The oocyte, or egg cell, is considered one of the most patient cells in the human body. While sperm are continuously produced, a female is born with a fixed number of oocytes, and no new ones are created thereafter. The oocyte remains dormant in the body for decades until it is used for pregnancy during adulthood.
A research team led by Elvan Böke, head of the Oocyte Biology & Cellular Dormancy Group at the Centre for Genomic Regulation (CRG) in Barcelona, has uncovered why oocytes can remain dormant for decades without sustaining damage. Their findings were published on the 16th in the international academic publication 'The EMBO Journal'.
Oocytes must protect themselves to remain viable for nearly 50 years until a woman reaches menopause. The team explains that the secret to the oocyte's survival is minimizing the activity of its internal “cleanup crew.”
Oocytes contain lysosomes and proteasomes (protein-degrading complexes) that function as a cleanup crew, disposing of unnecessary components. However, this cleanup process can generate harmful molecules and reactive oxygen species (ROS) that can damage the oocyte's cell membrane and DNA.
The research team received donations of over 100 oocytes from 21 women, aged 19 to 34, at a Barcelona fertility clinic. Of these, 70 were mature oocytes preparing for fertilization, and 30 were immature.
Using fluorescent probe technology to track the activity of lysosomes, proteasomes, and mitochondria, the team found that all showed lower activity inside the oocyte compared to the surrounding area. This activity decreased further as the oocyte matured. When mitochondrial activity produces damaged mitochondria, lysosomes clear them away. Thus, reduced mitochondrial activity leads to decreased lysosomal activity.
Just before ovulation, the oocyte expelled lysosomes and moved its mitochondria and proteasomes toward the cell's periphery. This suggests the oocyte creates an environment that minimizes the production of reactive oxygen species.
The research team stated, “It appears that oocytes can survive for decades without damage by intentionally skipping metabolic reactions that generate reactive oxygen species.” They added, “Conducting related research on women who have failed in vitro fertilization (IVF) is expected to help find ways to improve fertilization success rates.”
<References>
doi.org/10.1038/s44318-025-00493-2
