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Biomedical subjects

R Wevrick

Publications and source records attributed to R Wevrick.

At least 19 recordsLinked to original sources
PubMed2001

The role of genomic imprinting in human developmental disorders: lessons from Prader-Willi syndrome.

Normal human development involves a delicate interplay of gene expression in specific tissues at narrow windows of time. Temporally and spatially regulated gene expression is controlled both by gene-specific factors and chromatin-specific factors. Genomic imprinting is the expression of specific genes primarily from only one allele at particular times during development, and is one mechanism implicated in the intricate control of gene expression. Two human genetic disorders, Prader-Willi syndrome (PWS, MIM 176270) and Angelman syndrome (AS, MIM 105830), result from rearrangements of chromosome 15q11-q13, an imprinted region of the human genome. Despite their rarity, disorders such as PWS and AS can give focused insight into the role of genomic imprinting and imprinted genes in human development.

Alleles↗
PubMed2001

Establishment and maintenance of DNA methylation patterns in mouse Ndn: implications for maintenance of imprinting in target genes of the imprinting center.

Ndn is located on chromosome 7C, an imprinted region of the mouse genome. Imprinting of Ndn and adjacent paternally expressed genes is regulated by a regional imprinting control element known as the imprinting center (IC). An IC also controls imprint resetting of target genes in the region of conserved synteny on human chromosome 15q11-q13, which is deleted or rearranged in the neurodevelopmental disorder Prader-Willi syndrome. Epigenetic modifications such as DNA methylation, which occur in gametes and can be stably propagated, are presumed to establish and maintain the imprint in target genes of the IC. While most DNA becomes substantially demethylated by the blastocyst stage, some imprinted genes have regions that escape global demethylation and may maintain the imprint. We have now analyzed the methylation of 39 CpG dinucleotide sequences in the 5' end of Ndn by sodium bisulfite sequencing in gametes and in preimplantation and adult tissues. While sperm DNA is completely unmethylated across this region, oocyte DNA is partially methylated. A distinctive but unstable maternal methylation pattern persists until the morula stage and is lost in the blastocyst stage, where low levels of methylation are present on most DNA strands of either parental origin. The methylation pattern is then substantially remodeled, and fewer than half of maternally derived DNA strands in adult brain resemble the oocyte pattern. We postulate that for Ndn, DNA methylation may initially preserve a gametic imprint during preimplantation development, but other epigenetic events may maintain the imprint later in embryonic development.

Animals↗
PubMed2000

Expression and imprinting of MAGEL2 suggest a role in Prader-willi syndrome and the homologous murine imprinting phenotype.

Prader-Willi syndrome (PWS) is caused by the loss of expression of imprinted genes in chromosome 15q11-q13. Affected individuals exhibit neonatal hypotonia, developmental delay and childhood-onset obesity. Necdin, a protein implicated in the terminal differentiation of neurons, is the only PWS candidate gene to reduce viability when disrupted in a mouse model. In this study, we have characterized MAGEL2 (also known as NDNL1), a gene with 51% amino acid sequence similarity to necdin and located 41 kb distal to NDN in the PWS deletion region. MAGEL2 is expressed predominantly in brain, the primary tissue affected in PWS and in several fetal tissues as shown by northern blot analysis. MAGEL2 is imprinted with monoallelic expression in control brain, and paternal-only expression in the central nervous system as demonstrated by its lack of expression in brain from a PWS-affected individual. The orthologous mouse gene (Magel2) is located within 150 kb of NDN:, is imprinted with paternal-only expression and is expressed predominantly in late developmental stages and adult brain as shown by northern blotting, RT-PCR and whole-mount RNA in situ hybridization. Magel2 distribution partially overlaps that of NDN:, with strong expression being detected in the central nervous system in mid-gestation mouse embryos by in situ hybridization. We hypothesize that, although loss of necdin expression may be important in the neonatal presentation of PWS, loss of MAGEL2 may be critical to abnormalities in brain development and dysmorphic features in individuals with PWS.

Amino Acid Sequence↗
PubMed2000

Identification of novel imprinted transcripts in the Prader-Willi syndrome and Angelman syndrome deletion region: further evidence for regional imprinting control.

