An in vitro test to reduce the number of surplus mice

Many diseases have a genetic basis and to study the involvement of genes in a particular disease, so-called genetically modified mice can be helpful. In these mice, a particular gene is turned on or off and then studied to see what that change does in the living animal and what treatments might help.

In recent decades, there has been a huge increase in such genetically modified mouse lines – with some major drawbacks: On the one hand, it takes many mice to breed such lines, and on the other hand, these lines have to be further bred in a costly manner. In Switzerland alone, this leads to thousands of surplus animals every year. This is a delicate issue for which solutions are urgently needed.

In the meantime, an alternative to permanent breeding has been developed: Sperm from mouse strains that are no longer used in experiments are frozen. However, before freezing, researchers must be absolutely sure that the sperm are viable. To test this, mice are again needed: the sperm is tested for its ability to fertilize eggs from female mice in a test tube via in vitro fertilization (IVF). Large numbers of females are bred, hormonally treated and ultimately killed simply to obtain eggs and subsequently test frozen-thawed sperm. "This is a strategy that can by no means be considered an optimal application of the 3R principles," says Johannes vom Berg of the University of Zurich.

"With our project, we aim to provide the research community with an in vitro assay and diagnostic software to assess the fertility of frozen mouse sperm." To do this, the team will look for parameters that prove sperm fertility (for example, specific genes or proteins) as part of their research project.

A validated test would eliminate the need for IVF as a quality control measure for frozen mouse sperm. Applied to 60,000 mouse strains worldwide, such a test would save about 200,000 to 300,000 female mice.

An alternative to the use of live mouse oocytes for the quality control of cryopreserved mouse sperm