Human eggs are designed to hold out for a long haul. When a person is born with a female reproductive system, they've already developed all the eggs they'll have for the rest of their life. Yet, the ovaries' roughly 1 to 2 million immature egg cells, known as oocytes, can stay healthy and be successfully fertilized for up to 50 years, hinting to reproductive scientists that they must have a secret strategy to avoid damage for so long. Now, a team of developmental biologists based in Barcelona, Spain, have discovered that a key part of oocytes can shift into a "standby battery mode," preserving the finite reserve for longer.   

A study published on July 20 in the journal Nature reveals that the mitochondria in oocytes tap into a different energy pathway that sidesteps the production of free radicals—chemical molecules that can wreak havoc on DNA, proteins, and cell walls. The findings bring new light to the longevity of these cells and could potentially help advance fertility strategies.

"Female fertility decreases by age, and if you look at demographic studies, more and more women choose to give birth in their mid-30s," says Elvan Böke, senior author of the study and group leader in the Cell and Developmental Biology Program at the Center for Genomic Regulation in Barcelona. But around this age, "oocyte quality decreases, and that accounts for the majority of female fertility problems," she notes.