Deletions and other abnormalities of human chromosome 15q11-q13 are associated with two developmental disorders, Prader-Willi syndrome (PWS) and Angelman syndrome (AS). Loss of expression of imprinted, paternally expressed genes has been implicated in PWS. However, the number of imprinted genes that contribute to PWS, and the range over which the imprinting signal acts to silence one copy of the gene in a parent-of-origin-specific manner, are unknown. To identify additional imprinted genes that could contribute to the PWS phenotype and to understand the regional control of imprinting in 15q11-q13, we have constructed an imprinted transcript map of the PWS-AS deletion interval. The imprinting status of 22 expressed sequence tags derived from the radiation-hybrid human transcript maps or physical maps was determined in a reverse transcriptase-PCR assay and correlated with the position of the transcripts on the physical map. Seven new paternally expressed transcripts localize to an approximately 1.5-Mb domain surrounding the SNRPN-associated imprinting center, which already includes four imprinted, paternally expressed genes. All other tested new transcripts in the deletion region were expressed from both alleles. A domain of exclusive paternal expression surrounding the imprinting center suggests strong regional control of the imprinting process. This study provides the means for further investigation of additional genes that cause or modify the phenotypes associated with rearrangements of 15q11-q13.

Alleles↗
PubMed2000

Deconstructing Mendel: new paradigms in genetic mechanisms.

As knowledge of the mechanisms of genetic action expands, this new information must be incorporated into the whole. The result is that old concepts are modified or deleted or new paradigms are created. The authors review advances in the understanding of traditional and nontraditional inheritance, including genomic imprinting and mitochondrial inheritance.

DNA, Mitochondrial↗
PubMed1999

Disruption of the mouse necdin gene results in early post-natal lethality.

Prader-Willi syndrome (PWS) is a neurobehavioural disorder characterized by neonatal respiratory depression, hypotonia and failure to thrive in infancy, followed by hyperphagia and obesity among other symptoms. PWS is caused by the loss of one or more paternally expressed genes on chromosome 15q11-q13, which can be due to gene deletions, maternal uniparental disomy or mutations disrupting the imprinting mechanism. Imprinted genes mapped to this region include SNRPN (refs 3,4), ZNF127 (ref. 5), IPW (ref. 6) and NDN (which encodes the DNA-binding protein necdin; refs 7,8,9,10). The mouse homologues of these genes map to mouse chromosome 7 in a region syntenic with human chromosome 15q11-q13 (refs 7,11). Imprinting of the human genes is under the control of an imprinting center (IC), a long-range, cis-acting element located in the 5' region of SNRPN (ref. 12). A related control element was isolated in the mouse Snrpn genomic region which, when deleted on the paternally inherited chromosome, resulted in the loss of expression of all four genes and early post-natal lethality. To determine the possible contribution of Ndn to the PWS phenotype, we generated Ndn mutant mice. Heterozygous mice inheriting the mutated maternal allele were indistinguishable from their wild-type littermates. Mice carrying a paternally inherited Ndn deletion allele demonstrated early post-natal lethality. This is the first example of a single gene being responsible for phenotypes associated with PWS.

Alleles↗
PubMed1998

A mouse model for Prader-Willi syndrome imprinting-centre mutations.

Imprinting in the 15q11-q13 region involves an 'imprinting centre' (IC), mapping in part to the promoter and first exon of SNRPN. Deletion of this IC abolishes local paternally derived gene expression and results in Prader-Willi syndrome (PWS). We have created two deletion mutations in mice to understand PWS and the mechanism of this IC. Mice harbouring an intragenic deletion in Snrpn are phenotypically normal, suggesting that mutations of SNRPN are not sufficient to induce PWS. Mice with a larger deletion involving both Snrpn and the putative PWS-IC lack expression of the imprinted genes Zfp127 (mouse homologue of ZNF127), Ndn and Ipw, and manifest several phenotypes common to PWS infants. These data demonstrate that both the position of the IC and its role in the coordinate expression of genes is conserved between mouse and human, and indicate that the mouse is a suitable model system in which to investigate the molecular mechanisms of imprinting in this region of the genome.

Animals↗
PubMed1997

Human centromeric DNAs.

Human centromeres have been extensively studied over the past two decades. Consequently, more is known of centromere structure and organization in humans than in any other higher eukaryote species. Recent advances in the construction of a human (or mammalian) artificial chromosome have fostered increased interest in determining the structure and function of fully functional human centromeres. Here, we present an overview of currently identified human centromeric repetitive DNA families: their discoveries, molecular characterization, and organization with respect to other centromeric repetitive DNA families. A brief examination of some functional based studies is also included.

Animals↗
PubMed1997

The necdin gene is deleted in Prader-Willi syndrome and is imprinted in human and mouse.

