Notch signaling mediates between two pattern-forming processes during head regeneration in .

head regeneration consists of hypostome/organizer and tentacle development, and involves Notch and Wnt/β-catenin signaling. Notch inhibition blocks hypostome/organizer regeneration, but not the appearance of the tentacle tissue. β-Catenin inhibition blocks tentacle, but not hypostome/organizer regeneration. Gene expression analyses during head regeneration revealed the Notch-promoting expression of , , and the transcriptional repressor genes , , and , while blocking and the -related gene β-Catenin promotes the expression of the tentacle specification factor , but not of This suggests and as parts of a hypostome/organizer gene module, and , , and as parts of a tentacle gene module. Notch then functions as an inhibitor of tentacle production to allow regeneration of a hypostome/head organizer. is a candidate target gene for HvNotch-induced repressor genes. Inhibiting HyKayak attenuated the expression of Polyps of do not have tentacles and thus after head removal only regenerate a hypostome structure. Notch signaling was not needed for head regeneration in , corroborating the idea of its requirement during head regeneration to harmonize two co-operating pattern-forming processes.