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. 2020 Jan 9;8:1586. Originally published 2019 Sep 4. [Version 2] doi: 10.12688/f1000research.20062.2

Figure 3. Schematic diagram of the acrosome reaction and fertilization.

Figure 3.

1) Sperm cells are chemo-attracted to the oocyte and once in close proximity, interact with zona pellucida (ZP) glycoproteins. The arrangement of these glycoproteins are species specific and are responsible for preventing cross species fertilization. 2) ZP glycoproteins initiate a signaling cascade through receptor binding on the sperm surface leading to a degradation of the acrosome membrane and release of hyaluronase and acrosin, which breaks down the ZP. 3) Once through the ZP, the sperm enters the vitelline space and contacts the oocyte membrane. Binding occurs at the posterior portion of the sperm head. 4) The membranes of oocyte and sperm fuse, causing a rapid depolarization and hardening of the ZP, preventing polyspermy. The nucleus of the sperm enters the oocyte and the fertilized oocyte completes second meiosis.