Morphological, cellular and molecular changes during postovulatory egg aging in mammals

Area of Science:

• Reproductive Biology
• Cellular and Molecular Biology
• Developmental Biology

Background:

• Postovulatory aging negatively impacts egg quality, leading to reduced fertilization, embryo development, and reproductive outcomes.
• Aging-induced changes include morphological alterations, spontaneous egg activation, and apoptosis.
• The precise molecular mechanisms driving these age-related egg quality declines remain incompletely understood.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying postovulatory aging-induced spontaneous egg activation (SEA) in mammalian eggs.
• To identify key molecular players and pathways involved in egg quality deterioration with aging.
• To explore potential therapeutic targets for improving egg quality and assisted reproductive technologies (ARTs) outcomes.

Main Methods:

• Analysis of morphological and cellular changes in aged mammalian eggs, including cortical granule exocytosis and zona pellucida status.
• Quantification of molecular changes such as adenosine 3',5'- cyclic monophosphate (cAMP) and reactive oxygen species (ROS) levels.
• Investigation of the roles of cyclin-dependent kinase 1 (Cdk1), cyclin B1, and maturation promoting factor (MPF) in aged eggs.

Main Results:

• Postovulatory aging is characterized by partial cortical granule exocytosis, zona hardening, and progression from metaphase-II arrest.
• Molecularly, aging leads to decreased cAMP and increased ROS and cytosolic free calcium (Ca2+) levels.
• Elevated ROS and altered cAMP levels destabilize MPF by affecting Cdk1 phosphorylation and cyclin B1 degradation, triggering abortive SEA.

Conclusions:

• Postovulatory aging triggers abortive SEA and reduces egg quality through molecular pathways involving cAMP, ROS, and MPF destabilization.
• These age-related molecular changes negatively impact fertilization, embryo quality, and the success of ARTs.
• Pharmacological interventions to increase cAMP or decrease ROS show potential for preserving egg quality and enhancing ART outcomes in mammals, including humans.