Fig. 1

Phylogenetic relationships and conserved protein domains of Pdu-Tcf. a Phylogenetic analysis of Pdu-Tcf protein (shaded in yellow) sequence with top BLAST hits from selected organisms. The tree reveals that Pdu-Tcf clusters together with another polychaete Perinereis nuntia Tcf to the spiralian lineage of bilaterian Tcf sequences and is most similar to Tcf7l2 from the taxa where more Tcf genes are present. Protein sequences from taxa where we did not detect a β-catenin binding domain in addition to a HMG DNA binding domain using Pfam [63, 98], though their function as Tcfs was sometimes verified experimentally (e.g. Caenorhabditis elegans POP-1), were excluded from the analysis. The higher-order taxa are indicated on the right; Amb. = Ambulacraria. The tree with the highest log likelihood (− 6465.74) is shown. The percentage of trees in which the associated taxa clustered together is shown next to the branches. The tree is drawn to scale, with branch lengths measured in the number of substitutions per site. b Alignment of Pdu-Tcf with Tcf proteins known from other taxa shows the conservation of core domains necessary for Tcf function—N-terminal β-catenin binding domain, GBS—Groucho binding sequence, HMG box DNA binding domain with basic tail and the C-terminal C-clamp accessory DNA binding domain, characterised by the presence of the CRARF(Y) amino acid sequence. Asterisks denote conserved acidic amino acid residues within the β-catenin binding domain and cysteines within the C-clamp domains. Sequences which were incomplete (P. nuntia and L. polyphemus for HMG domain) or lacked the domain (Xenopus laevis for C-clamp) were excluded from the alignment. The extent of highlighted domains corresponds to those used previously by others [16, 21]