When lizards are attacked, they have the remarkable ability to detach their tails from their body in order to confuse their enemy, and then, to grow it back. If a salamander gets its leg chopped off, it can regenerate another one in a matter of weeks. So why can’t humans? From an evolutionary standpoint, it would be energetically wasteful to regenerate a body part that is not necessary for survival, like a finger. Conversely, if an important organ like the heart were significantly damaged, the individual would likely not survive long enough for regeneration to actually take effect. Instead, much of our bodies’ effort seems to have gone into wound healing, which actually inhibits potential cell regeneration. In 1974, Dr. Cynthia Illingworth found that young children could regenerate fingertips, but only if their wounds were left open rather than surgically re-covered with skin. In addition, studies in mice have shown that the formation of scar tissue blocks cell signaling necessary for regeneration. When salamanders lose their limbs, instead of covering the wound, cells near the site of the injury de-differentiate and form a group of cells collectively known as a blastema. They can then re-differentiate and build the lost structure, but the cells do not exhibit full pluripotency; instead, old skin cells become skin cells and former bone cells become bone once again. The inability of many higher-order species to undergo this process may be merely one explanation as to why regeneration in those species is rare.
Though humans do not have a great capacity for regeneration, the liver is able grow back from around 25% of its tissue. Research has suggested that this is achieved through the proliferation of cell division, rather than reversion back to an embryonic state. A recent study has discovered a mechanism for the regeneration of damaged tissue in the kidneys; interestingly enough, it occurs via the immune system.
Reference: Cincinnati Children's Hospital Medical Center. "Scientists Discover Molecular Pathway for Organ Tissue Regeneration and Repair." ScienceDaily 16 February 2010. 17 February 2010 <http://www.sciencedaily.com /releases/2010/02/100215174134.htm>.
Photo credit: Scientific American. Can be found here.
Linda Le is a contributing writer on biomedical research to TuftScope for Spring 2010.
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