Discovery of α-defensins in basal mammals

α-Defensins are essential molecules of the innate immune system that have broad spectrum antimicrobial activity against a range of bacteria and viruses. To date, α-defensins have only been identified in the Euarchontoglires branch of the mammals. This has led to speculation that α-defensins may be specific to this group, a somewhat surprising finding, given their importance in the immune system. The mammalian genome project provided us with the opportunity to search for α-defensins in previously unexamined mammalian superorders. Using hidden Markov model (HMM) profile searching, we report the discovery of α-defensins in the African savanna elephant, the lesser hedgehog tenrec, and the nine-banded armadillo genomes representing two of the most basal mammalian superorders, Afrotheria and Xenarthra. Furthermore, we identify an α-defensin-like gene in the gray short-tailed opossum, suggesting that α-defensins may have evolved much earlier than previously thought, before the divergence of placental mammals and marsupials approximately 130 mya.