Most of us have observed the phenomenon of limb regeneration. In my own personal experience, as a youth my parents purchased me a 'gold skink.' The
pet shop employee who had to catch the lizard caught it by its tail, and before he could box it - and much to my horror, the tail broke off. Wisely my
father agreed to purchase this particular reptile, despite the grisly looking stump that now existed in place of the skinks tail, knowing that the
tail would in fact grow back. This was a wise decision, I was certainly fascinated by the tails regeneration, and this incident may have sparked my
current interest in all things scientific. In a significant recent development researchers at the Salk Institute
able to stimulate growth of a new limb in a developing chick embryo, a species not normally known to regenerate.
Their study, published in the advance online edition of Genes and Development on Nov. 17, demonstrates that vertebrate regeneration is under the
control of the powerful Wnt signaling system: Activating it overcomes the mysterious barrier to regeneration in animals like chicks that can't
normally replace missing limbs while inactivating it in animals known to be able to regenerate their limbs (frogs, zebrafish, and salamanders) shuts
down their ability to replace missing legs and tails.
"In this simple experiment, we removed part of the chick embryo's wing, activated Wnt signaling, and got the whole limb back - a beautiful and perfect
wing," said the lead author, Juan Carlos Izpisúa Belmonte, Ph.D., a professor in the Gene Expression Laboratory. "By changing the expression of a few
genes, you can change the ability of a vertebrate to regenerate their limbs, rebuilding blood vessels, bone, muscles, and skin - everything that is
Manipulating Wnt signaling in humans is, of course, not possible at this point, Belmonte says, but hopes that these findings may eventually offer
insights into current research examining the ability of stem cells to build new human body tissues and parts. For example, he said Wnt signaling may
push mature cells go back in time and "dedifferentiate" into stem-like cells, in order to be able to then differentiate once more, producing all of
the different tissues needed to build a limb.
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This is a significant scientific development by any measure. It also demonstrates a further point regarding the ability of organisms to regenerate.
The results of this and relevant background experiments suggest that regeneration is not an evolved trait per se. Rather the ability to regenerate
limbs is something that has likely been lost by higher vertebrates such as chicks and humans. While certainly offering support for the theory of
common descent... the same pathways control limb development is organisms as diverse as fruitflies and chicks, but why the loss in regenerative
ability? Certainly one can see the selective advantage of being able to regenerate limbs.
Perhaps it won't matter in the long run. Science seems to have made a significant step towards being able to regenerate lost, and or developmentally
defective limbs. It's undeniably a long way from coming to fruition, but is undeniably a step in the right direction.
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