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N A Ellis

Publications and source records attributed to N A Ellis.

17 recordsLinked to original sources
PubMed1997

DNA helicases in inherited human disorders.

Six known or predicted helicases that are mutated in human syndromes are now recognized. These syndromes include xeroderma pigmentosum, Cockayne's syndrome, trichothiodystrophy, Bloom's syndrome, Werner's syndrome, and alpha-thalassemia mental retardation on the X chromosome. The clinical abnormalities in these syndromes cover a broad spectrum, pointing to different cellular processes of DNA manipulation that are defective in these syndromes.

Amino Acid Sequence↗
PubMed1996

Physical mapping of the bloom syndrome region by the identification of YAC and P1 clones from human chromosome 15 band q26.1.

The gene for Bloom syndrome (BLM) has been mapped to human chromosome 15 band q26.1 by homozygosity mapping. Further refinement of the location of BLM has relied upon linkage-disequilibrium mapping and somatic intragenic recombination. In combination with these mapping approaches and to identify novel DNA markers and probes for the BLM candidate region, a contiguous representation of the 2-Mb region that contains the BLM gene was generated and is presented here. YAC and P1 clones from the region have been identified and ordered by using previously available genetic markers in the region along with newly developed sequence-tagged sites from radiation-reduced hybrids, polymorphic dinucleotide repeat loci, and end sequences of YACs and P1s. A long-range restriction map of the 2-Mb region that allowed estimation of the distance between polymorphic microsatellite loci is also reported. This map and the DNA markers derived from it were instrumental in the recent identification of the BLM gene.

Adenosine Triphosphatases↗
PubMed1996

Molecular genetics of Bloom's syndrome.

Mutation of the Bloom's syndrome (BS) gene, BLM, results in genomic instability. As the first step toward positional cloning of the gene, tight linkage of BLM and FES at 15q26.1 was detected by genotyping affected in families in which the parents are cousins, so-called homozygosity mapping. Linkage disequilibrium between BLM and FES was detected in Ashkenazi Jews with BS, confirming the linkage results and supporting the hypothesis that the increased frequency of the BS mutation in the Ashkenazim is due to founder effect. The mutated BLM gene is inherited identical by descent in BS persons whose parents are cousins or Ashkenazi Jewish; in persons whose parents do not share a common ancestor, BLM can be mutant at different positions within the gene. In such persons, crossing-over within BLM can occur to form a functionally wild-type gene capable of correcting the mutant phenotype of BS cells. In half the cases in which such somatic intragenic recombination had occurred, reduction to homozygosity was detectable distal to BLM but not proximal to it. We localized the cross-over points in corrected cells to a 250 kb genomic segment and isolated therefrom a 4437 bp cDNA that encodes a 1417 amino acid protein homologous to the RecQ subfamily of DExH box-containing DNA and RNA helicases. The identification of BLM as a putative DNA helicase provides a new and powerful tool to investigate the primary defect in BS and the function of the BLM gene product in maintaining the integrity of the genome.

Alleles↗
PubMed1996

Bloom's syndrome. XIX. Cytogenetic and population evidence for genetic heterogeneity.

Cells with abnormally high rates of sister-chromatid exchange (SCE) are uniquely characteristic of Bloom's syndrome (BS). However, in one in five persons a minor population of cells with a low-SCE phenotype circulates in the blood. The origin and significance of the low-SCE cells in BS have never been understood, although they are assumed to arise by somatic mutation. In the present investigation, the enigmatic high-SCE/low-SCE mosaicism was investigated by comparing the incidence in several subpopulations of persons in the Bloom's Syndrome Registry who exhibit the two types of cells, and a striking negative correlation emerged: in persons with BS whose parents share a common ancestor, the case in approximately half of registered persons, low-SCE cells are found only rarely; conversely, the mosaicism occurs almost exclusively in persons with BS whose parents are not known to share a common ancestor. Because those who share a common ancestor are predominantly homozygous-by-descent at the mutated BS locus, the negative correlation is interpreted to mean that the emergence of low-SCE cells in BS in some way depends on the pre-existence of compound heterozygosity. A corollary to this is that BS is genetically heterogeneous.

