Dog-cloning innovation cheaper, more efficient

A research team in Shaanxi province has developed a new dog-cloning method that addresses a key technical bottleneck facing similar research worldwide, paving the way for a canine cloning system with greater stability, lower costs and improved compliance with animal welfare standards.

About one month after successfully cloning a male dog and a male cat, Wang Yongsheng, a professor at the College of Veterinary Medicine of Northwest A&F University in Yangling, Shaanxi province, said both animals are healthy and have been vaccinated. They are the first somatic cell-cloned cat and dog born in Northwest China.

Wang, who leads the project, said only China, South Korea and the United States have mastered mature dog-cloning technology, but the procedure remains difficult because of a high failure rate.

A major challenge is obtaining sufficient high-quality canine oocytes. Unlike many other animals, female dogs ovulate immature oocytes that must remain in the oviduct for two to three days before maturing. As a result, reliably obtaining mature oocytes suitable for somatic cell nuclear transfer has long limited cloning efficiency.

Conventional methods also rely on dedicated oocyte donor dogs or on collecting oocytes at specific stages of the reproductive cycle, resulting in low success rates, high costs and concerns over animal welfare.

To overcome these problems, Wang's team collects ovarian tissue discarded after routine sterilization surgeries at pet hospitals. Oocytes are isolated from the tissue and cultured in vitro for two to three days until they mature. Their nuclei are then removed and replaced with the nucleus of a somatic cell taken from the dog to be cloned. After an electric pulse fuses and activates the reconstructed embryo, it is transferred into the uterus of a surrogate dog. The entire cloning process takes at least three to four months.

"Ovarian tissues removed during pet sterilization surgeries are normally disposed of as medical waste, but they still contain abundant follicles and oocytes at different developmental stages," Wang said.

"Through standardized collection, transportation, follicle isolation and in vitro maturation, we can transform these discarded tissues into valuable biological resources for scientific research and technological development."

The team is able to collect dozens of ovaries every day, providing a stable source of research materials.

The new approach is expected to reduce the number of dedicated oocyte donor animals by more than 80 percent, lowering research costs while improving the ethical sustainability and public acceptance of cloning, Wang said.

The researchers also developed a new in vitro maturation system that mimics the environment of the canine oviduct. Compared with conventional methods, the maturation rate of canine oocytes increased by 5 to 10 percentage points, the cleavage rate of cloned embryos rose by about 5 percentage points, and blastocyst formation improved steadily. Overall, the production efficiency of early-stage cloned embryos increased by 10 percent to 15 percent.

The team also adopted a minimally invasive embryo-transfer technique, reducing the surgical incision by half to minimize trauma to surrogate dogs.

According to Wang, the technology can produce laboratory dogs and cats with highly consistent genetic backgrounds, reducing experimental variation caused by individual differences. Such animals are valuable for studying neurological diseases, tumors, cardiovascular disorders and inherited metabolic diseases, as well as for evaluating the safety of new pharmaceuticals.

The technology may also meet demand from pet owners wishing to clone deceased companion animals. However, Wang emphasized that cloning does not bring a pet back to life.

"A clone is a new life," he said. Although a cloned animal shares more than 95 percent physical similarity with the original, differences in coat color, markings, health, personality and behavior can still develop because of environmental influences, much like identical twins.

The cloning system was jointly developed by Northwest A&F University, the Laboratory Animal Center of Xi'an Jiaotong University and Yuanchu (Xi'an) Biotechnology.

chenmeiling@chinadaily.com.cn