Energy Metabolism Regulating Mammalian Oocyte Maturation

Oocyte maturation is a final step of gamete development that follows a prolonged period of cell growth within a growing follicle. Unlike oocyte growth that takes several weeks or months, maturation process is a short (hours or days), dynamic process. The period of oocyte maturation varies among species, ranging from 10-13 hours in the mouse (Edwards & Gates, 1959) to 16-24 hours in the cow (Dominko & First, 1997) and 48 -72 hours in the dog (Reynaud et al., 2005, Songsasen & Wildt, 2007). For an oocyte to fully capable of fertilizing and developing into an embryo, the gamete needs to undergo nuclear and cytoplasmic maturation. Nuclear maturation encompasses events associated with the separation of homologous chromosomes during meiosis I and the segregation of sister chromatids during meiosis 2 (Albertini & Limback, 2009). Events occur during this process include nuclear envelope breakdown, rearrangement of the cortical cytoskeleton and meiotic spindle assembly. Cytoplasmic maturation includes events of post-transcriptional and posttranslational processes, including mRNA synthesis, rearrangement of cytoplasmic organelles and glutathione production that are essential for successful fertilization and subsequent embryonic development (Albertini & Limback, 2009, Watson, 2007). For an oocyte to appropriately progress to these dynamic process of nuclear and cytoplasmic maturation, it requires enormous energy from various substrates, including glucose, amino acids and lipids (Sutton et al., 2003). In addition, tight regulation of reactive oxygen species (ROS) and calcium homeostasis are important during this process. This chapter will review current knowledge on mammalian oocyte development, the roles of mitochondria on cell functions and energy metabolism and its impact on gamete maturation.