PubMed Health⌕ Search

Biomedical subjects

D C Townend

Publications and source records attributed to D C Townend.

15 recordsLinked to original sources
PubMed1999

Reconstruction of the block matching profiles.

Block matching is a valuable tool for selecting donors for bone marrow transplantation. Identical, electrophoretic profiles of unrelated bone marrow donor-recipient pairs have been shown to be associated with long-term survival and a reduction of graft versus host disease (GVHD). This study was undertaken to determine the sequences of the PCR products which are generated. PCR products obtained with beta-block primers following the amplification of DNA extracted from cell lines homozygous for 7.1 and 8.1 ancestral haplotypes were cloned and sequenced. The PCR products were characterised and the beta block profiles reconstructed. The data indicate that the profiles consist of homoduplexes and heteroduplexes which are formed by the products of probably 3 different sequence locations.

Cell Line, Transformed↗
PubMed1998

New Australian aboriginal complotypes characterised by increased C4 gene copy number.

Complement component C4 genes are located within the central region of the human MHC. The genomic arrangement of these genes is complex, with each chromosome usually encoding either one or two C4 genes. C4 allotyping of a group of Western Australian Aborigines demonstrated certain discrepancies in the densitometric ratios between the C4A4 and the C4A3 protein bands; however, the mechanism causing the increase in density of the C4A4 band was unknown. Our aim was to determine whether the increase in densitometry was due to an increase in the expression of the C4A4 isotype, or whether these individuals carried a new complotype characterised by an increased gene copy number. Using pulsed-field gel electrophoresis and Taq I RFLP analysis we will show that the apparent increase in C4A4 protein expression was due to the existence of new, previously uncharacterised Aboriginal complotypes defined by at least three C4 genes. Segregation analysis from an extensive family suggests that one of the new C4 complotypes is likely to contain the duplicated C4A4 isotype together with a C4B2 gene (C4A4, C4A4, C4B2) and is the first such chromosomal arrangement seen in this population group.

Australia↗
PubMed1997

Genomic characterization of the region between HLA-B and TNF: implications for the evolution of multicopy gene families.

The major histocompatibility complex (MHC) contains genes which confer susceptibility to numerous diseases and must be important in primate evolution. In some instances, genes have been mapped to the region between human histocompatibility leukocyte antigen (HLA)-B and tumor necrosis factor (TNF) but precise localization has proven difficult especially since this region is subject to insertions, deletions, and duplications. Utilizing computer similarity searches and coding prediction programs, we have identified several potential coding sequences between HLA-B and TNF. Three of these sequences, PERB11.2, PERB15, and PERB 18, are similar to members of multicopy gene families that are located in other regions of the MHC. The identification of numerous fragmented and intact retroelements (L1, Alu, LTR, and THE sequences) flanking the PERB11 and PERB15 genes suggests that these retroelements are involved in the duplication process. The evaluation of candidate genes for disease susceptibility within the MHC is complicated by their similarity to other members of multicopy gene families. The determination of sequence differences within and between species provides a strategy with which to investigate the candidate genes between HLA-B and TNF.

Amino Acid Sequence↗
PubMed1997

The major histocompatability complex (MHC) contains conserved polymorphic genomic sequences that are shuffled by recombination to form ethnic-specific haplotypes.

The major histocompatibility complex (MHC) consists of polymorphic frozen blocks (PFBs) that are linked to form megabase haplotypes. These blocks consist of polymorphic sequences and define regions where recombination appears to be inhibited. We have been able to show, using a highly polymorphic sequence centromeric of HLA-B (within the beta block), that PFBs are conserved and contain specific insertions/deletions and substitutions that are the same for individuals with the same MHC haplotype but that differ between at least most different haplotypes. A sequence comparison between ethnic-specific haplotypes shows that these sequences have remained stable and predate the formation of these haplotypes. To determine whether the same conserved block has been involved in the generation of multiple haplotypes, we compared the block typing profiles of different ethnic specific haplotypes. Block typing profiles have previously been shown to be identical in individuals with the same MHC haplotype but, generally, to differ between different haplotypes. It was found that some PFBs are common to more than one haplotype, implying a common ancestry. Subsequently, haplotypes have been generated by the shuffling and exchange of these PFBs. The regions between these PFBs appear to permit the recombination sites and therefore could be expected to exhibit either low polymorphism or a localized "hotspot."

