Figure 4

Evolutionary analysis of the chordate secretin family members. The maximum likelihood (ML) optimal tree topology is presented and was constructed with Phyml 3.0 [99]. ML bootstrap values higher than 50% are indicated at nodes and to facilitate interpretation a hypothetical root was added to the tree between the PACAP-like and GCG-like clades based upon gene structure evidence and proposed models for secretin family evolution. The different peptide groups are indicated and teleost duplicate genes are marked by a and b; Xenopus GLP1 exons by a, b and c. Accession numbers of the sequences used are described in Table 2 and for human and mouse members are: PHM/VIP (P01282 and P32648); PRP/PACAP (P18509 and O70176); GHRH (P01286 and P16043); GCG/GLPs (P01275 and P55095); GIP (P09681 and P48756); and SCT (P09683 and Q08535), respectively.