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J Trowsdale

Publications and source records attributed to J Trowsdale.

At least 37 records · Page 2Linked to original sources
PubMed2001

Genetic and functional relationships between MHC and NK receptor genes.

HLA class I and NK receptors are encoded within dense clusters of immune loci. The MHC, at 6p21.3, and the complex containing the KIR loci, at 19q13.4, both feature variation in the number of genes, as well as sequence polymorphism. In addition to T cell receptors, several variable class I-related molecules interact with polymorphic NK receptors. Some of the lectin-related NK receptor genes, at 12p13.1, also have ligands belonging to the extended class I family. The expanding clusters of class I-related sequences and their receptors, some of which evolved recently, reveal further complexity in immune recognition of disease.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Divergent and convergent evolution of NK-cell receptors.

Natural killer (NK)-cell receptors specific for major histocompatibility complex (MHC) class I molecules have been identified in humans and mice. Some of the most important receptors are structurally unrelated in the two species: the murine Ly-49 receptors are C-type lectins, while human killer-cell inhibitory receptors (KIRs) belong to the immunoglobulin superfamily. Here, Roland Barten and colleagues describe the divergent and convergent evolution of NK-cell receptors.

Animals↗
PubMed2001

The genomic context of natural killer receptor extended gene families.

The two sets of inhibitory and activating natural killer (NK) receptor genes belong either to the Ig or to the C-type lectin superfamilies. Both are extensive and diverse, comprising genes of varying degrees of relatedness, indicative of a process of iterative duplication. We have constructed gene maps to help understand how and when NK receptor genes developed and the nature of their polymorphism. A cluster of over 15 C-type lectin genes, the natural killer complex is located on human chromosome 12p13.1, syntenic with a region in mouse that borders multiple Ly49 loci. The equivalent locus in man is occupied by a single pseudogene, LY49L. The immunoglobulin superfamily of loci, the leukocyte receptor complex (LRC), on chromosome 19q13.4, contains many polymorphic killer cell immunoglobulin-like receptor (KIR) genes as well as multiple related sequences. These include immunoglobulin-like transcript (ILT) (or leukocyte immunoglobulin-like receptor genes), leukocyte-associated inhibitory receptor genes (LAIR), NKp46, Fc alphaR and the platelet glycoprotein receptor VI locus, which encodes a collagen-binding molecule. KIRs are expressed mostly on NK cells and some T cells. The other LRC loci are more widely expressed. Further centromeric of the LRC are sets of additional loci with weak sequence similarity to the KIRs, including the extensive CD66(CEA) and Siglec families. The LRC-syntenic region in mice contains no orthologues of KIRs. Some of the KIR genes are highly polymorphic in terms of sequence as well as for presence/absence of genes on different haplotypes. Some anchor loci, such as KIR2DL4, are present on most haplotypes. A few ILT loci, such as ILT5 and ILT8, are polymorphic, but only ILT6 exhibits presence/absence variation. This knowledge of the genomic organisation of the extensive NK superfamilies underpins efforts to understand the functions of the encoded NK receptor molecules. It leads to the conclusion that the functional homology of human KIR and mouse Ly49 genes arose by convergent evolution. NK receptor immunogenetics has interesting parallels with the major histocompatibility complex (MHC) in which some of the polymorphic genes are ligands for NK molecules. There are hints of an ancient genetic relationship between NK receptor genes and MHC-paralogous regions on chromosomes 1, 9 and 19. The picture that emerges from both complexes is of eternal evolutionary restlessness, presumably in response to resistance to disease.

Animals↗
PubMed2001

Rat tapasin: cDNA cloning and identification as a component of the class I MHC assembly complex.

