Leg regeneration in Drosophila abridges the normal developmental program.

Regeneration of lost body parts has traditionally been seen as a redeployment of embryonic development. However, whether regeneration and embryonic development are controlled by identical, similar or different genetic programmes has not been fully tested. Here, we analyse proximal-distal regeneration in Drosophila leg imaginal discs using the expression of positional markers, and by cell-lineage experiments, and we compare it with the pattern already known in normal development. During regeneration, the first proximal-distal positional markers reappear in overlapping patterns. As the regenerate expands, they segregate and further markers appear until the normal pattern is produced, following a proximal to distal sequence that is in fact the reverse of normal leg imaginal disc development. The results of lineage tracing support this interpretation and show that regenerated structures derive from cells near the wound edge. Although leg development and leg regeneration are served by a set of identical genes, the ways their proximal-distal patterns are achieved are distinct from each other. Such differences can result from similar developmental gene interactions acting under different starting conditions.