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Biomedical subjects

A F Markham

Publications and source records attributed to A F Markham.

At least 109 records · Page 6Linked to original sources
PubMed1998

The CD4+ T lymphocyte is a site of steroid resistance in asthma.

Phytohaemagglutinin (PHA)-induced T-cell proliferation is suppressed completely in steroid-sensitive asthma (SSA) by fluticasone propionate (FP). By contrast, in patients with steroid-resistant asthma (SRA), this proliferative response is only partially attenuated by steroids, which suggests that the T lymphocyte may harbour a key molecular defect in these patients. Both CD4+ and CD8+ T cells may be involved in orchestrating the inflammation underlying asthma. We examined whether CD4+ or CD8+ T cells isolated from SRA and SSA patients are equally susceptible to steroid suppression of PHA-induced proliferation. Complete suppression of CD4+ T-lymphocyte proliferation was seen in both SSA and control subjects at concentrations of 10(-9) M FP. In contrast, proliferation of CD4+ T cells from SRA patients was only partially inhibited, even at 10(-6) M FP. CD8+ responses from SRA, SSA and controls were all similar, with only a partial suppression of proliferation at 10(-6) M FP. Differential suppression by FP of CD4+ T cells has thus been demonstrated between SRA and SSA patients.

Adult↗
PubMed1998

A Moroccan family with autosomal recessive sensorineural hearing loss caused by a mutation in the gap junction protein gene connexin 26 (GJB2).

We report a mutation in the connexin 26 gene (Cx26) in a consanguineous Moroccan family linked to the DFNA3/DFNB1 locus on human chromosome 13q11-q12. Affected subjects display congenital, bilateral, sensorineural hearing loss. We have previously identified Cx26 mutations in consanguineous Pakistani families. This current finding indicates that Cx26 mutations are not restricted to ethnically and geographically distinct populations. This is an important observation since it will help to determine the overall contribution of connexin 26 mutations to autosomal deafness in different populations.

Child, Preschool↗
PubMed1998

Genetic heterogeneity and HOMOG analysis in British malignant hyperthermia families.

Malignant hyperthermia (MH) is an autosomal dominant genetic condition that presents in susceptible people undergoing general anaesthesia. The clinical disorder is a major cause of anaesthetic morbidity and mortality. The UK Malignant Hyperthermia Group has performed genetic linkage analysis on 20 large, well defined malignant hyperthermia families, using hypervariable markers on chromosome 19q13.1, including the candidate MH gene RYR1, the gene coding for the skeletal muscle ryanodine receptor protein. The results were analysed using LINKAGE to perform two point and multipoint lod scores, then HOMOG to calculate levels of heterogeneity. The results clearly showed genetic heterogeneity between MH families; nine of the families gave results entirely consistent with linkage to the region around RYR1 while the same region was clearly excluded in three families. In the remaining eight MHS families there were single recombinant events between RYR1 and MH susceptibility. HOMOG analysis was of little added benefit in determining the likelihood of linkage to RYR1 in these families. This confirmation of the presence of heterogeneity in the UK MH population, along with the possibility of the presence of two MH genes in some pedigrees, indicates that it would be premature and potentially dangerous to offer diagnosis of MH by DNA based methods at this time.

Chromosomes, Human, Pair 19↗
PubMed1998

Evidence for a common mutation in hereditary pancreatitis.

Hereditary pancreatitis is an autosomal dominant disorder with incomplete penetrance. It is characterised by recurring episodes of severe abdominal pain and often presents in childhood. Recently, a mutation in the cationic trypsinogen gene was identified in this disease. Previously, only one mutation at residue 117 of the trypsinogen gene has been found in the five separate hereditary pancreatitis families, four from the USA and one from Italy. Alteration of the Arg117 site is believed to disrupt a fail-safe mechanism for the inactivation of trypsin, leading to autodigestion of the pancreas under certain conditions. Molecular analysis of the trypsinogen gene was carried out on a hereditary pancreatitis family from the UK. The same G to A mutation at residue 117 was identified in this family, suggesting that this is a common mutation in hereditary pancreatitis.

Chronic Disease↗
PubMed1998

Detailed genetic mapping around a putative prostate-specific membrane antigen locus on human chromosome 11p11.2.

