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Biomedical subjects

W Bickmore

Publications and source records attributed to W Bickmore.

17 recordsLinked to original sources
PubMed2001

Human diseases with underlying defects in chromatin structure and modification.

Chromatin structure is important for regulating gene expression and for the proper condensation and segregation of chromosomes during cell division. Several human genetic diseases have been found to be due to mutations in genes producing proteins known or suspected to be involved in maintaining or modifying chromatin structure. Here we describe these 'chromatin diseases' and review what is known about the associated chromatin proteins in light of recent advances in the understanding of chromatin components, modification and function.

Chromatin↗
PubMed2001

Dual Y-chromosome painting and immunofluorescence staining of archival human liver transplant biopsies.

Combining fluorescence in situ hybridization (FISH) and indirect immunofluorescence staining of protein markers provides a highly specific method for identifying chromosomes in phenotypically defined cells and tissues. We developed a technique enabling dual chromosome painting and immunofluorescence staining of archival formalin-fixed, paraffin-embedded material, and used this to phenotype chimeric cells in female-to-male human liver transplants.

Chromosome Painting↗
PubMed1996

Imprinting mutation in the Beckwith-Wiedemann syndrome leads to biallelic IGF2 expression through an H19-independent pathway.

The Beckwith-Wiedemann syndrome (BWS) is genetically linked to chromosome 11p15.5, and a variety of observations suggest that deregulation of imprinted genes in this region is causally involved in the pathogenesis of the disease. It has been shown that in some patients without cytogenetic abnormalities the otherwise repressed maternal copy of the insulin-like growth factor 2 (IGF2) gene is expressed, leading to biallelic expression of IGF2. In some of these cases, this is accompanied by repression and DNA methylation of the maternal (otherwise active) copy of the neighbouring H19 gene. Hence, it is attractive to think that mutations may interfere with some aspect of H19 imprinting, thus leading to an inactive maternal allele, and indirectly to activation of the maternal IGF2 allele as reported in mice with an H19 gene deletion. However, no mutations have been identified so far in these patients. The only known mutations associated with BWS are maternally transmitted translocations, which are clustered in two locations centrometric to IGF2. The first cluster is 200-400 kb from IGF2 and the second is several megabases away. Hence, genes located far from the translocation breakpoints are potentially deregulated by them. Here we provide the first evidence of alteration of imprinting in a translocation family, with biallelic expression of IGF2 and altered DNA replication patterns in the IGF2 region. Interestingly, H19 imprinting was normal, suggesting an H19-independent pathway to biallelic IGF2 transcription. DNA methylation in IGF2 remained monoallelic, suggesting that the mutation in this family had uncoupled allele-specific methylation from expression.

Alleles↗
PubMed1995

Imprinting mutations in the Beckwith-Wiedemann syndrome suggested by altered imprinting pattern in the IGF2-H19 domain.

Regional regulations of parental imprinting in the IGF2-H19 domain of imprinted genes was studied in the Beckwith-Wiedemann syndrome (BWS). We identified BWS patients who had inherited a normal biparental chromosome complement of the chromosome 11p15.5 region (where IGF2 and H19 reside), but had an altered pattern of allelic methylation of both genes, with the maternal chromosome carrying a parental imprinting pattern. In fibroblasts, IGF2 was expressed from both parental alleles and H19 was not expressed, precisely as predicted from the altered pattern of allelic methylation. Interestingly, DNA replication patterns of the 11p15.5 region remained asynchronous as in controls. Our results therefore provide the first example of the dissociation of regional control of DNA replication from regional control of allelic methylation and expression in imprinting. We suggest that the altered pattern of allelic methylation and expression arises in the germline or in the early embryo from defects in resetting or setting of imprinting in maternal germline. Potential candidate regions for mutations include the previously identified translocation breakpoint clusters and the H19 gene itself. The finding of possible 'imprinting mutations' in BWS raises the prospect of identifying genetic factors that control imprinting in this region.

Base Sequence↗
PubMed1995

DNA binding capacity of the WT1 protein is abolished by Denys-Drash syndrome WT1 point mutations.

