A human CpG island randomly inserted into a plant genome is protected from methylation |
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Authors: | Meza Trine Johansen Enerly Espen Børu Bente Larsen Frank Mandal Abul Aalen Reidunn B Jakobsen Kjetill S |
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Institution: | (1) Division of Molecular Biology, Department of Biology, University of Oslo, P.O. Box 1031 Blindern, N-0315 Oslo, Norway;(2) Department of Anatomy and Cell Biology, University of Bergen, Aarstadveien 19, N-5009 Bergen, Norway;(3) Department of Natural Sciences, University of Skövde, Box 408, SE-541 28 Skövde, Sweden |
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Abstract: | In vertebrate genomes the dinucleotide CpG is heavily methylated, except in CpG islands, which are normally unmethylated. It is not clear why the CpG islands are such poor substrates for DNA methyltransferase. Plant genomes display methylation, but otherwise the genomes of plants and animals represent two very divergent evolutionary lines. To gain a further understanding of the resistance of CpG islands to methylation, we introduced a human CpG island from the proteasome-like subunit I gene into the genome of the plant Arabidopsis thaliana. Our results show that prevention of methylation is an intrinsic property of CpG islands, recognized even if a human CpG island is transferred to a plant genome. Two different parts of the human CpG island – the promoter region/ first exon and exon2–4 – both displayed resistance against methylation, but the promoter/ exon1 construct seemed to be most resistant. In contrast, certain sites in a plant CpG-rich region used as a control transgene were always methylated. The frequency of silencing of the adjacent nptII (KmR) gene in the human CpG constructs was lower than observed for the plant CpG-rich region. These results have implications for understanding DNA methylation, and for construction of vectors that will reduce transgene silencing. |
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Keywords: | Arabidopsis CpG islands DNA methylation epigenetics silencing transgenic plants |
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