Evolutional relationship between trappin-18 and WFDC12. (A) Schematic illustration of conserved synteny around trappin(s). Illustrations of human, mouse, rat, and dog loci were generated based on the works by Clauss et al.  and Hurle et al. . Black and gray arrows indicate genes and pseudo genes, respectively. KCNS, potassium voltage-gated channel, member 1 (B) The WAP domains of WFDC12 and the WFDC12-like peptide encoded by intron 1 region of trappin-18. Conserved and semiconserved residues are indicated by light gray. Eight conserved Cys residues constituting the WAP motif signature sequence are shaded in black. (C) Harr plot analyses of the hyrax trappin-18 in comparison with the hyrax trappin-2 and human WFDC12. (D) Harr plot analyses of the elephant trappin-18 in comparison with the elephant trappin-2 and human WFDC12. Exons are indicated by boxes. WAP-coding regions are represented by black boxes. Black circles indicate regions encoding WFDC12 like peptide.