In a development that brings us one step closer toward the mass-cloning of animals for use in regenerative medicine, researchers from Meiji University have succeeded in creating the world's first fourth-generation pig clones.
Since creating a pair of pig clones in April 2004, professor Hiroshi Nagashima, the research team leader, has been recloning the clones using cells from their salivary glands. The fourth-generation piglets -- three of them born on July 23 -- are clones of clones of clones of clones, so they share the exact DNA as the original pig.
Scientists have been seeking to advance pig cloning technology because pig organs are physiologically similar to human organs, meaning they could be the key to alleviating the worldwide shortage of organs for transplant.
Past examples of animals that have been cloned through multiple generations include mice, which have been recloned up to the sixth generation, and cows, which have been recloned to the second generation. While recloning technology may promise to boost the productivity of cloning operations, there are some drawbacks. For instance, in somatic cell nuclear transfer -- a reproductive cloning technique where the nucleus from a donor adult cell (somatic cell) is transferred to a nucleus-free egg cell, which is then transferred into the uterus of a surrogate mother -- DNA damage accumulates with each generation that is cloned. After a number of generations, the cumulative damage to the DNA could result in an animal that is significantly different from the original.
So far, however, the fourth-generation pig clones show no signs of abnormalities, and the researchers are planning to reclone them again.
In addition to creating the world's first fourth-generation pig clones, Nagashima's team also reported success in using a combination of gene transfer technology and cloning technology to create transgenic diabetic pigs -- pigs with human genes that exhibit symptoms of diabetes mellitus. The researchers worked with BIOS Inc., a venture company based in Kanagawa prefecture, to engineer the pigs.
While we have seen transgenic diabetic mice in the past, these transgenic diabetic pigs are reportedly the first of their kind. With the anatomical similarities between man and swine, transgenic diabetic pigs could lead to a cure for diabetes by helping scientists develop transplant technology involving the use of pig pancreatic tissue, a potential source of insulin. In addition, the pigs can also serve as models for observing the complications associated with diabetes, such as arteriosclerosis, and they could help researchers develop new medicines.
Professor Nagashima suggests that in addition to serving as model animals for human diseases, individuals will be able to use their own cells in these bioengineered pigs to test the effectiveness and safety of regenerative medicine therapies.