Fig. 5

Phylogenetic and structural analyses of He-otd. a A phylogeny of PRD class homeobox genes based on analyses of the homeodomain. The full PRD class phylogeny is shown in Additional file 6: Fig. S2. The names of different PRD families—based on Ryan et al. [67]—are shown in large bold text. Maximum likelihood tree topology is shown. Bootstrap support values, based on 500 replicates, are shown above branches. Posterior probabilities, based on a Bayesian analysis, are shown below branches. The branch leading to He-OTD and its name are colored orange. The names of other PRD class homeobox genes from H. exemplaris are colored red. The OTX clade (boxed) is enlarged in A′. b Structure of the He-otd gene in the genome. Relative to the sense strand, 5′ is to the left. Thick lines represent exonic regions. Black = UTR. Orange = position of sequence that codes for the homeodomain. Gray = all other coding sequence. Thin black lines represent intronic regions. The numbers represent nucleotide positions (see Additional file 1: Table S1). c Structure of the He-OTD protein. The N-terminus is to the left. The region that corresponds to the homeodomain is colored orange. All other protein sequences are colored gray. Numbers represent amino acid positions (see Additional file 1: Table S1). Dm, Drosophila melanogaster; He, Hypsibius exemplaris; Hs, Homo sapiens; Lottia gigantea; Mm, Mus musculus; Sp, Strongylocentrotus purpuratus