The Niche

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.

Related articles

Commentary from Justin St John and Robin Lovell-Badge in Nature Cell Biology called “Human-animal cytoplasmic hybrid embryos, mitochondria, and an energetic debate”

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.

Ian Wilmut, who led the team that cloned Dolly, describes what could be learned from attempts to make embryonic stem cells from chimeras, even if they don’t work.

Nature’s news story

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