Paternal imprints can be established on the maternal Igf2-H19 locus without altering replication timing of DNA.
Genomic imprinting in mammals marks the parental alleles in gametes, resulting in differential gene expression in offspring. A number of epigenetic features are associated with imprinted genes. These include differential DNA methylation, histone acetylation and methylation, subnuclear localization and DNA replication timing. While DNA methylation has been shown to be necessary both for establishment and maintenance of imprinting, the connections with the other types of epigenetic marking systems are not clear. Specifically, it is not known whether the other marking systems, either on their own or in conjunction with DNA methylation, are required for imprinting. Here we show that in the mouse mutant Minute (Mnt) the Igf2-H19 locus acquires a paternal methylation imprint in the maternal germline. DNA methylation of the H19 DMR is established in oogenesis, maintained during postzygotic development on the maternal allele, and erased in primordial germ cells. The fact that a paternal type methylation imprint can also be established in the maternal germline indicates that trans-acting factors that target methylation to this imprinted region are likely to be the same in both germlines. Surprisingly, however, asynchrony of DNA replication of the locus is maintained despite the altered expression and methylation imprint of Igf2 and H19. These results show clearly that replication asynchrony of this region is neither the determinant factor for, nor a consequence of, epigenetic modifications that are critical for genomic imprinting. Replication asynchrony may thus be regulated differently from methylation imprints and have a separate function.
Cerrato
Flavia
F
Laboratory of Developmental Genetics and Imprinting, The Babraham Institute, Cambridge, UK.
Dean
Wendy
W
Davies
Karen
K
Kagotani
Kazuhiro
K
Mitsuya
Kohzoh
K
Okumura
Katsuzumi
K
Riccio
Andrea
A
Reik
Wolf
W
D000483:Alleles; D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D019175:DNA Methylation; D042522:DNA Replication Timing; D044127:Epigenesis, Genetic; D005260:Female; D018392:Genomic Imprinting; D005854:Germ Cells / Q000166:cytology; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008297:Male; D051379:Mice; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated / Q000235:genetics*; D012097:Repressor Proteins / Q000235:genetics
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; C094335:H19 long non-coding RNA; C484561:Mnt protein, mouse; D062085:RNA, Long Noncoding; D022661:RNA, Untranslated; D012097:Repressor Proteins; D007335:Insulin-Like Growth Factor II