Bloom Syndrome↗
PubMed1995

The Bloom's syndrome gene product is homologous to RecQ helicases.

The Bloom's syndrome (BS) gene, BLM, plays an important role in the maintenance of genomic stability in somatic cells. A candidate for BLM was identified by direct selection of a cDNA derived from a 250 kb segment of the genome to which BLM had been assigned by somatic crossover point mapping. In this novel mapping method, cells were used from persons with BS that had undergone intragenic recombination within BLM. cDNA analysis of the candidate gene identified a 4437 bp cDNA that encodes a 1417 amino acid peptide with homology to the RecQ helicases, a subfamily of DExH box-containing DNA and RNA helicases. The presence of chain-terminating mutations in the candidate gene in persons with BS proved that it was BLM.

Adenosine Triphosphatases↗
PubMed1995

Ecce Ohno!

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Animals↗
PubMed1995

The human Y chromosome homologue of XG: transcription of a naturally truncated gene.

The XG blood group gene spans PABX1, the pseudoautosomal boundary on the X chromosome. The first three exons are pseudoautosomal and the remaining seven are X-specific. On the Y chromosome SRY and RPS4Y are located in Y-specific sequences within 70 kb of the boundary. Transcription from the XG promoter on the Y chromosome has been detected by cDNA cloning and PCR-based methods. Splicing of the pseudoautosomal exon 3 of XG occurs to multiple sites in Y-specific sequences. Transcripts detected include antisense SRY sequences and XG approximately RPS4Y hybrid transcripts. The heterogeneity and low abundance of transcripts as well as the lack of maintenance of the XG open reading frame in all but one transcript argue against a specific Y-chromosome gene product. An expressed pseudogene of XG, XGPY, has been mapped to interval Yq11.21. XGPY is transcribed and subject to alternative splicing. Sequence comparison suggests that XGPY originated from XG by a gene duplication event in the primate lineage.

Alternative Splicing↗
PubMed1995

Somatic intragenic recombination within the mutated locus BLM can correct the high sister-chromatid exchange phenotype of Bloom syndrome cells.

Cells from persons with Bloom syndrome feature an elevated rate of sister-chromatid exchange (SCE). However, in some affected persons a minority of blood lymphocytes have a normal SCE rate. Persons who inherit the Bloom syndrome gene BLM identical by descent from a common ancestor very rarely exhibit this high-SCE/low-SCE mosaicism; conversely, mosaicism arises predominantly in persons who do not share a common ancestor. These population data suggested that most persons with Bloom syndrome in whom the exceptional low-SCE cells arise are not homozygous for a mutation at BLM but instead are compound heterozygotes. Following this clue, we carried out a genotype analysis of loci syntenic with BLM in 11 persons who exhibited mosaicism. In five of them, polymorphic loci distal to BLM that were heterozygous in their high-SCE cells had become homozygous in their low-SCE cells, whereas heterozygous loci proximal to BLM remained heterozygous. These observations are interpreted to mean that intragenic recombination between paternally derived and maternally derived mutated sites within BLM can generate a functionally wild-type gene and that low-SCE lymphocytes are progeny of a somatic cell in which such intragenic recombination had occurred.

Bloom Syndrome↗
PubMed1994

Bloom syndrome: an analysis of consanguineous families assigns the locus mutated to chromosome band 15q26.1.

By the principle of identity by descent, parental consanguinity in individuals with rare recessively transmitted disorders dictates homozygosity not just at the mutated disease-associated locus but also at sequences that flank that locus closely. In 25 of 26 individuals with Bloom syndrome examined whose parents were related, a polymorphic tetranucleotide repeat in an intron of the protooncogene FES was homozygous, far more often than expected (P < 0.0001 by chi 2). Therefore, BLM, the gene that when mutated gives rise to Bloom syndrome, is tightly linked to FES, a gene whose chromosome position is known to be 15q26.1. This successful approach to the assignment of the Bloom syndrome locus to one short segment of the human genome simultaneously (i) demonstrates the power of homozygosity mapping and (ii) becomes the first step in a "reverse" genetics definition of the primary defect in Bloom syndrome.

