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#sperm penetration

3 public questions tagged with this topic.

Fertilization in mammals-ll

Structure secreting enzymes for sperm penetration:

Acrosome is large cap-shaped vesicle covering anterior half of sperm nucleus, derived from Golgi apparatus and considered modified lysosome packed with hydrolytic enzymes. Upon capacitation and zona binding, calcium-dependent exocytosis releases outer acrosomal membrane fusing with plasma membrane, liberating hyaluronidase, acrosin serine protease and glycosidases. Hyaluronidase disperses cumulus hyaluronan matrix, acrosin digests zona glycoproteins locally. Exposed inner acrosomal membrane displays secondary receptors for ZP2, ensuring sustained binding. Specialized secretory organelle thus enables enzymatic penetration of egg investments essential for reaching oolemma for fusion and activation.

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Acrosome – Golgi-derived lysosome-like organelle and enzyme release.

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Fertilization in mammals-iv

Enzyme aiding corona radiata penetration:

Corona radiata consists of cumulus granulosa cells embedded in hyaluronic acid-rich extracellular matrix surrounding ovulated oocyte. Sperm must disperse this layer before contacting zona pellucida. Acrosomal membrane associated hyaluronidase hydrolyzes beta-1,4 linkages of hyaluronan polymers, breaking intercellular cement and creating paths for motile sperm. This action is complemented by flagellar thrust and other proteases. Hyaluronidase activity is greatly enhanced after capacitation and is localized on sperm surface, allowing efficient penetration of cumulus oophorus without damaging oocyte, facilitating species-specific approach to zona glycoproteins.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Fertilization - corona radiata, hyaluronidase and cumulus matrix dispersal.

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Fertilization in mammals-iv

Acrosomal reaction primarily involves:

Acrosomal reaction is calcium-dependent exocytosis of acrosomal vesicle at anterior sperm head occurring after zona pellucida binding. Fusion of outer acrosomal membrane with plasma membrane releases soluble enzymes including acrosin, hyaluronidase and other proteases. These lysins locally digest zona pellucida glycoprotein matrix, creating penetration slit allowing sperm to reach perivitelline space. Reaction also exposes inner acrosomal membrane proteins like Izumo1 essential for egg fusion. Without zona digestion sperm cannot traverse thick extracellular coat, making this enzymatic breaching crucial for successful fertilization in mammals.

Ref: NCBI Bookshelf, Gilbert Developmental Biology, Chapter 7: Fertilization - acrosome reaction, acrosin and zona pellucida penetration.

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