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Molecular and Cellular Biology, April 2001, p. 2384-2392, Vol. 21, No. 7
Department of Medical Genetics, University of
Alberta, Edmonton, Alberta, Canada
Received 17 July 2000/Returned for modification 17 August
2000/Accepted 22 November 2000
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.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.7.2384-2392.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Establishment and Maintenance of DNA Methylation
Patterns in Mouse Ndn: Implications for Maintenance of
Imprinting in Target Genes of the Imprinting Center
*
Corresponding author. Mailing address: Department of
Medical Genetics, 8-42 Medical Sciences Building, University of
Alberta, Edmonton, Alberta, Canada T6G 2H7. Phone: (780) 492-7908. Fax: (780) 492-1998. E-mail: rachel.wevrick{at}ualberta.ca.
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