Discuss how model organisms have been useful in understanding named aspects of regenerative biology and/or regenerative medicine.

A model organism is a non-human species that is studied to understand biological phenomena. They are used when human experiments are difficult or unethical. One of the model organisms that was the focus of regenerative medicine for a long time was axolotl, one of the urodele amphibian species. Their capacity to completely regenerate their limbs has shown that it is possible for an organism to completely regenerate after quite significant damage. For the most past after most injuries humans scar producing fibroblasts rather than all the different cells that a healed limb would need, however the axolotl has shown that whole limb regeneration is indeed possible in a living organism. This shows that model organisms can be useful in understanding the extent of nature’s ability to regenerate.However the issue with amphibians like axolotl is that it is rather poorly genetically related to humans. It functions very differently from humans. For example its much simpler immune system may be part of the reason why its regeneration is so effective as an inflammatory response often inhibits the regeneration process. In order to study the regenerative response in people it is necessary to look at organisms closer to ourselves, for example mice. Mice have been extremely useful in regenerative biology studies as their immune response is very similar to that of humans and thus their healing process is more or less comparable. An example of discovery that was made thanks to mice models was the existence of a Galert state. This is the state stem cells are in when an adjacent tissue becomes injured. It was first observed during regeneration studies where a mouse had its leg injured and the other leg was meant to be used as a control. However cells in the uninjured leg showed a reduced delay for entrance into the cell cycle. SCs in a muscle contralateral to the muscle which was injured (contralateral satellite cells, CSCs) responded to that distant injury and had cycling properties that were different from those in a non-injured animal (quiescent satellite cells, QSCs) and from the injured tissue (activated satellite cells, ASCs). This was only discovered thanks to the careful characterisation of mouse models. Animal models are also easier to study for longer periods of time. For example its difficult to study age based repair in humans as often it happens over extremely extended periods of time. In those periods of time they will often move to different areas or lose contact with the study, making them unavailable for follow up. It is also difficult to maintain people in a controlled environment as even within the same city different areas will have different air quality different risks associated with them, within the a couple of weeks humans may completely change their diet. The issue with human models in general is that they are difficult to control and due to ethical constrains often not easy to carry out tests on. Model organisms not only allow us to carry out more invasive test but also allow observation in a fully controlled environment. Of course an uncontrolled environment is the most accurate but it is important to understand the mechanism before we evaluate how it is affected by the environment