Authors
F Jarero1; U KoziolP D Olson1; 1 Natural History Museum, London; 2 University of the Republic, Uruguay, Uruguay Discussion
Wnt/Hedgehog signalling in free-living planarians is responsible for mediating head/tail decision making during early development and in regeneration. More broadly, canonical Wnt signalling has been found to underlie AP axis formation in animals generally. We show that AP specification during larval metamorphosis in tapeworms also involves canonical Wnt signalling, with scolex formation taking place at the site(s) of Wnt repression. Moreover, we show that the same system has been co-opted during strobilar development, with segmental boundaries expressing opposing ‘stripes’ of anteriorizing (SFRP) and posteriorizing (Wnt1) signals—tapeworm strobilation therefore being a form of paratomy. Expression of Hedgehog and Hox also appear linked to the system, upstream and downstream of Wnt signaling, mirroring the model of AP signalling in planarians as presently understood. Taken together, we show that parasitic and free-living flatworms share the same underlying AP patterning system despite their highly disparate body plans. 