Physical mapping of the human prostate-specific membrane antigen gene (FOLH) has not been straightforward. Previously, localisations of this gene to either 11p11.2 or 11q14 have been described. This raised the possibility of the presence of more than one related FOLH gene in man. We now present detailed characterisation of the region around a FOLH gene in a 500-kb non-chimaeric YAC clone, putatively assigned to 11p11.2. This clone contains two known microsatellites, D11S1326 and D11S1357 which have been previously mapped unequivocally to the 11p11.2 region at 62.5 cM. This data strongly supports the original 11p11.2 localisation of FOLH. The YAC clone also has a putative EST at each of its ends and these have thus been physically positioned on this chromosome. However, the two regions previously highlighted at 11p11.2 and 11q14 are apparently extensively duplicated, as evidenced by the appearance of dual FISH signals with a number of different genomic probes selected across this 500-kb 11p11.2 region.

Animals↗
PubMed1998

Fine mapping of 12 previously unassigned EST clones to individual YACs in the familial Alzheimer's disease (FAD) region of chromosome 14q24.3.

We have constructed an approximately 4-Mb YAC contig spanning the microsatellite markers D14S1028-D14S61 on chromosome 14q24.3 using oligonucleotide primers to microsatellite markers, ESTs and the genes PSEN1, FOS, TGFB3 and UBE2L1. This contig consists of 44 ICI YACs and 5 megaCEPH YACs. The data reported here should aid the final construction of an integrated map of chromosome 14 and allow the identification and accurate mapping of additional novel ESTs within this region.

Alzheimer Disease↗
PubMed1998

DNA mismatch repair genes and their association with colorectal cancer (Review).

Mismatch repair genes are involved in increasing the fidelity of replication by specific repair of DNA polymerase incorporation errors. In Escherichia coli, the best studied mismatch repair (MMR) pathway is the methyl-directed long patch repair system which is mediated by three gene products; MutS, MutL and MutH. These are conserved in higher eukaryotes. Mutations in human homologues of these proteins have been shown to be implicated in hereditary non-polyposis colorectal cancer (HNPCC). Alterations in the coding regions of MMR genes result in a mutator phenotype with marked instability of microsatellite sequences, indicative of a deficiency in DNA repair.

Colorectal Neoplasms, Hereditary Nonpolyposis↗
PubMed1998

New splicing mutations in the human factor XIIIA gene, each producing multiple mutant transcripts of varying abundance.

Coagulation factor XIII, a transglutaminase which stabilises blood clots by covalently cross-linking fibrin, is essential for normal haemostasis. FXIII deficiency results in a life-long bleeding disorder with added complications in wound healing and tissue repair. Sequence changes in the human FXIIIA gene, largely missense mutations, are primarily responsible for inherited FXIII deficiency. We have carried out molecular analysis of the FXIIIA gene in two unrelated FXIII deficient individuals and identified three splice site mutations; a g-->a at the exon 6 acceptor splice site, a g-->a at the exon 7 donor splice site and a coding sequence T-->G at the exon 8 donor splice site. We have also examined the FXIIIA mRNA in these patients and find that each mutation gives rise to multiple transcripts which vary in their relative abundance. The precise molecular mechanisms which result in these variant transcripts, and their relative abundance in our FXIII deficient patients, are discussed.

Adolescent↗
PubMed1997

Alu sequences.

Alu sequences are frequently encountered during study of human genomic nucleic acid and form a major component of repetitive DNA. This review describes the origin of Alu sequences and their subsequent amplification and evolution into distinct subfamilies. In recent years a number of different functional roles for Alu sequences have been described. The multiple influences of Alu sequences on RNA polymerase II-mediated gene expression and the presence of Alu sequences in RNA polymerase III-generated transcripts are discussed.

Cell Nucleus↗
PubMed1997

Expression of beta-catenin and the adenomatous polyposis coli tumour suppressor protein in mouse neocortical cells in vitro.

