A French team of fertility experts has revealed for the first time that maternal genetic imprinting errors can occur at the very earliest stages of egg follicle development when the follicles are matured in-vitro.
The research was done in mouse oocytes, and Dr. Catherine Poirot from Groupe Hospitalier Piti Salptrire in Paris, who presented the team's findings today (Monday 30 June) at the annual meeting of the European Society of Human Reproduction and Embryology, said it was not possible yet to say whether the same would be true of human eggs.
However, the team are concerned that these very early errors could be involved in subsequent abnormal development.
Normally, genes act in the same way whether they are transmitted by the mother or the father. But, a few genes break this genetic rule. Whether they are switched on (expressed) or off depends on whether they are inherited from the mother or the father. The process of inheriting specifically from the mother or the father is called imprinting.
Imprinting genes can be found on chromosomes 7 (H19), 6 (Mest/Peg1) and 17 (Igf2R genes) and these were three key genes all involved in growth analysed by Dr Poirot and her team. From the ovaries of 11 and 12-day-old mice they isolated pre-antral follicles. These are follicles that have begun to grow but which are still a solid mass of cells containing the nucleus of immature oocytes. They cultured the follicles for 11 days until the antral stage when the central cavity filled with follicular fluid develops inside the follicle. As controls, the team collected immature oocytes from antral follicles visible on the surface of adult mouse ovaries. They then studied the methylation status of the three genes in the immature in-vitro oocytes and in the controls.
Contact: Margaret Willson
European Society for Human Reproduction and Embryology