Localization of planarian β-CATENIN-1 reveals multiple roles during anterior-posterior regeneration and organogenesis.

The βcatenin-dependent Wnt pathway exerts multiple context-dependent roles in embryonic and adult tissues. In planarians, βcatenin-1 is thought to specify posterior identities through the generation of an anteroposterior gradient. However, the existence of such gradient has not been directly demonstrated. Here, we use a specific polyclonal antibody to demonstrate that nuclear βCATENIN-1 exists as an anteroposterior gradient from the pre-pharyngeal region to the tail of the planarian Schmidtea polychroa . High levels in the posterior region steadily decrease towards the pre-pharyngeal region but then increase again in the head region. During regeneration, βCATENIN-1 is nuclearized in both anterior and posterior blastemas, but the canonical wnt1 ligand only influences posterior nuclearization. Additionally, βcatenin-1 is required for proper anterior morphogenesis, consistent with the high levels of nuclear βCATENIN-1 observed in this region. We further demonstrate that βCATENIN-1 is abundant in developing and differentiated organs, and is particularly required for the specification of the germ-line. Altogether, our findings provide the first direct evidence of an anteroposterior nuclear βCATENIN-1 gradient in adult planarians, and uncover novel, context-dependent roles for βcatenin-1 during anterior regeneration and organogenesis.