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Biomedical subjects

A F Markham

Publications and source records attributed to A F Markham.

At least 91 records · Page 5Linked to original sources
PubMed1998

EB1, a protein which interacts with the APC tumour suppressor, is associated with the microtubule cytoskeleton throughout the cell cycle.

The characteristics of the adenomatous polyposis coli (APC) associated protein EB1 were examined in mammalian cells. By immunocytochemistry EB1 was shown to be closely associated with the microtubule cytoskeleton throughout the cell cycle. In interphase cells EB1 was associated with microtubules along their full length but was often particularly concentrated at their tips. During early mitosis, EB1 was localized to separating centrosomes and associated microtubules, while at metaphase it was associated with the spindle poles and associated microtubules. During cytokinesis EB1 was strongly associated with the midbody microtubules. Treatment with nocodazole caused a diffuse redistribution of EB1 immunoreactivity, whereas treatment with cytochalasin D had no effect. Interestingly, treatment with taxol abolished the EB1 association with microtubules. In nocodazole washout experiments EB1 rapidly became associated with the centrosome and repolymerizing microtubules. In taxol wash-out experiments EB1 rapidly re-associated with the microtubule cytoskeleton, resembling untreated control cells within 10 min. Immunostaining of SW480 cells, which contain truncated APC incapable of interaction with EB1, showed that the association of EB1 with microtubules throughout the cell cycle was not dependent upon an interaction with APC. These results suggest a role for EB1 in the control of microtubule dynamics in mammalian cells.

Adenomatous Polyposis Coli Protein↗
PubMed1998

Fine-mapping, genomic organization, and transcript analysis of the human ubiquitin-conjugating enzyme gene UBE2L3.

The human UBE2L3 gene encodes the ubiquitin-conjugating enzyme UbcH7, demonstrated to participate in the ubiquitination of p53, c-Fos, and NF-kappaB in vitro. We report the fine-mapping of this four-exon gene to chromosome 22q11.2. We have constructed a comprehensive genomic clone contig across this gene, demonstrating that the gene lies adjacent to the microsatellite marker D22S446 and spans approximately 57 kb. Four mRNA species are transcribed from this gene, differing in the length of their 3' UTR. Sequence comparison of the UBE2L3 cDNA with its murine homologue reveals a remarkably high degree of sequence conservation within the 3'UTR.

Base Sequence↗
PubMed1998

Organization of the human glucokinase regulator gene GCKR.

Glucokinase plays an important role in regulating insulin secretion in response to changes in blood glucose levels. As a result, one form of maturity onset diabetes of the young (MODY) results from haploinsufficiency of glucokinase. In both liver and pancreatic islet, glucokinase is allosterically regulated by an inhibitory protein (glucokinase regulatory protein, GCKR). GCKR has therefore become an important gene for functional analysis in type 2 diabetes. To allow genetic assessment of any such role, we have determined the structure of the human GCKR gene. Characterization of P1 and YAC clones containing GCKR shows it to consist of 19 exons spanning 27 kb. RT-PCR, RACE, and RNase protection experiments defined a transcriptional start site for GCKR 66 bp upstream of the initiation codon, but provided no evidence for islet cell specific alternative splicing in the rat. By SSCP screening, a common polymorphic sequence variant has been defined within exon 15 of human GCKR, at nt 1400 of the cDNA. This alters amino acid residue 446 from proline, conserved in rat and Xenopus, to leucine.

Adaptor Proteins, Signal Transducing↗
PubMed1998

cDNA cloning, genomic organization, and chromosomal localization of a novel human gene that encodes a kinesin-related protein highly similar to mouse Kif3C.

We report the cloning and characterization of a novel human kinesin-like gene with strong homology to the mouse kinesin Kif3c. The full-length cDNA contains an open reading frame of 2382 nucleotides encoding a predicted 793 amino acid peptide that includes a 389 amino acid motor domain conserved among other kinesins. PCR and DNA sequence analysis of PAC clones containing the human KIF3C sequence revealed that the gene contains 8 exons. All introns have the conserved GT and AG dinucleotides present at their donor and acceptor sites, respectively. We have localized KIF3C to chromosome band 2p23 by fluorescence in situ hybridization.

Amino Acid Sequence↗
PubMed1998

Identification of a large deletion, spanning exons 4 to 11 of the human factor XIIIA gene, in a factor XIII-deficient family.

