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Biomedical subjects

A F Markham

Publications and source records attributed to A F Markham.

At least 127 records · Page 7Linked to original sources
PubMed1997

Identification and characterisation of a sequence related to human sorbitol dehydrogenase.

The polyol pathway comprises the enzymes aldose reductase and sorbitol dehydrogenase which convert glucose to fructose via sorbitol. Accumulation of sorbitol within the cell has been suggested to contribute to the progression of secondary complications of diabetes. High levels of sorbitol accumulate within the cell due to inadequate regulation of blood glucose levels. It has also been suggested that polymorphism in either the aldose reductase or sorbitol dehydrogenase genes might contribute to sorbitol accumulation. The human sorbitol dehydrogenase gene (SORD) has been described previously and a range of putative polymorphic variants were identified. Further analysis of human SORD yeast artificial chromosome clones has now shown that there is a second SORD-like sequence in man, which is extremely similar in sequence to SORD itself and which also maps to chromosome 15. Detailed sequence analysis suggests that this SORD-related gene cannot be expressed as a full-length sorbitol dehydrogenase isoenzyme. However, knowledge of the presence of this highly similar sequence in the human genome is essential to ensure that sequence variations identified during genetic analysis of SORD are not attributed to polymorphisms within that gene itself.

Amino Acid Sequence↗
PubMed1997

Analysis of the mismatch and insertion/deletion binding properties of Thermus thermophilus, HB8, MutS.

The methyl-directed long patch repair pathway in Escherichia coli is involved in increasing the fidelity of replication specific repair of DNA polymerase incorporation errors. This pathway is mediated by three gene products, MutS, MutL, and MutH, which 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). A MutS homologue has recently been identified in the extremely thermophilic bacterium, Thermus thermophilus. Here we describe analysis of the binding properties of this protein, which has indicated it can identify all specific base mismatches as well as one, two and three base pair insertion/deletion mutations. We therefore believe this protein may be generally useful for applications involving mismatch detection.

Adenosine Triphosphatases↗
PubMed1997

Mapping the minimal domain of hMSH-2 sufficient for binding mismatched oligonucleotides.

The human MSH-2 gene product is a member of a highly conserved family of proteins involved in post-replication mismatch repair. Germline mutations in this gene have been implicated in hereditary non-polyposis colorectal cancer (HNPCC). Alterations in the coding region of the hMSH-2 gene result in a mutator phenotype with marked instability of microsatellite sequences, indicative of a deficiency in DNA repair. We have previously shown that a region of high homology between MutS proteins of different species containing a nucleotide binding domain, is sufficient to bind DNA containing specific mismatched residues. In order to determine the minimal domain of hMSH-2 necessary for binding mismatch-containing oligonucleotides, deletion analysis of the C-terminal region was performed. We have constructed a 5' and 3' deletion series, expressed each deletion as a bacterial fusion protein and assessed it for ATPase activity and its ability to identify mismatch containing DNA. Here we demonstrate that a 585 bp fragment encoding 195 amino acids within the C-terminal domain of hMSH-2 is sufficient to bind to DNA containing mismatches.

Adenosine Triphosphatases↗
PubMed1997

The human gene encoding FKBP-rapamycin associated protein (FRAP) maps to chromosomal band 1p36.2.

FKBP-rapamycin associated protein (FRAP) is a phosphatidylinositol kinase (PIK)-related kinase implicated in the inhibition of progression through G1 of the cell cycle. The PIK-related kinases are a growing family of proteins involved in cell-cycle checkpoints, DNA repair and recombination. We have mapped the human FRAP gene to chromosome 1p36.2, a region consistently deleted in neuroblastomas.

Base Sequence↗
PubMed1997

Characterisation of human patched germ line mutations in naevoid basal cell carcinoma syndrome.

Mutations in the human patched gene have recently been detected in patients with naevoid basal cell carcinoma syndrome. We have characterised a further 5 novel germ line mutations in patients presenting with multiple odontogenic keratocysts. Four mutations cause premature stop codons and one mutation results in an amino-acid substitution towards the carboxyl terminus of the predicted patched protein. No obvious genotype-phenotype correlations could be interpreted, consistent with previous studies.

