Complex sentence: After the acrosome reaction, the sperm is believed to remain bound to the zona pellucida through exposed ZP2 receptors, which are unknown in mice but have been identified in guinea pigs.
Split into simpler sentences: After the acrosome reaction, the sperm is believed to remain bound to the zona pellucida through exposed ZP2 receptors. These receptors are unknown in mice but have been identified in guinea pigs.