Eggs that stay fresh for 50 years

Yes, there is such an egg – the human egg, or oocyte. Each woman enters the world with a finite number of egg cells. They need to survive for some five decades, which is an unusually long time for cells. Some human cells like those in the eyes and brain can last as long as you do, but most have much shorter lives because the processes that enable them to function also damage them in the course of time.

The key seems to be how the human egg disposes of its waste in a slowed manner, which in all probability reduces wear and tear and explains its longevity. Cells have to recycle their proteins as part of their necessary housekeeping, but at a cost. The energy consumed in so doing can cause reactive oxygen species (ROS) which cause random damage to the cell.

Researchers at the Centre of Genomic Regulation in Spain harvested human eggs which were placed in a liquid containing fluorescent dyes that bind to lysosomes, which function as recycling plants. Under a microscope it appeared that the waste-disposing lysosomes were less active in the eggs than in other human cells. This is believed to be a sort of self-preservation. Some oocytes, however, do not benefit from such lysosome activity which explains their poorer health later on.

Another life-lengthening property of the human egg seems to be how mitochondrial mutations do not appear to accumulate in women's eggs as they age, suggesting that they may have evolved a mechanism to avoid this. It was observed that mitochondrial mutations in women’s eggs didn’t actually increase as they aged, while this was the case for the mitochondria in their salivary and blood cells.

This insight may eventually help improve fertility treatments. We know that protein degradation is essential for the survival of the cell, so it most definitely also affects fertility. And high ROS in the cell equals poor IVF outcomes.