title: Prediction of the prototype of the human Toll-like receptor gene family from the pufferfish, Fugu rubripes, genome.
abstract: The insect Toll family of proteins and their mammalian counterparts seemingly shared one common ancestor and evolved independently. Here we demonstrated that the prototype of the mammalian-type (M-type) Toll family is shared by the fish and humans. According to the draft of the pufferfish Fugu genome project, the signature Toll-IL-1 receptor homology domain (TIR domain) has been conserved during evolution. FuguTLR2, 3, 5, 7, 8 and 9 members correspond structurally to respective mammalian TLRs. One Fugu TLR showed equally high amino acid identity to human TLR1, 6 and 10, and we named it FuguTLR1. Fugu rubripes has genes for TLR21 and 22, which are unique to fish. One possible interpretation of these findings is that TLR1, 2, 3, 4, 5, 7, 8, 9, 21 and 22 existed in the ancestral genome common to fish and mammals, and that TLR4 was lost in the fish lineage, while TLR21 and 22 were lost in the mammalian lineage. Strikingly, a solitary ascidian, Halocynthia roretzi, has only a few Toll-like proteins, which, like Caenorhabditis elegans Toll, represent primitive ones before the expansion of the Toll family. Therefore, the expansion of TLR genes should have occurred earlier than fish, but not C. intestinalis, separated evolutionarily from mammals. These results infer that the appearance of the M-type innate system was completed before or concomitant with the appearance of acquired immunity. We interpret the present data to mean that the differences of TLRs identified in this study between fishes and humans may be rather peripheral, partially due to selection pressure exerted by pathogens in distinct environments.
authors.affiliation: Department of Immunology, Osaka Medical Center for Cancer and Cardiovascular Diseases, Higashinari-ku, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Oshiumi
authors.forename: Tadayuki
authors.initials: T
authors.lastname: Tsujita
authors.forename: Kyoko
authors.initials: K
authors.lastname: Shida
authors.forename: Misako
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Kazuho
authors.initials: K
authors.lastname: Ikeo
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Seya
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D015870:Gene Expression; D006801:Humans; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics* / Q000276:immunology; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D023741:Takifugu / Q000235:genetics* / Q000276:immunology*; D051194:Toll-Like Receptor 1; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors
chemical_list: D029721:Drosophila Proteins; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; C495345:TLR4 protein, human; D051194:Toll-Like Receptor 1; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D004247:DNA