Maintenance of genetic integrity in frozen and freeze-dried mouse spermatozoa.

Chromosome stability was maintained in mouse spermatozoa after freeze-drying or freezing without cryoprotection in a simple Tris.HCl buffer containing EGTA (50 mM) and NaCl (50 mM). The ability of spermatozoa to activate oocytes spontaneously was not destroyed by freeze-drying or freezing without cryoprotection in this solution. Embryos derived after injecting oocytes with sperm heads from rehydrated freeze-dried and from thawed spermatozoa developed normally. Provided the DNA integrity of the sperm nucleus is maintained, embryos can be generated by the intracytoplasmic sperm injection technique (ICSI) from severely damaged spermatozoa that are no longer capable of normal physiological activity. This procedure was effective for preserving spermatozoa from strains (C57BL/6J, 129/SvJ, and BALB/c) in which the fertility of spermatozoa frozen conventionally is extremely poor. The technique provides an effective means of storing mouse spermatozoa from many different inbred, mutant, and transgenic strains for biomedical research.