1 – Fertilization and Activation of the Embryonic Genome

This chapter discusses the fertilization and activation of the embryonic genome. The full-grown oocyte arrested in prophase of the first meiotic division contains all of the molecules that are utilized to bridge the period of transcriptional silence that begins with the completion of oocyte growth. Under hormonal stimulation the full-grown oocyte begins maturation, completing the first meiosis and the first half of the second meiotic division before arresting in metaphase of the second meiotic division. During this period the extensive stores of maternal messages are selectively utilized, which can result in the synthesis of a new and perhaps a different set of proteins. Simultaneously, preexisting maternal proteins can undergo post-translational modification and degradation. These programmed events result in an oocyte that is ready for fertilization. Fertilization initiates a cascade of events, also dependent on protein modifications and on the timely synthesis of new proteins from maternal mRNA stores that leads to completion of the second meiotic division, remodeling of egg and sperm chromatin, DNA synthesis, entry into the first mitosis, and activation of the embryonic genome.