FIGURE 1.

Current evolutionary model for Secretin peptide family members. The exons of the peptide coding region are represented. PACAP-like family members are proposed to have evolved from a common ancestor exon early in the chordate radiation via exon and gene/chromosome duplication events (Sherwood et al., 2000; Cardoso et al., 2007a, 2010; Ng et al., 2012; Hwang et al., 2013). The same ancestral molecule is also suggested to originate the glucagon(GCG)-like peptides but for simplicity this is not represented in the figure. Boxes represent exons and lines introns and the peptide coding exons are indicated by the peptide abbreviation. Dashed lines indicate undefined evolutionary pathways. PACAP and PRP and VIP and PHI share the same gene precursor and GHRH and SCT are encoded by a single exon. The predicted position of each gene block in the Gnathostome Ancestral Genome (GAC) linkage groups are indicated (Hwang et al., 2013). The genome tetraploidization events (1R and 2R) are represented.