Stem cell researchers in the U.S. say that eggs from cows, rabbits and other animals are not a good source for creating embryonic stem cells.
Embryonic stem cells are considered to be master human tissue building material because they are exceptionally versatile, primitive cells able to develop into any tissue of the body and scientists hope that in the future they could be used to repair tissue damage, replace organs and reverse degenerative diseases.
The scientists at the Advanced Cell Technology laboratory in Massachusetts say each time the nuclei of rabbit, mice and cow embryos were replaced with a human nucleus, something went wrong and instead of turning on the right genes the animal eggs would turn them off.
The cloning technique called somatic cell nuclear transfer involves removing the nucleus from an egg cell and replacing it with the nucleus from another type of cell from the donor animal or person who is to be cloned and the scientific team used a new method called global gene expression analysis to see which genes were turned on and off as the eggs grew.
If successful the cloning technique process starts the egg growing and dividing as if it had been fertilized by a sperm, but the resulting embryo carries mostly the DNA of the donor.
Their research did nevertheless provide some encouraging results as a significant advance in the cloning of human embryos, which could be a path to producing a host of patient-specific treatments, was made. Dr Robert Lanza, the chief scientific officer at Advanced Cell Technology, and co-author of the study says for the very first time it was seen that cloning really does work and that DNA is reprogrammed but mixing human and animal cells does not appear to programme the egg properly.
Dr Lanza and his team were able to replace the nucleus of a number of embryos and bring the clones to the morula stage, where they had divided into eight to 16 cells - in the human embryos, they were able to prove that the DNA was reprogrammed because the same genes were activated as in a normal embryo.
Lanza's team used a new method called global gene expression analysis to see which genes were turned on and off as the eggs grew.