RESUMO
The transmembrane signaling subunits (TSSs) bearing the immunoreceptor tyrosine-based activation motif (ITAM) play a crucial role in triggering the effector functions of mammalian leukocytes. The involvement in key immune reactions and obvious extension through duplication events make TSSs valuable markers of the evolution of the immune system. We surveyed the genomic sequences of the teleostean fish Fugu rubripes for the presence of genes encoding these accessory molecules. Automatic gene prediction was not efficient because of the poor ability of the programs used to recognize the short exons encoding the intracellular regions of TSSs. However, the unique compactness of the Fugu genome and the conservation of the exon/intron arrangements of the TSS genes facilitated their recognition by visual inspection of the candidate genomic sequences. Evidence for the presence of the CD3epsilon, CD3gamma/delta, CD79a, CD79b, TCRzeta, FcRgamma, DAP12 and DAP10 genes in the Fugu genome was obtained. Furthermore, conserved synteny for the short regions including the TSS genes was revealed by comparison of the Fugu and human genomes. The data demonstrate that the set of TSSs arose before the teleost-tetrapod split and provide a starting point for experimental investigation of the molecular evolution of the leukocyte-activating receptor complexes from fish species to mammals.
Assuntos
Antígenos CD/genética , Complexo CD3/genética , Proteínas de Membrana/genética , Receptores de Antígenos de Linfócitos B/genética , Receptores Imunológicos/genética , Takifugu/genética , Sequência de Aminoácidos , Animais , Antígenos CD/metabolismo , Complexo CD3/metabolismo , Antígenos CD79 , Biologia Computacional , Proteínas de Membrana/metabolismo , Dados de Sequência Molecular , Estrutura Terciária de Proteína , Receptores de Antígenos de Linfócitos B/metabolismo , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T/metabolismo , Receptores Imunológicos/metabolismo , Takifugu/metabolismoRESUMO
The genes encoding FcRgamma and TCRzeta homologs were identified using a bioinformatic approach in the amphibian Xenopus laevis. Deduced amino acid sequence of Xenopus TCRzeta is highly similar to the mammalian and avian counterparts, whereas that of FcRgamma differs by the presence of an additional ITAM-like motif. The presence of the negatively charged residue in the transmembrane regions of both subunits suggests their ability to serve as signal transducing modules in complex with activating receptors. The short extracellular regions contain characteristic cysteine residues responsible for dimerization in the mammalian subunits. According to Southern blot analysis, Xenopus laevis may possess two non-allelic genes for each subunit. Northern blots revealed FcRgamma transcripts of two sizes differentially expressed in thymus, spleen, intestine, liver and kidney. TCRzeta mRNA was predominantly expressed in the thymus and spleen. These data indicate that the amphibian immune system employs activating receptor complexes arranged in a mammalian-like way.
Assuntos
Proteínas de Membrana/genética , Receptores de Antígenos de Linfócitos T/genética , Receptores de IgG/genética , Homologia de Sequência de Aminoácidos , Xenopus laevis/imunologia , Sequência de Aminoácidos , Animais , Northern Blotting , Southern Blotting , Expressão Gênica/imunologia , Humanos , Proteínas de Membrana/química , Proteínas de Membrana/imunologia , Dados de Sequência Molecular , Subunidades Proteicas/química , Subunidades Proteicas/genética , Subunidades Proteicas/imunologia , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/imunologia , Receptores de IgG/química , Receptores de IgG/imunologia , Xenopus laevis/genéticaRESUMO
A group of genes encoding proteins structurally related to the leukocyte Fc receptors (FcRs) and termed the IFGP family was identified in human and mouse. Sequences of four human and two mouse cDNAs predict proteins differing by domain composition. One of the mouse cDNAs encodes a secreted protein, which, in addition to four immunoglobulin (Ig)-like domains, contains a scavenger receptor superfamily-related domain at the C-terminus. The other cDNAs code for the type I transmembrane proteins with the extracellular parts comprised of one to six Ig-like domains. Five homologous types of the Ig-like domains were defined and each protein was found to have a unique combination of the domain types. The cytoplasmic tails of the transmembrane proteins show different patterns of the tyrosine-based signal motifs. While the human IFGP members appear to be B-cell antigens, the mouse genes have a broader tissue distribution with predominant expression in brain. Sequence comparisons revealed that the IFGP family may be regarded as a phylogenetic link joining the leukocyte FcRs with the rat NK cell-specific gp42 antigen and platelet endothelial cell adhesion molecule-1 (PECAM-1), two mammalian leukocyte receptors whose close relatives were not found previously. It is suggested that FcRs, the IFGP proteins and gp42 have arisen by a series of duplications from a common ancestor receptor comprised of five Ig-like domains. The organization of the human genes shows that the IFGP family evolved through differential gain and loss of exons due to recombination and/or mutation accumulation in the duplicated copies.
Assuntos
Antígenos CD , Antígenos de Neoplasias , Antígenos de Superfície , Proteínas Aviárias , Proteínas Sanguíneas , Glicoproteínas de Membrana/genética , Molécula-1 de Adesão Celular Endotelial a Plaquetas/genética , Receptores Fc/genética , Sequência de Aminoácidos , Animais , Linfócitos B/metabolismo , Basigina , Genes , Humanos , Imunoglobulinas/química , Leucócitos/imunologia , Camundongos , Dados de Sequência Molecular , Filogenia , Estrutura Terciária de Proteína , RNA Mensageiro/biossíntese , Receptores Fc/biossíntese , Receptores Fc/química , Homologia de Sequência de Aminoácidos , Especificidade da Espécie , Distribuição TecidualRESUMO
A novel conserved member of the leukocyte Fc receptor (FcR) family was identified in human and mouse. The presumably secreted protein, designated FCRL (FcR-like) is comprised of four domains. The three N-terminal domains are related to the extracellular region of FcgammaRI, with the second (35-37% residue identity) and the third (46-52%) domains showing highest similarity. The C-terminal domain is a unique sequence enriched with proline residues. In humans, alternative transcripts for six FCRL isoforms were revealed. Spleen and tonsils were found to be the major sources of FCRL mRNA in human tissues. Western blotting of tonsil cell lysate using FCRL-specific antibodies recognized a 44-kDa protein produced as a monomer containing free sulfhydryl groups. The monomer, however, was able to form disulfide-linked homo-oligomer upon oxidation. In COS-7 cells transiently transfected with two human FCRL isoforms, both resided intracellularly. Immunohistochemical staining of tonsil sections demonstrated the FCRL expression in germinal centers, suggesting that the protein may be implicated in germinal center-specific stages of B cell development. The phylogenetic analysis of the FCRL relationships with the leukocyte FcR supports a view that the three-domain structure was primordial in the evolution of the family.