Beta-catenin is known to associate with the tumour suppressor protein adenomatous polyposis coli (APC), which is highly expressed in developing brain. We have therefore investigated the distribution of beta-catenin and APC in primary cultures of mouse neocortex. Western blotting demonstrated the presence of a single beta-catenin species in our cultures. Immunocytochemistry showed that beta-catenin was plasma membrane associated and concentrated in growth cones in cultured neurons. The APC tumour suppressor protein was also concentrated in growth cones. In glial cells, beta-catenin was localised at cell-cell contacts in a manner similar to that previously described in other cell types. This data suggests a role for both APC and beta-catenin in neuronal growth cones, and for beta-catenin in the formation of cell to cell contacts between glia.

Adenomatous Polyposis Coli↗
PubMed1997

Rapid determination of the complexity of cDNA bands extracted from DDRT-PCR polyacrylamide gels.

A band extracted from a differential display polyacrylamide gel often represents a composite of heterogeneous products. We have developed a non- radioactive method to simply and rapidly analyse its complexity. A fluorescent restriction enzyme fingerprint of the composite mixture is generated. The number of individual bands observed in this fingerprint indicates the complexity of the re-amplified cDNA mixture. Restriction fingerprints of the inserts of cDNA subclones derived from the re-amplified cDNA mixture are compared to the composite fingerprint to select those representing the most intense bands in the composite. This dramatically reduces the number of clones required for further characterisation.

Base Sequence↗
PubMed1997

Human tenascin-C: identification of a novel type III repeat in oral cancer and of novel splice variants in normal, malignant and reactive oral mucosae.

Tenascin-C is a mosaic, linear glycoprotein that is up-regulated during many normal and pathological processes involving either cell migration or tissue morphogenesis, such as invasion of malignant cells and wound healing. Human tenascin-C contains 8 consecutive type III fibronectin (TNCfn) domains that are involved in alternative splicing and potentially generate a large number of isoforms that code for tenascin-C proteins with subtly different functions. Human tenascin-C splice variants were investigated by RT-PCR in a range of normal and pathological oral mucosal tissues. A novel, 9th human TNCfn domain involved in alternative splicing was identified. It shares 70% nucleic acid and 55% protein sequence homology with chicken TNCfn-ad2. As in avians, this novel repeat was located between TNCfn-B and TNCfn-ad1 and accordingly was designated human TNCfn-ad2. Human TNCfn-ad2 was detected in only 2 of 10 oral cancers. However, TNCfn-ad2 was absent from 40 normal, reactive, pre-malignant and other oral mucosal specimens investigated. Previous studies have described 8 splice variant transcripts for human tenascin-C. By systematic investigation we identified further novel splice variants for human tenascin-C. Furthermore, our results indicate that many potential splice variants probably do not exist in the tissues investigated. Thus, we have demonstrated that human tenascin-C transcripts generate a complex but selected repertoire of different alternative splice products.

Alternative Splicing↗
PubMed1997

Characterization of human SHC p66 cDNA and its processed pseudogene mapping to Xq12-q13.1.

SHC is an adapter protein in the Ras-MAPkinase pathway that is involved in the regulation of cell growth and differentiation. The p46 and p52 isoforms are thought to be produced by the use of two alternative translation initiation sites in a 3.4-kb transcript from the SHCA gene, which maps to chromosome 1q21. The p66 isoform could be encoded by a different 3.8- or 2.8-kb transcript of the same gene or alternatively by a SHC-related gene. To characterize other putative genes coding for SHC-like proteins, primers from the 3' UTR of the SHCA gene were used to screen a yeast artificial chromosome (YAC) library by polymerase chain reaction (PCR). Two YAC clones, 20D11B and 36D1D, were isolated and used as probes for fluorescence in situ hybridization analysis. Both these probes hybridized to chromosome Xq12-q13.1. This novel SHC-related sequence was characterized by direct sequencing of vectorette library PCR products produced from clone 20D11B. A transcript of 3.2 kb that was 85% identical to the mouse Shc cDNA encoding the p66 isoform was identified. Sequence analysis demonstrated the presence of multiple stop codons identifying this isoform of SHC as a processed pseudogene. Using primers designed on the basis of the nucleotide sequence of the pseudogene, we have now amplified and sequenced a human cDNA that encodes the SHC p66 protein. Thus, we have characterized the human SHC p66 isoform cDNA and identified a processed SHC pseudogene that maps to chromosome Xq12-q13.1.

Adaptor Proteins, Signal Transducing↗