Path followed:
- Is the fault in the components that perform any physical action?
Answer: Yes
- Is the fault in components that move?
Answer: Yes
- Is the fault in components that make the mechanism move?
Answer: Yes
- Is the faulty component designed to move the mechanism around?
Answer: No
- Is the faulty component a joint?
Answer: No
- Is the faulty component needed for stability?
Answer: No
- Do the characteristics of the system change after regeneration?
Answer: No
1) Mexican Axolotl, Ambystoma mexicanum
The Mexican Axolotl is a salamander in the amphibian class. It can live 10 to 15 years in the wild but are considered endangered due to the water pollution, trading business, and being a food delicacy in Mexico (“Mexican Axolotls”). The Axolotl has a great ability of regenerating its limbs as true limbs, muscles, and differentiated cells, not as scar tissues.
After the limb is amputated a plasma clot forms and the epidermal cells from the stump migrate to cover the wound surface and form the obligatory wound epidermis. This layer continues to reproduce and forms the apical ectodermal cap. The cells under the apical ectodermal cap undergo dedifferentiation and genes that express differentiated tissues, such as MRF4 and myf5, are down-regulated and msxI, proliferating progress zone, is up-regulated (Gilbert). The undifferentiated cells beneath the apical ectodermal cap are called the regeneration blastema. These cells will multiply and differentiate into the structures of the limb by PAX7+ cells, which are regulated by TGF-beta1. Down-regulation of p53 is essential to form the blastema, and later on in the healing process up-regulation is needed for re-differentiation of the cells (Yun et al.). A major difference James W. Godwin found in Axolotl regrowth compared to mammalian healing is that the presence of macrophages and pro-inflammatory and anti-inflammatory cytokine signals in the blastema within hours of the amputation are required to stimulate and sustain regeneration. This allows for no tissue scarring and perfect regrowth of the limb.
“Mexican Axolotls.” National Geographic. National Geographic, n.d. Web. 05 Nov. 2014.
http://animals.nationalgeographic.com/animals/amphibians/axolotl/
Gilbert, Scott F. “Regeneration.” Regeneration. U.S. National Library of Medicine, 18 Dec. 2000. Web. 05 Nov. 2014.
http://www.ncbi.nlm.nih.gov/books/NBK9971/
Godwin, J. W., A. R. Pinto, and N. A. Rosenthal. “Macrophages Are Required for Adult Salamander Limb Regeneration.” Proceedings of the National Academy of Sciences 110.23 (2013): 9415-420.Proceedings of the National Academy of Sciences. Web. 5 Nov. 2014.
http://www.pnas.org/content/110/23/9415.full
Yun, Maximina H., Phillip B. Gates, and Jeremy P. Brockes. “Regulation of P53 Is Critical for Vertebrate Limb Regeneration.” Proceedings of the National Academy of Sciences 110.43 (2013): 17392-7397.Proceedings of the National Academy of Sciences of the United States of America. Web. 5 Nov. 2014.