Sea anemone Frizzled receptors play partially redundant roles in oral-aboral axis patterning.

Canonical Wnt (cWnt) signalling is involved in a plethora of basic developmental processes such as endomesoderm specification, gastrulation and patterning the main body axis. To activate the signal, Wnt ligands form complexes with LRP5/6 and Frizzled receptors, which leads to nuclear translocation of β-catenin and a transcriptional response. In Bilateria, the expression of different Frizzled genes is often partially overlapping, and their functions are known to be redundant in several developmental contexts. Here, we demonstrate that all four Frizzled receptors take part in the cWnt-mediated oral-aboral axis patterning in the cnidarian Nematostella vectensis but show partially redundant functions. However, we do not see evidence for their involvement in the specification of the endoderm - an earlier event likely relying on maternal intracellular β-catenin signalling components. Finally, we demonstrate that the main Wnt ligands crucial for the early oral-aboral patterning are Wnt1, Wnt3 and Wnt4. Comparison of our data with knowledge from other models suggests that distinct but overlapping expression domains and partial functional redundancy of cnidarian and bilaterian Frizzled genes may represent a shared ancestral trait.