What can be stored in the pantry for months then made whole just by adding water? Evaporated milk, instant coffee, Tang--and freeze-dried mouse sperm. In a first, scientists report in the July Nature Biotechnology that mice fertilized artificially with reconstituted sperm can give birth to live offspring. The technique might find use for stockpiling valuable strains of mice or preserving endangered species.
Occasionally scientists have claimed to raise live animals from dried sperm, but most reports are dubious and unreproducible. Mouse are doubly hard to work with, because of the challenge of successfully injecting any sperm--regular or reconstituted--into their fragile eggs. Thus the idea to attempt the feat in mice, says Robin Lovell-Badge of the Medical Research Council's National Institute for Medical Research in London, "would not occur to most people."
The idea did, however, occur to Ryuzo Yanagimachi and postdoc Teruhiko Wakayama of the University of Hawaii School of Medicine, Honolulu. "We wondered what would happen if we injected freeze-dried sperm into an egg," he says. The duo freeze-dried mouse sperm and stored one batch at room temperature and another at 4 degrees Celsius. Freeze-drying ruptured the sperms' plasma membranes, leaving them technically "dead." The researchers left the sperm on the shelf from 1 day to 3 months, reconstituted the dead sperm, and injected the DNA-packed sperm heads into mouse eggs. No matter the temperature or length of time spent in powder form, the sperm showed surprisingly strong potency: on average, 86% of eggs became fertilized normally, 86% of injected eggs developed into embryos, and 26% of embryos transferred into foster mothers were born live, most of which grew up into normal adults. Even a sample of sperm powder carried by Yanagimachi on a 3-week round trip between Hawaii and Japan retained its life-giving potency. "Metal detectors and jet lag also have no effect," says Lovell-Badge.
Experts say the technique might find use as a cheap way to archive and transport the burgeoning number of mutant and transgenic mouse strains used in biomedical research. "One day, perhaps, you will be reaching for a 'male'-order catalogue to obtain your favorite mouse mutant," says Lovell-Badge. As the freeze-drying technique "should work well for most species," he adds, it could be used to stockpile and preserve viable sperm from endangered species.