Cryopreservation Decision Tree

Use of genetically engineered rodent models in research requires maintaining the lines through some level of continuous breeding. This can be costly, labor intensive, and result in inefficient use of limited vivarium space — while leaving valuable genetic lines vulnerable to catastrophic loss and genetic drift.

This Insight provides guidance on choosing between embryo or sperm cryopreservation based on the attributes of the model to be preserved.

Choosing between Sperm and Embryo Cryopreservation

There are four attributes to consider when making this decision:

Species

The first attribute is species. Embryo cryopreservation is the only option available for genetically modified rat models.

Background

The second attribute refers to the genetic background. Because the genetic background is only partially preserved through sperm cryopreservation, embryos are the recommended format for genetically modified models on an outbred or mixed genetic background.

Genetic Modifications

The third attribute refers to the number of genetic modifications carried by the model. For models carrying a single genetic modification, sperm cryopreservation is a preferred method (provided it meets the criteria of the previously applied attributes).

For models with multiple genetic modifications, sperm cryopreservation may require multiple rounds of natural breeding to return an animal that possesses all the desired genetic modifications. Embryo cryopreservation is the desired format for these types of models.

Sex-Linked Modifications

The final attribute pertains to whether the desired genetic modification is sex-linked, and if so, on which of the two sex chromosomes. Again, either cryopreservation format is applicable, but certainly one is preferred over the other depending on the sex-linkage.

Cryopreservation Decision Tree

The following line-diagram serves as a decision-tree to determine the recommended cryopreservation format for any genetically modified line.

Criteria may come into play beyond those dealt with in the provided decision tree. For example, the cost of the cryopreservation may impact the decision, as sperm cryopreservation is most often much less expensive relative to embryo cryopreservation.

Also, having a limited number of animals available or tight cryopreservation timelines makes sperm cryopreservation the more viable option.