Researchers who tried to use mouse, cow and rabbit eggs to make human clones said on Monday the effort failed to produce workable embryos but added that they showed human cloning should work in principle. Mixing human and animal cells does not appear to program the egg properly, said Dr. Robert Lanza of Massachusetts-based Advanced Cell Technology.
But using human cells did reprogram the egg cell or oocyte and activate the genes needed to make a viable embryo, Lanza and colleagues reported in the journal Cloning and Stem Cells. Several teams have tried to make animal-human hybrids as a source of embryonic stem cells, the master cells of the body. Because human eggs are scarce — it requires a surgical procedure to get them from a woman — some scientists came up with the idea of using animal egg cells. The cloning technique is called somatic cell nuclear transfer. The nucleus is removed from an egg cell and replaced with the nucleus from another type of cell from the donor animal or person who is to be cloned. Done right, the 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.
“The idea was to simply to plunk a patient’s DNA into an empty cow or rabbit egg — and presto — you reprogram the DNA back into a stem cell,” Lanza said in a telephone interview. But teams that have tried to do this have always ended up with what looks like a cell dividing over and over to become an embryo, but which eventually fizzles out. Mixing human and animal cells does not appear to program the egg properly …
“We got beautiful little hybrid embryos, but it didn’t work no matter how hard we tried.” … A mouse-human hybrid petered out after just one division. The cow and rabbit human hybrids went further, but stopped at the point when maternal DNA is supposed to kick in and turn the ball of cells into a proper embryo, Lanza said.
via NewsDaily: Animal-human clones don’t work: study.