So here is my speculation of what happens when a salamander attempts to regenerate the lost limb.
First, the missing limb wound place sends a signal requesting macrophages for stem cell generation and subsequent microRNA to rebuild the limb. Alright, macrophages are presented in the salamander's blood stream, and the missing limb might or might not send a signal requesting for the macrophages, but it definitely needs to send a signal requesting for microRNA, that might or might not be presented in the blood stream at that time. Why is it not in the blood stream? Because the microRNA normally required for limb regeneration is not needed in the blood stream.
How does this signal request for microRNA? Well, microRNA is made by RNA Polymerase II, and you need to regulate RNA Polymerase II to produce the microRNA you need for limb regeneration at certain cells. This is a bit broad, you might ask what cell types need to code for the microRNA for wound regeneration, it might be in the head or in the bone, I dunno. Knowing where microRNA is produced could be easier in monitoring microRNA as a whole. So far we only measure its concentration and location. The wound repair mechanism, however, is quite precise, there should be more mechanisms at work here.
Now to reproduce this model in humans, we could forget the signal producing microRNA pathway and inject artificial microRNA of our own and the macrophages requires for stem cell generation at the wound place. Since the human microRNA normally would not code for limb regeneration anyway, I think.
Edited by Fredreload, 08 April 2017 - 12:22 AM.