Inherited deficiency of factor XIIIA subunit (FXIIIA) is an autosomal recessive disorder that is characterized by a life-long bleeding tendency and complications in wound healing. Molecular genetic studies have shown the deficiency can be due to small sequence changes within the FXIIIA gene, such as point mutations or microdeletions. On molecular analysis of the FXIIIA gene in an FXIII-deficient patient, of United Kingdom origin, we identified a putative homozygous missense mutation, Arg408Gln. However, the father of this patient is homozygous normal for arginine at codon 408. Having proved paternity in this pedigree by microsatellite analysis, we examined the FXIIIA RNA of the patient by reverse transcriptase-polymerase chain reaction and found the paternal allele to lack exons 4 through 11 inclusive. Hence, a huge deletion extending from intron 3 to intron 11 and the Arg408Gln mutation are jointly responsible for FXIIIA deficiency in this family. This is the first finding of such a large deletion in the FXIIIA gene.

Adult↗
PubMed1998

Identification of mutations in the connexin 26 gene that cause autosomal recessive nonsyndromic hearing loss.

Mutations in the Cx26 gene have been shown to cause autosomal recessive nonsyndromic hearing loss (ARNSHL) at the DFNB1 locus on chromosome 13q12. Using direct sequencing, we screened the Cx26 coding region of affected and nonaffected members from seven ARNSHL families either linked to the DFNB1 locus or in which the ARNSHL phenotype cosegregated with markers from chromosome 13q12. Cx26 mutations were found in six of the seven families and included two previously described mutations (W24X and W77X) and two novel Cx26 mutations: a single base pair deletion of nucleotide 35 resulting in a frameshift and a C-to-T substitution at nucleotide 370 resulting in a premature stop codon (Q124X). We have developed and optimized allele-specific PCR primers for each of the four mutations to rapidly determine carrier and noncarrier status within families. We also have developed a single stranded conformational polymorphism (SSCP) assay which covers the entire Cx26 coding region. This assay can be used to screen individuals with nonsyndromic hearing loss for mutations in the CX26 gene.

Alleles↗
PubMed1998

Structural and evolutionary characterization of the human sorbitol dehydrogenase gene duplication.

We have established that two very closely homologous human sorbitol dehydrogenase sequences lie within 0.5 Mb on Chromosome 15. We have defined the relative orientation of SORD1 and SORD2 genes with respect to both the centromere and each other and established their exact chromosome location. In addition, we have identified polymorphic variants in the locus, which may be useful, in association studies to predict predisposition to clinical problems resulting from decreased conversion of cellular sorbitol to fructose. To define the evolutionary relationship of these human genes, SORD from the marmoset was also sequenced for comparison. Marmoset SORD, which appears to be a single gene in this species, shows significantly less homology with either SORD1 or SORD2 than they do with each other, suggesting that the human homologs represent a recent gene duplication event. A hypothesis is presented to explain the retention of the redundant SORD2 sequence in the human genome.

Amino Acid Sequence↗
PubMed1998

PAX 6 is normal in most cases of Peters' anomaly.

Mutations in the PAX 6 gene are known to cause many cases of inherited and sporadic aniridia. Although embryologically similar to aniridia, the cause of Peters' anomaly has received far less attention. Two reports have been published demonstrating mutations in the PAX 6 gene in Peters' anomaly. We have analysed the PAX 6 gene in 15 individuals with Peters' anomaly (7 familial, 8 sporadic). This is the largest cohort of Peters' anomaly described. The PAX 6 gene was screened using a combination of single-strand conformational polymorphism gel electrophoresis and direct sequencing. No mutations were found in the coding region of the PAX 6 gene. We feel that Peters' anomaly is a heterogeneous condition and that for the majority of cases PAX 6 is not the 'Peters' anomaly gene'.

Anterior Eye Segment↗
PubMed1998

Splicing and missense mutations in the human FXIIIA gene causing FXIII deficiency: effects of these mutations on FXIIIA RNA processing and protein structure.

