Friday, July 5, 2013

What cloning is and what it isn't

There is a new story about cloning, which we saw on the BBC (but which is published in the journal Biology of Reproduction).  Mice have been cloned from blood cells, rather than any sort of stem cells.  The procedure was the same one used to clone Dolly the sheep and has been used in other instances more recently.

According to the BBC, this technique can be used to improve methods for producing "high-quality" animals for farming or conservation.  And, according to the authors of the paper, " This strategy will be applied to the rescue of infertile founder animals or a "last-of-line" animal possessing invaluable genetic resources."  They specifically have in mind inbred mouse lines that would be difficult to impossible to reproduce.  

This may be valuable scientific progress but it raises (again) the ethical issues about what and when cloning is permissible, especially if it comes to humans.  But let's again be clear: the nucleus of the blood cell was inserted into a recipient egg cell, that then developed into a whole, new mouse.  But this is not a clone of the donor mouse in several ways.

First, the mitochondrial DNA (mtDNA) which is vital to life and involved in many processes that integrate with the nDNA, or nuclear DNA (which is what most people mean by "DNA").  So the new mice are hybrids between the donor and the recipient.

Second, each cell is somewhat different.  The new mice have adult-mouse DNA, which means that it has been affected by mutation during the donor mouse's own embryologic development and subsequent mouse, and different donor cells even from the same mouse would be genetically somewhat different.  It may, among other things, age more rapidly and so on, depending on what mutations had arisen before the nucleus was obtained from the blood cell.

These caveats don't mean the method doesn't 'work' but they simply raise, and raise again, the importance of a better understanding of what 'cloning' actually means.  The ethical issues are not affected one way or another by this work.  It may lead to great biomedical advances, if your own DNA (well, except for the mtDNA) could be used to grow cloned tissues that could be used in therapy for you.  The idea is that these are your own cells, so you won't reject them, one of the major problems in organ and tissue transplants.  But because of mutations and the issues we raise, some recipients might in fact have an immunological rejection problem.

So, this may become a routine practice and may have terrific benefit if properly monitored.  But beware of misleading enthusiasm.

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