During the assembly of major histocompatibility complex (MHC) class I molecules transient associations are formed with the endoplasmic reticulum resident chaperones calnexin and calreticulin, ERp57 oxidoreductase, and also with tapasin, the latter mediating binding of the class I molecules to the transporter associated with antigen processing (TAP). We report here the isolation of a cDNA encoding rat tapasin from a DA (RT1av1) library. The cDNA encodes a proline-rich (11.3%) polypeptide of 464 residues with a potential ER-retention KK motif at its COOH-terminus, and a predicted molecular mass of 48 kDa. Matrix-assisted laser-desorption ionisation (MALDI) mass spectrometry of peptides derived from in-gel tryptic digestion of a TAP-associated protein match regions of the predicted translation product. A species of the correct molecular mass and predicted pl was also identified in association with radiolabelled immunoprecipitates of the rat TAP complex analysed by two-dimensional gel electrophoresis. This confirms rat tapasin as a component of the rat MHC class I assembly complex.

Amino Acid Sequence↗
PubMed2001

Characterization of clustered MHC-linked olfactory receptor genes in human and mouse.

Olfactory receptor (OR) loci frequently cluster and are present on most human chromosomes. They are members of the seven transmembrane receptor (7-TM) superfamily and, as such, are part of one of the largest mammalian multigene families, with an estimated copy number of up to 1000 ORs per haploid genome. As their name implies, ORs are known to be involved in the perception of odors and possibly also in other, nonolfaction-related, functions. Here, we report the characterization of ORs that are part of the MHC-linked OR clusters in human and mouse (partial sequence only). These clusters are of particular interest because of their possible involvement in olfaction-driven mate selection. In total, we describe 50 novel OR loci (36 human, 14 murine), making the human MHC-linked cluster the largest sequenced OR cluster in any organism so far. Comparative and phylogenetic analyses confirm the cluster to be MHC-linked but divergent in both species and allow the identification of at least one ortholog that will be useful for future regulatory and functional studies. Quantitative feature analysis shows clear evidence of duplications of blocks of OR genes and reveals the entire cluster to have a genomic environment that is very different from its neighboring regions. Based on in silico transcript analysis, we also present evidence of extensive long-distance splicing in the 5'-untranslated regions and, for the first time, of alternative splicing within the single coding exon of ORs. Taken together with our previous finding that ORs are also polymorphic, the presented data indicate that the expression, function, and evolution of these interesting genes might be more complex than previously thought.

Amino Acid Sequence↗
PubMed2000

Peptide specificity of RT1-A1(c), an inhibitory rat major histocompatibility complex class I natural killer cell ligand.

The rat major histocompatibility complex class Ia allelomorph RT1-A1(c) is a potent ligand for the recently identified inhibitory rLy-49 receptor, STOK-2. With the ultimate objective of studying the interactions of these molecules using structural and functional methods, we undertook a detailed study of its peptide specificity. The study revealed that designing an "ideal peptide" by choosing the most abundant residues in the "binding motif" obtained by pool sequencing does not necessarily yield an optimal binding peptide. For RT1-A1(c), as many as four positions, P2, P4, P5, and P9, were detected as putative anchors. Since this molecule displays a preference for highly hydrophobic peptides, we tested binding of peptides derived from the known leader peptide sequences of other rat histocompatibility complex class I molecules. One such peptide, found to bind well, requiring 1.6 microm peptide to achieve 50% stabilization, was searched for in vivo. Natural RT1-A1(c) binding peptides were purified from rat splenocytes and characterized by mass spectrometry using a combined matrix-assisted laser desorption ionization/time-of-flight and quadrupole time-of-flight approach. Results showed that the signal sequence-derived peptide was not detectable in the purified peptide pool, which was composed of a complex spectrum of peptides. Seven of these self-peptides were successfully sequenced.

Animals↗
PubMed2000

DC-SIGN; a related gene, DC-SIGNR; and CD23 form a cluster on 19p13.