Alleles↗
PubMed1994

Cloning of PBDX, an MIC2-related gene that spans the pseudoautosomal boundary on chromosome Xp.

The pseudoautosomal boundaries are the interface between pseudoautosomal and sex chromosome-specific DNA sequences. We have isolated a gene, PBDX, from the human pseudoautosomal boundary region of Xp. The three exons at the 5' end of PBDX are situated in the pseudoautosomal region immediately downstream of MIC2, whereas the other seven exons are in the X-specific region. Hence, PBDX is inherited in two modes: its 5' end is pseudoautosomally inherited and its 3' end is X-linked. The predicted amino acid sequence of the 540 bp coding region is 48% homologous to 12E7, the product of MIC2. By virtue of its position, PBDX becomes an excellent candidate for the XG blood group gene.

12E7 Antigen↗
PubMed1994

PBDX is the XG blood group gene.

We have identified the Xga antigen, encoded by the XG blood group gene, by employing rabbit polyclonal and mouse monoclonal antibodies raised against a peptide derived from the N-terminal domain of a candidate gene, referred to earlier as PBDX. In indirect haemagglutination assays, these anti-peptide antibodies react with Xg(a+) but not Xg(a-) erythrocytes. In antibody-specific immobilization of antigen (ASIA) and immunoblot assays, the anti-peptide antibodies react with the same molecule as does human anti-Xga. Therefore, by its identity with PBDX, Xga is identified as a cell-surface protein that is 48% homologous to CD99 (previously designated the 12E7 antigen), the product of MIC2 which is tightly linked to XG. PBDX is renamed here XG.

12E7 Antigen↗
PubMed1994

Linkage disequilibrium between the FES, D15S127, and BLM loci in Ashkenazi Jews with Bloom syndrome.

Bloom syndrome (BS) is more common in the Ashkenazi Jewish than in any other population. Approximately 1 in 110 Ashkenazi Jews carries blm, the BS mutation. The locus mutated in BS, BLM, maps to chromosome subband 15q26.1, tightly linked to the proto-oncogene FES. We have investigated the basis for the increased frequency of blm in the Ashkenazim by genotyping polymorphic microsatellite loci tightly linked to BLM in affected and unaffected individuals from Ashkenazi Jewish and non-Ashkenazi populations. A striking association of the C3 allele at FES with blm (delta = .422; p = 5.52 x 10(-7)) and of the 145-bp and 147-bp alleles at D15S127 with blm (delta = .392 and delta = .483, respectively; p = 2.8 x 10(-5) and p = 5.4 x 10(-7), respectively) was detected in Ashkenazi Jews with BS. This linkage disequilibrium constitutes strong support for a founder-effect hypothesis: the chromosome in the hypothetical founder who carried blm also carried the C3 allele at FES and either the 145-bp or the 147-bp allele at D15S127.

Bloom Syndrome↗
PubMed1989

The pseudoautosomal boundary in man is defined by an Alu repeat sequence inserted on the Y chromosome.

The Y chromosome, which in man determines the male sex, is composed of two functionally distinct regions. The pseudoautosomal region is shared between the X and Y chromosome and is probably required for the correct segregation of the sex chromosomes during male meiosis. The second region includes the sex-determining gene(s), the presence of which is necessary for the development of testes. The two regions have contrasting genetic properties: the pseudoautosomal region recombines between the X and Y chromosome; the Y-specific region must avoid recombination otherwise the chromosomal basis of sex-determination breaks down. The pseudoautosomal region is bounded at the distal end by the telomere and at the proximal end by X- and Y-specific DNA. We have found that the proximal boundary was formed by the insertion of an Alu sequence on the Y chromosome early in the primate lineage. Proximal to the Alu insertion there is a small region where similarity between the X and Y chromosomes is reduced and which is no longer subject to recombination.

Base Sequence↗
PubMed1988

The family of mouse phosphoglycerate kinase genes and pseudogenes.

