Biomedical subjects
Publications and source records attributed to E Martínez-Naves.
The mouse CD1 system is formed by two closely related genes named Cd1d1 and Cd1d2. Cd1d1 encodes a molecule that presents antigens to NKT cells. The function of the Cd1d2 gene has not been elucidated. Here we described a method to analyse variations in mouse Cd1 genes. We found a new allele for Cd1d2 characterized by a point mutation, resulting in a replacement of alanine at position 176 by a valine.
We characterized the MHC-related 1 ( MR1) locus in two nonhuman primates species, Pongo pygmaeus and Pan troglodytes. MR1 cDNA sequences encoding several isoforms generated through alternative splicing were observed in both species. Amino acid alignment between the five species in which MR1 has been characterized to date - human, chimpanzee, orangutan, mouse, and rat - reveals a very high degree of conservation specially in the alpha1 and alpha2 domains of the molecule. The main differences concentrate in the transmembrane and cytoplasmic domains. In the three primates species there is a lysine residue inside the putative transmembrane domain which is not present in rodents. Furthermore, the MR1 cytoplasmic region is longer in rodents, with a conserved serine-containing motif that could be involved in endocytosis; remarkably, this motif is absent in the three primate species. We also describe the presence in the chimpanzee of a sequence homologous to the MR1P1 pseudogene previously found in humans.
CD1 molecules are specialized in presenting lipidic antigens to T lymphocytes. They are structurally and evolutionary related to MHC molecules and show very limited polymorphism. We have previously described and partially characterized a new human CD1A allele differing from the wild type CD1A by a substitution of Cysteine by Tryptophan at position 52 in the alpha1 domain of the CD1A molecule. The frequency of this allele varies from 10% in individuals of Caucasian origin to 56% in Chinese people. The aim of the present work was to structurally characterize this CD1A allele. To do this we have cloned and sequenced the full-length cDNA encoding the new CD1A allele. The cDNA sequence of this allele encodes a protein differing the wild type in two amino acids at positions 14 (Threonine versus Isoleucine) and 52 (Cysteine versus Tryptophan). The cDNAs encoding both wild type and mutant CD1A were cloned in the expression vector pSRalphaNeo and transfected into C1R and L721.221 cells. Cell surface expression of the protein products in transfected cell lines were analyzed by flow cytometry and immunoprecipitation using CD1a-specific monoclonal antibodies. Our results indicate that both allelic products are efficiently expressed on the cell surface.
CD1 is a family of proteins structurally related to major histocompatibility complex (MHC) molecules and specialized in presenting lipids or glycolipids to T cells. In humans, there are five CD1 genes (CD1A to CD1E). It has been shown that, in contrast with classical MHC genes, CD1 loci display a very limited polymorphism. In the present work we describe two novel CD1E alleles found in two healthy Caucasian individuals. One allele differs from the wild-type by a point mutation resulting in a replacement of arginine at position 154 by a tryptophan. In the second allele we found a substitution of the leucine 184 by a proline.
Human MR1 is a recently discovered, ubiquitously transcribed gene very similar to the HLA class I loci and of unknown function. Mouse and rat MR1 sequences have also been described showing high similarity with the human gene. The goal of this work was to investigate if human MR1 was polymorphic. We have found that DNA sequences of MR1-specific polymerase chain reaction (PCR) products obtained from samples of diverse ethnic origin were invariant except in one case in which two silent mutations were detected. We also found an MR1-like sequence displaying significant differences with the previously described, the most remarkable of which is a STOP codon in the alpha2 domain indicating that is a pseudogene.
CD1 molecules are able to present unusual antigens, lipids or glycolipids from mycobacterium cell walls to T lymphocytes. Previous studies have suggested that polymorphism of these genes is very limited, in contrast with classical major histocompatibility complex (MHC) antigen-presenting molecules. Our aim was to study possible allelic variations of exons 2 and 3, encoding for the alpha1 and alpha2 domains, respectively, of human CD1A, -B, -C and -D genes. We analyzed genomic samples of unrelated, healthy individuals from different ethnic background: 70 Caucasians from Europe, 33 Black Africans (13 from Tanzania and 20 Zulus), 19 Caucasians from the Sahara and 44 Asian individuals. We have found CD1A to be a biallelic locus with a common allele which was present in the majority of the individuals studied. The second allele differed from the common one by a single-point mutation, resulting in a change of Cys to Trp at position 52 in the alpha1 domain. This second allele was found in heterozygosis in 7 out of 70 Caucasians from Europe (allelic frequencies P=0.95 and q=0.05). In the Chinese population, we found the second allele present in heterozygosis in 19 from the 44 individuals studied, and we also found 6 homozygous individuals for the second allele (allelic frequencies P=0.64 and q=0.35). In addition, we detected a synonymous mutation (C to T transition) in codon 34 of CD1C exon 2 in 4 out of 20 Zulus and in 2 of the 13 Blacks from Tanzania.
