ABSTRACT
A regeneration-competent organism, such as a salamander, faces many of the same challenges as an early developing embryo. Assuming it can generate a pool of cells capable of reproducing and differentiating into different cell types (in other words, stem cells), these cells still need instructions to produce a functional tissue, organ, or appendage. Morphogens (form producers) are a set of diffusible molecules that act during an early embryonic development to direct the development of cells along different fates by establishing gradients across fields of cells. During development, these morphogens only need to travel short distances, because the embryo is small. However, to regenerate a complex appendage such as an adult limb, re-creation of these patterning mechanisms would require significant scaling up of the system to cover the much larger distances involved. Recent research on morphogen scale regulation is leading to the development of better mathematical models, and new strategies for engineering experimental regeneration are emerging from this synthesis.
