Changes in H3K79 methylation during preimplantation development in mice

Area of Science:

• Developmental Biology
• Epigenetics
• Molecular Biology

Background:

• Oocyte gene expression is reprogrammed to totipotent embryonic patterns post-fertilization.
• Histone modifications play crucial roles in regulating gene expression during development.

Purpose of the Study:

• To investigate the role of histone H3 lysine 79 dimethylation (H3K79me2) and trimethylation (H3K79me3) in oocyte-to-embryo reprogramming.
• To understand the dynamic changes of H3K79me2 and H3K79me3 during early embryonic development.

Main Methods:

• Immunocytochemistry was used to detect H3K79me2 and H3K79me3 in oocytes and preimplantation embryos.
• Somatic nuclei transplantation into enucleated oocytes was performed to assess reprogramming in vivo.

Main Results:

• H3K79me2 was widespread in somatic cells and oocytes, while H3K79me3 localized to pericentromeric heterochromatin.
• Both H3K79me2 and H3K79me3 levels decreased significantly after fertilization, with H3K79me2 showing a transient increase during mitosis.
• Transplanted somatic nuclei showed demethylation of H3K79me2 after parthenogenetic activation, but this was not observed in nuclei transferred later.

Conclusions:

• The differential distribution and dynamic changes of H3K79me2 and H3K79me3 suggest distinct roles for methylation states.
• The elimination of H3K79 methylation following fertilization appears to be a critical event in genomic reprogramming of oocytes to totipotent embryos.