The freeze drying process really punches above its (very light) weight. It makes a delicious chocolate-covered strawberry, gives astronauts expanded nutritional options, and now the technique can be used to store DNA and cellular information for cloning purposes.
With a low success rate of 0.2 percent, cell freeze-drying still has a long way to go before it becomes a standard cloning and storage strategy, but it’s a really exciting step.
“Maintaining biodiversity is a major task, but preserving germ cells as genetic resources using liquid nitrogen is difficult, expensive, and easily destroyed during disasters,” researchers led by Sayaka Wakayama of Yamanashi University write in their new paper. in Japan.
“Here we show that lyophilized somatic cells can produce healthy, fertile clones, suggesting that this technique could be important for creating alternative, cheaper and safer biobanking solutions without liquid nitrogen.”
Freeze drying is a gentle, if intensive, process. Imagine freezing something in several stages until it reaches about -80 degrees Celsius (-112 degrees Fahrenheit) before placing it in a high-pressure vacuum chamber.
The process turns the water into ice without large ice crystals breaking through the cell walls, while the pressure turns the water from a solid state straight into a gas, which is then sucked out of the product. This happens several times until the item is light and crispy but still has most of its structure intact.
Freeze drying is mostly used in the food industry where it keeps the nutrients and flavors intact. It is also used for pharmaceuticals and even sometimes for decoctions.
Once the freeze-dried item arrives at its destination, it can be rehydrated, keeping many properties the same. It’s a fairly simple process and has been happening successfully for decades. But doing that to cells that are then used in reproduction is a whole other fish.
So far, the same team of researchers has experimented with storing freeze-dried sperm in a desk drawer (without temperature control) for over a year and on the International Space Station for over 5 years. Both produced viable offspring, although the success rate was in the teens.
“Freeze-drying may be the best way to preserve genetic resources for a long period of time in a safe, inexpensive and location-independent manner,” the researchers wrote in their paper.
“However, to date, the only cells that have produced offspring after freeze-drying are mature sperm. Collecting sperm from infertile men and oocytes/embryos from fertile women is difficult.”
When you clone animals, you need a non-reproductive cell (called a somatic cell) with all of the animal’s DNA. This nuclear package full of DNA can then be inserted into an egg cell and with a little tinkering you can begin the process of growing a baby.
Cloning is not the easiest way to store genetic material for the future, but it allows you to have all of an animal’s genetic material, as opposed to only half found in reproductive cells.
Currently, somatic and reproductive cells – for biobanking or other purposes – can be stored in liquid nitrogen, the temperature of which can be quickly raised to bring the cells back to life.
But the researchers wanted to see how freeze-drying stacks up, so they used mouse somatic cells (in this case, fibroblasts and cumulus cells) freeze-dried and kept at -30 degrees Celsius (-22 degrees F) for up to nine months.
The cells did die and there was some DNA damage, but the team was able to extract the rest of the genetic information and put it into new cells that became early embryonic cell lines.
These cell lines then had theirs nuclear information extracted and inserted into a new embryo that succeeded in creating cloned mice. So yes, it’s not a perfect process. Each correct step—from rehydration, to creating a cell line, to actually growing the cloned mice—occurs only 0.2 percent of the time. This puts the method at an even lower chance of success than cloning Dolly the sheep, which had only a 0.4 percent chance of existing.
Some mice are also not correct clones, carrying epigenetic abnormalities due to DNA damage. In one interesting case, the cell line lost its Y chromosome and went from male to female, so much more research needs to be done to refine this process.
With all that said, if success rates eventually improve, the ability to clone animals using such degraded cells and DNA would be a boon in other fields as well. Over time, even the best-preserved DNA degrades; if we want to have any luck cloning extinct animals, we’re going to have to get better at cloning from incomplete or degraded DNA.
It’s worlds away from where we are now, but the future looks interesting.
The study was published in Nature Communications.