Advances in Oocyte Maturation In Vivo and In Vitro in Mammals

Abstract

The quality and maturation of an oocyte not only play decisive roles in fertilization and embryo success, but also have long-term impacts on the later growth and development of the fetus. Female fertility declines with age, reflecting a decline in oocyte quantity. However, the meiosis of oocytes involves a complex and orderly regulatory process whose mechanisms have not yet been fully elucidated. This review therefore mainly focuses on the regulation mechanism of oocyte maturation, including folliculogenesis, oogenesis, and the interactions between granulosa cells and oocytes, plus in vitro technology and nuclear/cytoplasm maturation in oocytes. Additionally, we have reviewed advances made in the single-cell mRNA sequencing technology related to oocyte maturation in order to improve our understanding of the mechanism of oocyte maturation and to provide a theoretical basis for subsequent research into oocyte maturation.

Keywords: folliculogenesis; in vitro maturation; in vivo maturation; oocyte; oogenesis; single-cell mRNA sequencing.

Figure 1

Folliculogenesis and oogenesis in humans, pigs, and mice.

Figure 2

Granulosa cells and follicle development. Primordial follicles begin as oocytes, which are surrounded by a single layer of flattened cells called preantral granulosa cells. As the follicle develops, the flat granulosa cells become cubic and surround the oocyte in the primary follicle, accompanied by the appearance of a zona pellucida. In secondary follicles, one layer of granulosa cells multiplies into multiple layers. In the antral follicular stage, granulosa cells differentiate into mural granulosa cells and cumulus granulosa cells under the action of FSH.