Regrowth of lost organs and limbs

[MirceaKitsune]

I remember hearing about this many years ago, and now I'm curious if any progress in this domain was made recently. From what I'm hearing, it's been a struggle for the medical community to discover how to allow the body to regrow lost organs and limbs. Which obviously, would be the most awesome thing to happen for people who had faulty organs removed or lost limbs in accidents.

 

It was said that lizards provide clues regarding this, because if something cuts off their tail they will eventually grow a perfect new one. Earth worms are even more fascinating and even scary in this sense, since I often heard that cutting a worm in half will cause it to become two worms, each re-generating a head / tail where the cut took place (this might be incorrect however). From what I further understood, humans and all / most animals should be natively capable of this. Only problem is that the genes responsible for regrowing lost parts were shut down by evolution long ago, and no one found how to reactivate them yet. Last updates that reached my ears stated that scientists should be close to figuring it out... but it's happened for someone to have thought they're close while it took years / decades more for a discovery.

 

So how does this really work? How are some creatures able to re-generate lost body parts, both internal and external? And how could this ability be enabled for other living beings that no longer have it?

[iNow]

Much progress is being made with the 3d printing of tissues and biological matter, but I'm not sure that's what you have in mind.

[wisejanesm]

At the tail of the worm and lizard - a simple biological structure. The human body is more complex than. Therefore, the growth of limbs in humans - is a complex process.

[Phi for All]

There's a decent SciAm article on it, but they want you to pay for more than this preview. Basically, we still have access to embryonic cell regeneration, but we lose that access shortly before birth. If we can figure out how to keep it from switching off, we could regenerate lost limbs. Currently, we've evolved to develop scar tissue, which allows us to heal more quickly if not more fully. Since we're no longer as concerned with becoming damaged while hunting, and thus becoming the hunted, regeneration might be preferable.

 

But it can take years with small animals like lizards, and it takes longer the bigger they are. Stem cells cover the wounded area and eventually a small version of the limb grows, becoming functional yet undersized. Salamanders have three other legs to help them move while conditioning the new one as it grows to full size. We have prostheses that could help our own transition.

 

It must not work to regenerate just any old damaged cells, otherwise would a salamander's body ever wear out? Since we don't see 500 year old salamanders, it must be specific to things the salamander needs to grow back. Regenerating limbs would be fantastic, but regenerating teeth would be a benefit to more humans. Plenty of other animals regrow teeth, so the precedent is there.

 

Here's an abstract on another study of a specific protein that has regrown digits in mice: http://www.cell.com/cell/abstract/S0092-8674(13)01278-6

[Dekan]

I think post #3 by wisejanesm is very valuable, in pointing out that worms and lizards have simple, small, biological structures.

 

These structures, for example in the form of a lizard leg or a tail, contain only a small amount of tissue. No more than 20 or 30 grammes, perhaps. Such a small weight can be speedily regenerated.

 

Whereas, the situation is very different with human structures. A structure such as a human leg, is quite a massive affair. It weighs several kilos, and contains variegated components like bone, muscles, tendons, veins, skin, hairs, and the like. All these components take a long time to grow. We note, for instance, that a human baby takes several years to fully grow its legs.

 

This shows that human regeneration is bound to take a long time. And this length of time is, I think, the key to understanding why humans haven't got the ability to regenerate legs.

 

Consider humans in their primeval, natural, condition. Before they got civilised and invented doctors and hospitals. Suppose some primeval human fell down a cliff and smashed his leg.

If he didn't die immediately from loss of blood, he'd soon fall victim to predators. His broken leg would make him unable to run away from them. And would also make him unable to forage for food. So he'd soon starve, even if he hid from the predators. Either way, he'd be dead within a week or so.

 

So - what good would the ability to regenerate a leg in 6 months do him? None at all - he'd never live that long. Even if he had genes with the potential to regenerate a leg in 6 months, that genetic potential wouldn't get transmitted to his offspring. Because he wouldn't have any offspring, and his genes would die with him.

 

Doesn't that explain it?

[Phi for All]

Doesn't that explain it?

 

It may explain why we evolved the ability to form scar tissue in lieu of embryonic regeneration, but most of the species has moved away from the hunter/gatherer practices that provided the selective pressure. It may be better for our modern civilization to regrow limbs instead of form scar tissue, or perhaps be able to choose based on the type of damage.

 

Figuring out how to switch our regenerative abilities on and off is the first step in figuring out how to make the process fast enough to be a viable option.

[Endy0816]

We do have some limited abilities when young and we retain the ability to regenerate our liver as adults.

Edited July 25, 2014 by Endy0816