UH research
breeds mice
from dead sperm

Biologist breaks
new ground with freeze-dry
reproductive technology

By Helen Altonn
Star-Bulletin

A University of Hawaii researcher has created live mice using dead sperm, and now he's going to try it on other animals.

Ryuzo Yanagimachi has shown that mouse sperm can be freeze-dried -- just as coffee or other foods -- and used to fertilize eggs.

"If it works for rabbits, I think it will work on every species of mammal," said the acclaimed scientist in the John A. Burns School of Medicine's Anatomy and Reproductive Biology Department.

A world authority on fertilization, Yanagimachi's work contributed to the cloning of Dolly, a sheep in Scotland.

He is believed to have accomplished a similar feat with mice, but said he can't talk about it until a paper he submitted to a scientific journal is published.

His work on freeze-dried spermatozoa, with Teruhiko Wakayama, was published this week by Nature Biotechnology.

Vincent De Feo, chairman of the Anatomy and Reproductive Biology Department, said Yanagimachi is the first to prove that sperm can remain fertile though technically killed through freeze-drying.

Sperm for use in cattle and humans normally is stored in liquid nitrogen at minus 385 degrees Fahrenheit. The liquid nitrogen "ends up going from liquid into a gas state, and you always have to replenish it because it evaporates," De Feo said.

Yanagimachi's method eliminates that expensive process by preserving the sperm like any freeze-dried food. It's stored in vacuum-sealed vials, then rehydrated to inject into eggs.

"He has only taken it to the point of three months," De Feo said. "But there is good reason to believe, like other freeze-dried things, that it can last longer. That makes the technique very, very important because of the simplicity of handling it."

Yanagimachi took a few vials of the freeze-dried spermatozoa to Japan on a three-week trip last fall. He rehydrated the sperm after returning here and injected it into eggs. The result: two females and one male that grew into fertile adults.

"Philosophically, it's interesting," De Feo said, pointing out that sperm is alive -- though slowed down and frozen -- in the previous way of preserving.

"Here, the sperm are dead, so he's using a sperm whose chemical constituency is DNA, and it's that that triggers the whole response," De Feo said.

"The whole concept is like, 'Wow, we hadn't thought of that before now.' "

Yanagimachi said the freeze-dried sperm retain a nucleus of DNA with genetic reproductive potential. "We will try to see how applicable it is to other species," he said.

Now that his work with mice has been published, he said, "I think many other researchers will jump in."

He wants to try freeze-drying sperm for fertilization in rabbits because they're closer to humans. But it's not easy to work on rabbits, he added, "because they're so cute. There are so many rules."

De Feo brought Yanagimachi to UH in 1966 from a research group in Massachusetts.

Working with mice or hamsters on basic research, "his discoveries have flourished," De Feo said.

Yanagimachi said he started out as a zoology student studying fish. Since coming to UH, he has done basic research on fertilization mechanisms, winning international recognition.

Douglas Vincent, UH chairman of animal sciences, said if Yanagimachi has cloned a mouse, "it's a natural progression to what he has been doing."

Yanagimachi has been a leader in basic knowledge of how a sperm and egg interact, Vincent said, adding, "There are ways in which you can trick the egg into thinking sperm is present, and it can become activated."