Keeping Egg Cells Fresh With Epigenetics
Source: Babraham Institute
Summary: A new study sheds some light on the role of epigenetics in placing egg cells into stasis. Researchers studied a protein called MLL2 and discovered how it produces a distinctive pattern of epigenetic marks that are needed for egg cell stasis.
A fertilized egg cell is the start of every human life. Egg cells are created inside a woman’s body before she is born and is then kept in stasis throughout childhood until they’re needed as an adult. Keeping egg cells in stasis during childhood is a key part of female fertility. If egg cells don’t go into stasis they can’t become mature eggs and they will never have the chance to form a new life. Putting an egg cell into stasis involves adding many epigenetic marks (Ex. DNA methylation) throughout its DNA. Epigenetic marks attached to DNA act as footnotes, indicating which genes are turned ‘on’ or ‘off’. A new study sheds some light on the role of epigenetics in placing egg cells into stasis. Researchers from Babraham Institute studied a protein called MLL2 and discovered how it produces a distinctive pattern of epigenetic marks that are needed for egg cell stasis. The research findings were published in the journal Nature Structural and Molecular Biology.
The research team created new, highly sensitive ways to detect epigenetic marks and found that, as eggs develop, a mark called H3K4me3 spreads throughout the genome. They showed that the MLL2 protein is responsible for this unusual placement of H3K4me3 in egg cells. Without MLL2, most H3K4me3 marks in egg cells are lost and the cells die before getting the chance to form a new life. They also reported that H3K4me3 is created in two ways. MLL2 can add the H3K4me3 epigenetic mark without any nearby gene activity while another process, that doesn’t use MLL2, places the same mark around active genes. The researchers hope that this study helps to expand the knowledge of epigenetics and the understanding of fertility.
Lead scientist, Dr. Kelsey said, “We are only beginning to unravel the details of the connection between epigenetics and egg development, a fundamental aspect of biology that may play a part in transmitting information from mother to fetus. Discoveries like this highlight some of the unusual biological processes that take place in these highly important cells.”
More Information: Courtney W. Hanna et al, “MLL2 conveys transcription-independent H3K4 trimethylation in oocytes”, Nature Structural & Molecular Biology (2017). DOI: 10.1038/s41594-017-0013-5