Figure 3. Phases of Parhyale leg regeneration.
Three phases of regeneration are defined based on distinct cellular events and behaviours observed by live imaging (see text). Immediately after amputation, haemocytes adhere to the wound surface and close the wound (phase 1). In the hours that follow, a melanized scab (shown in brown) forms at the site of the wound, surrounding the haemocytes (early phase 2). The leg epithelium (depicted as a thin line surrounding the leg) then closes over the wound, under the surface of the melanized scab. Muscles (shown in red) at the distal part of the limb stump usually detach and degenerate, while those in proximal parts remain intact. During phase 2 we observe very limited or no cell proliferation. Phase 3 is marked by the onset of extensive cell proliferation and cell movements, leading to extensive growth and morphogenesis. This phase results in the formation of an elongated and patterned leg primordium within the amputated limb stump. Mesodermal cells, haemocytes and macrophages (shown in red), as well as nerves (in blue), are present in the inner spaces of the leg stump throughout the regenerative process.