| Summary: | <p>Abstract</p> <p>Background</p> <p>Trappin is a multifunctional host-defense peptide that has antiproteolytic, antiinflammatory, and antimicrobial activities. The numbers and compositions of <it>trappin </it>paralogs vary among mammalian species: human and sheep have a single <it>trappin-2 </it>gene; mouse and rat have no <it>trappin </it>gene; pig and cow have multiple <it>trappin </it>genes; and guinea pig has a <it>trappin </it>gene and two other derivativegenes. Independent duplications of <it>trappin </it>genes in pig and cow were observed recently after the species were separated. To determine whether these <it>trappin </it>gene duplications are restricted only to certain mammalian lineages, we analyzed recently-developed genome databases for the presence of duplicate <it>trappin </it>genes.</p> <p>Results</p> <p>The database analyses revealed that: 1) duplicated <it>trappin </it>multigenes were found recently in the nine-banded armadillo; 2) duplicated two <it>trappin </it>genes had been found in the Afrotherian species (elephant, tenrec, and hyrax) since ancient days; 3) a single <it>trappin-2 </it>gene was found in various eutherians species; and 4) no typical <it>trappin </it>gene has been found in chicken, zebra finch, and opossum. Bayesian analysis estimated the date of the duplication of <it>trappin </it>genes in the Afrotheria, guinea pig, armadillo, cow, and pig to be 244, 35, 11, 13, and 3 million-years ago, respectively. The coding regions of <it>trappin </it>multigenes of almadillo, bovine, and pig evolved much faster than the noncoding exons, introns, and the flanking regions, showing that these genes have undergone accelerated evolution, and positive Darwinian selection was observed in pig-specific <it>trappin </it>paralogs.</p> <p>Conclusion</p> <p>These results suggest that trappin is an eutherian-specific molecule and eutherian genomes have the potential to form <it>trappin </it>multigenes.</p>
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