Cortical granule exocytosis

Definition

Cortical granule exocytosis is the process by which cortical granules release their contents into the perivitelline space following fertilization, playing a critical role in modifying the egg's outer layer to prevent polyspermy. This exocytosis occurs immediately after a sperm successfully fuses with the egg, leading to changes that block additional sperm from entering. The process is essential for proper fertilization and early embryonic development, ensuring that only one sperm fertilizes the egg, thus maintaining genetic integrity.

5 Must Know Facts For Your Next Test

1. Cortical granules are specialized vesicles located just beneath the plasma membrane of an oocyte, filled with enzymes and other molecules that are released during exocytosis.
2. The release of cortical granules alters the egg's zona pellucida, creating a physical barrier that prevents additional sperm from penetrating the egg.
3. Calcium ions play a crucial role in triggering cortical granule exocytosis immediately following sperm entry, acting as a secondary messenger in the signaling pathway.
4. This process also contributes to the activation of the egg, leading to metabolic changes necessary for early embryonic development.
5. Cortical granule exocytosis is not only vital for preventing polyspermy but also helps in initiating embryogenesis by modifying the egg environment post-fertilization.

Review Questions

• How does cortical granule exocytosis contribute to the prevention of polyspermy during fertilization?
  • Cortical granule exocytosis releases enzymes and other molecules into the perivitelline space, leading to changes in the egg's zona pellucida. This modification creates a barrier that prevents additional sperm from penetrating the egg after the first sperm has successfully fertilized it. By ensuring that only one sperm can fertilize an egg, this process maintains genetic integrity and normal development.
• Discuss the role of calcium ions in the process of cortical granule exocytosis following fertilization.
  • Calcium ions act as secondary messengers that initiate cortical granule exocytosis when a sperm successfully fuses with an egg. The influx of calcium triggers a cascade of signaling events leading to the fusion of cortical granules with the plasma membrane. This release is crucial for altering the egg's protective layers and initiating further developmental processes.
• Evaluate the significance of cortical granule exocytosis in early embryonic development and potential implications if this process fails.
  • Cortical granule exocytosis is essential not only for preventing polyspermy but also for triggering metabolic changes that activate the egg and prepare it for early embryonic development. If this process fails, it could lead to polyspermy, resulting in abnormal chromosomal numbers and developmental issues. Such failures could severely impact fertility and result in miscarriages or congenital abnormalities in embryos.

Related terms

Polyspermy: The condition in which an egg is fertilized by more than one sperm, which can lead to abnormal development and genetic complications.

Fertilization envelope: A protective layer formed around the egg after fertilization, primarily resulting from cortical granule exocytosis, which helps prevent polyspermy.

Oocyte: A female gamete or egg cell that undergoes maturation and is capable of being fertilized by a sperm.