Although freeze-dried (FD) sperm can be stored at room temperature, making it cheaper and safer to store and transport, freeze-drying can damage the sperm's DNA, which can decrease the birth rate compared to frozen sperm. In this study, we examined whether adding monosodium glutamate (MSG), a compound used to dry and preserve yeast, to the drying medium could improve the quality of mouse FD sperm. FD sperm stored using MSG showed lower morphological and DNA damage, and the birth rate of embryos fertilized using those sperm improved to a similar level (50%) to that obtained with frozen-thawed sperm. The offspring showed normal growth and reproductive performance. Similar results were obtained for embryos derived from other mouse strains, even using FD sperm stored for 3 months at room temperature. These results suggest that MSG can protect not only microorganisms but also the DNA of mammalian FD sperm and improve the birth rate to a practical level. This method is not only inexpensive and safer than cryopreservation using liquid nitrogen but has expansion potential to maintain a large number of genetically modified mouse strains.
Ushigome et al. (Sat,) studied this question.