Article Review: A novel amniote model of epimorphic regeneration: the leopard gecko, Eublepharis macularius

Eublepharis macularius showing the original and regenerated tail

It’s probably safe to assume that most people know about certain lizards’ ability to regrow their tails.  It’s a pretty common site to see a lizard running around with a nub (some of us might have even been the cause).  However, most people do not stop and wonder how the lizard will actually regrow its tail.  While regeneration is far from uncommon in the animal world, most of the research has been done on non-amniotes.  This article by Katherine McLean and Matthew Vickaryous, published in BMC Developmental Biology, looks at epimorphic regeneration in amniotes.  Specifically they looked at leopard geckos (Eublepharis macularius).  

They used a total of 89 E. macularius in three trials of experiments.  To collect the tails, they caused autotomy by firmly grasping the tail between the thumb and index finger and applying pressure.  The first time they did this it was halfway between the vent and the tail tip.  The geckos were allowed to regenerate and then the tails were caused to autotomize another time.  This time they grasped the tail closer to the gecko’s body causing a portion of the tail to autotomize that contained ‘half’ of the original tail and regenerated tail.  Histochemistry was used to determine the tissue and cellular composition of the original and regenerated tails throughout the regeneration process.  

McLean and Vickaryous found that the removal of the tails resulted in a consistent series of regeneration each time.  This regeneration took place in a seven stage sequence.  Stage one was immediately following the tail loss and the tail resembled an open wound.  Interestingly, due to the muscle arrangement of arterial sphincters there was minimal bleeding.  In stage two, the exposed soft tissues retracted at the autotomy surface, which resulted in the remaining bits of the vertebral column sticking out farther than the wound.  At this point, a clot forms that spans the entire wound and will last into stage three.  Now in stage three, there is newly formed wound epithelium exposed yet the vertebral remnant is no longer protruding.  By the end of stage three the wound epithelium has thickened.  It should be noted that an interesting discovery of the research was E. macularius ability to regenerate without a scar.  In other words, there is no visible sign of healing whereas we would have a big, nasty scab covering our wound. 

In stage four, there is a well-defined portion of visible regenerating tail that is cone shaped.  Now that the tail is beginning to appear, it is important to note that the regenerated tail is only superficially similar to the original.  The original skeleton is replaced by a cartilaginous cone, which is what is immerging here.  Stage five is very similar to stage four except that the cone is now shaped like an elevated dome.  By stage six, a pattern of scales is finally becoming visible on the regenerated tail.  It takes until stage seven for pigmentation to appear in the regenerated tail (it had been pink for the entire process).  Finally in stage seven, the tail lengthens and closely resembles that of the original.  

The authors found that blastema played an important role in the reformation of the lost tail.  The blastema cells developed within the tail after autotomy but, although they continued to proliferate, they did not differentiate until around stage five.  This differentiation forms cartilage, muscle, adipose tissue and fibrous connective tissue that are important for the regeneration of the tail. 

The importance of the whole article can be summed up in the fact that it provides valuable information on blastema-mediated regeneration in amniotes.   A majority of the former research had been done on non-amniotes, some of which possess near perfect systems of regeneration.  While the method found in E. macularius seems to be an intermediate stage between mammals and perfectly regenerating non-amniotes, it is an impressive action for amniotes.  This article provides valuable information on the actual process of regeneration since it does vary from other known systems.  Another interesting thing found by the authors was that the regeneration of the tail followed a specific sequence.  Regeneration is not a haphazard event but an evolutionary wonder.  So as a take-away from this article, if you happen to break the tail off of a leopard gecko, you can rest easy knowing that it will grow back (somewhat).  

If you are interested in reading more about this fascinating topic, the article can be found here.