Britain gives go-ahead on chimeras. Will science now block the way?
Today, the Human Fertilisation and Embryology Authority (HFEA) in the UK said that scientists could combine human chromosomes with animal eggs and try to make embryonic stem cells. It’s easier to collect unfertilized eggs from, say, cows than it is to collect them from women.
Interested scientists will learn in November if they’ll be licensed to make the attempts, which must be carried out under certain guidelines, but an article this month in Nature Cell Biology reminds us that even if the government says `yes’, some laws of science might say ‘no’.
In chimera-embryos (properly called `cybrid-embryos’ in this context), the chromosomes will be human, but at least some of the mitochondria will not.
(If you want to read more on the ethics and science involved in cybrids, scroll to the end.)
A mouse oocyte contains about 100,000 mitochondria; adult cells may contain only a few hundred. About a dozen essential mitochondrial genes lie in the mitochondria; about six dozen in the chromosomes. There is already some evidence from cybrids that cross-species communication is not perfect, so the mitochondria in cybrids produce less power for the cell.
Cells might not have a problem with this until the mitochondria need to kick into high gear, and that may only occur in certain cell types. Mitochondrial diseases, often in children, are known to affect the brain, heart, liver, skeletal muscles, kidney and the endocrine and respiratory systems. Thus, even if embryonic stem cells can be made from cybrids, they are much, much more likely to be used in research than in cell therapies.
Of course, many people feel the same way about purely human ESCs as well. That doesn’t mean they are not useful.
A succinct summary of the UK Acadamy of Medical Sciences report on how chimeras should be regulated.
Ted Peters, a theologian, puts forward his views for chimeras.
Comments
Cybrid research could be very useful for understanding what mixture of proteins and nucleic acids can reprogram. By applying mixtures of non-human animal cellular components to human nuclei, scientists may be able to drill down to some essential components that can turn a differentiated, human somatic cell into something embryonic and stem-cell like. Once this is understood, "cleaner" technologies for generating pluripotent cells with the minimum of risk would follow. The Yamanaka factors were identified by such an approach, but using a genetic screen. A complementary approach would be to directly apply cellular fractions and components to the human nuclei. Stem cell science is at a cusp and all approaches that lead to understanding reprogramming should be encouraged, as long as they are ethical. As Monya says, at this point cybrids will be an important research tool and should not be scrutinized for safety for patients, as that is not their intended use.
Posted by: Natalie DeWitt | September 12, 2007 02:36 AM