Adolescent↗
PubMed1997

The cellular distribution of the adenomatous polyposis coli tumour suppressor protein in neuroblastoma cells is regulated by microtubule dynamics.

The adenomatous polyposis coli tumour suppressor protein is highly expressed in developing rodent brain, but its function is unclear. Recent studies have suggested a role for this protein in regulating microtubule dynamics. Neuro 2A mouse neuroblastoma cells were previously thought not to express this protein. Using immunochemical techniques, this report corrects this observation. Immunoreactive bands of a size consistent with that of the full-length protein were observed by western blotting. Using immunocytochemistry, punctate immunoreactivity localized to areas of the cell containing microtubules, particularly neurite growth cones, in a distribution suggesting a role in neuritogenesis and growth cone extension. The protein did not localize to actin-rich cellular structures, and perturbation of the actin cytoskeleton had no effect upon this distribution. Treatment of cells with taxol to stabilize microtubules caused the concentration of the immunoreactive puncta to the tips of microtubules and areas along the axis of potential microtubule assembly. Treatment of cells with the microtubule disrupting reagent nocodazole showed that over shorter times the punctate distribution was not dependent upon polymerized microtubules. However, at longer incubation times a decrease in punctate immunostaining was observed. These results indicate that the intracellular distribution of the adenomatous polyposis coli protein is dependent upon microtubule but not actin dynamics. A role for this protein in the regulation of directed microtubule assembly is suggested.

Adenomatous Polyposis Coli↗
PubMed1997

RT-PCR investigation of fibronectin mRNA isoforms in malignant, normal and reactive oral mucosa.

This study aimed to establish patterns of cellular fibronectin mRNA splice variants in normal oral mucosa, oral squamous cell carcinoma, oral leukoplakias with and without atypia, and focal reactive overgrowths of oral mucosa. Particular emphasis was placed on evaluation of either the EDA or EDB domains as markers of malignancy. Total RNA was extracted from normal oral mucosa, oral squamous cell carcinoma, oral leukoplakias with and without atypia, reactive epulides, fibroepithelial polyps and denture-related hyperplasia. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to identify different fibronectin transcripts at three splice sites (EDA, EDB and IIICS). All the tissues investigated produced EDA+, EDA-, EDB+ and EDB- splice variants, and this study did not support RT-PCR-based detection of either EDA or EDB domains as markers of malignancy in oral tissues. Variations in IIICS splice patterns were observed, although these were not specific to any lesion group. In particular, there were differences in either the inclusion or omission of the domain coding for the CS-5 binding site for alpha 4 beta 1 integrin, whereas the CS-1 binding site for alpha 4 beta 1 integrin was typically present when additional domains were included at the IIICS splice site. In conclusion, complex patterns of fibronectin splice variant transcripts exist in normal and pathological oral mucosa. This may reflect the multiple biological functions identified for fibronectin proteins, although the significance of different specific fibronectin splice variants has yet to be fully elucidated.

Alternative Splicing↗
PubMed1997

A new locus for non-syndromal, autosomal recessive, sensorineural hearing loss (DFNB16) maps to human chromosome 15q21-q22.

Non-syndromal, recessive deafness (NSRD) is the most common form of inherited deafness or hearing impairment in humans. NSRD is genetically heterogeneous and it has been estimated that as many as 35 different loci may be involved. We report the mapping of a novel locus for autosomal recessive, non-syndromal deafness (DFNB16) in three consanguineous families originating from Pakistan and the Middle East. Using multipoint analysis (HOMOZ/MAPMAKER) a maximum combined lod score of 6.5 was obtained for the interval D15S1039-D15S123. Recombination events and haplotype analysis define a 12-14 cM critical region between the markers D15S1039 and D15S155 on chromosome 15q15-q21.

Chromosome Mapping↗
PubMed1997

Genetic heterogeneity in Schwartz-Jampel syndrome: two families with neonatal Schwartz-Jampel syndrome do not map to human chromosome 1p34-p36.1.

