ABSTRACT
Mammalian oocytes are exceptional cells. Unlike male germ cells they are extremely long-lived and initiate the meiotic program during fetal development in the embryonic ovary. Much unlike most other cell types, they arrest for long periods at the G2-phase of the cell cycle and thus undergo a discontinuous meiosis. Their development is associated with major starts and stops in meiotic progression as well as major changes in gene expression patterns during transitional phases of oogenesis, e.g. when oocytes complete the first stages of prophase of meiosis I1, when oocytes become meiotically arrested, or when follicles and oocytes become recruited from the resting to the growing pool2. Before resumption of maturation oocytes undergo extensive growth, accompanied by high transcription rates. However, fully mature oocytes subsequently become transcriptionally repressed3,4, whereas specific stored messages are recruited by polyadenylation to be translated during maturation or early embryogenesis5,6.
