Supply and Demand of Energy in the Oocyte and the Role of Mitochondria

The sole purpose of any mammalian oocyte is to combine with a spermatozoon and form a viable embryo that implants into the uterus and forms a viable foetus. Most of the structures and mechanisms for this reside within the oocyte itself. The sperm limits itself to fertilisation of the oocyte; apart from this, its only contribution is the male genome and the centrosome, required for cell division. Both intrinsic and extrinsic factors determine the formation of a viable embryo. However, the fundamental necessity for successful reproduction resides within the capacity for the developing embryo to generate sufficient levels of energy for optimal development to occur. Energy is generated principally within mitochondria. In this chapter, we discuss some of the fundamental processes of preimplantation embryo development and the role of mitochondria in providing sufficient energy for the successful completion of these processes. We discuss mitochondrial genetics, replication and energy production. Ageing appears to affect the capacity of the mitochondrion to produce sufficient energy to balance the requirements of the embryo. We discuss some of the theories of the effect of maternal age on mitochondrial physiology and the role this plays in reproduction. We propose that maternal age has longer-term effects on individuals than simply on the efficiency of reproduction. We also discuss some of the procedures assisted reproduction has proposed to alleviate the effect of maternal age on reproduction.