Constitutional point mutations in the zinc finger (ZF) region of the Wilms' tumour suppressor gene 1 (WT1) lead to Denys-Drash syndrome (DDS). Patients with this syndrome display renal failure, Wilms' tumour (WT) and pseudohermaphroditism. DDS WT1 mutations fall into three major categories: (a) missense mutations altering amino acids which directly interact with the DNA target; (b) substitution of amino acids involved in zinc complexing; and (c) nonsense mutations leading to the removal of at least two zinc fingers. We have expressed the WT1 zinc fingers as glutathione-S-transferase fusion proteins, with the lysine-threonine-serine (KTS) alternate splice between ZF3 and ZF4 either present or absent. WT1 fusion constructs with all three classes of DDS mutation were also created. Wild-type and mutant fusion proteins were assayed for their DNA-binding affinity using four previously identified WT1 DNA targets: an EGR1 consensus site; murine insulin-like growth factor 2 promoter 2 (IGF2P2); a (TCC)n motif from the PDGFA-chain promoter; and +P5, a genomic fragment isolated by its affinity for WT1 + KTS. WT1-KTS bound all four targets, but WT1 + KTS only bound +P5. All three classes of DDS mutation investigated, with or without KTS, abolished binding to all four targets. This provides evidence that DDS mutations act either as dominant-negative antimorphs, or elicit their effect through disturbed isoform dosage balance.

Abnormalities, Multiple↗
PubMed1995

Aniridia-associated cytogenetic rearrangements suggest that a position effect may cause the mutant phenotype.

Current evidence suggests that aniridia (absence of iris) is caused by loss of function of one copy of the PAX6 gene, which maps to 11p13. We present the further characterisation of two aniridia pedigrees in which the disease segregates with chromosomal rearrangements which involve 11p13 but do not disrupt the PAX6 gene. We have isolated three human YAC clones which encompass the PAX6 locus and we have used these to show that in both cases the chromosomal breakpoint is at least 85 kb distal of the 3' end of PAX6. In addition, the open reading frame of PAX6 is apparently free of mutations. We propose that the PAX6 gene on the rearranged chromosome 11 is in an inappropriate chromatin environment for normal expression and therefore that a 'position effect' is the underlying mechanism of disease in these families.

Aniridia↗
PubMed1990

The candidate Wilms' tumour gene is involved in genitourinary development.

Wilms' tumour is an embryonic kidney tumour thought to arise through aberrant mesenchymal stem cell differentiation and to result from loss of function of a 'tumour suppressor' gene(s). Both sporadic and syndrome-associated Wilms' tumours are accompanied by an increased frequency of abnormalities of the urinary tract and genitalia. Deletional analysis of individuals with the WAGR syndrome (for, Wilms' tumour, aniridia, genitourinary abnormalities and mental retardation) showed that a Wilms' tumour gene lies at chromosomal position 11p13. This led to the isolation of a candidate Wilms' tumour gene, encoding a zinc-finger protein which is likely to be a transcription factor. To gain insight into the role of this candidate gene in normal development and tumorigenesis, we have now performed in situ messenger RNA hybridization on sections of human embryos and Wilms' tumours. The candidate Wilms' tumour gene is expressed specifically in the condensed mesenchyme, renal vesicle and glomerular epithelium of the developing kidney, in the related mesonephric glomeruli and in cells approximating these structures in tumours. The other main sites of expression are the genital ridge, fetal gonad and mesothelium. These data suggest that (1) this candidate is indeed a Wilms' tumour gene, (2) the associated genital abnormalities are pleiotropic effects of mutation in the Wilms' tumour gene itself, in support of recent genetic analysis, and (3) this gene has a specific role in kidney development and a wider role in mesenchymal-epithelial transitions.

Blotting, Northern↗
PubMed1989

Close linkage of the human cytochrome P450IIA and P450IIB gene subfamilies: implications for the assignment of substrate specificity.

