RESUMO
In order to characterize the Major histocompatibility complex (MHC) class II A genes of the channel catfish (Ictalurus punctatus) a cDNA library was screened and PCR was performed. Four different full-length cDNA sequences for MHC class II A genes were obtained from a clonal B cell line derived from an outbred fish. Two different genomic sequences and corresponding cDNAs were obtained from a presumably homozygous gynogenetic catfish. The A genes have five exons and four phase one introns. The first exon encodes the 5' untranslated region (UTR) and leader peptide; the second and third exons encode the alpha1 and alpha2 domains, respectively. The connecting peptide, transmembrane and cytoplasmic domains, as well as part of the 3' UTR, are encoded by the fourth exon and the rest of the 3' UTR is encoded by the fifth exon. Southern blot analyses using an exon three probe revealed two to four hybridizing fragments with considerable restriction fragment length polymorphisms evident among randomly selected outbred channel catfish. These findings are consistent with the presence of at least two functional polymorphic MHC class II A gene loci. An unusual aspect of the channel catfish MHC class II alpha chain is its lack of N-linked glycosylation sites.
Assuntos
Genes MHC da Classe II/genética , Antígenos de Histocompatibilidade Classe II/genética , Ictaluridae/genética , Ictaluridae/imunologia , Sequência de Aminoácidos , Animais , Sequência de Bases , Southern Blotting , Linhagem Celular , DNA Complementar/isolamento & purificação , Biblioteca Gênica , Antígenos de Histocompatibilidade Classe II/química , Dados de Sequência Molecular , Filogenia , Reação em Cadeia da Polimerase/métodos , Reprodução/genética , Reprodução/imunologia , Alinhamento de SequênciaRESUMO
We have isolated two major histocompatibility complex (MHC) class II B genes from the inbred fish strain Xiphophorus maculatus Jp 163 A. We mapped one of these genes, designated here as DXB, to linkage group III, linked to a malic enzyme locus, also syntenic with human and mouse MHC. Comparison of genomic and cDNA clones shows the gene consists of six exons and five introns. The encoded beta1 domain has three amino acids deleted and a cytoplasmic tail nine amino acids longer than in other teleost class II beta chains, more similar to HLA-DRB, clawed frog Xela-F3, and nurse shark Gici-B. Key residues for disulfide bonds, glycosylation, and interaction with alpha chains are conserved. These same features are also present in a swordtail (Xiphophorus helleri) genomic DXB PCR clone. A second type of class II B clone was amplified by PCR from X. maculatus and found to be orthologous to class II genes identified in other fishes. This DAB-like gene is 63% identical to the X. maculatus DXB sequence in the conserved beta2-encoding exon and was mapped to new unassigned linkage group LG U24. The DXB gene, then, represents an unlinked duplicated locus not previously identified in teleosts.
Assuntos
Ciprinodontiformes/genética , Genes MHC da Classe II , Sequência de Aminoácidos , Animais , Sequência de Bases , Mapeamento Cromossômico , Clonagem Molecular , Sequência Conservada , Ciprinodontiformes/classificação , Primers do DNA/genética , Éxons , Feminino , Ligação Genética , Humanos , Hibridização Genética , Íntrons , Masculino , Camundongos , Dados de Sequência Molecular , Família Multigênica , Filogenia , Reação em Cadeia da Polimerase , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido Nucleico , Especificidade da EspécieRESUMO
Peptides derived from parasites are presented to T helper cells by major histocompatibility complex (MHC) class II alpha beta heterodimeric cell-surface molecules. In mice and humans, the genes encoding these antigen-presenting molecules are known to be polymorphic and polygenic. Multiple loci for MHC class II A and B genes are proposed to allow for an increased peptide-binding repertoire. The multigenic nature of expressed MHC class II loci and the differences between these loci in fishes are the focus of this review. Particular emphasis is placed on an evolutionary comparison of class II B loci, especially two class II B loci that have undergone dramatic changes from one another suggesting an ancestral gene duplication event that took place at an early stage in the evolution of teleosts. The number of functional class II alpha beta heterodimers may have a profound impact on the organisms ability to battle constantly evolving parasitic infections.
Assuntos
Peixes/genética , Expressão Gênica , Genes MHC da Classe II , Sequência de Aminoácidos , Animais , Sequência de Bases , Evolução Molecular , Éxons , Peixes/imunologia , Humanos , Íntrons , Camundongos , Dados de Sequência MolecularRESUMO
Two different cDNA sequences for major histocompatibility complex (MHC) class II beta chains from the channel catfish (Ictalurus punctatus) have been identified. Homology between these sequences and those previously identified as MHC class II B genes in other teleosts suggests they represent alleles of the DAB locus. The inferred amino acid sequences show strong evidence for a functional polypeptide chain with a peptide binding region. Southern blot analysis reveals polymorphism in the MHC class II B gene(s) of the channel catfish and suggests the presence of two to four genes.
