Molecular Mechanisms Responsible for Increased Vulnerability of the Ageing Oocyte to Oxidative Damage

Figure 1

Stages of folliculogenesis and oocyte maturation. Primordial follicles consist of an immature GV oocyte arrested at prophase I, which is encapsulated by pregranulosa cells. Activation of primordial follicles to primary follicles is marked by a morphological change of pregranulosa cells from squamous to cuboidal. The development of the secondary follicle is marked by the acquisition of two or more layers of granulosa cells and the presence of a theca layer and contains an oocyte with a completely formed zona pellucida. The antral or Graafian follicle is the last stage of follicular development. This stage is marked by the presence of a follicular fluid-filled antral cavity adjacent to the oocyte. In the final stage of folliculogenesis, the oocyte achieves meiotic resumption, undergoing germinal vesical breakdown, and progresses through anaphase I and telophase I to complete meiosis I. At the completion of the first meiotic division, the first polar body is extruded and the ovulated oocyte becomes arrested once more at metaphase II until after fertilisation. Once the follicle is ruptured to release the mature oocyte, the remaining granulosa and theca cells differentiate into the corpus luteum.