The mammalian genome contains two genes encoding phosphoglycerate kinase; the pgk-1 gene is X-linked and is expressed in all cells except sperm, while the pgk-2 gene is expressed exclusively in sperm cells. The mouse genome contains no pseudogenes derived from pgk-2. On the other hand, the genomes of Balb/c and C3H/He strain mice contain six other regions with sequences homologous to those of pgk-1 cDNA. These pgk-related sequences are likely derived from the pgk-1 gene by retroposition because all are located on autosomal chromosomes and because none appear to be interrupted by introns. Two of the presumed pseudogenes contain sequences homologous to all regions of the pgk-1 cDNA while the other four genomic regions were truncated at the 5', 3', or both ends. One of the truncated pseudogenes was sequenced. Its pgk-related sequence was not flanked by direct repeats, suggesting that loss of the 5' and/or 3' ends of this retrogene may have occurred following its integration into the genome. Our evidence suggests that pgk-1-derived retroposons arose initially more than 100 million years ago and have continued to arise until so recently that some are unique to different mouse strains.

Animals↗
PubMed1988

Demethylation of specific sites in the 5' region of the inactive X-linked human phosphoglycerate kinase gene correlates with the appearance of nuclease sensitivity and gene expression.

X8/6T2, a hamster-human hybrid cell line which contains an inactive human X chromosome, was treated with 5-azacytidine and selected for derepression of hypoxanthine-guanine phosphoribosyltransferase. Clones were examined for coreactivation of the phosphoglycerate kinase gene (Pgk). Of 68 of these hybrids, approximately 20% expressed measurable human phosphoglycerate kinase (PGK) activity. A 600-base-pair region of the Pgk 5' CpG cluster was examined for the methylation status of eight CCGG sites (site 1 being 5'-most) in a number of PGK-negative and PGK-positive cell lines. The inactive X chromosome is normally methylated at all eight sites, and this was also true for the majority of X8/6T2 cells. However, several PGK-negative hybrids were demethylated in the site 3 to site 6 region. PGK activity correlated with demethylation at both sites 6 and 7. The data for PGK-positive and -negative hybrids indicate that demethylation at or near site 7 was necessary for reactivation of Pgk. Chromatin sensitivity to MspI digestion in the nuclei of male lymphoblastoid cells and several PGK-positive and PGK-negative hybrids was examined. PGK-positive cell lines were hypersensitive to digestion, while PGK-negative hybrids were resistant. Cleavage at sites 6 and 7 was observed in all PGK-positive cell lines at each MspI concentration examined. Sites 7 and 8 were less accessible to digestion than site 6. Cleavage in the site 2 to site 5 region was observable at the lowest MspI concentration. In most PGK-positive hybrids, a nonspecific endogenous nuclease detected the presence of a hypersensitive region spanning at least 450 base pairs, bounded at the 3' end near HpaII site 6. Nuclease hypersensitivity appears to be related to promoter activity, because sites 7 and 8 are in transcribed regions of the gene. These data indicate that specific sites within the CpG cluster have a dominant controlling influence over the Pgk promoter conformation and the transcriptional activation of Pgk.

Animals↗
PubMedDate not supplied

Genetic evidence that ZFY is not the testis-determining factor.

In mammals, the testis determining gene (TDF), present on the Y chromosome, induces the undifferentiated gonads to form testes. The position of TDF on the human Y chromosome has been defined by analysing the genomes of XX males and XY females, generated by abnormal genetic exchange between the X and Y chromosomes in male meiosis. In this way TDF has been localized close to the pseudoautosomal region shared by the sex chromosomes, in the distal Y-specific region. A recently cloned human gene, ZFY, has many features indicating that it is TDF. For example, ZFY encodes a protein with many features of a transcription factor including a domain with multiple 'zinc-finger' motifs. Less consistent with ZFY being TDF, however, is the presence of a very similar gene, ZFX, on the X chromosome, and the presence of a sequence related to ZFY on autosomes in marsupials. We now report on analysis of XX males lacking ZFY. In these individuals, the male phenotype could be explained by a mutation in a gene 'downstream' of ZFY in the sex-determining hierarchy; but in that case there should be no exchange of material between the X and Y chromosomes. We find on the contrary that in 4 XX males lacking ZFY, there is exchange of Y-specific sequences next to the pseudoautosomal boundary, redefining the region in which TDF must lie.

Blotting, Southern↗