Physiologic Course of Female Reproductive Function: A Molecular Look into the Prologue of Life

Figure 3

Cellular stages and signaling in female germ cell development. Syngamy produces a single totipotent cell, the zygote, which evolves through various structural stages. After gastrulation, extraembryonic ectoderm induces some epiblastic cells into pluripotency and entry into somatic lineage. These later undergo epigenetic reprogramming to regain totipotentiality and become primordial germ cells. These migrate to the gonadal ridges and suffer intense mitosis, becoming oogonia, which are then induced by retinoic acid to enter meiosis I. Primary oocytes are then arrested in this division and appear to survive until ovulation due to elevated intracellular cAMP levels. With ovulation, meiosis I is completed and meiosis II begins in secondary oocytes. Nonetheless, this division is only fulfilled if union with a male gamete occurs, which ultimately leads to formation of a zygote.