Revealing the Birth Process of China's First Cloned Piglet

After more than a year of scientific and technological research, the research group led by Professor Li Ning of China Agricultural University was finally rewarded on August 5, 2006, at Minghui@#@227@#@Company in Sanhe City, Hebei Province, where China's first independently completed somatic cell cloned piglet was successfully born. Its birth filled a gap in this field in our country.

China is the seventh country to have obtained somatic cell cloned offspring of pigs

At 10:50 a.m. on August 5, at Minghui Pig Farming Company in Sanhe City, Hebei Province, a cloned piglet weighing 1130 grams with glossy black hair was successfully born. Everyone present was overjoyed. After more than a year of hard work, the two doctoral students Pan Dengke and Zhang Yunhai, under the leadership of Professor Li Ning, finally saw the long-awaited fruitful results on this day.

According to staff at Minghui Pig Farming Company in Sanhe City, Hebei Province, the cloned piglet is currently in very good health. The pig farming company is its future home. It is living happily with its "surrogate mother." It currently mainly survives by drinking its "surrogate mother's" milk, and after each feeding it crawls all over its "surrogate mother," which is very adorable. The cloned piglet could already run at birth. It will live and play together with its companions of different species in the future. Whether in living environment or food, it will be no different from other piglets.

The birth of the cloned piglet indicates that our country has entered the international advanced ranks in this research. It is understood that previously only the United Kingdom, Japan, the United States, Australia, South Korea and Germany had obtained somatic cell cloned offspring of pigs. Our country is the seventh country to have obtained somatic cell cloned offspring of pigs.

Three Rounds of Experiments Produced One Cloned Piglet

From a biological perspective, cloning is an artificially induced form of asexual reproduction or a form of asexual reproduction in plants. A clone is a multicellular organism that is genetically completely identical to another organism.

Somatic cell cloning refers to the process of using certain equipment and technical means to recombine an animal's somatic cell with an oocyte from which the nuclear genetic material has been removed to form an embryo in vitro, and then at a specific developmental stage implanting the recombinant embryo into the uterus of a surrogate mother to complete development, producing offspring genetically identical to the somatic cell nuclear donor.

According to Dr. Pan Dengke, the main researcher responsible for the project, when Professor Li Ning assigned him and Zhang Yunhai this quite difficult topic, they did not expect to achieve today's results, because at that time several laboratories in China were already conducting cloned pig experiments, and some laboratories had already reached the transplantation stage but had not achieved pregnancy. A blastocyst rate of 20% was already quite difficult to achieve in China.

Dr. Pan said that at the time they would have been satisfied if the blastocyst rate could catch up with and surpass their 20%. The blastocyst rate is a measure of a laboratory's level of early-stage cloning technology. Later, the blastocyst rate far exceeded other laboratories, to the point of reaching transplantation. At this point the preliminary work had been done very well, so the research group members, taking the risk of failure, thought they must clone an animal, but this path was not smooth sailing either.

Dr. Pan also told reporters that the research group conducted 3 experiments in total, in January, April and May of this year respectively. In the first experiment, the research group implanted cloned embryos constructed in the laboratory into 10 white sows for a preliminary trial, but it was not successful. In the second experiment, cloned embryos were implanted into 3 sows, and only one became pregnant. In the last experiment, cloned embryos were implanted into 2 sows, and one miscarried after 21 days of pregnancy. These three experiments did not let their efforts go to waste.

At 10:50 a.m. on August 5, the sow that had become pregnant in April finally gave birth after 116 days to 3 black piglets, but only one survived; the other two died due to abnormal phenomena.

According to Dr. Pan, the main reason for the piglets' deaths is that current cloning technology is still not very mature. The mortality rate of cloned animals internationally is very high. Current cloning technology can only achieve cloning animal individuals, but exactly how to make cloned animals all healthy has not yet been researched. Many animals show deformities after birth. For example, of the two cloned piglets that died this time, one had an unhealed abdominal cavity with its internal organs outside; the other was stillborn, with relatively long forelimbs and some organs that were not fully developed. This phenomenon is still relatively common internationally at present. Current scientists' research in this area is still not very thorough, and the hot topic in recent years has been the mechanism of cloning.

Where Lies the Difficulty of Cloning Pigs

Relevant reports indicate that Taiwan, China, with the help of the United States, once produced somatic cell cloned pigs. This time, however, it was independently completed by Chinese people.

Experts say that at the time Taiwan, China, used somatic cells from a sow's ear as the "nuclear donor," then transferred them into enucleated egg cells for "nuclear transfer" engineering. Mainland scientists, however, used fetal fibroblast cells from Chinese experimental miniature pigs, which is relatively common internationally. This proves that in cloning technology we have reached the international average level.

From the perspective of cloning technology, compared with cloning cattle and sheep, in what aspects does the difficulty of cloning pigs manifest? Dr. Pan Dengke explained that cattle and sheep are both single-fetus animals. People have conducted relatively more and more thorough research on cattle and sheep, and the requirements for manipulating cattle and sheep egg cells in vitro are not very high. Pigs, however, are multi-fetus animals. Pig eggs are particularly sensitive to low temperatures, and the in vitro temperature requirement is around 30°C, with no large deviation, otherwise the experiment cannot proceed. The quality of eggs matured in vitro is also very poor, and the time required is relatively long, so they are not easy to survive. For multi-fetus animals, when cloned embryos are injected into the "surrogate embryo mother," the required number is much greater than for cattle and sheep. In the early stages, generally more than 100 cloned embryos must be transplanted. Therefore, from this aspect, pig cloning may be relatively more difficult.

Compared with cloned pigs, in what aspects does the difficulty of the cloned dog recently born in South Korea manifest? Dr. Pan explained that the eggs of dogs and pigs are both relatively dark and not easy to enucleate. The greatest difficulty in cloning dogs lies in the fact that their eggs are not easy to control. Domestically, the difficulty of cloning pigs is equivalent to the international difficulty of cloning dogs.

The Prospects of Cloned Pigs

Internationally, cloning technology has shown broad application prospects. Cloning technology will be applied in four aspects: breeding excellent livestock breeds and producing experimental animals; producing transgenic animals; producing human embryonic stem cells for cell and tissue replacement therapy; and reproducing endangered animal species and preserving and disseminating animal species resources.

Regarding the prospects of cloned pigs, Professor Li Ning, head of the research group, said that carrying out somatic cell cloning of pigs is of extremely important significance. In medicine, it can provide ideal materials for research on human xenotransplantation and the development of disease models. In agriculture, it can enrich the means for improving local pig breeds and preserving excellent local pig breeds.

Because the internal organs of pigs are very similar to human organs in physiological function, shape and size, they are considered ideal organ donors for human xenotransplantation. Scientists believe that by genetically modifying pig cells and then using cloning technology to breed transgenic pigs in large numbers, organs suitable for transplantation can be obtained. The birth of this first somatic cell cloned pig will lay a solid foundation for our country to carry out in-depth xenotransplantation, the breeding of high-quality pigs, and the preservation of excellent local pig breeds. In the near future, cloned pig farms are very likely to become suppliers of transplant organs.