By: Dr. Andrew J. Rochman
Regeneration has been a fascinating and intriguing subject for scientists for a long time. Regeneration can be simply described as the rebuilding of tissues as a way to heal themselves after injury. It occurs rapidly in young human tissue but the process appears to slow down with the advancement of age. However, some animals are known for their regenerative capabilities such as frogs and salamanders, and research is underway to comprehend the underlying mechanism of regeneration so that it may be used as a form of therapy in the future.
While mammals may be limited in their ability to regenerate, other organisms such as amphibians, planarians (flat worms) and fish are known for their regeneration capability. These organisms have the astonishing ability to regenerate adult tissue completely by rapid cell proliferation. The key to their ability to regenerate tissue is in the stem cells’ proliferation and action during injury (EuroStemCell, 2014).
Regeneration of Tissues in Amphibians
Regeneration in amphibians happens at a truly impressive scale: they are able to regenerate a variety of body parts, such as upper and lower jaw, lens, retina, limb, tail, spinal cord, and intestine. This happens by the initial formation of a blastema, a mass of undifferentiated stem cells. These stem cells gather at the site of injury and differentiate to form specialized cells of the body. An important area of research is related to finding out how the blastema is formed and what cells contribute to making it. The results of an experiment show that amphibian cells from the connective tissues, muscles and neural sheath migrate and give rise to the formation of blastema (Stembook.org, 2014).
Regeneration in Planarians
Planarians also possess astonishing abilities to regenerate their different organs. A common example is that of a flat worm: when it is cut in half, each part can generate itself into a complete organism (Media.hhmi.org, 2014). Regeneration in planarians occurs by employing a type of adult stem cells known as neoblasts. Neoblasts have a large nucleus and are thought to be the only cells responsible for regeneration in adult planarian population. Experiments show that when neoblast functions are lost, it results in complete fragmentation of the organism (Stembook.org, 2014).
Regeneration in Zebra fish
Zebra fish also possess powerful regeneration abilities and are capable of regenerating retina, fins, and heart, among other tissues of the body. Zebrafish are known to have a reservoir of progenitor cells, and fish appendages are composed of many rays, each of which give rise to blastema. Wound healing occurs by the formation of a mass formed by the migration of epithelial cells that help to cover the wound site, and allow mesenchymal stem cells to gather at the site of injury and differentiate into the required type of cells. With the passage of time, the wound is healed and the stem cells from the blastema take on the role of different types of cells to carry out various functions of the body (Stembook.org, 2014).
EuroStemCell, (2014). Regeneration: what does it mean and how does it work?. [online] Available at: http://www.eurostemcell.org/factsheet/regeneration-what-does-it-mean-and-how-does-it-work [Accessed 16 May. 2014].
Stembook.org, (2014). Stem cells in animal models of regeneration | StemBook. [online] Available at: http://www.stembook.org/node/533 [Accessed 16 May. 2014].
Media.hhmi.org, (2014). HHMI's BioInteractive - Click and Learn - Tissue Regeneration in Animals. [online] Available at: http://media.hhmi.org/biointeractive/click/Regeneration/06.html [Accessed 16 May. 2014].