Fig. 1.

Main POA-related morphological and molecular alterations in mammalian oocytes. After ovulation of the MII-stage oocyte, POA-related mechanisms occur in unfertilized oocytes. Morphological alterations include ZP hardening, mt and CGs abnormal distribution patterns, CGs vacuolization, and spindle organization. On a molecular level, POA induces the increase of intracellular ROS levels and oxidative stress mechanisms, inducing lipids peroxidation, mt and DNA oxidative damages (arrows), and Ca²⁺ release from ER. Oxidative stress and cytochrome C release from mt activate apoptotic mechanisms that, together with higher intracellular Ca²⁺ levels, inactivate the cell cycle regulators (MPF, MAPK) and destabilize the epigenetic pattern (i.e., histone acetylation). Abbreviations: ATP, adenosine triphosphate; Ca²⁺, calcium; cAMP, cyclic adenosine monophosphate; Cas 3, caspase 3; CGs, cortical granules; Cyt C, cytochrome C; ER, endoplasmic reticulum; MAPK, mitogen-activated protein kinase, MII: metaphase II; MPF, maturation promoting factor; mt, mitochondria; POA, postovulatory aging; ROS, reactive oxygen species; ZP, zona pellucida