Japanese researchers have successfully grown a mouse based on a freeze-dried body cell. This may be a way to conserve endangered species and bring them back to life later, although there are some obstacles.
It sounds a bit like Frankenstein when researchers write that body cells from cadavers can grow into new, viable mice. However, this technique offers new opportunities to save endangered species, researchers Sayaka Wakayama and colleagues write in the scientific journal. Nature Communications† You can store body cells from animal species that can no longer be reproduced until conditions become more favorable. Freeze-dried cells are easier to store than refrigerated cells.
Since the cloning of Dolly the sheep in 1996, biomolecular experts have made steady progress in raising animals in all kinds of unnatural ways. Frozen and then thawed sperm cells have been used for years to fertilize female animals and in 2019 a mouse was successfully grown on the basis of a freeze-dried sperm cell. The latter was performed by the same group of researchers who have now managed to grow a mouse from a freeze-dried body cell.
Freeze drying, commonly known in the food industry, is a method in which water is extracted from the fabric by frosting, after which the dried residue can be stored at room temperature. Thus, freeze-dried cells are easier to store than cryogenic cells. In addition, this method of preservation is less susceptible to disturbances, natural disasters or human error. Additionally, you don’t necessarily need sperm cells for that. Obtaining this can be difficult in endangered species, for example when fertilized males are not alive.
Wakayama and colleagues describe how they extracted body cells from fibroblasts, a type of skin cell in mice, and then freeze-dried them. Those freeze-dried cells were rehydrated after nine months. Then they took the cell’s nucleus and implanted it in an egg to grow a type of embryo.
“It’s impressive what they’ve done, but they had to jump through many hoops to do it,” says Nils Jaisen, professor of evolutionary biology and regenerative medicine at Leiden University Medical Center (LUMC).
Usually, in animal cloning, the embryo is implanted into a surrogate mother. “But in this case they first created a line of stem cells and then transplanted them further.”
Stem cells are a type of flexible basal cell. Geijsen: “Then they take another nucleus of those, which is inserted into an egg cell and implanted into a female.”
Small success rate
This laborious intermediate step is necessary due to the significant damage to DNA during freeze drying. When stem cells grow, the DNA damage is partially repaired and the less successful cells die. “The success rate is very low: 0.02, but it was really successful,” Jason says.
The question is how useful it is in preserving animal species, says Alexandra van der Geer, an evolutionary biologist at the Naturalis Center for Biodiversity in Leiden. A researcher specializing in the evolution of (small groups) of mammals on the islands does not immediately see a panacea. “It’s a first step, and the researchers aren’t asking for more, but there’s still a lot to be done.”
For example, eggs and surrogates are still needed. “If you already have this, what are you doing so hard?”
In addition, the survival of the species does not require a single specimen, but rather the full range of genetic diversity necessary. In a scenario where there are only one or two copies of an animal species that are likely to have already died, this becomes difficult.
Perhaps the most important point is that an animal species lives in an ecosystem and its disappearance is the main cause of its extinction. Van der Geer: “Actually, you have to bring back this entire ecosystem.”
In short: Great achievement, interesting research, but there is a risk that such a flashy technological solution will stand in the way of milder but more difficult measures, based on the idea that we can always fix this later.