Cumulus Oophorus

Last Updated: April 1, 2019

Definition - What does Cumulus Oophorus mean?

The cumulus oophorus is a raised nest of cells encircling the egg both within the ovarian follicle and outside after ovulation. At the time of ovulation, the follicle bursts to release the egg along with its "crown" of attached cumulus cells, now referred to as the corona radiata. Sperm needs to penetrate this layer of cells in order to access the egg and fertilize it.

FertilitySmarts explains Cumulus Oophorus

Cumulus cells play a vital role in egg development, ovulation, fertilization, and natural conception. Some of the important functions are as follows:

  • At first, the cumulus cells have crosstalk with the egg facilitating the transfer of nutrients and substances that nurture both the cumulus cells and egg.
  • They encircle the egg at the time of fertilization. Removal of the cumulus oophorus at this time can interfere with fertilization.
  • The cumulus cells entrap the normal sperm and guide it towards the egg.
  • They create an ideal milieu for the sperm, which allows the normal sperm to penetrate into the egg.
  • The cumulus cells also prevent the entry of the abnormal into the cumulus cells.
  • They prevent changes in the egg that can halt its normal meeting with the sperm

The cumulus oophorus also play a role in a procedure called intracytoplasmic sperm injection (ICSI) that is often used in conjunction with in vitro fertilization (IVF). During ICSI, the eggs are first retrieved, pooled together, and incubated. Approximately 2-3 hours after retrieval, the cumulus cells around the eggs are “stripped” or broken down by the embryologist to expose the egg and assess its development. The mature eggs are pooled together and preserved for ICSI while the immature eggs are pooled and set aside.

The timing of the removal of cumulus cells is important. Where the cumulus cells promote fertilization by creating a favorable milieu for both the egg and sperm, long-term exposure to cumulus cells can cause damage to the egg by producing toxic products. Hence, early cumulus cell removal may minimize the risk of egg damage and the subsequent adverse effect on the vitality and quality of the embryo.

Moreover, if mechanical stimulation applied during the stripping of cumulus cells from the egg is not appropriate, it can induce epigenetic changes, resulting in low-birth-weight babies. More importantly, the mechanical stress can harm the egg coat allowing the entry of multiple sperms that fertilize the egg - a condition known as polyspermy.

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