Varied follicle growth buffers egg cell lifespans in mice

In female mice, researchers used a genetic tracking method to label activated egg cells and follow their development across the lifespan. The animal experiment showed that activated egg cells do not all mature at the same rate. Some eggs activated in early adulthood progressed rapidly, whereas others survived into late or even final reproductive stages, supporting long-term fertility. This lifespan was governed by the growth of secondary follicles, the structures of supporting cells that nurture developing eggs. The researchers found that secondary follicle progression acted as a buffer for reproductive capacity. Activated eggs displayed varied gene activity and metabolic states. Different levels of FURIN, a protein that processes other molecules, changed the release of chemical signals from the eggs, coordinating their development with surrounding follicles to regulate egg survival.