Fig. 2

Comparison of the exon/intron structure of genes encoding relaxin/Dilp8-type precursors and Dilp7-type precursors in selected bilaterian species. Schematic representations of the gene structures are shown, with protein-coding exons displayed as rectangles and introns shown as lines (with intron length stated above). The phase of introns is stated at the start of each intron above each diagram. Protein-coding exons are color-coded to show regions that encode the N-terminal signal peptide (blue), the B-chain (pink), monobasic or dibasic cleavage sites (green), the C-chain and other regions of the precursors (black), and the A-chain (orange). The residue numbers of the first and last amino acids are labeled underneath each diagram. A Genes encoding relaxin-type precursors in chordates, the starfish A. cf. solaris and A. rubens (RGP1 and RGP2), the annelid O. fusiformis and D. melanogaster (Dilp8) have a conserved phase 1 intron that interrupts the coding sequence for the C-chain region. B Genes encoding Dilp7-type precursors in the hemichordate S. kowalevskii, the starfish A. cf. solaris and A. rubens, the annelid O. fusiformis, the mollusk C. virensis, and the arthropod D. melanogaster (Dilp7) also have a conserved phase 1 intron that interrupts the coding sequence for the C-chain region, like that found in relaxin/Dilp8-type precursor genes. However, in addition, the Dilp7-type precursor genes have a second intron (phase 2) located between exons that encode the signal peptide and B-chain and this feature distinguishes Dilp7-type precursor genes from relaxin/Dilp8-type precursor genes. Accordingly, unlike in relaxin/Dilp8-type precursors where the B-chain is located immediately after the signal peptide, in Dilp7-type precursors the signal peptide and B-chain are separated by a polypeptide sequence (shown in black). The accession numbers and sequences of precursor proteins included in this figure are listed in Additional file 14: Dataset S7