Researchers at the Smithsonian Conservation Biology Institute (SCBI) have generated mature sperm from frozen testicular tissue for the first time. Their findings were published in PLOS ONE today. The technique, called xenografting, has been successful in several domestic species but has never been done with frozen tissue before.
The team harvested testes tissue from newborn domestic sheep and placed it into live mice, then waited to see if the tissues would mature and produce live sperm. The team tried three different preparations of testicular tissue: one fresh, one frozen slowly and one vitrified. Vitrification is a very quick freezing process. They found that the slow-frozen testes produced the most viable sperm. Scientists believe the slow-frozen testes may have produced the best results because the fresh tissue was sometimes stored for 12 or 15 hours before xenografting, whereas the frozen tissue was frozen immediately.
"This could have really exciting implications for vulnerable and endangered species," said Budhan Pukazhenthi, SCBI reproductive physiologist and lead author of the paper. "If we can generate viable sperm from frozen testes, we can potentially begin to recover sperm even from immature animals."
Seventeen weeks after xenografting, tissues showed mature sperm developing in seminiferous tubules—the location of sperm development—of each specimen. Sperm developed in 1 percent of the tubules in the fresh tissue, 2 percent in the vitrified sample and in 10 percent of the slow-frozen sample.
The successful xenografting of the testes of domestic sheep could have implications for endangered species. SCBI scientists hope that further perfecting the technique in sheep will help them preserve testes tissue and generate sperm in endangered ungulate species such as the scimitar-horned oryx (a species extinct in the wild) and addra gazelles (a critically endangered species). Such sperm could then be used in in vitro fertilization to produce embryos and boost the genetic diversity of endangered species. Being able to xenograft testes of young animals could also mean scientists could produce live offspring from them, even if they do not survive to sexual maturity.