Human chromosome 15q11-q13 contains genes that are imprinted and expressed from only one parental allele. Prader-Willi syndrome (PWS) is due to the loss of expression of one or more paternally expressed genes on proximal human chromosome 15q, most often by deletion or maternal uniparental disomy. Several candidate genes and a putative imprinting centre have been identified in the deletion region. We report that the human necdin-encoding gene (NDN) is within the centromeric portion of the PWS deletion region, between the two imprinted genes ZNF127 and SNRPN. Murine necdin is a nuclear protein expressed exclusively in differentiated neurons in the brain. Necdin is postulated to govern the permanent arrest of cell growth of post-mitotic neurons during murine nervous system development. We have localized the mouse locus Ndn encoding necdin to chromosome 7 in a region of conserved synteny with human chromosome 15q11-q13, by genetic mapping in an interspecific backcross panel. Furthermore, we demonstrate that expression of Ndn is limited to the paternal allele in RNA from newborn mouse brain. Expression of NDN is detected in many human tissues, with highest levels of expression in brain and placenta. NDN is expressed exclusively from the paternally inherited allele in human fibroblasts. Loss of necdin gene expression may contribute to the disorder of brain development in individuals with PWS.

Amino Acid Sequence↗
PubMed1997

An imprinted mouse transcript homologous to the human imprinted in Prader-Willi syndrome (IPW) gene.

The Prader-Willi syndrome (PWS) is caused by genomic alterations that inactivate imprinted, paternally expressed genes in human chromosome region 15q11-q13. IPW, a paternally expressed gene cloned from this region, is not expressed in individuals with PWS, and is thus a candidate for involvement in this disorder. The IPW transcript does not appear to encode a polypeptide, suggesting that it functions at the level of an RNA. We have now cloned a mouse gene, named Ipw, that has sequence similarity to a part of IPW and is located in the conserved homologous region of mouse chromosome 7. The Ipw cDNA also contains no long open reading frame, is alternatively spliced and contains multiple copies of a 147 bp repeat, arranged in a head-to-tail orientation, that are interrupted by the insertion of an intracisternal A particle sequence. Ipw is expressed predominantly in brain. In an interspecies (M.musculus x M.m.castaneus) F1 hybrid animal, expression of Ipw is limited to the paternal allele. We propose that Ipw is the murine homolog of IPW.

Alleles↗
PubMed1996

Diagnostic test for the Prader-Willi syndrome by SNRPN expression in blood.

BACKGROUND: Prader-Willi syndrome (PWS) is caused by alterations of the paternally derived chromosome 15 or by maternal uniparental disomy. The gene for the small nuclear ribonucleoprotein polypeptide N (SNRPN) is expressed only from the paternally derived chromosome 15, due to epigenetic imprinting. The SNRPN gene is not expressed in any patients with PWS regardless of the underlying cytogenetic or molecular causes. METHODS: To develop a rapid molecular diagnostic assay for PWS, we tested the expression of the SNRPN gene and a control gene in 9 patients with PWS and 40 control individuals by PCR analysis of reverse transcribed mRNA from blood leucocytes. We then tested 11 blood samples from patients with suspected PWS. FINDINGS: SNRPN expression could readily be detected in blood leucocytes by PCR analysis in all control samples but not in samples from known PWS patients. Four suspected plus were negative for SNRPN expression were found to have chromosome 15 rearrangements, while the diagnosis of PWS was excluded in the remaining seven with normal SNRPN expression based on clinical, molecular, and cytogenetic findings. INTERPRETATION: The SNRPN-expression test is rapid and reliable in the molecular diagnosis of Prader-Willi syndrome.

Autoantigens↗
PubMed1995

Expression of the Fanconi anemia gene FAC in human cell lines: lack of effect of oxygen tension.

Fanconi anemia (FA) is a recessively inherited disease characterized by bone marrow failure, congenital anomalies, chromosomal instability and hypersensitivity to crosslinking agents. Some of the cellular defects of FA are known to be responsive to the ambient oxygen concentration. We examined the responsiveness of the FA complementation group C (FAC) gene to changes in oxygen concentration using two types of human cell lines, hypoxia-responsive Hep3B hepatoma cells and Epstein-Barr virus-immortalized lymphoblasts (normal and FA complementation groups B and C). Although the expression of erythropoietin in Hep3B cells was induced in response to the hypoxia-mimicking agent CoCl₂, there was no concomitant induction in FAC expression as assessed by mRNA levels and immunoprecipitable protein, and no detectable change in the cytoplasmic location of the FAC polypeptide as determined by indirect immunofluorescence. In human lymphoblasts we examined the effect of oxygen (0.1% -95% O₂) on cell proliferation and FAC expression. FA lymphoblasts had a normal sensitivity to the cytostatic effect of hyperoxia, while in both control and FA lymphoblasts FAC mRNA levels were unaffected by oxygen. Our results indicate that ambient oxygen is not a regulator of the FAC gene.