DC-SIGN is a C-type lectin, expressed on a dendritic cell subset. It is able to bind ICAM3 and HIV gp120 in a calcium-dependent manner. Here we report the genomic organization of DC-SIGN and map it to chromosome 19p13 adjacent to the C-type lectin CD23 (FcepsilonRII). We also report a novel, closely linked gene, DC-SIGNR, which shows 73% identity to DC-SIGN at the nucleic acid level and a similar genomic organization. Proteins encoded by both genes have tracts of repeats of 23 aa, predicted to form a coiled coil neck region. They also possess motifs that are known to bind mannose in a calcium-dependent fashion. We show concomitant expression of the two genes in endometrium, placenta, and stimulated KG1 cells (phenotypically similar to monocyte-derived dendritic cells). The existence of a DC-SIGN-related gene calls for reinterpretation of the HIV data to consider possible DC-SIGN/DC-SIGNR hetero-oligomerization.

Amino Acid Sequence↗
PubMed2000

Plasticity in the organization and sequences of human KIR/ILT gene families.

The approximately 1-Mb leukocyte receptor complex at 19q13.4 is a key polymorphic immunoregion containing all of the natural killer-receptor KIR and related ILT genes. When the organization of the leukocyte receptor complex was compared from two haplotypes, the gene content in the KIR region varied dramatically, with framework loci flanking regions of widely variable gene content. The ILT genes were more stable in number except for ILT6, which was present only in one haplotype. Analysis of Alu repeats and comparison of KIR gene sequences, which are over 90% identical, are consistent with a recent origin. KIR genesis was followed by extensive duplication/deletion as well as intergenic sequence exchange, reminiscent of MHC class I genes, which provide KIR ligands.

Alu Elements↗
PubMed2000

Modulation of the major histocompatibility complex class II-associated peptide repertoire by human histocompatibility leukocyte antigen (HLA)-DO.

Antigen presentation by major histocompatibility complex class II molecules is essential for antibody production and T cell activation. For most class II alleles, peptide binding depends on the catalytic action of human histocompatibility leukocyte antigens (HLA)-DM. HLA-DO is selectively expressed in B cells and impedes the activity of DM, yet its physiological role remains unclear. Cell surface iodination assays and mass spectrometry of major histocompatibility complex class II-eluted peptides show that DO affects the antigenic peptide repertoire of class II. DO generates both quantitative and qualitative differences, and inhibits presentation of large-sized peptides. DO function was investigated under various pH conditions in in vitro peptide exchange assays and in antigen presentation assays using DO(-) and DO(+) transfectant cell lines as antigen-presenting cells, in which effective acidification of the endocytic pathway was prevented with bafilomycin A(1), an inhibitor of vacuolar ATPases. DO effectively inhibits antigen presentation of peptides that are loaded onto class II in endosomal compartments that are not very acidic. Thus, DO appears to be a unique, cell type-specific modulator mastering the class II-mediated immune response induced by B cells. DO may serve to increase the threshold for nonspecific B cell activation, restricting class II-peptide binding to late endosomal compartments, thereby affecting the peptide repertoire.

Antigen Presentation↗
PubMed2000

Arrangement of the ILT gene cluster: a common null allele of the ILT6 gene results from a 6.7-kbp deletion.

The leukocyte receptor cluster (LRC) is a highly polymorphic region of human chromosome 19q13.4 that encompasses at least 24 members of the immunoglobulin superfamily (Ig-SF). The centromeric end of the LRC contains eight Ig-SF loci, namely LAIR1 and seven ILT genes. All ILT genes conform to prototypic ILT gene structures. ILT6 is the only member of the ILT family that lacks a transmembrane and cytoplasmic domain. Close examination of the ILT6 genomic sequence reveals high similarity of this locus with the organization of activating ILT genes. However, the ILT6 transcript runs through the putative splice site of exon 8 that encodes for an extracellular stalk region, leading to a premature in-frame stop codon. Downstream of exon 8 are three pseudo exons that are not included in any of the known ILT6 transcripts, but share high homology to the equivalent region in activating ILT loci, suggesting that these genes have evolved from a common ancestral sequence. Comparison of two haplotypes over this region revealed a remarkable polymorphism with respect to the ILT6 gene which lacks exons 1-7 in one allele, reminiscent of the presence/absence variation displayed by the closely related and genetically linked KIR loci. Detailed sequence analysis of the two LAIR/ILT clusters suggests that the two complexes may have evolved from an inverted duplication.