The role of HLA class II alleles in genetic predisposition to insulin-dependent diabetes mellitus (IDDM) was examined using Polymerase Chain Reaction/oligonucleotide probe typing (PCR/SSOs) of eight HLA class II loci in 58 IDDM patients and 50 healthy controls from the Northwest of Spain (Asturias). We compared the distribution of HLA class II alleles, haplotypes and genotypes between IDDM patients and controls, and tested three recently proposed HLA-IDDM susceptibility theories. By using the aetiologic fraction (delta) as an almost absolute measure of the strongest linkage of disequilibrium of a HLA marker to the putative Type I susceptibility locus, it has been found that the strength of association of the HLA markers may be quantified as follows: DQA1*03-DQB1*0302 or DQA1*0501-DQB1*0201 > DR3 or DR4; presence of more than one dimer DQ alpha beta of the six proposed by Rønningen > non-Asp57 DQ beta and Arg52 DQ alpha > Arg52 DQ alpha > non-Asp57 DQ beta/non-Asp57 DQ beta > DRB1*0301; DQA1*0501-DQB1*0201 > DQA1*03-DQB1*0302; DQB1*0302. The presence of at least one Asp57 DQ beta allele was the best protection HLA marker to IDDM in our population. Therefore, the above data confirm that IDDM susceptibility to HLA locus is linked more to DQ than DR.
Recently several reports have described contradictory results after studying the association between restriction fragments length polymorphisms (RFLP) of T cell receptor (TcR) beta-chain genes and multiple sclerosis (MS). We studied the allelic, genotypic and haplotypic distribution of RFLPs of TcR beta chain gene segments C beta, V beta 8 and V beta 11 in 97 unrelated multiple sclerosis (MS) patients, 11 with chronic progressive MS and 86 with relapsing/remitting (R/R) MS. We found the distribution of the TcR haplotypes defined by the alleles of the three loci studied in the MS patients was significantly different from that found in control individuals. The distribution of TcR haplotypes in R/R MS patients was also different from that observed in controls. Our data suggest that the TcR beta chain gene complex contains one or more genes involved in genetic susceptibility to develop MS.
We have studied the genotypic, haplotypic, and allelic distribution of germline Restriction Fragment Length Polymorphism (RFLP) of T-cell receptor (Tcr) alpha, gamma, and delta loci in 75 insulin-dependent diabetes mellitus (IDDM) patients and 84 healthy blood donors as control population. The restriction endonuclease PvuII produces three allelic fragments of Tcr C gamma (TcrCG) gene segment of 16, 13, and 11.3 Kb respectively. Our observations revealed that PvuII/TcrCG RFLP allelic distributions were not significantly different in the IDDM and the control group. However, 85% of IDDM patients carried HLA DR3 and/or DR4 haplotypes, and when comparing these patients with a second group of HLA DR3+ and/or DR4+ healthy individuals, the 11.3 Kb/PvuII fragment of TcrCG gene was found to be associated with IDDM patients (chi 2 = 11.4, P = 0.003). 54.9% of IDDM patients carried at least one 11.3 Kb allele vs. 21% in controls (chi 2 = 10.77, P = 0.004). No significant association was found between RFLP in Tcr, C alpha, C delta, V gamma 9 loci and IDDM.
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In this report we describe the linkage between genes encoding human complement components C6, C7, and C9. Polymorphisms have been described at the DNA level for the C7 and C9 genes. We have studied 20 individuals by Southern blot analysis with four C6 cDNA subclones to detect restriction fragment length polymorphisms (RFLPs). We have found a Taq I polymorphism defined by two alleles of 8.0 (C6 H) and 6.0 (C6 L) kilobases (kb). RFLP segregation for the C6, C7, and C9 loci in informative families allowed us to estimate the maximum Lod scores at a recombination fraction of theta = 0.0 (C6-C7), theta = 0.0 (C7-C9), and theta = 0.0 (C6-C9). Significant linkage disequilibrium was found between C6 and C7 and between C7 and C9 loci in directly determined haplotypes of unrelated parents. Data from this study show that the genes encoding the human terminal complement components C6, C7, and C9 define a cluster in the short arm of chromosome 5. We propose that the clusters involving the C8A and C8B and the C6, C7, and C9 genes be referred to as MACI and MACII, respectively.
We have investigated the genotype and allelic distribution of germline restriction fragment length polymorphisms of the T-cell receptor beta chain, segment C beta, and two variable segments which are in linkage disequilibrium, V beta 8 and V beta 11, in 42 insulin-dependent diabetes mellitus (IDDM) patients and in 51 healthy blood donors used as controls. Recently, several works have reported contradictory results showing or not showing an association between polymorphic alleles of the C beta gene and diabetes type I. We found no significant differences in the allele, genotype, and haplotype distribution of the gene segments studied, between IDDM patients and control populations.
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A C7 cDNA probe detecting a TaqI restriction fragment length polymorphism has been used to examine the segregation of the "silent allele" (C7*Q0) in two familial deficiencies. Carrier diagnosis in healthy children is possible when both parents are heterozygotes. Only one of these two families was informative. The "silent allele" is linked to different TaqI alleles in both families. This suggests that at least two different C7*Q0 alleles are present in our population. This paper gives a protocol for genetic studies of hereditary traits in which the C7 gene and other genes tightly linked to it are involved.