One Step Forward: Salamanders and Limb Regeneration

Problems with Prosthetics

A prosthetic is as close to a lost limb that an amputee can have. It may look the part, but it lacks a great deal in functionality and feasibility. As US Army captain Dan Berschinski, who lost both legs when he stepped on a buried explosive in Afghanistan, notes: “It takes more effort to take one step now than it took to take ten steps with my own legs.” On top of that, each prosthetic leg costs about $40,000 (Kules, 2011). In addition, prosthetics are sometimes so uncomfortable and painful that limb amputees opt not to wear them. Lieutenant Dawn Halfaker lost her right arm in combat. Although she worried about carrying a baby and doing other routine tasks of motherhood with only one arm, she decided that her ill-fitting prosthetic was “more trouble than it was worth” (Kules, 2011).

Our body regenerates itself at the cellular level throughout our lifetime. In other words, humans constantly replace old cells and recycle out wastes. According to David M. Gardiner, professor of developmental and cell biology at the University of California-Irvine and principal investigator in the UCI Limb Regeneration research program, “Regeneration is a fundamental, basic, biological property, just like reproduction” (Kiger et al., 2013). However, this re-growing capacity of ours is extremely limited. We routinely replace cells and can heal small cuts and scrapes, but if limbs or major organs become severely damaged, we cannot regenerate new ones to replace them.

What Can Salamanders Teach Us?
Looking for a better answer for amputees, researchers have turned to nature’s expert in limb regeneration, the salamander.

When a salamander limb is amputated, blood vessels in the stump contract quickly to prevent massive bleeding. Then, a layer of skin cells covers the surface of the amputation site. This layer of skin cells transforms into a layer of signaling cells called the apical epithelial cap (AEC). Simultaneously, fibroblasts detach from connective tissues and travel to the center of the amputation site where they will transform into a blastema, a sac of stem cells that will serve as the critical forebears for the new limb regeneration (Kiger, 2013).

The human body initially reacts similarly to that of a salamander. We immediately form a scar to prevent the open wound from infections and major blood loss, but our bodies stop there. Unlike the salamanders, we cannot reactivate or naturally form a blastema to regenerate a new limb in a few weeks (Conger et al., 2008).

[“Stem Cell Division Three Dimensional Shape” (Artist’s depiction). License: Public Domain]

Dr. Gardiner and his team of research scientists discovered that human blastema cells are equivalent to the developing blastema cells of the salamander embryo (Muneoka et al., 2008). This observation suggests that humans have the same embryonic genetic program as salamanders. In essence, humans should have the genetic capability to regenerate limbs in adulthood as well. Researchers found that mammalian embryos do have a limited ability to replace developing limb buds, hinting that an important step in limb regeneration research is to figure out how to induce the formation of a blastema. Now, Dr. Gardiner and his research team are focusing on gene expression patterns specific to the regenerating ability of the salamander (Monaghan et al., 2012).

A Leg Up!

We owe the salamander, one of the smallest vertebrates, a great big “thank you”. For amputees like Captain Berschinski and Lieutenant Halfaker, limb regeneration could significantly reduce the emotional, physical and financial costs associated with losing a limb. For them, limb regeneration would offer a second chance to live their lives to the fullest.

In Brief

Researchers are studying the ability of salamanders to regenerate limbs as a clue to limb regeneration in humans.
The blastema, a sac of stem cells, is a vital component of limb regeneration.
Human embryos have the genetic information needed to form blastemas.

Works Cited

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