Why+can+some+animals+regrow+limbs+while+some+can't?


 * __lWHY CAN SOME ANIMALS REGROW LIMBS WHILE SOME CAN'T?__**

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For more then a century, the reasons for basic limb regeneration have been evident. Scientists have determined that first the animal heals the wound at the site of the missing limb. Then, various specialized cells at the site, such as bone, skin, and blood cells, lose their identity in a process called dedifferentiation. The resulting blastema, a mass of unspecialized cells, proliferates rapidly to form a limb bud. The cells ultimately take on new specialized roles as the new limb takes place. Wondering what dedifferentiation is? Dedifferentiation is the process of cells or tissue undergoing a reversal of their specific purpose differentiation and lose their specialized characteristics. And blastemas are the primary material used in cells of plants and animals. So that’s how limbs are re-generated. How come certain animals, like newts and cockroaches, can re-grow limbs while other animals can’t? One possible answer discovered by scientists (un-named) is as simple as switching off the gene p21. This new research suggests that humans can heal without scarring, or possibly re-growing a limb. The secret lies dormant in human cells, but may be kept in check with the p21 gene. The scientists tested this on a group of specially engineered mice that did not have the p21 gene. They were able to regenerate tissue that was surgically removed, up to the point that no evidence of the surgery remained. A standard procedure for lab animals is punching holes in their ears to tag them. These holes that were punched in the mice’s ears healed perfectly, leaving no trace of scar tissue or previous damage. Basically, switching off the p21 gene allows adult cells to act like pluripotent, immature stem cells, allowing them to ‘decide’ the types of tissues that they need to be. But there is give-and-take. The p21 gene is closely related to the gene p53, a cell-division regulator, that if allowed to run out of control, can lead to many types of cancer. The p21 works as a safety valve for p53, stopping cell division in the case of DNA damage. However, there was no surge of cancer in the lab mice. Instead there was an increase in cell suicide, which directs damaged cells to destroy themselves. So by striking a controlled balance between these two genes, it appears that we would be able to apply this to humans in the future.

Jaime Abels, 2.22.12

Ellen Heber-Katz, a professor at the Wistar Institute in Philadelphia, led the study. Article posted 3.15.10. http://www.popsci.com/science/article/2010-03/humans-could-regenerate-tissue-newts-switchin-single-gene or http://www.guardian.co.uk/science/2010/mar/15/mice-genetics-p21-heal-no-scar

Article posted 11.1.97. Written by John Travis, numerous scientists contributed. http://planaria.neuro.utah.edu/news/ScienceNewsOnline.htm

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