Every day at college, during the break, I stand outside the class and notice a guy. Holding his bag on the right shoulder, just like a regular student attending lectures. But what makes me, and in fact everyone notice him is the fact that he doesn't have a left arm. Watching him bravely living his life makes me or any curious mind wonder as to how this unfortunate disability be tackled? Indeed advanced co-integrated fields of biology and robotics have shown promising future in prosthetic arms and other organs but still, replicating the "beautiful" sense of touch and feel through a prosthetic arm seems a farfetched dream. So the question as a science devotee and as a human being is that, Can we help these people? If yes, then how? Why can't we grow back organs like lizards do, or can we? These and many other questions regarding regeneration of severed limbs and organs may be answered by the field of regeneration biology.
Regeneration biology deals with studies of renewal, restoration and growth in organism making them resilient to natural fluctuations or events that cause disturbance or damage to the organism. As an organism grows and develops from the zygote, cells divide multiply and differentiate to specialized functioning under guidance of their pre-programmed genome. In general cases as seen in most human cells, differentiated cells get arrested in the stage and cannot be reverted back to progenitor cell. On the other hand organisms like lizard's and starfish's cells, somehow, retain the property of cellular dedifferentiation and re-differentiation. In adult humans this ability of de-differentiation, re-differentiation and regeneration still lingers, as in case of liver cells and adult stem cells. As Elly M. Tanaka (2003) accurately puts it, -"The discovery of somatic stem cells in many locations suggests that adult tissue may have the latent capacity to regenerate". Therefore, scientists all over the globe are studying and researching over simpler organisms to understand this phenomenon. The regeneration experiments of Tremblay (hydras), Reaumur (crustaceans), and Spallanzani (salamanders) set the standard for experimental research and for the intelligent discussion over the topic. A series of experiments conducted in 2004 by scientists Endo, Bryant and Gardiner published an article titled," A stepwise model system for limb regeneration" in which axolotl (a species of Mexican Salamander) provides basic understanding of how the process occurs. In salamanders, regeneration begins when a clump of cells called Blastema forms at the tip of a lost limb. From the blastema comes skin, muscle, bone, blood vessels and neurons, ultimately growing into a limb virtually identical to the old one. In the experiments, series of wounds involving the presence or absence of nerve supply alongside tissue grafts and their responses were studied. Interesting parameters like the"critical size defect" have also been discussed. This research gave a series of steps which are necessary in limb regeneration. It concluded that the presence of a nerve and fibroblast cells at the site of amputation played an important role in generation of a "bump" to "blastema" to the "limb". This ability is something the mankind has dreamt of since the beginning of self consciousness.
When we try to see the picture as a whole with respect to ourselves, a number of intricate problems arise because of the complexity of our biological system and the defence mechanisms of human body. A major setback in our ability to regenerate, the human wound environment is handy in everyday life. Cuts or bruises are easy to heal for our bodies - keeping out infections and preventing diseases. Scar formation and extracellular matrix formation are essential for successful healing, but in turn prevents regeneration. Thus, in an environment where we are much more susceptible to cuts and bruises than losing a limb, it only makes sense that we revert to healing instead of regeneration in response to injury. Growing back say, a severed leg, would require, somehow de-differentiating the cells following their rapid division. Something like cancerous cell growth but with precise control over it! (Difficult but not impossible) But the same checkpoints that stop our cells from growing uncontrollably into tumours might also stop the formation of tissue that will be analogous to blastema tissue in salamanders. One possible way to produce regenerative tissue at human wounds is by the use of genetically modified adult stem cells along with advanced medicine. Transgenic approach to tackle this problem is a potential way around. Indeed this will require intense advancements in the fields of molecular and cell biology because we still lack knowledge of our own DNA and not to mention that the average size of the salamander genome is 10 times larger than ours making the studies even more complicated!
So assessing the current position we are in, we still need advancements in many disciplines but regeneration is not a far-off fiction of sci-fi movies. Our failure thus far lies in creating the correct environment to initiate this fascinating process and understanding more about our own genome. Theoretically we are not far from understanding human regeneration but it still remains a future science because of ethical limitations in our current society. So for now it is just the cool plot of "The Amazing Spiderman" movie.
A stepwise model system for limb regeneration http://www.ncbi.nlm.nih.gov/pubmed/15136146
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A 3rd year biotechnology student understanding the world through the eye of biotechnologist.
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