title: Identification and characterization of a second CD4-like gene in teleost fish.
abstract: In fish, T cell subdivision is not well studied, although CD8 and CD4 homologues have been reported. This study describes a second teleost CD4-like gene, CD4-like 2 (CD4L-2). Two rainbow trout copies of this gene were found, -2a and -2b, encoding molecules sharing 81% aa identity. The 2a/2b duplication may be related to tetraploid ancestry of salmonid fishes. In the Fugu genome CD4L-2 lies head to tail with an earlier reported, very different CD4-like gene [Suetake, H., Araki, K., Suzuki, Y., 2004. Cloning, expression, and characterization of fugu CD4, the first ectothermic animal CD4. Immunogenetics 56, 368-374], which was designated CD4L-1 in the present article. The flanking genes of the Fugu CD4L-1 and CD4L-2 are reminiscent of the genes surrounding CD4 and LAG-3 in mammals. However, neither synteny nor phylogenetic analysis could decide between CD4 and LAG-3 identity for the fish CD4L genes. CD4L-1 and CD4L-2 share a tyrosine protein kinase p56(lck) binding motif in the cytoplasmic tail with CD4 but not with LAG-3. Trout CD4L-2 expression is highest in the thymus, similar to mammalian and chicken CD4, whereas Fugu CD4L-1 expression was highest in the spleen. However, CD4L-2 encodes only two IG-like domains, whereas CD4L-1, CD4 and LAG-3 encode four. The CD4-like genes 1 and 2 in fish apparently went through an evolution different from that of LAG-3 and CD4 in higher vertebrates.
authors.affiliation: Institute for Comprehensive Medical Science, Fujita Health University, Dengakugakubo 1-98, Toyoake, Aichi 470-1192, Japan. dijkstra@fujita-hu.ac.jp
authors.forename: Johannes Martinus
authors.initials: JM
authors.lastname: Dijkstra
authors.forename: Tomonori
authors.initials: T
authors.lastname: Somamoto
authors.forename: Lindsey
authors.initials: L
authors.lastname: Moore
authors.forename: Ivar
authors.initials: I
authors.lastname: Hordvik
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Ototake
authors.forename: Uwe
authors.initials: U
authors.lastname: Fischer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015704:CD4 Antigens / Q000235:genetics*; D019976:Cloning, Organism; D018076:DNA, Complementary / Q000235:genetics; D005796:Genes; D006720:Homozygote; D006801:Humans; D008969:Molecular Sequence Data; D017686:Oncorhynchus mykiss / Q000235:genetics* / Q000276:immunology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D023741:Takifugu / Q000235:genetics*; D023721:Tetraodontiformes / Q000235:genetics; D014714:Vertebrates / Q000235:genetics
chemical_list: D015704:CD4 Antigens; D018076:DNA, Complementary