Fig. 7.

Model for the role of teashirt in planarian head-tail regeneration. A developmental pathway for the initiation of head versus tail regeneration. wnt1 is activated by wounding and, through Wnt signaling, activates teashirt. During anterior regeneration, notum inhibits Wnt signaling (later notum roles are not the focus of this model). During initiation of posterior regeneration, teashirt helps promote the expression of posterior position control genes (PCGs) (such as wntP-2) and inhibit the expression of anterior PCGs to give a tail regeneration signature. It is unknown whether these effects (depicted by black arrows) reflect direct action. Gray arrows indicate that it is unknown whether all action of β-catenin-1 will involve teashirt.