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#acrosome reaction

3 public questions tagged with this topic.

Fertilization in mammals-l

Acrosome reaction releases enzymes such as:

Acrosome reaction is calcium-triggered exocytosis fusing outer acrosomal membrane with overlying plasma membrane releasing enzymatic contents stored during spermiogenesis. Key enzymes liberated include hyaluronidase which hydrolyzes hyaluronan matrix surrounding cumulus cells, and serine protease acrosin plus esterases that locally digest ZP glycoproteins to create penetration slit. Additional glycosidases modify sugar residues. Enzymatic dispersal allows sperm to traverse cumulus oophorus and zona barriers. Without these hydrolases sperm cannot access oolemma, rendering fertilization impossible despite normal motility, capacitation status, successful cumulus navigation and zona binding and attachment attempts.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 7: Acrosome reaction enzymes – hyaluronidase and acrosin in penetration.

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Fertilization in mammals-l

Protein involved in sperm-egg membrane fusion:

Membrane fusion between sperm and egg requires specialized fusogenic proteins beyond simple adhesion. Fertilin, heterodimer of ADAM1 and ADAM2 disintegrin containing metalloproteases on sperm equatorial segment, binds alpha6beta1 integrin on egg microvillar membrane organized by tetraspanin CD9 microdomains. Interaction following Izumo1-Juno adhesion stabilizes close apposition, lowers energy barrier for lipid merger and promotes mixing of outer leaflets. Genetic ablation reducing fertilin shows impaired binding-fusion. Hence fertilin contributes crucial binding-fusion activity ensuring gamete coalescence, cytoplasmic continuity, successful zygote formation during fertilization event, activation and developmental initiation.

Ref: NCBI Bookshelf, ADAM proteins in fertilization: fertilin role in sperm-egg binding and fusion mechanisms.

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Fertilization in mammals-iv

Sperm lysins include:

Sperm lysins are hydrolytic enzymes stored in acrosome, a Golgi-derived cap-like vesicle covering anterior nucleus. Principal lysins are hyaluronidase which disperses corona radiata hyaluronan and serine protease acrosin which cleaves zona pellucida glycoproteins ZP1-ZP3 to facilitate drilling. Additional esterases and acid hydrolases assist matrix degradation. Upon zona binding triggered acrosomal exocytosis releases these enzymes in focused manner to locally digest extracellular coats. Catalase, oxidase, pepsin or lipases are not acrosomal components, so sperm relies specifically on hyaluronidase-acrosin duo for barrier penetration and eventual membrane fusion.

Ref: Gilbert, Developmental Biology, Chapter 7: Sperm lysins - hyaluronidase and acrosin roles in extracellular coat penetration.

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