We have isolated from human liver libraries two cytochrome P450 cDNA clones (lambda MP14 and lambda MP3) which are highly similar (83% over the coding region) to mouse testosterone 15 alpha hydroxylase and are therefore part of the cytochrome P450IIA gene subfamily. The P450IIA (CYP2A) gene subfamily was found to be closely linked to the P450IIB (CYP2B) subfamily and their chromosomal location could not be distinguished using somatic cell hybrids containing fragments of chromosome 19 between 19q12 and 19q13.2. Pulsed field gel electrophoresis indicates that both gene subfamilies are contained within 350-kb genomic DNA fragments, but were separated using various restriction enzymes. Northern blot analysis identified three P450IIA mRNAs each showing a wide inter-individual variation in their levels in the liver. High levels of P450IIA transcript were associated with high levels of P450IIB transcript suggesting that common factors may influence the expression of genes within these subfamilies. Genetic analysis has suggested previously that a member of the P450IIB subfamily is responsible for coumarin hydroxylase activity in the mouse. We discuss the possibility, based on our findings of tight linkage of the human P450IIA and IIB subfamilies, that a member of the IIA subfamily is a better candidate for this enzyme activity.

Amino Acid Sequence↗
PubMed1989

Wilms tumour: a developmental anomaly.

Wilms tumour (WT) is a developmental anomaly of the kidney which results from loss of function of at least one so called tumour suppressor gene on chromosome 11. The position of the gene at chromosome 11p13 is known through the association of WT with aniridia (lack of an iris), mental retardation and genitourinary abnormalities in the WAGR syndrome. Here we discuss the high resolution mapping studies to locate the position of the gene and conclude that the gonadal abnormalities in WAGR patients may be due to a defect in the WT gene itself. In support of this role in genitourinary development we show that a candidate WT gene is expressed in specific regions of the developing kidney and in fetal and embryonic gonads.

Abnormalities, Multiple↗
PubMed1988

Hitch-hiking from HRAS1 to the WAGR locus with CMGT markers.

The clinical association of Wilms' tumour with aniridia, genitourinary abnormalities and mental retardation (WAGR syndrome) is characterised cytogenetically by variable length, constitutional deletion of the short arm of chromosome 11, which always includes at least part of band 11p13. HRAS1-selected chromosome mediated gene transfer (CMGT) generated a transformant, E65-6, in which the only human genes retained map either to band 11p13 or, with HRAS1, in the region 11p15.4-pter. Human recombinants isolated from E65-6 were mapped to a panel of five WAGR deletion hybrids and two clinically related translocations. We show that E65-6 is enriched congruent to 400-fold for 11p15.4-pter markers and congruent to 200-fold for 11p13 markers. 'Hitch-hiking' from HRAS1 with CMGT markers has allowed us to define seven discrete intervals which subtend band 11p13. Both associated translocations co-locate within the smallest region of overlap for the WAGR locus, which has been redefined by identifying a new interval closer than FSHB.

Animals↗
PubMed1987

HRAS1-selected chromosome transfer generates markers that colocalize aniridia- and genitourinary dysplasia-associated translocation breakpoints and the Wilms tumor gene within band 11p13.

We show that chromosome-mediated gene transfer can provide an enriched source of DNA markers for predetermined, subchromosomal regions of the human genome. Forty-four human DNA recombinants isolated from a HRAS1-selected chromosome-mediated gene transformant map exclusively to chromosome 11, with several sublocalizing to the Wilms tumor region at 11p13. We present a detailed molecular map of the deletion chromosomes 11 from five WAGR (Wilms tumor/aniridia/genitourinary abnormalities/mental retardation) syndrome patients, three of which are at the limits of cytogenetic resolution but shown here to be molecularly distinguishable and overlapping. We can define ten distinct regions of the short arm of chromosome 11, five of which subdivide band 11p13. We also map two independent 11p13 translocation breakpoints to within the smallest region of overlap defined by the WAGR deletions. The first comes from a patient with familial aniridia, and the second from a patient with Potter facies and genitourinary dysplasia. The close similarities in map location and affected cell lineage for Wilms tumor and genitourinary dysplasia suggest that they may be alternative manifestations of mutation at the same locus.

Animals↗