Country: United States
Date: March 2007
If the genes for differentiation of cells (which
have been switched off at time of birth or even before it) are
switched on after 20 years of age can regeneration takes place in a
man with one arm to replace a second one?
There's a lot of research going on right now to try to figure out if this is
theoretically possible. Most scientists think it *is* theoretically possible
(although not all). But theory and practice are very different things.
It's an extremely complex thing to set up all the necessary genes
(thousands) and chemical signals to coax cells to form anything -- let alone
something like an arm. We have trouble getting cells to just live, let alone
differentiate into complex structures.
While it might be theoretically possible, right now we are very, very far
away from actually being able to grow a new arm.
Regeneration science is in its infancy. To build an arm requires a lot of
coordination and synchronization between tissues and other major organ
development; such as the torso and muscles that will be attached elsewhere
in order for the arm to move. The agents of this development is the so
called "Hox" genes. These genes are the planners and executors for major
area development and are in control at the earliest stage of development.
In human development, these genes work with others to develop the whole
organism and it seems that we have an issue when it comes to just growing an
arm when the rest of the body is totally developed. This will lead to a
lack of the necessary feedback mechanisms for the specific hox genes to
operate. We may be able to mediate this problem in the future, but right
now we are not close to understanding how this can be realized.
In view of the fact that differentiated mammalian cells (e.g. mammary and
skin cells) have been used to clone sheep, cows, dogs and cats, it would
appear that any cell might have the ability to de-differentiate and then
re-differentiate. Based on this, I would say that it's theoretically
possible to regenerate a human limb.
Ron Baker, Ph.D.
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Update: June 2012