Northwestern University Feinberg School of Medicine

Center for Genetic Medicine

Embryo vs Sperm Cryopreservation

Cryopreservation, the process of freezing viable germplasm for stable, long-term storage in liquid nitrogen, is an essential service for modern mouse based genomics. It is a safe method for preserving both pre-implantation embryos and sperm that can be easily recovered to revive the line.

The TTML offers cryopreservation and long term storage of mouse embryos, sperm, and ovaries from many of the most commonly used mouse strains.  Over 684 mouse lines have successfully been frozen since these services were established.

Cryopreservation of pre-implantation embryos has been available through the TTML since May 2007. Using the method known as "speed cryogenics", hundreds of embryos can be generated by IVF when oocytes collected from hormonally-treated females are incubated with freshly isolated sperm. However, not all mouse strains are suitable for embryo cryopreservation. Embryos from some strains are not hardy enough to withstand the freeze/thaw process. Other strains have low fertilization capacity and do not readily yield sufficient numbers of fertilized embryos. In addition, individual mouse lines as well as individual mice within a line can vary substantially in their fertilization capacity regardless of background strain. Surprisingly, C57BL/6 and B6 hybrid strains are among the best performing strains in IVF and embryo cryopreservation.  Embryo cryopreservation is still considered the 'gold standard' for preserving mouse lines.  However, due to inherent technical inefficiencies associated with the procedure and strain differences, it is more costly than freezing sperm.

Sperm cryopreservation is a simple, highly cost effective alternative to embryo cryopreservation. Recent technical advances on traditional methods have resulted in improved and reliable fertility rates of cryopreserved sperm following thaw, particularly for common strains such as C57BL/6 and BALB/c. Although there are some disadvantages of preserving lines as frozen sperm as compared to embryos, cryopreservation of sperm is significantly more cost effective and faster. It can also be used to complement embryo cryopreservation.

Comparison of two methods

Embryo Cryopreservation

  • Robust and reliable (gold standard for mouse cryopreservation)
  • Donor genotype is preserved
  • Homozygous embryo can be frozen
  • Recovery of line is inexpensive and simple
  • Cost to freeze: expensive upfront costs (requires lots of females donors)
  • Does not work efficiently for all lines/strains

Sperm Cryopreservation

  • Simple and inexpensive
  • Lots of material is preserved (~30 million sperm/male)
  • Sperm can be isolated from unhealthy/dead male in emergency situation
  • Preserves only one half of the genome
  • More expensive to recover a line (embryos must be created by IVF)
  • May not work work efficiently for all lines/strains

Total Number of Mouse Lines Cryopreserved, January 2008 - August 2015

Number of lines cryopreserved for long-term storage since service was established.