Journal
MOLECULAR REPRODUCTION AND DEVELOPMENT
Volume 65, Issue 1, Pages 41-50Publisher
WILEY-LISS
DOI: 10.1002/mrd.10264
Keywords
primordial germ cells (PGCs); mouse; genomic imprinting; Igf2r; DNA methylation
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During germ cell differentiation in mice, the genome undergoes specific epigenetic modifications. These include demethylation of imprinted genes and subsequent establishment of parental allele-specific methylation. The mouse lgf2r gene is an imprinted gene that shows maternal-specific expression. Maternal-specific methylation of differentially methylated region 2 (DMR2) of this gene may be necessary for its maternal-specific expression. Before the allele-specific methylation is established, DMR2 is demethylated in both male and female primordial germ cells (PGCs) by 13.5 days post coitum (dpc), indicating that the demethylation of this region occurs earlier in PGC development. The timing of the demethylation has been, however, unknown. In this study, we attempted to determine the timing of methylation erasure of lgf2r DMR2 in developing PGCs, using transgenic mice expressing green fluorescent protein specifically in the germ line. We purified migrating PGCs from the transgenic mice and examined the methylation status of DMR2. The results show that some CpG sites within DMR2 start demethylation at 9.5 dpc in some migrating PGCs, before the cells colonize genital ridges, and the progression of demethylation is rapid after colonization of the genital ridges. To examine whether the gonadal environment is involved in demethylation, we analyzed the methylation of DMR2 after culturing migrating PGCs in the absence of a gonadal environment. These culture experiments support the idea that a gonadal environment is not required for demethylation of the region in at least a fraction of PGCs. (C) 2003 Wiley-Liss, Inc.
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