Schwartz-Jampel syndrome (SJS) is a rare autosomal recessive disorder characterised by the presence of myotonia with a mask-like face, skeletal dysplasia, and growth retardation. Two types have been defined by the age of manifestation of the symptoms. Linkage of Schwartz-Jampel syndrome to human chromosome 1p34-p36.1 has been shown in families where probands presented during infancy or early childhood. We have investigated two well documented families segregating severe neonatal SJS with microsatellite markers spanning the critical region of 1p34-p36. No demonstrable linkage to chromosome 1 was found in either family, suggesting that a second locus is responsible for the severe form of neonatal Schwartz-Jampel syndrome.

Chromosomes, Human, Pair 1↗
PubMed1997

Male pseudohermaphroditism resulting from a novel mutation in the human steroid 5 alpha-reductase type 2 gene (SRD5A2).

The enzyme steroid 5 alpha-reductase, via NADPH, catalyses the conversion of testosterone to dihydrotestosterone, which is required for the embryonic differentiation of the external male genitalia and the prostate. An impairment of this reaction causes a form of male pseudohermaphroditism in which genetic males differentiate predominantly as phenotypic females. Molecular analysis of the 5 alpha-reductase type 2 gene in a patient with confirmed biochemical 5 alpha-reductase deficiency has resulted in the identification of a novel mutation, GAA to AAA, at codon 200. This mutation produces an amino acid change from glutamic acid to lysine, and may affect the ability of the enzyme to bind its co-factor.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1997

A new mutation in the human lipoprotein lipase gene causing familial hyperchylomicronaemia.

Lipoprotein lipase plays a major role in the regulation of lipid metabolism. The enzyme acts to hydrolyse triglycerides, providing free fatty acids for energy generation or storage, thus affecting the maturation of circulating lipoproteins. Biochemical and molecular analyses were performed on two siblings of consanguineous Pakistani origin, presenting with hyperchylomicronaemia, which revealed that the disorder resulted from lipoprotein lipase deficiency. Molecular analysis of the lipoprotein lipase gene has revealed a novel homozygous mutation, leucine to proline at amino acid residue 303, within the amino terminal domain of the protein.

Child↗
PubMed1997

Rapid isolation of genomic clones for individual members of human multigene families: identification and localisation of UBE2L4, a novel member of a ubiquitin conjugating enzyme dispersed gene family.

We describe a rapid, PCR-based, screening procedure for the isolation of human genomic clones in lambda bacteriophage, containing sequences coding for individual homologous members of a multigene family. The approach is based upon the identification, by dilution, of sub-pools of the genomic library that contain members of the gene family, prior to phage isolation. The presence of specific genes is established by PCR of aliquots of individually amplified library pools, using consensus primers and subsequent sequencing. We have used the approach to isolate a fourth member of the UBE2L gene family, UBE2L4, and located it on chromosome 19q13.1-->q13.2. This PCR-based approach to library screening has wider applicability in that it could be used to isolate alternate-spliced products from cDNA libraries.

Bacteriophage lambda↗
PubMed1997

Automated differential display using a fluorescently labeled universal primer.

We have modified the automated differential display reverse transcription polymerase chain reaction technique (DDRT-PCR) such that a single fluorescently labeled universal primer (d(F)CTCACG-GATCCGTCGATTTT) is used in all PCRs together with a selection of arbitrary primers. We term this fluorescent detection procedure FDDRT-PCR. Anchoring primers of general structure dTGGTCTCACGGATCCTCGA-(T)12 VN (where N can be any deoxynucleoside and V can be any deoxynucleoside other than thymidine) are used for the RT step, and the universal primer together with selected arbitrary primers are then used for the PCR amplification. Advantages of this approach are: (i) the fluorescently labeled universal primer is a constant feature in every PCR, so that changes in banding profile are highly likely to reflect the incorporation of different arbitrary 10-mer primers; (ii) artifacts that result from arbitrary 10-mer to arbitrary 10-mer primer amplifications are not observed by fluoresence detection on an automated gene scanner because such products are not fluorescently labeled; (iii) sample throughput and ease of data handling are increased when compared with the conventional radioactive/manual approach and (iv) using a single fluorescently labeled primer in all PCRs is highly cost-effective.

Autoradiography↗