

Remove p21 Gene = Grow new limbs like lizards tail - keltecp11
http://www.physorg.com/news187879295.html#top

======
reasonattlm
Article slightly overhyped. Title should be "Single gene finally pinpointed as
source of unusual regenerative powers of MRL mice". They can't regenerate
limbs, but they can regrow heart sections, ear holes, fingers, etc.

[http://www.fightaging.org/archives/2010/03/regeneration-
in-m...](http://www.fightaging.org/archives/2010/03/regeneration-in-mice-
through-a-single-gene-deletion.php)

The MRL breed existed for a while (created for another purpose) before their
regenerative powers were noticed. Similarly, the p21-knockout breed used to
confirm the findings here also existed for years, and no-one noticed they
could regrow ear tissues without scarring, etc. Makes you wonder what else
exists in the hundreds of common lab breeds.

Anyway, the significance of this is that from a single gene, researchers can
now walk through the list of biochemical mechanisms that gene pertains to, and
perhaps more quickly answer the questions:

a) do mammals still have all the necessary machinery to regenerate like
salamanders? b) can it be activated easily?

My gut feel on the bigger picture is that evolution ditched regeneration in
favor of cancer suppression in mammals - though mice are not a good example of
that process in action, being pretty much cancer factories in comparison to
other mammalian species. If you look at p21, it's central to all sorts of stem
cell related and cancer suppression mechanisms. It's surprising and unknown as
to why p21-knockout mice are so normal, frankly.

Cancer, embryonic development, and blastema-style regrowth in adult creatures
all look quite similar in many ways. A heavy duty anti-cancer mechanism and
regrowth of tissues in adults may just not be terribly compatible from an
evolutionary perspective. Which isn't they aren't compatible from a biotech
perspective; many small single or few gene changes that produce favorable
outcomes have not been selected for, but demonstrated in the lab to increase
mouse life span, boost cancer resistance, provide regenerative powers at
little cost, and so forth.

------
jacquesm
So, does that make it a valid question what evolutionary advantage was gained
by _losing_ that gene ?

~~~
jazzyb
Maybe I misread the article, but it sounded like having the gene could raise
one's risk of cancer.

~~~
anateus
It could (particularly since p21's suppression is related to general anti-
cancer processes), though they explicitly said they did not observe it in the
mice trials (they were actively looking for cancer).

~~~
rbanffy
Mice have short lives. I am not sure how frequent cancer is in mice compared
to humans.

------
rue
Wonder what happens if you _split_ a limb?

~~~
catch23
It'll be just like earthworms. You can cut off your finger and plant it
somewhere and create a clone of yourself.

------
zackattack
It's cuz p21 regulates the cell cycle (mitosis). p21 is a CDK inhibitor. CDK
is necessary for the cell cycle to proceed past "checkpoints". So when you
have p21, you have CDK inhibitors, so cell division doesn't proceed. No p21 =
less inhibition = more growth. (And unchecked growth is one main cause of
tumors).

