Figure 2.

This figure illustrates the ways in which activity from the mTOR signaling pathway contributes to appendage (a) or muscle regeneration (b,c): (a) Concerning appendage regeneration, the Wnt/β-catenin pathway and insulin-like growth factor (IGF-1) activate mTORC1. This activity leads to the wound covering, blastema formation and regenerative outgrowth of the appendage. (b) During muscle regeneration, mTORC1 activity is necessary for myofiber growth but not myogenesis. mTORC1 inhibition by rapamycin treatment inhibits regeneration whereas the leucine amino acid, insulin-like growth factor 1 or Akt activity contribute to mTORC1-mediated muscle regeneration. SPAR regulatory protein (small regulatory polypeptide of amino acid response) can inhibit mTORC1 activity and hinder muscle regeneration. (c) mTORC1 signaling is necessary for muscle regeneration in the injured limb and to induce a G_alert state in the contralateral limb. The G_alert cells enter the cell cycle more rapidly and show an increase in size compared to quiescent satellite cells.