Keeping egg cells in stasis during childhood is a key part of female fertility in humans. New research published online on January 1, 2018 in Nature Structural and Molecular Biology sheds some light on the role of epigenetics in placing egg cells into stasis. A team led by Dr. Gavin Kelsey at the Babraham Institute in the UK and colleagues in Dresden and Munich studied a protein called MLL2 and discovered how it produces a distinctive pattern of epigenetic marks that are needed for egg cell stasis. The article is titled “MLL2 Conveys Transcription-Independent H3K4 Trimethylation in Oocytes.” A fertilized egg cell is the start of every human life. Yet, egg cells are created inside a woman's body before she is born. The eggs are then kept in stasis throughout childhood until they're needed as an adult. 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 throughout its DNA. Epigenetic marks attached to DNA act as footnotes, indicating which genes are turned “on” or “off.” The scientists wanted to understand where these marks come from in egg cells and how mistakes can cause disease. It is particularly challenging to study epigenetics in egg cells as there are so few of them. The team had to create new, highly sensitive ways to detect epigenetic marks in such small numbers of cells. Using this approach, they found that, as eggs develop, a mark called H3K4me3 spreads throughout the genome. Scientists have already seen the same mark close to the start of active genes in many cells, but the team discovered that its role in egg cells is different.
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