Freeze drying mouse spermatozoa on weighing sheets

Husna, Amity University Kolkata

Why is the preservation of mammalian sperms needed?

Preservation of mammalian sperm is crucial for treating infertility, for production of livestock, for maintaining the strains of genetically modified individuals, and for conserving genetic resources, including those of endangered species. Usually, cryopreservation of sperm is done in liquid nitrogen. Then, artificial insemination or in vitro fertilization after thawing gives rise to healthy offspring. But, using liquid nitrogen for preserving spermatozoa has many drawbacks. 

The drawback of liquid nitrogen for preserving sperm are:

• Storage in liquid nitrogen requires an ultra-low temperature of -196°C which might not be readily available in some countries and regions. 
• There’s a risk of suffocation due to the saturation of nitrogen gas in the storage room.
• Moreover, maintenance costs are expensive due to the constant need for re-filling liquid nitrogen, which makes it difficult for some countries to maintain their genetic resources. 

Freeze-drying of spermatozoa: 

In order to solve the existing problems, researchers have developed a technique of freeze-drying the spermatozoa of mice. They stored the sperm at 4°C for 3 months, and then at room temperature (RT) for 1 month in glass ampoules. This was done without any damage to the viability or usefulness of the sperm. Although all spermatozoa died, DNA was found to be intact after freeze-drying, and healthy offspring were obtained by injecting the sperms into oocytes. This technique has also been applied to the sperm of other species including rats, hamsters, rabbits, horses, and sheep. 

Advantages of freeze-dried (FD) spermatozoa: 

• The researchers have found a strong tolerance to frequent temperature changes in the nuclei of freeze-dried spermatozoa of mice, in comparison to the fresh spermatozoa. 
• Even after storing the freeze-dried sperm at room temperature (RT) for more than a year, there was no degradation in the success rate.
• Now, mouse spermatozoa could even be sent to the International Space Station, which was never possible before, as this technique does not require preservation by liquid nitrogen. 

But, the storage of freeze-dried (FD) sperm in glass ampoules can result in breakage of the glass by falling due to shaking during earthquakes or through human error, which makes it impossible to continue storing sperm afterwards. Moreover, glass cases are quite small and require a lot of volume when thousands of such cases are stored, cushions had to be used as well for preventing breakage during the rocket launch, so only a small amount was carried.

Storing freeze-dried sperm (FD) in weighing sheets (Recent Study):

In recent studies, published in Journal ISciences, researchers have attempted to store FD sperm in thin materials such as weighing sheets, as an alternative to the glass ampoule method. 

This method of freeze-drying sperm on sheets has enabled the safe management of numerous mouse strains in a single book, such as a card folder, and it transports them internationally at a very low cost. Now, the researchers don’t need to stress over the breaking of bottles stored with mouse sperm. Samples of sperm have even been sent to the space station for studying the effects of space radiation on baby mice. 

Significance of the study:

Genetic resources are an asset to humanity’s future so, it is very essential to preserve them. Weighing paper can handle freeze-dried sperm easily and has the highest offspring rate, it is the most suitable method for preserving a large amount of valuable genetic resources safely. This method of preservation has made it possible to store thousands of mouse strain’s sperm in a single book, named as sperm book. The next goal of scientists is to check whether the freeze-dried sperm preserved in weighing paper could be stored for at least one month at room temperature. Moreover, now the scientists want to plot a way that will allow the freeze-dried sperm to come back to life and fertilize on their own after being rehydrated.

Significance of the study:

The genetic resources are an asset to humanity’s future so, it is very essential to preserve them. Weighing paper can handle freeze-dried sperm easily and has the highest offspring rate, it is the most suitable method for preserving a large amount of valuable genetic resources safely. This method of preservation has made it possible to store thousands of mouse strain’s sperm in a single book, named as sperm book. The next goal of scientists is to check whether the freeze-dried sperm preserved in weighing paper could be stored for at least one month at room temperature. Moreover, now the scientists want to plot a way that will allow the freeze-dried sperm to come back to life and fertilize on their own after being rehydrated.

Also read: High-Grade Serous Ovarian Carcinoma & its radical treatment

References:

1.  Ito, D., Wakayama, S., Emura, R., Ooga, M., & Wakayama, T. (2021). Mailing viable mouse freeze-dried spermatozoa on postcards. IScience, 0(0). https://doi.org/10.1016/j.isci.2021.102815
2. Press, C. (n.d.). Scientists mail freeze-dried mouse sperm on a postcard. Retrieved August 7, 2021, from https://phys.org/news/2021-08-scientists-mail-freeze-dried-mouse-sperm.html

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Author’s info: Husna is an undergraduate student of BTech Biotechnology at Amity University Kolkata. She is a research enthusiast in Immunology and Immunotherapy but she has a keen interest in various other Bioscience subjects as well. She is constantly focused on improving her knowledge and laboratory skills through various internships. She is a Scientific content writer who has knowledge in diverse backgrounds of Biotechnology.