Long term maintenance of frozen mouse spermatozoa at −80 °C

We have previously reported that spermatozoa frozen using standard laboratory protocols can be safely stored in a −80 °C freezer or in dry ice (−79 °C) for at least seven days. We now report the extension of this period of maintenance at −80 °C up to two 2 years both for wild type and mutant strains, indicating that once frozen, mouse spermatozoa are quite resistant and can be transported, shared and stored at −80 °C for a long time without a significant loss of viability. The importance of this finding will be especially relevant for small laboratories with no constant access to liquid nitrogen and for labs generating many mouse mutant lines by CRISPR/Cas9 who do not want to saturate the limited space of a LN2 tank, using a more accessible −80 °C freezer.