Freezing Mouse Sperm: A New, Efficient, Cost-Effective Method

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."



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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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Here For Full Length Article



Written by Anna Sophia McKenney