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Scientists Demonstrate Mammalian Tissue Regeneration
telomerewhythere writes "A quest that began over a decade ago with a chance observation has reached a milestone: the identification of a gene that may regulate regeneration in mammals. The absence of this single gene, called p21, confers a healing potential in mice long thought to have been lost through evolution and reserved for creatures like flatworms, sponges, and some species of salamander. 'Unlike typical mammals, which heal wounds by forming a scar, these mice begin by forming a blastema, a structure associated with rapid cell growth and de-differentiation as seen in amphibians. According to the Wistar researchers, the loss of p21 causes the cells of these mice to behave more like embryonic stem cells than adult mammalian cells, and their findings provide solid evidence to link tissue regeneration to the control of cell division. "Much like a newt that has lost a limb, these mice will replace missing or damaged tissue with healthy tissue that lacks any sign of scarring," said the project's lead scientist.' Here is the academic paper for those with PNAS access."
Not necessarily. A lot of small animals are pretty much disposable: they're sufficiently fragile that there's only a very narrow boundary between a trivial injury and a fatal one. (And anyone who's kept small birds and animals will know that if they're hurt beyond a certain point they'll simply go into shock and die.)
So it's entirely plausible that the gene might have been caused by a spot mutation very early on while all mammals were basically mice, and it then had a sufficiently small effect on actual survivability that the trait didn't get bred out. Later, once the small, disposable animals turned into large, expensive ones, it was too late.
It is interesting that both birds and animals appear to lack this trait, though. We both descend from much the same sort of lizards but in different directions. Finding out exactly where this gene sequence appeared might be productive.
(Of course, I want to know when we'll be able to get gene therapy to suppress the gene. Assuming it works in humans, and that the gene doesn't do anything else critical, it might even be fairly straightforward! But probably won't happen soon and I'm certainly not volunteering to be the guinea pig...)
The cancer concern is a legitimate one. These p21 knockouts are lab mice kept in clean conditions. They may not develop cancers in a three year span, but that demonstrates little about the oncogenic potential in humans.
I'm assuming there is some evolutionary reason for curtailing a vigorous healing response. It maybe to reduce the cancer rate, but it could just as simply be something else very important - regulation of immune response for example.
One potentially useful experiment would be to challenge these mice with carcinogen (like ENU) and see what their cancer rate is compared to controls. Alternatively, you could use genetic means (insertion of oncogenes or mating to mice with knocked out tumor suppressor genes) to see if the cancers they develop are more aggressive or more likely to metastasize. In any case, this is a very cool finding.
Something useful... like ending actual ongoing *human* slavery? Nah... PETA finds it more worthwhile to kill (uhhh 'rescue') some more animals: http://www.petakillsanimals.com/.
The worst part of it is, science believes that cats 'self domesticated'. If anything, denying humans the right to keep cats as pets is animal abuse, since it is denying them an adaptation they developed themselves.
Who ever said these people used logic though?
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You are correct. In point of fact, around 90% of the time when you hear that "X gives you cancer" what you should instead read it as is "X causes cancer to happen sooner". Usually this means that exposure to risk factor X reduces your ability to fight off cancer. You've probably got a few carcinogenic cells in you right now that are going to be killed off before they do you any harm. Obviously this doesn't apply in every single case - ionizing radiation falls into that other 10% that really does cause cancer directly - but when you see cancer linked to, say, stress, that falls under the other 90%.
I don't think that tissue regeneration will cause cancer to happen more frequently, for two reasons. The first is that the healing process in humans already accelerates cancer. As do certain immune responses. Essentially, every bit of damage you pick up over your lifetime accelerates the inevitable rise of carcinogenesis by some tiny amount. Regeneration, done correctly, probably won't worsen this.
The second reason is that the reason mammals don't regenerate naturally has to do with speed, not safety. The healing process in mammals essentially slaps a quick patch over the damage in order to get you healthy sooner; we call this patch a scar. Regenerating vertebrates (amphibians, some reptiles) take longer to heal, but heal more completely, which is substantially more viable when you're cold blooded and can go a few days without more food. At some point in our distant evolutionary past, scarring became a more viable approach to damage, as it fixed us up sooner, so selection pressure favored the scarring over the regenerating. Lack of regeneration in humans is a matter of what worked in the wild for our ancestors, not what works today, where the injured have plenty of time to recuperate, and don't run the risk of starvation or predation.
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