A new study in mice, published in the May issue of Science, has identified two key proteins critical for ovulation. The proteins, called extracellular-regulated protein kinases 1 and 2 (ERK 1 and ERK 2), appear to bring about the maturation and release of the egg. "Ovulation results from a complex interplay of chemical sequences," said Duane Alexander, M.D. "The researchers have identified a crucial biochemical intermediary controlling the release of the egg. The finding advances our understanding and may one day contribute to new treatments for infertility as well as new ways to prevent pregnancy from occurring."
An immature egg is contained inside the ovarian follicle, which mainly consists of granulosa cells. Each month during a woman's cycle the pituitary gland releases follicle stimulating hormone (FSH) and luteinizing hormone (LH) which cause the egg and the granulosa cells to grow and develop into a mature follicle. Midway through the cycle the pituitary gland releases a large surge of LH which causes the follicle to rupture and release the egg. The granulosa cells become luteal cells which produce progesterone. Until now researchers did not know how LH triggered these events. The theory is that LH signals the ERK 1 and ERK 2 proteins to trigger a chain of chemical sequences leading to the release of the egg and the transformation of the granulosa cells to luteal cells.
The study used mice who lacked the genes needed to produce ERK 1 and ERK 2. The ovaries of these mice still produced eggs but did not release them after being exposed to LH. Furthermore the granulosa cells did not transform into luteal cells. In contrast, mice with working versions of the genes for ERK1 and ERK 2 were fertile.