Regeneration is initiated by wounding, but it is unclear how injury-induced signals precisely convey the identity of the tissues requiring replacement. In the planarian Schmidtea mediterranea, the first event in head regeneration is the asymmetric activation of the Wnt inhibitor notum in longitudinal body-wall muscle cells, preferentially at anterior-facing versus posterior-facing wound sites. However, the mechanism driving this early symmetry-breaking event is unknown. We identify a noncanonical Wnt11 and Dishevelled pathway regulating notum polarization, which opposes injury-induced notum-activating Wnt/β-catenin signals and regulates muscle orientation. Using expression analysis and experiments to define a critical time of action, we demonstrate that Wnt11 and Dishevelled signals act prior to injury and in a growth-dependent manner to orient the polarization of notum induced by wounding. In turn, injury-induced notum dictates polarization used in the next round of regeneration. These results identify a self-reinforcing feedback system driving the polarization of blastema outgrowth and indicate that regeneration uses pre-existing tissue information to determine the outcome of wound-induced signals.
Keywords: Dishevelled; Wnt; Wnt11; blastema; injury signaling; muscle; notum; planaria; polarity; regeneration.
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