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W Reik

Publications and source records attributed to W Reik.

99 records · Page 6Linked to original sources
PubMed1988

Genomic imprinting: a possible mechanism for the parental origin effect in Huntington's chorea.

Huntington's disease (HD) is an autosomal dominant condition with almost complete penetrance. The age of onset of the symptoms, however, is variable and depends on the parental origin of the gene. A high proportion of early onset cases inherit the HD gene from their father, whereas a considerable proportion of late onset cases inherit the gene from their mother. Modification of the HD gene by maternally inherited extrachromosomal factors has been invoked to account for the parental origin effect. Recent experimental evidence suggests genomic imprinting as an alternative mechanism, by which the gene itself becomes modified in a different way depending on whether it is passed through the maternal or the paternal germline. This modification may involve methylation of DNA and could result in earlier or higher level expression of the gene when it is transmitted by the father.

Age Factors↗
PubMed1988

CpG methylation of an X-linked transgene is determined by somatic events postfertilization and not germline imprinting.

The process of X-inactivation in mammals requires at least two events, the initiation of inactivation and the maintenance of the inactive state. One possible mechanism of control is by methylation of DNA at CpG dinucleotides to maintain the inactive state. Furthermore, the paternal X-chromosome is frequently inactivated in the extraembryonic membranes. The relationship between the parental origin of the chromosome, nonrandom inactivation and DNA methylation is not clear. In this paper, we report on the CpG methylation of an X-linked transgene, CAT-32. The levels of methylation in embryonic, extraembryonic and germline cells indicates that the modifications of the transgene are broadly similar to those reported for endogenous X-linked genes. Interestingly, the methylation of CAT-32 transgene in extraembryonic tissues displays patterns that could be linked to the germline origin of each allele. Hence, the maternally derived copy of CAT-32 was relatively undermethylated when compared to the paternal one. The changes in DNA methylation were attributed to de novo methylation occurring after fertilization, most probably during differentiation of extraembryonic tissues. In order to determine whether or not the patterns of DNA methylation reflected the germline origin of the X-chromosome, we constructed triploid embryos specifically to introduce two maternal X-chromosomes in the same embryo. In some of these triploid conceptuses, methylation patterns characteristic of the paternally derived transgene were observed. This observation indicates that the methylation patterns are not necessarily dependent on the parental origin of the X-chromosome, but could be changed by somatic events after fertilization. One of the more likely mechanisms is methylation of the transgene following inactivation of the X-chromosome in extraembryonic tissues.

Alleles↗
PubMed1987

Provision of the immunoglobulin heavy chain enhancer downstream of a test gene is sufficient to confer lymphoid-specific expression in transgenic mice.

To test whether the immunoglobulin heavy chain enhancer is sufficient to direct lymphoid specific gene expression in vivo, we have incorporated into the mouse germ line a test gene (chloramphenicol-acetyl transferase) whose transcription is potentiated by the enhancer. Analysis of transgenic mice bearing single-copy integrations of the injected DNA indicates that provision of the enhancer downstream of the test gene (beyond the polyadenylation site) is sufficient to direct lymphoid-specific expression. The tissue specificity is considerable as judged by the fact that transgene expression is at least one thousandfold higher in spleen than in liver. Within the lymphoid family, expression of the transgene is much higher in surface IgM+ spleen cells than in thymocytes high in Thy-1 expression, suggesting that the enhancer preferentially directs expression to cells of the B lineage.

Acetyltransferases↗
PubMed1987

Retrovirus integration and chromatin structure: Moloney murine leukemia proviral integration sites map near DNase I-hypersensitive sites.

The chromatin conformation of mouse genome regions containing Moloney murine leukemia proviral intergration sites in two Mov mouse strains and randomly selected integration sites in virus-infected mouse 3T3 fibroblasts was analyzed. All integrations have occurred into chromosomal regions containing several DNase-hypersensitive sites, and invariably the proviral integration sites map within a few hundred base pairs of a DNase-hypersensitive site. The probability that this close association between proviral integration sites and DNase-hypersensitive sites was due to chance was calculated to be extremely low (2 X 10(-4]. Because the proviral integrations analyzed were not selected for an altered phenotype, our results suggest that DNase-hypersensitive regions are preferred targets for retrovirus integration.

Animals↗
PubMed1985

Replication-competent Moloney murine leukemia virus carrying a bacterial suppressor tRNA gene: selective cloning of proviral and flanking host sequences.