Asian People↗
PubMed1997

Allelic and interlocus comparison of the PERB11 multigene family in the MHC.

The major histocompatibility complex (MHC) contains at least a hundred genes over 4 megabases of DNA. Within the MHC there are several new multigene families which have been recently described. PERB11 is a multigene family which occurs over the class I and central region of the MHC. Two members of the family have been shown to be functional and share domains with members of the supergene family including HLA class I, FcRn, and Zn-alpha2-glycoprotein molecules. The two functional members are contained within an area of the MHC which has been associated with increased susceptibility to autoimmune diseases such as insulin-dependent diabetes mellitus and also rapid progression to AIDS following HIV-1 infection. Intralocus and interlocus differences between PERB11.1 and PERB11.2 include: (1) several nucleotide substitutions leading to amino acid changes; (2) presence and absence of potential glycosylation sites; (3) insertions and deletions leading to a frame shift resulting in diversity at the amino acid level and an early termination signal. There are ten different alleles of PERB11.1 including one allele which contains a frame shift in the transmembrane region causing a putative truncated molecule lacking the cytoplasmic tail. The significance of this polymorphism in disease associations is under investigation. The most divergent domain is the transmembrane region when PERB11.1 and PERB11.2 are compared. The results suggest that these two molecules may have different functions.

Alleles↗
PubMed1996

The primate MHC contains sequences related to the fibroblast growth factor receptor gene family.

We have cloned and sequenced a genomic region centromeric of the HLA-B locus from different MHC ancestral haplotypes. These haplotypes are associated with several diseases. The sequences were analyzed for coding potential and their relevance to disease associations were assessed with respect to the level of polymorphism. Analysis of sequences located approximately 25kb centromeric of HLA-B reveals the existence of fibroblast growth factor receptor related sequences. These sequences designated PERB1 (FGFR6) reveal 80% homology, at both nucleic acid and amino acid level, to the immunoglobulin domain 1 (Ig-1) of the human fibroblast growth factor receptor 3 (FGFR3) gene. Amino acid comparison of the Ig-1 domain of PERB1 to those of other FGFR molecules indicates that PERB1 is more closely related to FGFR3 and FGFR5 than to FGFR1, FGFR2 or FGFR4. Genomic sequence analysis, however, reveals no consensus splice sites and indicates the existence of inframe premature stop codons in the putative coding sequences. The results suggest that these sequences may represent FGFR gene fragments existing within the central MHC. Sequence analysis of the Mhc in 6 chimpanzee and one orangutan indicates that the existence of PERB1 predates the speciation of the three species. The fact that the MHC contains a mixture of functional and nonfunctional (pseudo) genes suggests that a functional copy of PERB1 (FGFR6) may exist within or in close proximity to the MHC.

Amino Acid Sequence↗
PubMed1994

A new polymorphic and multicopy MHC gene family related to nonmammalian class I.

We have used genomic analysis to characterize a region of the central major histocompatibility complex (MHC) spanning approximately 300 kilobases (kb) between TNF and HLA-B. This region has been suggested to carry genetic factors relevant to the development of autoimmune diseases such as myasthenia gravis (MG) and insulin dependent diabetes mellitus (IDDM). Genomic sequence was analyzed for coding potential, using two neural network programs, GRAIL and GeneParser. A genomic probe, JAB, containing putative coding sequences (PERB11) located 60 kb centromeric of HLA-B, was used for northern analysis of human tissues. Multiple transcripts were detected. Southern analysis of genomic DNA and overlapping YAC clones, covering the region from BAT1 to HLA-F, indicated that there are at least five copies of PERB11, four of which are located within this region of the MHC. The partial cDNA sequence of PERB11 was obtained from poly-A RNA derived from skeletal muscle. The putative amino acid sequence of PERB11 shares approximately 30% identity to MHC class I molecules from various species, including reptiles, chickens, and frogs, as well as to other MHC class I-like molecules, such as the IgG FcR of the mouse and rat and the human Zn-alpha 2-glycoprotein. From direct comparison of amino acid sequences, it is concluded that PERB11 is a distinct molecule more closely related to nonmammalian than known mammalian MHC class I molecules. Genomic sequence analysis of PERB11 from five MHC ancestral haplotypes (AH) indicated that the gene is polymorphic at both DNA and protein level. The results suggest that we have identified a novel polymorphic gene family with multiple copies within the MHC.

