Washington: There are a few contenders for the title of “weirdest critter in the world”. There is, for example, the three-toed sloth of Central America, which plays host to an entire ecosystem, including cyanobacteria, insects and other creatures that live in its sticky green fur.
Then there is the bizarre star-nosed mole, Condylura cristata, the only tentacled mammal, whose nose contains 30,000 microscopic sensory organs and which probably “sees” the world through touch. Or the mole-like Pyrenean desman, which looks like it has been put together out of random components — part rat, part mole, part shrew and part platypus. But surely the award must go to the mysterious and curiously engaging naked mole rat, Heterocephalus glaber, which is so weird in every respect that it resembles a creature from outer space.
Not only is it so unlike any other mammal that it almost seems to deserve its own category, but scientists now believe it may hold the key to curing cancer - and even, as Prof Steve Jones has mentioned before on these pages, extending the human life span. Uncommonly among mammals, mole rats do not get cancer, and last week, scientists announced that they have finally discovered why. They hope the “gloop” that they have identified in the animal could, in due time, form the basis of a host of new medicines to treat not only cancer but diseases ranging from atherosclerosis to arthritis.
It seems odd that the naked mole rat could spark any kind of medical revolution. In terms of its ecology and physiology, these animals are outliers. Naked mole rats are small, almost hairless rodents, about four inches long, that live in eastern and southern Africa. They are the only known “eusocial” mammal; the structure of a mole rat colony is identical to that of hive insects such as bees, and other arthropods such as termites.
There is one female, a queen, who mates with a handful of fertile males; the rest of the colony, which may number 80 or so, consists of sterile “workers”. That is only the start of the weirdness. They are, as their name suggests, naked (or nearly so — the odd whisker sprouts from their faces). They can run backwards as fast as forwards, and can manipulate their goofy incisor teeth individually, like chopsticks.
Unlike all other mammals, naked mole rats are not truly warm-blooded: they regulate their temperature in a crude fashion, more like a lizard than, say, a mouse. The oddities continue. Mole rats, which live off underground roots and tubers, appear not be able to feel pain, at least on their skin. The pain receptors found in all mammals — called nociceptors — are there, but they appear to be turned off, as German scientists found when they studied the way the receptors reacted to being immersed in corrosive chemicals. Douse a naked mole rat in acid, and it will not flinch. (It is finding out how these nociceptors operate that could be the key to new treatments for arthritis.) Mole rats can also survive extraordinarily high degrees of carbon dioxide, which builds up in their tunnels to levels that would kill a human in minutes.
In terms of cancer, numerous studies have failed to find a single tumour in the thousands of individuals sampled. Finally, there is the curious fact that these little rodents live for around 30 years — 10 to 20 times the life span of relatives such as rats and mice. For most species, there is a rough correlation between size and longevity. Big animals, the theory goes, tend to live longer because they are less likely to die quickly of cold or starvation or be eaten. Thus genes that confer health into old age can be passed on. That is why whales and giant tortoises live longer than shrews and mice. Mole rats should live a few years at most, but instead they can outlast chimpanzees. It is, however, that resistance to cancer — which is probably related to their longevity — that has proved the most intriguing puzzle. Now, Vera Gorbunova and colleagues at the University of Rochester in New York have identified a polysaccharide — a gloopy, sugar-based natural polymer - found in naked mole rat cells that stops tumours growing. The scientists, whose study was published in the current edition of Nature, suggest that the finding “opens new avenues for cancer prevention and life-extension”.
The chemical, called high-molecular-mass hyaluronan (HMM-HA), acts as a kind of lubricant, allowing mole rats to squeeze their Plasticine-like bodies through the smallest and most convoluted tunnels:
“They can virtually turn somersaults in their skin,” Chris Faulks, a scientist at Queen Mary, University of London said this week. It seems, therefore, that the ability of HMM-HA to confer cancer resistance was a happy evolutionary accident. And one day, it may be possible to engineer the ability to produce HMM-MA in human tissues — hopefully without the side effect, as Dr Faulks says, of making us all end up looking like naked mole rats.
Of course, this isn’t the first time that an extraordinary feature in an animal has been seized on as a possible cure for human ailments. While the thesis of Dr I. William Lane’s Sharks Don’t Get Cancer, published in 1992, is now widely held to be incorrect, crocodiles have an extraordinary ability to fight off bacterial infections: injured crocs have been in bacterially infested swamps, blood pouring out of open wounds, yet remained infection-free. Then there is one of the most intriguing findings of recent decades — that chimpanzees do not get Aids, despite being susceptible to the same group of retroviruses as humans. In fact, it is now believed that the Aids epidemic started when the virus jumped species from ape to human, probably in the forests of west Africa around 100 years ago, as a result of a hunting accident or by consumption of ape meat.
While chimps can get infected by the virus, they do not go on to suffer the disease: the reason why may lurk in the one per cent of the chimp genome that differs from ours. That we can solve medical mysteries by looking at our close cousins is not surprising; yet finding that an animal so weird, and so ugly, as the naked mole rat could one day lead to a cure for cancer seems utterly bizarre. However, this creature has gained the respect of an increasing number of scientists: robust to the point of near-indestructibility, living in perfect conflict-free communes, immune to pain and capable of spending years underground at a time, this meekest of animals could, should the apocalypse strike, be in pole position to inherit the Earth.
