Freeze-dried sperm postcards could help guarantee humanity's future

“In today’s world, emails are often sent by computer and conversations take place via telephone and chat, but new demands are likely to increase. I’m glad I’m thin and light myself.”

Written in Japanese, the text, which is translated for Inverse, is at first glance a cheery note on a perfectly ordinary postcard. But this is no typical postcard.

Thin and light indeed: Fixed to the postcard, freeze-dried sperm were nestled between two plastic sheets, each 0.2 millimeters thick.

What’s new — This isn’t a quirky new subscription package for animal DNA, straight to your mailbox, but a potential strategy to safely, cheaply, and efficiently transport biological material.

With this postcard, researchers from Japan’s University of Yamanashi have unlocked a method to store and send freeze-dried genetic material at room temperature for up to three days. And perhaps even more incredibly — once at its destination, the DNA in the sperm can be used to produce healthy offspring.

The findings, published Thursday in the journal iScience, details how these researchers experimented with six materials and ultimately mailed their thin, light parcel.

The innovation could one day scientists enable to keep a cache of sperm cards in the way one might save baseball cards, with different species in different slots of an album, ready to use when needed.

“It is now recognized that genetic resources are an asset to humanity’s future. Even though many genetic traits are not needed for survival, depending on the environmental context, it is necessary to preserve them,” says senior author Teruhiko Wakayama, also of the University of Yamanashi in Japan, in a statement.

What they did — The researchers did more than mail an unusual postcard — Daiyu Ito, a life sciences Ph.D. student and the study’s lead author, explains that the storage and delivery method tested here could revolutionize the life sciences, from basic research involving mouse models to fertility therapies.

Ito tells Inverse that this method allows researchers to send genetic material “via only postcard and mailbox without any special cold storage equipment or special protection for mailing.”

And the sperm’s DNA, once retrieved at its destination lab, was then used to fertilize an egg and produced healthy mouse pups.

“We were really impressed when the mouse offspring were actually born because the sperm was stored in very thin sheets and sent by postcard without any protection,” Ito says.

Typically, mailing genetic material to other labs requires expensive storage and courier services, and there’s no guarantee the samples will arrive without breaking or becoming damaged.

The postcard really is just the icing on the cake — the discovery of a cheap, safe way to transport genetic material from one lab to another could foster new scientific collaboration and study that previously would have been impossible due to cost and other constraints.

“I’m surprised by the whole study,” Maite Olaciregui, a professor of animal pathology at the Universidad de Zaragoza in Spain, tells Inverse. (Olaciregui’s answers were given in Spanish and Inverse translated and edited them for clarity.) “It seems like they found a simple method for something very complex. Hopefully, they can continue research to improve this technique.” Olaciregui was not involved in the study.

How they did it — It took some trial and error before finding the perfect combination of materials and preparation to make this special delivery.

Ito and his team found that the nuclei of freeze-dried mouse sperm can tolerate frequent temperature changes compared with fresh sperm. With a strong vacuum seal, these freeze-dried swimmers could be stored in glass ampules for more than a year and still be used to produce healthy offspring.

Then it was a matter of finding a substitute material that was cheaper than the glass ampule.

Ito and his team started with washi — traditional Japanese paper — as well as plastic wrap, vinyl sheets, weighing paper (this is a kind of paper that helps protect a substance being weighed in a lab study), filter paper, and oblate. Essentially they were trying to freeze-dry the sperm within two leaves of these materials.

“Unexpectedly, the best results were obtained when the weighing paper was used,” Ito says.

“They found a simple method for something very complex.”

Why it matters — Freeze-drying sperm isn’t new. When they are freeze-dried, the sperm technically all perish, but their DNA remains intact. As a result, once this material is injected into an egg, it can fertilize the egg and produce healthy offspring. This technique is used in many different animals such as rats, hamsters, rabbits, horses, and sheep, to name but a few.

Before Ito and his team made this discovery, transporting sperm from one lab to another required bulky freezers or glass ampules full of liquid nitrogen, which came with myriad risks of breaks and damage.

“Until now, sending mouse sperm to other researchers has required a freezing environment such as liquid nitrogen or a freezer,” Ito says.

“Not only is the constant supply of liquid nitrogen and electricity needed for transportation expensive to maintain, but if there is a road disruption or power outage due to an earthquake, all the sperm will melt and become unavailable.”

Liquid nitrogen could also accidentally suffocate anyone who handles the specimens.

Olaciregui notes that there are other alternatives to glass ampules that the authors didn’t account for. “Only glass ampules are mentioned as a means of conservation, but other studies have used plastic cryovials, which are more resistant,” she says.

But the postal specimens still produced healthy offspring having been preserved for three days at room temperature, which is a major step forward. But Ito and his team found that after five days at room temperature, the DNA was no longer viable, so there is a time limit.

“Storing dried genetic material at room temperature while maintaining its integrity, that’s the dream.”

From a postcard, start to think bigger. Imagine a book of trading cards with each slot perfectly filled out. Now imagine that instead of cards, each plastic sleeve holds a different sample of freeze-dried mouse sperm. This could help create the ultimate library of DNA material, organized and ready to be used at a moment’s notice.

This method can lead to the preservation of thousands of samples of genetic material from different mouse models of different human conditions in a single cardholder, allowing for more collaboration between labs and better conservation of genetic resources. Mouse models like these are often the first step in drug development and other discoveries to do with human health.

What’s next — If we can store and transport sperm as easily as Pokémon cards, could this shape the future of human fertility and genetic medicine?

“The application of this technology will be in the distant future,” Ito says. So, no — right now this method is just for lab work, but as Ito’s colleague Wakayama points out, the potential is certainly there.

For now, Ito wants to perfect the vacuum-sealing method.

“It is likely that humidity and oxygen contained in this small amount of air had a negative effect on the [freeze-dried] sperm during preservation at [room temperature], Ito says.

“It is needed to consider how sperm oxidation is less likely to occur.”

This improvement could help freeze-dried sperm last even longer at room temperature, which Olaciregui says is the ultimate goal.

“The greatest achievement would be the conservation of freeze-dried sperm at room temperature for a prolonged period of time. Storing dried genetic material at room temperature while maintaining its integrity, that’s the dream,” she says.

“Our next goal is to make them at least longer than a month,” Ito confirms.

Abstract: Freeze-drying techniques allow the preservation of mammalian spermatozoa without using liquid nitrogen. However, the current method requires the use of glass ampoules, which are breakable, expensive, and bulky to store or transport. In this study, we evaluated whether mouse freeze-dried (FD) spermatozoa can be preserved and transported on thin materials. In this study, we demonstrated that FD sperm can be preserved in thin plastic sheets. Its DNA integrity was comparable to that of glass ampoule spermatozoa, and healthy offspring were obtained after preservation at -30C for more than 3 months. We attached preserved FD sperm to postcards, and transported these to other laboratory inexpensively at room temperatures without any protection. This method will facilitate the preservation of thousands of mouse strains in a single card holder, promote collaboration between laboratories, conservation of genetic resources, and assisted reproductive technology.