A study on freeze-drying as a method of preserving mouse sperm.

This review describes the study of freeze-dried mouse sperm for practical application in preserving and transporting genetic resources. Freeze-dried sperm can be used to preserve and transport genetic resources; however, there still remain many areas which need to be studied. In particular, it is essential to assure long-term preservation over several decades or centuries. Recently, the theory of accelerated degradation kinetics to freeze-dried mouse sperm has been applied, and found that long-term preservation by conventional methods requires temperatures lower than -80 C. When the relationship between the pressure at primary drying and the preservation potential of freeze-dried mouse sperm was examined, a pressure of 0.37 mbar at primary drying significantly improved the developmental rate to the blastocyst stage. In addition, it has been shown that freeze-dried sperm stored at -80 C with and without transportation can retain their ability to generate viable offspring after storage for up to 2 years. Sperm chromatin structure assay (SCSA) was applied to mouse sperm freeze-dried under several conditions and compared the results with the embryonic developmental rates of freeze-dried sperm after intracytoplasmic sperm injection (ICSI) and with comet assay results. Furthermore, SCSA might be useful for estimation of developmental potential of fertilized eggs derived from ICSI using freeze-dried sperm in mice.