle tissue and in some other parts of his body, the cells were preserved so well that they could see a separate nucleus.
Using techniques already worked out in the past, Japanese and Russian biologists were able to extract 88 intact nuclei from mammoth cells and transplant some of them into mouse eggs. In parallel, they performed the same operation with genetic material extracted from frozen elephant tissues.
These experiments ended with partial success – a small part of the cells with the "transplanted" mammoth DNA began to show signs of activity in the first hours after transplantation. The spindle of division, the "blank" of the second nucleus, the so-called pronucleus, and some other structures critical for the formation of new cells began to form in them.
Despite this, none of them was able to move on to the next stages of division, prepare copies of chromosomes and "pull apart" them into the halves of daughter cells. As scientists suggest, this is due to the fact that mammoth DNA has accumulated too many double breaks and other damages that genome repair systems could not eliminate.
"On the one hand, our experiments have shown that mammoths cannot be cloned using modern core transfer technologies. On the other hand, now we can study the biological processes that occur in the cell nuclei of long–extinct animals," the scientists conclude.
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