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  • 1
    ISSN: 0730-2312
    Keywords: rDNA ; lymphoblastoid ; methylation ; hypermethylation ; DNA ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In human lymphoplastoid cell line (Z83) in which rDNA genes on chromosomes 22 are amplified but transcribed at a low level, immunocytological studies with antibodies to 5 methylcytidine provided evidence for hypermethylation of the rDNA. The extent of methylation of the 5′ flanking sequence of the ribosomal DNA was examined by comapring the size of restriciton fragments obtained by digestion of genomic DNA with EcoRI and Hpall or EcoRI and Mpsl. Southern blots indicated hypermethylation of the 5′ flanking sequences of many copies of rRNA genes in these cells, but not in a control lymphoblastoid cell line without rDNA amplification. Results obtained with somatic hybird human-hamster cell line, in which the rRNA genes on the single human chromosomes 22 are inactive, showed that only a small fraction of the CCGG sites in the 5′ flanking sequences of the transcriptionally silent rRNA genes in this hybird were methylated. Since inactive rRNA genes can show such a minimal level of methylation, it is likely that the extreme hypermethylation of the apmlified rRNA genes in Z83 association with their inactivation rather than following it. © 1992 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0730-2312
    Keywords: methylation ; DNA ; chromosomes 11p and 17 p13.3 ; human breast adenocarcinoma ; human colon adenocarcinoma ; γ-globin ; Ha-ras ; parathyroid hormone ; catalase ; calcitonin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In breast and colon adenocarcinomas methylation patterns at CCGG sites of several loci located on the short arm of chromosome 11 were determined by Southern blot analysis. Results obtained indicate that all tumor samples (20/20) exihibit DNA methylation changes when compared to their normal counterparts. In colon tumors,i-globin gene is usually hypomethylated (9/10), whereas Ha-ras gene, which is located in the same region, retains an unmodified DNA methylation pattern. Hypomethylation of parathyroid hormone (5/10) and catalase genes (4/10) are also frequently detected in colon tumor specimens. For the catalase gene the region around exon is the only one which is affected by these changes. In breast adenocacinoma, modifications of the methylation patterns are less frequently observed. However, hypomethylation of the i-globin gene is a very common event in these tumors (8/10), and it is also detected (2/2) in lobular carcinoma in situ which is an early step in breast tumorgenesis. In addition, hypermethylation of a CpG island is also observed at the locus 17p13.3 in both colon (5/5) and breast (4/9) adenocarcinomas. In the tumoral tissues which containj a limited amount of CpG. Some of these alterations seen, therefore, to be tumor and sequence specific.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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