Carcinoma, Hepatocellular↗
PubMed1994

Identification of a novel paternally expressed gene in the Prader-Willi syndrome region.

We have isolated a novel gene from the Prader-Willi syndrome (PWS) smallest region of deletion overlap in proximal human chromosome 15q. IPW (Imprinted gene in the Prader-Willi syndrome region) was isolated using the direct selection method and yeast artificial chromosomes localized to the deletion region. IPW is spliced and polyadenylated but its longest open reading frame codes for only 45 amino acids, suggesting that it functions as an RNA, similar to H19 and XIST. The RNA is widely expressed in adult and fetal tissues and is found in the cytoplasmic fraction of human cells, which is also the case for the H19 non-translated RNA, but differs from the XIST RNA which is found predominantly in the nucleus. Using a sequence polymorphism, exclusive expression from the paternal allele in lymphoblasts and fibroblasts was demonstrated; monoallelic expression was found in fetal tissues. IPW is located about 150 kb distal to SNRPN, the only other known gene in the deletion interval, and about 50 kb proximal to the breakpoint of a translocation which defines the distal end of the PWS region and the proximal end of the Angelman syndrome (AS) region. As is the case with SNRPN, PWS patients with 15q11-q13 deletions do not express IPW, whereas expression is normal in Angelman syndrome patients. Lack of expression of IPW may contribute to the PWS phenotype directly. Alternatively, the mRNA product of IPW may play a role in the imprinting process, acting either on genes located proximally in the PWS region or distally in the AS region.

Alleles↗
PubMed1993

Mapping of the murine and rat Facc genes and assessment of flexed-tail as a candidate mouse homolog of Fanconi anemia group C.

Fanconi anemia is a rare, autosomal recessive disorder characterized at the cellular level by a combination of hypersensitivity to DNA-damaging agents and chromosomal instability. Clinical features include pancytopenia, often associated with specific congenital malformations, and a predisposition to leukemia. We previously cloned the gene defective in Fanconi anemia group C by complementation of the intrinsic sensitivity of Fanconi anemia cells to DNA cross-linking agents, and we recently cloned its mouse homolog (Facc). In this report, we localized Facc to mouse Chromosome (Chr) 13 and its rat homolog to rat Chr 17. A previously described anemic mouse mutant, flexed-tail, maps to the same chromosomal region. Differences were detected between DNA of the flexed-tail and congenic mice, indicating the proximity of the Facc probe to the disease mutation. Analysis of flexed-tail RNA did not reveal detectable difference in Facc message level or size between flexed-tail and congenic mice. On this basis, we conclude that, although flexed-tail remains a candidate for Fanconi anemia in the mouse, there is no evidence currently that Facc is mutated in flexed-tail mice.

Animals↗
PubMed1993

Mammalian DNA-repair genes.

The sequence and functional homology of certain genes between mammalian and non-mammalian eukaryotes has facilitated significant advances in our understanding of mammalian DNA repair. Several novel DNA damage and repair genes have been identified by using a variety of approaches. Study of these genes will lead to an increased understanding of the biological consequences of aberrant DNA maintenance in humans and other species.

Animals↗
PubMed1993

Cloning and analysis of the murine Fanconi anemia group C cDNA.

Fanconi anemia (FA) is one of a group of disorders characterized at the cellular level by a combination of hypersensitivity to DNA-damaging agents, chromosomal instability, and defective DNA repair. Clinical features of FA include pancytopenia, often accompanied by specific congenital malformations, and a predisposition to leukemia. Since the hematological manifestations are the critical defect in terms of prognosis, FA is a candidate disease for gene replacement therapy, and the development of a mouse model system is essential for the initial stages of this work. Previously, we have cloned the gene defective in FA group C by complementation of the intrinsic sensitivity of FA cells to DNA cross-linking agents. We have now cloned the murine homologue of the human FACC cDNA. The mouse cDNA (Facc) shares 79% amino acid sequence similarity with the human gene product. The expression of the mouse cDNA in human FA(C) cells restores the cellular drug sensitivity to normal levels. Thus, the function of the protein has been conserved despite the significant sequence divergence. PCR analysis of mouse tissue RNA reveals that the gene is expressed in all adult tissues, while in situ RNA hybridization experiments show tissue specific expression at late stages of fetal development. Cross-hybridizing sequences exist in DNA from other mammals, chicken and Drosophila. These results support the hypothesis that the FACC gene product has a role in a basic aspect of cellular protection against DNA damaging agents and that this function has been conserved during evolution.

Amino Acid Sequence↗