Alleles↗
PubMed2000

BTL-II: a polymorphic locus with homology to the butyrophilin gene family, located at the border of the major histocompatibility complex class II and class III regions in human and mouse.

Comparison of human and mouse genomic sequence at the border of the major histocompatibility complex (MHC) class II and class III regions revealed a locus encoding six exons with homology to the butyrophilin gene family and the location of a previously described gene, testis-specific basic protein (TSBP). We named the new locus BTL-II, for butyrophilin-like MHC class II associated. The six discernable exons of the BTL-II locus encode a small hydrophobic amino acid sequence (which may be a signal peptide), two immunoglobulin domains, a small 7-amino acid, heptad repeat-like exon, and a further two immunoglobulin domains. In mouse, an additional butyrophilin-like gene (NG10) is situated adjacent to BTL-II. Expression studies of the BTL-II locus in mouse showed that it is expressed in a range of gut tissues. We demonstrate that like many other genes from the MHC, BTL-II is polymorphic in a selection of diverse HLA haplotypes. In the light of the newly discovered locus, we revisit and discuss the possible origin of the butyrophilin gene family.

Amino Acid Sequence↗
PubMed2000

Polymorphisms in olfactory receptor genes: a cautionary note.

The hundreds of human olfactory receptor (OR) genes are organized into clusters occurring on nearly every chromosome. Although their sequences are not always closely related, they share stretches of considerable similarity, both at the amino acid and nucleotide levels. We demonstrate here that an HLA complex-linked OR sequence, FAT11, for which recently a number of alleles have been claimed within the Hutterites, contains sequences derived from two closely related, linked OR genes, hs6M1-12 and hs6M1-16. Instead of indicating a difference between alleles of a given locus, two of the polymorphisms described for FAT11 (at amino acids 48 and 220 of the deduced protein sequence, respectively) may in fact reflect distinct sequences of hs6M1-12 and a further, closely related HLA-linked OR locus, hs6M1-13P. As a consequence, recombination rates in Hutterites in the region telomeric of HLA-G may have to be reconsidered.

Amino Acid Substitution↗
PubMed2000

TAP deficiency syndrome.

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ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

MHC-linked olfactory receptor loci exhibit polymorphism and contribute to extended HLA/OR-haplotypes.

Clusters of olfactory receptor (OR) genes are found on most human chromosomes. They are one of the largest mammalian multigene families. Here, we report a systematic study of polymorphism of OR genes belonging to the largest fully sequenced OR cluster. The cluster contains 36 OR genes, of which two belong to the vomeronasal 1 (V1-OR) family. The cluster is divided into a major and a minor region at the telomeric end of the HLA complex on chromosome 6. These OR genes could be involved in MHC-related mate preferences. The polymorphism screen was carried out with 13 genes from the HLA-linked OR cluster and three genes from chromosomes 7, 17, and 19 as controls. Ten human cell lines, representing 18 different chromosome 6s, were analyzed. They were from various ethnic origins and exhibited different HLA haplotypes. All OR genes tested, including those not linked to the HLA complex, were polymorphic. These polymorphisms were dispersed along the coding region and resulted in up to seven alleles for a given OR gene. Three polymorphisms resulted either in stop codons (genes hs6M1-4P, hs6M1-17) or in a 16-bp deletion (gene hs6M1-19P), possibly leading to lack of ligand recognition by the respective receptors in the cell line donors. In total, 13 HLA-linked OR haplotypes could be defined. Therefore, allelic variation appears to be a general feature of human OR genes.

Alleles↗