We have investigated the molecular basis of factor XIII (FXIII) deficiency in a family from the north-west region of the U.K. and identified two sequence changes in the FXIII subunit A (FXIIIA) gene. We report a novel Asn to Lys mutation at codon 541, and a g-->a mutation at the intron 5/exon 6 splice junction in the FXIIIA gene. The splicing mutation results in two abnormal FXIIIA transcripts. The Asn541 residue is important for stabilizing an external fold in the FXIIIA barrel 1 domain. The Asn541Lys mutation is expected to result in inappropriate folding and therefore an unstable FXIIIA molecule.

Adult↗
PubMed1998

Association study of asthma and atopy traits and chromosome 5q cytokine cluster markers.

BACKGROUND: Linkage studies have provided evidence for the presence of gene(s) in the 5q cytokine cluster region which control total serum immunoglobulin E (IgE) concentration, and bronchial hyperreactivity (BHR). However, the identification of the gene(s) involved has been confounded by the lack of power of the published linkage studies and the presence of multiple candidate genes mapped to the region. OBJECTIVE: To define the important loci on 5q31-33 which are implicated in the control of total serum IgE and BHR through a case/control study of association. METHODS: We performed an association study between 11 polymorphic markers (spanning the region 5q31.1-33.1) and total serum IgE and BHR traits. A case/control sample of 181 individuals was drawn from a larger set of 2415 adults, sampled at random from a district in Nottingham, UK. Half of the subjects in this case/control sample were hyperreactive to methacholine and asthmatic (cases), while the other half were non-reactive and non-asthmatic (controls). Association analysis was performed using the non-parametric chi-squared and Mann-Whitney U-tests. RESULTS: We observed no evidence of strong allelic association between any of the above markers and the studied traits. Markers D5S404, interferon regulatory factor 1 (IRF-1) and D5S210 showed evidence of borderline association with BHR (P = 0.04, 0.03 and 0.04 respectively), and D5S404 showed borderline significance with IgE levels (P = 0.029). CONCLUSIONS: This study presents evidence against the presence of a strong association between markers mapped to 5q31-33 and either BHR or total serum IgE. The significance of the weaker associations observed with markers D4S404, IRF-1 and D5S210 is not clear. Whether this represents a type I error secondary to multiple hypothesis testing or a true association is uncertain.

Adolescent↗
PubMed1998

A syndrome of severe mental retardation, spasticity, and tapetoretinal degeneration linked to chromosome 15q24.

Nine affected individuals are described from a large extended Pakistani family manifesting a syndrome characterized by a triad of varying degrees of spasticity, severe mental retardation, and visual impairment resulting from tapetoretinal degeneration. In all cases, the parents were at least first cousins, since there was complex consanguinity within the pedigree. The clinical features differ from previously reported syndromes involving pigmentary retinal degeneration and appear to represent a new recessively inherited neurodegenerative condition. Linkage to a 4-5 cM-region between markers D15S211 and D15S152 on 15q24 has been established by autozygosity mapping.

Abnormalities, Multiple↗
PubMed1998

Autozygosity mapping, to chromosome 11q25, of a rare autosomal recessive syndrome causing histiocytosis, joint contractures, and sensorineural deafness.

We describe a highly consanguineous family, originating from Pakistan, displaying histiocytosis, joint contractures, and sensorineural deafness. The form of histiocytosis exhibited by this family does not fit readily into any of the recognized classes of this disease. It appears to represent a novel form of familial histiocytosis demonstrating autosomal recessive inheritance. Using autozygosity mapping, we have identified a homozygous region of approximately 1 cM at chromosome 11q25, in affected individuals. A maximum two-point LOD score of 3.42 (recombination fraction straight theta = .00) was obtained with marker D11S968. This is the first genetic locus to be described that is involved in the molecular pathogenesis of histiocytosis.

Abnormalities, Multiple↗
PubMed1998

Primary autosomal recessive microcephaly (MCPH1) maps to chromosome 8p22-pter.

Primary (or "true") microcephaly is inherited as an autosomal recessive trait and is thought to be genetically heterogeneous. Using autozygosity mapping, we have identified a genetic locus (MCPH1) for primary microcephaly, at chromosome 8p22-pter, in two consanguineous families of Pakistani origin. Our results indicate that the gene lies within a 13-cM region between the markers D8S1824 and D8S1825 (maximum multipoint LOD score of 8.1 at D8S277). In addition, we have demonstrated the genetic heterogeneity of this condition by analyzing a total of nine consanguineous families with primary microcephaly.

Chromosome Mapping↗