title: The immune gene repertoire encoded in the purple sea urchin genome.
abstract: Echinoderms occupy a critical and largely unexplored phylogenetic vantage point from which to infer both the early evolution of bilaterian immunity and the underpinnings of the vertebrate adaptive immune system. Here we present an initial survey of the purple sea urchin genome for genes associated with immunity. An elaborate repertoire of potential immune receptors, regulators and effectors is present, including unprecedented expansions of innate pathogen recognition genes. These include a diverse array of 222 Toll-like receptor (TLR) genes and a coordinate expansion of directly associated signaling adaptors. Notably, a subset of sea urchin TLR genes encodes receptors with structural characteristics previously identified only in protostomes. A similarly expanded set of 203 NOD/NALP-like cytoplasmic recognition proteins is present. These genes have previously been identified only in vertebrates where they are represented in much lower numbers. Genes that mediate the alternative and lectin complement pathways are described, while gene homologues of the terminal pathway are not present. We have also identified several homologues of genes that function in jawed vertebrate adaptive immunity. The most striking of these is a gene cluster with similarity to the jawed vertebrate Recombination Activating Genes 1 and 2 (RAG1/2). Sea urchins are long-lived, complex organisms and these findings reveal an innate immune system of unprecedented complexity. Whether the presumably intense selective processes that molded these gene families also gave rise to novel immune mechanisms akin to adaptive systems remains to be seen. The genome sequence provides immediate opportunities to apply the advantages of the sea urchin model toward problems in developmental and evolutionary immunobiology.
authors.affiliation: Sunnybrook Research Institute and Department of Medical Biophysics, University of Toronto, 2075 Bayview Ave., Room S-126b, Toronto, Ontario, Canada M4N 3M5.
authors.forename: Taku
authors.initials: T
authors.lastname: Hibino
authors.forename: Mariano
authors.initials: M
authors.lastname: Loza-Coll
authors.forename: Cynthia
authors.initials: C
authors.lastname: Messier
authors.forename: Audrey J
authors.initials: AJ
authors.lastname: Majeske
authors.forename: Avis H
authors.initials: AH
authors.lastname: Cohen
authors.forename: David P
authors.initials: DP
authors.lastname: Terwilliger
authors.forename: Katherine M
authors.initials: KM
authors.lastname: Buckley
authors.forename: Virginia
authors.initials: V
authors.lastname: Brockton
authors.forename: Sham V
authors.initials: SV
authors.lastname: Nair
authors.forename: Kevin
authors.initials: K
authors.lastname: Berney
authors.forename: Sebastian D
authors.initials: SD
authors.lastname: Fugmann
authors.forename: Michele K
authors.initials: MK
authors.lastname: Anderson
authors.forename: Zeev
authors.initials: Z
authors.lastname: Pancer
authors.forename: R Andrew
authors.initials: RA
authors.lastname: Cameron
authors.forename: L Courtney
authors.initials: LC
authors.lastname: Smith
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Rast
mesh_terms: D000818:Animals; D003165:Complement System Proteins / Q000235:genetics; D016207:Cytokines / Q000235:genetics; D016678:Genome; D007109:Immunity / Q000235:genetics*; D010802:Phylogeny; D051116:Receptors, Scavenger / Q000235:genetics; D012617:Sea Urchins / Q000145:classification / Q000235:genetics* / Q000276:immunology*; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D014714:Vertebrates / Q000276:immunology
chemical_list: D016207:Cytokines; D051116:Receptors, Scavenger; D003165:Complement System Proteins