A new, simple, economical process of freezing mouse sperm while achieving high subsequent fertilization rates will help researchers using mouse models of human disease, according to an article released on July 29, 2008 in the open access journal PLoS ONE.

Thanks to the similarities between humans and mice in genetic code and physiology, they are very often used as model organisms for diseases effecting humans, especially those of genetic origin. Combined with their fast reproductive rates and relatively cheap maintenance, the standard of using mice in scientific experiments is wide-spread. To facilitate this, mouse sperm are often frozen to conserve and distribute certain genetic combinations in the research and clinical worlds. Unfortunately, when the sperm from the most popular mouse strain, the C57BL/6 or “Black 6,” are frozen, they woefully underperform.

The Jackson Laboratory, known for its study and breeding of mice for mammalian genetics research, has previously addressed this problem by freezing and storing fertilized mouse embryos in a process called cryopreservation. This way, rare strains could be preserved. However, this process is much less efficient than freezing sperm, and the reanimation process can have many failures. “If you freeze 250 embryos,” Dr. Wiles, an author on the study said, “you can only count on about 125 live pups. But a single male mouse can produce millions of sperm, which can give rise to 100s or even 1,000s of offspring.  Thus, making sperm cryopreservation work has long been a goal of ours.”

In an effort to resolve this inefficiency in the Black 6 mice, Drs. Michael Wiles and Chuck Ostermeier in Jackson’s Technology Evaluation and Development group, and Dr. Robert Taft and Ms. Jane Farley in the Reproductive Sciences group of Jackson Laboratories have published this new technique, which has gained the interest of both academic and pharmaceutical laboratories. In this process, the sperm are collected into cocktail composed of raffinose sugar, skim milk, and monothioglycerol antioxidant. This mixture is suspended and loaded into small tubes, then slowly cooled before being stored in liquid nitrogen, which has a temperature of almost -200 degrees Celsius. When needed for fertilization of mouse eggs, they are thawed and incubated in an in vitro fertilization media for approximately one hour before the oocytes are added in clusters.

This technique is reported to fertilize at a rate of 70%. This marks a rate six times the previous rates of other mouse sperm freezing techniques. According to Dr. Wiles, the mouse model is so prevalent in science that “the world research community is making literally thousands of new mouse models.” This new technique would help reduce costs and make this research more flexible. “The problem is that it costs about $10,000 a year to maintain a particular mouse strain, and worldwide only a few hundred strains are in actual laboratory experiments at any given time.”

About PLoS ONE

All works published in PLoS ONE are open-access. Everything is immediately available – to read, download, redistribute, include in databases and otherwise use – without cost to anyone, anywhere, subject only to the condition that the original authorship and source are properly attributed. Copyright is retained by the authors. The Public Library of Science uses the Creative Commons Attribution License.

PLoS ONE is the first journal of primary research from all areas of science to employ both pre- and post-publication peer review to maximize the impact of every report it publishes. PLoS ONE is published by the Public Library of Science (PLoS), the Open-access publisher whose goal is to make the world’s scientific and medical literature a public resource.

About The Jackson Laboratory

The Jackson Laboratory is a nonprofit research laboratory with 37 research groups investigating the genetic basis of human diseases. In addition, the Laboratory has a unique role of creating, maintaining and distributing mouse models to the worldwide research community. More than 3,500 mouse models are available from the Laboratory, far more than any other source. Drs. Taft, Wiles and Ostermeier, Ms. Farley and others make up the Laboratory’s team of resource scientists who innovate techniques to improve and streamline mouse model-based research.

Conserving, Distributing and Managing Genetically Modified Mouse Lines by Sperm Cryopreservation.
Ostermeier GC, Wiles MV, Farley JS, Taft RA
PLoS ONE 3(7): e2792.
doi:10.1371/journal.pone.0002792
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Written by Anna Sophia McKenney