Looking after the maternal legacy: Mitochondrial dynamics and function in the oocyte to embryo transition. (#6)
Mitochondria have a particularly important place in the development of the oocyte and early mammalian embryo. The mitochondrial genome is inherited through the oocyte thereby coupling the integrity and efficiency of the electron transport chain to the maternal lineage. Furthermore, ATP production in oocytes and early embryos is almost exclusively provided by the mitochondria. As such the viability of the mammalian oocyte and embryo is very much dependent on the quality of the mitochondrial population present in the oocyte. During oocyte maturation the mitochondria are highly dynamic. They aggregate around the developing first mitotic spindle in a microtubule and dynein-mediated mechanism. They then undergo a dramatic reorganization at the time of polar body formation and redistribute through the oocyte cytoplasm.
Measurement of oocyte ATP levels using a new FRET-based probe has provided new insights into the levels of ATP during maturation, revealing significant excursions in ATP levels at particular times during oocyte maturation. At fertilization, mitochondrial ATP production is coupled to sperm-induced calcium signaling such that each Calcium transient is detected by the mitochondria and results in an increase in mitochondrial activity. This coupling of ATP production to Calcium signaling provides a means of dynamically matching ATP supply and demand. Finally, a number of recent studies suggest that the function and dynamics of oocyte mitochondria are influenced by maternal diet and therefore act as sensors that link the maternal environment with reproductive potential.