[Research progress on the asymmetric division in mammalian oocytes]

The mammalian oocyte maturation process consists of two consecutive asymmetric divisions, and produces three daughter cells of vastly different sizes: one larger egg cell and two smaller polar bodies. Asymmetric division is a typical feature of mammalian oocyte meiosis that results in a highly polar egg cell. The mitosis of the cell after fertilization exhibits restored symmetric division, but the polarity characteristics formed during meiosis of oocytes are preserved and affect the polarity of early embryos. In this review, we summarize the research progress on asymmetric division of mammalian oocytes in recent years, and mainly focus on the asymmetric division of cytoplasmic and the asymmetric division of nucleus, including the functions of chromosome and cytoskeleton in asymmetric division of mammalian oocytes, the redistribution of cytoplasmic organelles occurring in oocyte maturation, and chromosome nonrandom separation. We aim to demonstrate the main mechanism of asymmetry division in mammalian oocytes from both cellular and molecular levels.