The breakthrough, described in a study published online in the journal Public Library of Science ONE, opens the door for conserving endangered canid species, using gene-editing technologies to eradicate heritable diseases in dogs and for study of genetic diseases. Canines share more than 350 similar heritable disorders and traits with humans, almost twice the number as any other species. Nineteen embryos were transferred to the host female dog, who gave birth to seven healthy puppies, two from a beagle mother and a cocker spaniel father, and five from two pairings of beagle fathers and mothers.
For successful in vitro fertilization, researchers must fertilize a mature egg with a sperm in a lab, to produce an embryo. They must then return the embryo into a host female at the right time in her reproductive cycle. The first challenge was to collect mature eggs from the female oviduct. The researchers first tried to use eggs that were in the same stage of cell maturation as other animals, but since dogs’ reproductive cycles differ from other mammals, those eggs failed to fertilize. Through experimentation they found if they left the egg in the oviduct one more day, the eggs reached a stage where fertilization was greatly improved.
The second challenge was that the female tract prepares sperm for fertilization, requiring researchers to simulate those conditions in the lab. The researchers found that by adding magnesium to the cell culture, it properly prepared the sperm. By making these two changes they achieved fertilization rates at 80 to 90 percent. The final challenge for the researchers was freezing the embryos, allowing then to be inserted into the recipient’s oviducts at the right time in her reproductive cycle. In vitro fertilization allows conservationists to store semen and eggs and bring their genes back into the gene pool in captive populations. In addition to endangered species, this can also be used to preserve rare breeds of show and working dogs.
With new genome editing techniques, researchers may one day remove genetic diseases and traits in an embryo, ridding dogs of heritable diseases. While selecting for desired traits, inbreeding has also led to detrimental genetic baggage. Different breeds are predisposed to different diseases; Golden retrievers are likely to develop lymphoma, while Dalmatians carry a gene that predisposes them to blockage with urinary stones. With a combination of gene editing techniques and IVF, genetic disease can potentially be prevented.
(Source: PLOS ONE, December 9, 2015 DOI:10.1371/journal.pone.0143930) .