A bacterial suppressor tRNA gene was introduced into the long terminal repeat of the Moloney murine leukemia virus (Mo-MuLV) proviral genome to construct a retrovirus that allows easy cloning of the provirus with flanking host sequences. A replication competent virus, Mo-MuLV sup containing a tRNA amber suppressor gene, was derived that replicates to high titers in tissue culture cells and stably transduces the bacterial gene. The recombinant virus can efficiently replicate in vivo when microinjected into midgestation embryos or when injected into newborn mice and displays the same tissue tropism as wild-type Mo-MuLV. The suppressor gene in Mo-MuLV sup is functional in bacteria and allows efficient recovery of proviral genomes. This was shown by ligation of DNA from infected cells to phage lambda Charon 4A arms and selective growth of recombinant phages on su- host cells. All recovered phages contained Mo-MuLV proviral sequences and, because of the high cloning capacity of phage lambda, 1-11 kilobases of flanking host DNA. This virus should facilitate studying virus-host interactions in tissue culture cells and in animals.

Animals↗
PubMedDate not supplied

Fetal growth restriction: a workshop report.

Intrauterine growth restriction (IUGR) is associated with significantly increased perinatal morbidity and mortality as well as cardiovascular disease and glucose intolerance in adult life. A number of disorders from genetic to metabolic, vascular, coagulative, autoimmune, as well as infectious, can influence fetal growth by damaging the placenta, leading to IUGR as a result of many possible fetal, placental and maternal disorders. Strict definitions of IUGR and of its severity are needed in order to eventually distinguish among different phenotypes, such as gestational age at onset, degree of growth restriction and presence of hypoxia. This report explores and reviews some of the most recent developments in both clinical and basic research on intrauterine growth restriction, by seeking mechanisms that involve genetic factors, utero-placental nutrient availability and vascular growth factors. New exciting findings on the genomic imprinting defects potentially associated with IUGR, and the placental anomalies associated with the decreased nutrient transport are summarized. Moreover, recent data on angiogenic growth factors as well as new information arising from application of gene chip technologies are discussed.

Adult↗
PubMedDate not supplied

Genomic imprinting determines methylation of parental alleles in transgenic mice.

Mouse embryogenesis relies on the presence of both the maternal and the paternal genome for development to term. It has been proposed that specific modifications are imprinted onto the chromosomes during gametogenesis; these modifications are stably propagated, and their expression results in distinct and complementary contributions of the two parental genomes to the development of the embryo and the extraembryonic membranes. Genetic data further suggest that a substantial proportion of the genome could be subject to chromosomal imprinting, the molecular nature of which is unknown. We used random DNA insertions in transgenic mice to probe the genome for modified regions. The DNA methylation patterns of transgenic alleles were compared after transmission from mother or father in seven mouse strains carrying autosomal insertions of the same transgenic marker. One of these loci showed a clear difference in DNA methylation specific for its parental origin, with the paternally inherited copy being relatively undermethylated. This difference was observed in embryos on day 10 of gestation, but not in their extraembryonic membranes. Moreover, the methylation pattern was faithfully reversed upon each germline transmission to the opposite sex. Our findings provide evidence for heritable molecular differences between maternally and paternally derived alleles on mouse chromosomes.

Alleles↗
PubMedDate not supplied

Culture of preimplantation embryos and its long-term effects on gene expression and phenotype.

A growing number of medical, scientific and biotechnological procedures rely on culture of mammalian preimplantation embryos. This review presents currently available data on aberrant offspring development that sometimes arises from commonly applied in-vitro procedures in humans, ruminant species and mice. Comparison between mammalian species reveals similarities in the phenotypic abnormalities that are observed at fetal and perinatal stages of development. In particular, aberrant effects on fetal growth have been observed in multiple studies in which serum complemented the preimplantation culture medium. Although it remains to be determined whether there is a common causal mechanism(s) involved, several hypotheses have been put forward to account for the variety of the observed developmental abnormalities. One of these postulates that culture can result in the epigenetic deregulation of developmentally important genes, and that such epigenetic alterations would affect in particular the expression of genes that are subject to genomic imprinting. Imprinted genes play key roles in the control of fetal growth, and altered imprinting can cause growth defects. Some recent in-vitro culture studies on mice and ruminant species now lend support to this hypothesis.

Animals↗