Regeneration (biology)
From Freepedia
Regeneration is the ability to restore lost or damaged tissues, organs or limbs. It is a common feature in invertebrates, but far more limited in most vertebrates. Nevertheless, even humans possess some degree of regeneration ability. Children under 6 years of age are capable of regenerating lost fingertips and the human liver retains its ability to regenerate throughout a person's lifetime.
Aside from being used to generally describe any number of specific healing processes, regeneration also is a specific method of healing that is noted for its ability to regrow lost limbs, severed nerve connections, and other wounds. This is present in some animals such as the newt, hydra, and a type of mouse. [1] [2]. With the exception of the MRL mice, mammals do not in general have the ability to regenerate. If the processes behind regeneration are fully understood, it is believed this would lead to better treatment for individuals with nerve injuries, broken backs, paralysis, and missing limbs.
Regeneration of a lost limb occurs in two major steps, first de-differentiation of adult cells into a stem cell state similar to embryonic cells and second, development of these cells into new tissue more or less the same way it developed the first time. Some animals like planarians instead keep clusters of non-differentiated cells within their bodies, which migrate to the parts of the body that need healing.
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Regeneration in salamanders
In urodeles (or salamanders), the regeneration process begins immediately after amputation. Limb regeneration in the axolotl has been extensively studied. After amputation, epidermis covers the stump within 24 hours, forming a structure called the apical epidermal crest (AEC). This results in the formation of a blastema (or a layer of dedifferentiated cells). At the same time, pattern formation genes – such as HoxA and HoxD – are activated as they were when the limb was formed in the embryo. Distal structures such as toes form first from the blastema. Intermediate layers are filled in afterwards. Motor neurons grow with the regenerated limb, and innervate the same target muscles they originally controlled. The entire process takes around three months in the adult and then the limb becomes fully functional.
Regeneration in MRL mice
MRL mice is a strain of mice that have been found to have a regenerative ability that in some cases rival urodele regeneration. Since this mice strain demonstrate that mammals possibly can regenerate, it is thought that humans also might have an innate regenerative ability that might be able to activate.
By comparing the differential gene expression of scarless healing MRL mice and poor healing C57BL/6 mice strain, 36 genes have been identified that are good candidates for studying how the healing process differs in MRL mice and other mice.[1]
The regenerative abilities of MRL mice does however not protect against myocardial infarction. MRL mice show the same amount of cardiac injury and scar formation as normal mice after a heart attack.[2]
External links
References
- Biochem Biophys Res Commun. 2005 Apr 29;330(1):117-22. PMID 15781240
- Wound Repair Regen. 2005 Mar-Apr;13(2):205-8. PMID 15828946
- Tanaka EM. Cell differentiation and cell fate during urodele tail and limb regeneration. Curr Opin Genet Dev. 2003 Oct;13(5):497-501. PMID 14550415
- Nye HL, Cameron JA, Chernoff EA, Stocum DL. Regeneration of the urodele limb: a review. Dev Dyn. 2003 Feb;226(2):280-94. PMID 12557206