Adult↗
PubMed1993

Differences in the central major histocompatibility complex between humans and chimpanzees. Implications for development of autoimmunity and acquired immune deficiency syndrome.

Chimpanzees (Pan Troglodytes) and humans are closely related and belong to the same subfamily, Homininae. The approximately 1.8% genetic difference that exists between humans and the chimpanzees must be responsible for observed differences between these two species. It has been shown that chimpanzees can be infected with HIV, but AIDS has not been reported. Furthermore, the prevalence of autoimmune diseases may be low in this species. For instance, type II diabetes occurs, but type I (autoimmune) diabetes (IDDM), to our knowledge, has not been reported. In humans, susceptibility genes for MG and IDDM have been localized to the region between TNF and HLA-B. This region may also influence the rate of progression to death after HIV infection. We have identified differences in this region between humans and the chimpanzees. As shown by PFGE, the TNF to Patr-B region in the chimpanzees is approximately 130-160 kb shorter than the equivalent in humans. Southern and sequence analyses indicate that the deletions in chimpanzees (insertions in humans) include one copy of CL (approximately 10 kb) and the X sequences (< 30 kb). Obviously, other deletions/insertions (approximately 120 kb) need to be identified. Since CL has been shown to be transcribed, the results imply the lack of the gene or, at least, a different gene copy number in the chimpanzees, and we propose that such differences may be relevant to the observed functional differences. We demonstrate here a strategy to identify critical genes responsible for disease development.

Acquired Immunodeficiency Syndrome↗
PubMed1993

A region centromeric of the major histocompatibility complex class I region is as highly polymorphic as HLA-B. Implications for recombination.

Two hallmarks of the MHC are the high degree of polymorphism apparent at multiple loci and "linkage disequilibrium." The data presented here suggest that a consequence of selection at a particular locus may be the inhibition of recombination through the accumulation of DNA sequence polymorphisms. Equivalent 6.4 kb regions from a locus, CL1, located approximately 25-30 kb centromeric of HLA-B, were sequenced for three ancestral haplotypes: A1,B8,DR3; A30,B18,DR3; and A1,B57,DR7. Comparison of the sequences indicated that the level of DNA sequence polymorphism was high when compared with the TNF region; approximately 80 single nucleotide differences were found when comparing any two sequences. In addition, multiple deletions/insertions were present. We believe that the degree of polymorphism within the CL interval may be adequate to at least partially inhibit recombination between the haplotypes studied.

Base Sequence↗
PubMed1993

The MHC influences acute graft versus host disease in MHC matched adults undergoing allogeneic bone marrow transplantation.

To determine whether the MHC plays an antigen non-specific role in the development of acute GVHD, the prevalence of acute GVHD in relation to MHC genotype was examined in 51 adult patients undergoing allogeneic BM grafting. The majority of patients received grafts from HLA-identical siblings. HLA-B7 haplotypes were associated with a decreased risk of acute GVHD (2 of 15, p = 0.005) whereas HLA-B44 haplotypes were associated with a higher risk of acute GVHD (11 of 14, p = 0.02). As these alleles have been reported previously as having opposite effects in relation to inflammatory mediators, these findings may have important implications with respect to donor selection and patient management.

Acute Disease↗
PubMed1985

Plasma sex hormone binding globulin concentration and binding capacity in children before and during puberty.

The steroid binding capacity and concentration of plasma sex hormone binding globulin have been compared in 116 children aged between 2 and 14 years. Concentration was measured by electroimmunodiffusion standardised with reference to the mass of the pure protein and binding capacity by quantitating the binding of radiolabelled 5 alpha-dihydrotestosterone. Binding capacity correlated highly with concentration in all subjects and neither differed significantly between the sexes before or during puberty. However, both were significantly lower in pubertal than in pre-pubertal children. These findings suggest the metabolism of the protein is similar in boys and girls and that the fall in its steroid binding capacity at puberty in fact is due to a fall in its concentration rather than to changes in its physicochemical properties.

Adolescent↗