26. Human sperms are allowed to fertilize ova having non- functional ovastacin. The following possibilities may be of significance in the fusion of these gametes:
    A. The sperms will not fertilize ova.
    B. The sperms will bind and penetrate the zonapellucida but will not be able to fuse with ovum
    membrane.
    C. ZP2 will not be clipped by cortical granule protease.
    D. CD9 protein of egg membrane microvilli will not be able to interact with sperm membrane proteins in the absence of ovastacin.
    E. Polyspermy may occur frequently.
    Which combination of statements represent the outcome of the above event?
    (1) A and B (2) C and E
    (3) C and D (4) B and C

Ovastacin, a metalloprotease released from cortical granules of the oocyte during fertilization, plays an essential role in safeguarding monospermic fertilization by modifying the zona pellucida (ZP), specifically through cleavage of the ZP2 glycoprotein. This process prevents multiple sperm from fertilizing a single egg, a lethal condition known as polyspermy.

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Role of Ovastacin and ZP2 Cleavage

Before fertilization, the ZP facilitates sperm binding via intact ZP2. Upon the first sperm fusion, ovastacin is released, cleaving ZP2 and causing biochemical hardening and structural changes to the ZP, effectively blocking further sperm binding and penetration.

Without functional ovastacin, this cleavage does not occur, leaving the ZP receptive to multiple sperms, increasing the risk of polyspermy.

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Consequences of Non-Functional Ovastacin

• Increased Polyspermy: Without ZP hardening triggered by ovastacin, polyspermy incidence rises, leading to embryos with abnormal chromosome numbers.

• Fertilization May Still Occur: Initial sperm binding and fusion are not prevented by ovastacin deficiency; rather, the block to additional sperm is compromised.

• Fertility Implications: Non-functional ovastacin is linked to reduced fertility due to polyspermy-related embryonic lethality.

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CD9 Protein and Its Independent Role

CD9 on the egg membrane facilitates sperm-egg membrane fusion but functions independently of ovastacin’s zona pellucida modulation.

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Conclusion

In cases of non-functional ovastacin, ZP2 is not cleaved, failing to harden the zona pellucida, which heightens polyspermy risk despite enabling initial fertilization. Understanding ovastacin’s action underscores its critical role in ensuring monospermic fertilization and healthy embryonic development.

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This article elucidates the biological importance of ovastacin in fertilization, highlighting mechanisms preventing polyspermy and their implications for reproductive success.

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Final answer:
(2) C and E