Comparison between Regeneration and Embryonic Development
By now you must have realized that the procedures of regeneration and embryonic development have several fundamental similarities. Both need an external stimulus to 'begin; it is the penetration of the sperm into the egg (fertilization) in the case of embryogenesis and injury (accidental or intentional) in the case of regeneration. Both of the phenomena involve basically identical cellular activities involving cell division, cell movements, tissue interactions, morphogenesis, histogenesis, induction, progressive determination, cytodifferentiation and growth.
Though, there are significant differences between regeneration and embryonic development. Regeneration in multicellular animals does not start from a totipotent single egg cell but from a group of cells recruited from the tissues of the functioning body of an organism. These cells might be derived by dedifferentiation of already differentiated cells of several tissues of the residual part of the body or organ, or mobilized from a few reserve of undifferentiated cells, if any such reserve is maintained by the organism for utilize in emergency. Cells participating in regeneration may not be even pluripotent if no reserve of undifferentiated cells is obtainable. Regeneration may include initial growth by proliferation of these cells to form a bud or blastema, or it may include remodelling of the lost parts by cells of existing tissues or reserves without including proliferation.
Furthermore, the process of regeneration is influenced by the systemic factors (nerves, hormones) and physiological conditions of the organism, while embryonic development is free from such influences. At a fundamental level both regeneration and embryonic development are epigenetic processes, including gene expression and programming. The information of regenerative processes can, therefore, be very rewarding for a better understanding of the developmental processes during embryogenesis. Regeneration studies help in answering the following questions among others. How stable is the differentiated state of a cell? Are any or all differentiated cells able of dedifferentiating and then re-differentiating in a new pathway (metaplasia)? Or do differentiated cells fluctuate only between an overtly differentiated phenotype and a dedifferentiated but determined state (modulation)? Do cells throughout embryonic development get irreversibly committed into germinal or somatic cell lines? Is there any interaction between several tissues or organs of an adult leading to maintenance of their integrity or size.