Freeze-drying is a process where a completely frozen sample is placed under a vacuum to remove water or other solvents from it. This helps the ice to transform directly from a solid to a vapor without passing through a liquid phase. The technique is mostly used in the food industry where it keeps nutrients and flavors intact. Now, it could be used to store DNA and cell information for cloning purposes.
In the latest work, researchers from the University of Yamanashi in Japan showed that somatic cells (non-reproductive cells) can be used to clone healthy mice.
"Here, we demonstrate that freeze-dried somatic cells can produce healthy, fertile clones, suggesting that this technique may be vital for the development of alternative, cheaper, and safer liquid nitrogen biobanking strategies," according to researchers led by Sayaka Wakayama from the University of Yamanashi in Japan.
Currently, somatic and reproductive cells can be stored in liquid nitrogen. To bring the cells back to life, the liquid nitrogen has to be quickly raised in temperature. This is considered an expensive and risky process because if liquid nitrogen is not replenished regularly, the cells will thaw and become unusable.
For this study, the researchers used mouse somatic cells, freeze-dried, and kept them at -30°C (-22°F) for up to nine months before attempting to clone them.
Interestingly, the freeze-drying processes killed the cells, but the team found they could secure the remaining genetic information and place it into new cells - this eventually became early embryo cell lines.
The researchers then extracted nuclear information from these cell lines and inserted it into a new embryo. This finally helped them create cloned mice. From these early-stage embryos, the scientists created stocks of stem cells for another round of cloning. They implanted the stem cells into the eggs of mice emptied of their nuclei, leading to the creation of embryos that the mice’s mothers could carry.
The first cloned mouse, named Dorami, was followed by 74 other mice. To check the fertility of the cloned mice, nine females and three males were mated with non-cloned mice. All the females went on to produce a healthy litter.
In some of the cells, however, the Y chromosome was lost and went from male to female. Furthermore, the success rate of creating young female and male mice was only 0.2-5.4%. For cloning extinct animals, we’ll need to get better at cloning degraded or incomplete DNA. Therefore, there’s plenty of scope for fine-tuning this technique, but if the success rate is eventually improved, it could open up great possibilities for saving the hundreds of thousands of species that are being wiped out from the Earth.
“If the same treatment could be performed in endangered species where only males survived, it would be possible to produce females and naturally preserve the species,” the authors write in their research paper published in Nature Communications. The research team hopes to give conservation efforts further options for collecting genetic material in the future.
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