Not getting cancer: a sequel to sequencing and evolution

The previous Kamilah the gorilla story leads us – where else – to the Naked Mole Rat. Addicted Naturists will have read last year that it too had been sequenced. Why on earth would they want the DNA code of the NMR? Maybe part of some fiendish chimeric cloning experiment inspired by The Wind in the Willows – these boffins need to get out more. But wait a minute! Despite the advances that mean genomes can be sequenced in a day, it’s still a complicated and expensive business – so there has to be a good reason for tackling another strain or species, as we saw with the gorillas. But what might that be for the humble NMR?

Water vole

Naked mole rat

It turns out that NMRs are far more astonishing chaps than even Kenneth Grahame could have imagined. In a way they’re rather well-named, being neither mole nor rat but a distinct species that diverged from rats and mice about 70 million years ago – much as the water vole (aka ‘Ratty’) is only distantly related to a true rat – and it parted company from us 20 million years earlier still. It’s a burrowing rodent so has to get by on low levels of oxygen, which it manages by having very small lungs and haemoglobin that is unusually efficient at picking up oxygen. When times get tough it can reduce its metabolic rate to a quarter of normal, its body temperature follows that of its surroundings, it doesn’t feel pain because its skin doesn’t make the required neurotransmitter, it lives in communes with a queen (the only one to reproduce – like some ants and bees) and it’s the longest-living rodent (over 30 years).

How amazing is that for a set of party pieces? But these stunning little tunnelers have one other trick that puts everything else in the shade. NMRs don’t get cancer. At least tumours have never been found in these fellers and if you take some of their cells, make them express a cancer-promoting gene and put them back into animals they still don’t form tumours – even though you get very aggressive growths if you do the same thing with mouse or rat cells.

What’s the secret of Naked Rats not getting cancer?

So what has the full DNA sequence of the NMR told us? Two genes have come to the fore that are very slightly altered compared with their human counterparts, and they’re of particular interest because we know they play major roles in protecting us – to the extent that they are knocked out in the majority of human cancers. What’s different in the NMR? Perhaps surprisingly, their variant genes make proteins that are just a little bit smaller than the human versions. Surprising because intuitively you might think that bigger would be better. However, proteins are almost incomprehensibly subtle creations – recall that changing just one amino acid out of 1480 in a protein made in the lung is enough to cause cystic fibrosis – and it may be that the slight changes in the DNA code do just enough to the shape of these proteins to make them ‘super’ protectors. The next step is to see what the NMR proteins do when they’re expressed in transgenic mice.

None of this means that the NMR is going to save mankind from one of its greatest scourges but it is encouraging that it has focussed attention on some of the key genes that stop us getting cancer. The other upshot is that it has reminded us how extraordinarily delicate is the balance in living things and how the slightest of changes in a protein can have immense effects.

Reference

Kim, E.B. et al. (2011). Genome sequencing reveals insights into physiology and longevity of the naked mole rat. Nature 479, 223–227.

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2 comments on “Not getting cancer: a sequel to sequencing and evolution

  1. Pingback: Bigger is Better | Betrayed by Nature: The War on Cancer

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