Molecular mechanism of poor embryo development in postovulatory aged oocytes: Mini review

Oocyte quality is a key factor in determining embryo development; however, we have a poor understanding of what constitutes oocyte quality or the mechanisms governing it. Postovulatory aging of oocytes that have not been fertilized for a prolonged time after ovulation is known to significantly impair oocyte quality and subsequent embryo development after fertilization. Embryos derived from postovulatory-aged oocytes are prone to undergo apoptosis due to the decreased Bcl-2 expression. Postovulatory aging of oocytes changes the patterns of Ca2+ oscillations at fertilization as a result of impaired Ca2+ regulation in the endoplasmic reticulum. Moreover, postovulatory aging of oocytes impairs mitochondrial adenosine triphosphate production as a result of increasing oxidative stresses. Oxidative stresses also affect intracellular Ca2+ regulation and impair embryo development after fertilization. Collectively, the mechanism of postovulatory oocyte aging might be involved in reactive oxygen species-induced mitochondrial injury followed by abnormal intracellular Ca2+ regulation in the endoplasmic reticulum.