Japanese scientists tried sending freeze-dried mouse sperm on a postcard – here’s what they found

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This is a photo of a mouse produced from semen sent by envelope. Credit: Daiyu Ito, Yamanashi University

Scientists no longer have to worry about their vials of mouse semen breaking during transport. Japanese researchers have developed a way to freeze-dry sperm on a plastic sheet in weighing paper so that samples can withstand postcard mailing. This method makes it possible to transport mouse sperm easily, inexpensively and without the risk of breaking the glass cases. The article was published on August 5, 2021 in the journal iScience.

“When I developed this method of storing mouse sperm by freeze-drying it on a leaf, I thought it should be able to be posted on a postcard, and so when the offspring are born after being posted, i was very impressed. Says lead author Daiyu Ito from Yamanashi University in Japan. “The postcard strategy was simpler and cheaper than any other method. We believe the sperm never expected the day to come when they would be in the mailbox.

Semen pound

This photo shows how a sperm sheet from hundreds or thousands of mouse strains can be preserved with a single card holder or “sperm pound”. It is very easy to handle. This method also reduces the risk of non-preservation, preservation costs and space requirements. Credit: Daiyu Ito, Yamanashi University

Ito is part of the laboratory of Teruhiko Wakayama, who had previously been the first team to successfully freeze-dry and store mammalian sperm, which they sent to the space station to study the effects of space radiation on baby mice. The semen was originally stored in a glass ampoule, which is a glass bottle; although these vials were small, they were quite large and broke easily, rendering the semen they carried unusable. The team needed large volumes of mouse sperm for their space research, but since cushions had to be used to prevent breakage during rocket launch, they could only carry a small amount.

Card with freeze-dried mouse sperm

This photo shows a Happy New Year Japan card attached with freeze-dried mouse sperm. Credit: Daiyu Ito, Yamanashi University

So, with these setbacks in mind, the lab began its search for a new method of preservation, one that did not break or require a lot of storage space. Plastic sheets were best suited as they were compact and did not break. But the leaves were toxic to the sperm, so the team tried and failed by testing various materials to fit inside the plastic sheets. Finally, the researchers found that the weighing paper was the easiest to handle and had the highest offspring rate.

With the new preservation method, thousands of sperm from mouse strains could be stored in a single book, dubbed the “sperm book” by scientists. The book was stored in a -30 ° C freezer until further use for experiments.

Ito, Wakayama and the team wanted to know if the sperm would still be potent after being sent tens of miles away and, to their delight, it was. Scientists were able to send the mouse sperm from the “sperm book” as postcards by attaching the plastic sheet to the postcard without any protection. One scientist even sent another a “Happy New Year” card with mouse sperm as a gift.

Scientists believe that the “semen book” and method of sending, once developed, will have a strong impact in their field around the world. Their next goal is to be able to store them for at least a month at room temperature. In the future, they also hope to develop a method that will allow freeze-dried sperm to come back to life and fertilize on their own when rehydrated.

Semen leaves in the envelope

This photo shows how the semen sheets were put into the envelope. The sheet and envelope were posted in the mailbox without any protection. Credit: Daiyu Ito, Yamanashi University

“It is now recognized that genetic resources are an asset for the future of humanity. Even though many genetic traits are not necessary for survival, depending on the environmental context, it is necessary to preserve them. says lead author Teruhiko Wakayama, also from Yamanashi University in Japan. “The method of preserving plastic sheets in this study will be the most suitable method for the safe preservation of a large amount of valuable genetic resources due to the resistance to breakage and less space required for it. storage.”

Mouse offspring derived from freeze-dried sperm

This photo shows offspring of mice derived from freeze-dried sperm that grew to adulthood and demonstrated normal fertility. Credit: Daiyu Ito, Yamanashi University

Reference: “Sending Lyophilized Sperm from Viable Mice on Postcards” by Daiyu Ito, Sayaka Wakayama, Rina Emura, Masatoshi Ooga and Teruhiko Wakayama, August 5, 2021, iScience.
DOI: 10.1016 / j.isci.2021.102815

This work was partially funded by the Naito Foundation, Asada Science Foundation, Takeda Science Foundation, and Japanese Society for the Promotion of Science for Young Scientists Research Fellowships.

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