Mitochondrial Calcium Disorder Affects Early Embryonic Development in Mice through Regulating the ERK/MAPK Pathway

The homeostasis of mitochondrial calcium ([Ca²⁺]_mt) in oocytes plays a critical role in maintaining normal reproductive cellular progress such as meiosis. However, little is known about the association between [Ca²⁺]_mt homeostasis and early embryonic development. Two in vitro mouse MII oocyte models were established by using a specific agonist or inhibitor targeting mitochondrial calcium uniporters (MCU) to upregulate or downregulate [Ca²⁺]_mt concentrations. The imbalance of [Ca²⁺]_mt in MII oocytes causes mitochondrial dysfunction and morphological abnormity, leading to an abnormal spindle/chromosome structure. Oocytes in drug-treated groups are less likely to develop into blastocyst during in vitro culture. Abnormal [Ca²⁺]_mt concentrations in oocytes hindered epigenetic modification and regulated mitogen-activated protein kinase (MAPK) signaling that is associated with gene expression. We also found that MAPK/ERK signaling is regulating DNA methylation in MII oocytes to modulate epigenetic modification. These data provide a new insight into the protective role of [Ca²⁺]_mt homeostasis in early embryonic development and also demonstrate a new mechanism of MAPK signaling regulated by [Ca²⁺]_mt that influences epigenetic modification.