DNA debate branches out

Recent weeks have seen a furore erupt over controversial laws that would allow the creation of human-animal embryos for research, with much talk of the sacredness of human life and the danger of scientists playing God.

But there are some, both professors and priests, who are using the facts in ways that are, at best, selective and, at worst, misleading. More importantly, even though proponents say there is a moral imperative to do hybrid embryo research to find cures, some scientists are sceptical that it is worth diverting money from more promising research.

Recently, the news emerged that Newcastle University had created the first European hybrids, a blend of cow and human. The coverage made much of how the embryos could yield stem cells, that could be used in a dizzying array of treatments, from diabetes to heart disease.

This is precisely the kind of science that Britain's Embryology Bill is designed to address and that has caused such bitter argument. Opponents of the Bill try to convince the public that embryos are “people'' whose “body parts'' will be raided by monstrous researchers to make “Frankenstein creations''.

Yet some scientists have also been manipulating the media when it comes to the most divisive part of proposed legislation — to allow “admixed human embryos''.

They have underplayed concerns by their peers that this work is speculative by downplaying the role of animal DNA.

In the Bill, these embryos could result from a human egg and animal sperm, or blends of cells from animal and human embryos (chimaeras).

The Newcastle team made another version, a “cybrid''. This is created by inserting human DNA, in the form of a broken human cell, into an empty animal egg, in the same cloning method used to make Dolly the sheep.

This work was high on the agenda of the first national stem cell research conference held in Edinburgh. There is a need for more science in the public debate because the animal DNA does a special job in these embryos, one which diminishes their direct relevance to cures.

The cells in our bodies contain two kinds of DNA. Most research concerns nuclear DNA. This DNA comes from our parents, and provides the recipe for the proteins that make and run the body.

The animal DNA in the cybrids would be of the second kind, which resides in the mitochondria. Scientists say that cybrids of human and animal are “99.9 per cent human'', in order to comfort those who think (wrongly) that an embryo would end up with horns or hooves.

The 99.9 per cent figure probably refers to the fact that there are 37 instructions (genes) in mitochondrial DNA, compared with 29,000 in nuclear, which means 0.1 per cent animal instructions.

But this is hardly reassuring. Decades of work has shown that even one genetic spelling mistake in the three billion letters of the nuclear code can be fatal — just 0.0000001 per cent. And mitochondria are important: Faults in them are responsible for nearly 50 metabolic disorders that affect one in every 6,500 people.

Some claim that using animal mitochondrial DNA in cybrids would be like changing a battery in a computer, leaving the “hard disk'' — the nuclear DNA — unaffected.

But Dr Marc Vermulst of the University of Washington in Seattle, who has linked changes in mitochondria to premature ageing, says: “By evolving together, mitochondria and nuclei have become very finely tuned to each other. I am not sure how well human and cow DNA would communicate with each other.''

Although a pioneering study in China suggested rabbit and human could be successfully blended, using animal mitochondria in human cells could sometimes be like trying to put AA batteries into an AAA compartment.

“It is clear that human embryos with animal mitochondrial DNA may develop in the initial stage, but [they] could not survive any further,'' says Prof Neil Scolding, a Catholic stem cell researcher at Bristol University.

Scolding points out that, thanks to pioneering work in Japan, there is now an egg and embryo-free alternative source of stem cells, albeit one that might present other ethical issues (such as the ability of men to make eggs).

For many scientists, such as British stem cell pioneer and Nobel prizewinner Sir Martin Evans, resolving such issues provides a clear scientific rationale for using cybrids to find out more about the role of mitochondria in development and disease.

When even human stem cells are poorly understood, it will take a lot of slogging to show whether cybrid stem cells will behave properly. Here, even Sir Martin feels the immediate potential has been hyped and claims about cures “overheated''.