Maternal instincts: Protection of 5mC?
DNA modification by 5-methylcytosine (5mC) was the only recognized DNA modification for many years in mammals and 5mC plays important roles in cell differentiation and development. Recently, a novel 5-hydroxymethylcytosine (5hmC) DNA modification has been reported and the balance between 5mC and 5hmC in the genome is a critical step for regulating gene expression to maintain cellular functions.
A recent study by the Nakano group from Osaka University in Japan shows that the maternal factor PGC7 (also known as Dppa3, Stella) protects 5mC from conversion to 5hmC in the maternal genome during early embryogenesis. The authors found that PGC7 binds to maternal chromatin containing di-methylated histone H3 lysine 9 (H3K9me2) and blocks the binding of Tet (enzyme that mediates the conversion of 5mC to 5hmC) to chromatin.
These data suggest that the binding of PGC7 to H3K9me2-containing chromatin is critical for the protection of DNA methylation and this type of regulatory mechanism could be involved in DNA modifications in somatic cells as well as in early embryos.
Toshinobu Nakamura, Yu-Jung Liu, Hiroyuki Nakashima, Hiroki Umehara, Kimiko Inoue, Shogo Matoba, Makoto Tachibana, Atsuo Ogura, Yoichi Shinkai & Toru Nakano(2012)PGC7 binds histone H3K9me2 to protect against conversion of 5mC to 5hmC in early embryos. Nature June 3