World's first test-tube puppies born in US

Scientists in the US have created the world's first litter of puppies conceived in a test tube, a breakthrough that may help eradicate disease in dogs and humans.
The advance through in vitro fertilisation (IVF) 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.

"Since the mid-1970s, people have been trying to do this in a dog and have been unsuccessful," said Alex Travis, associate professor in Cornell University's College of Veterinary Medicine.
For successful in vitro fertilisation, researchers must fertilise a mature egg with a sperm in a lab to produce an embryo. They must then insert 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 fertilise.

Through experimentation, Jennifer Nagashima, a graduate student in Travis' lab and colleagues found if they left the egg in the oviduct one more day, the eggs reached a stage where fertilisation was greatly improved.
The second challenge was that the female tract prepares sperm for fertilisation, requiring researchers to simulate those conditions in the lab.
Nagashima and Skylar Sylvester found that by adding magnesium to the cell culture, it properly prepared the sperm.
"We made those two changes, and now we achieve success in fertilisation rates at 80 to 90 per cent," Travis said.
The final challenge for the researchers was freezing the embryos. Travis and colleagues delivered Klondike, the first puppy born from a frozen embryo in the Western Hemisphere in 2013.

Freezing the embryos allowed the researchers to insert them into the recipient's oviducts (called fallopian tubes in humans) at the right time in her reproductive cycle, which occurs only once or twice a year.
"We can freeze and bank sperm, and use it for artificial insemination. We can also freeze oocytes, but in the absence of in vitro fertilisation, we couldn't use them. Now we can use this technique to conserve the genetics of endangered species," Travis said.
Since dogs and humans share so many diseases, dogs now offer a "powerful tool for understanding the genetic basis of diseases," Travis added.

The research was published in the journal Public Library of Science ONE.