Fig. 4

Structure and chromosomal location of genes encoding candidate ligands for A. rubens kisspeptin-type receptors. A Comparison of the exon/intron structure of genes encoding precursors of candidate ligands for kisspeptin-type receptors in A. rubens (Ar) and genes encoding kisspeptin-type precursors in Homo sapiens (Hs), Xenopus tropicalis (Xt), and Lepisosteus oculatus (Lo). Exons are shown as rectangles, with non-coding regions white and protein-coding regions black or colored (regions encoding the N-terminal signal peptide, neuropeptides and predicted monobasic/dibasic cleavage sites are shown in blue, red, and green, respectively). Introns are shown as lines, with length underneath. The presence of a phase 1 intron interrupting the coding sequence between exons encoding the N-terminal signal peptide and one or more neuropeptides is a feature that is conserved between the A. rubens KPP1 gene and vertebrate kisspeptin precursor genes, providing evidence of orthology, whereas ArKPP2 is encoded by a single exon. The presence of an intron that interrupts the coding sequence between an exon encoding the N-terminal signal peptide and an exon encoding multiple neuropeptides is also a feature of the two A. rubens SALMFamide precursor genes, but this is a phase 0 intron. The presence and position of introns shown here in A. rubens neuropeptide precursor genes are conserved in orthologs in other echinoderm species (see Additional file 17). The accession numbers for the sequences of the precursors shown in this figure are listed in Additional file 17. B Diagram showing the chromosomal locations of four genes encoding precursors of candidate ligands for kisspeptin-type receptors in A. rubens: ArKPP1, ArKPP2, ArL-SALMFaP, and ArF-SALMFaP. Genes encoding ArKPP1 and ArKPP2 are located on chromosome 22 and genes encoding ArL-SALMFaP and ArF-SALMFaP are located on chromosome 13, indicating that these are two pairs of paralogous genes that originated by gene duplication and intrachromosomal translocation