Mammalian Fertilization

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Mammalian Fertilization

• Sperm must be capacitated in female reproductive
  tract
• Fertilization occurs in Fallopian tube (a.k.a.
  oviduct)

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Fertilization

• Ovulated eggs surrounded by granulosa cells
• Zona Pellucida glycoprotein layer with three
  major roles
• Sperm binding
• Initiates acrosome reaction
• Prevents polyspermy

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Zona Pellucida

• Consists of three major glycoproteins ZP1, ZP2
  ZP3
• ZP3 is sperm binding protein
• Evidence
• Purified ZP3 competes with intact zona for sperm
  binding
• Zona reaction (prevention of polyspermy) occurs
  when ZP2 and ZP3 are modified by cortical granule
  enzymes

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Fertilization

• Sperm-egg recognition conducted by sperm ADAM
  proteins that bind to integrins on the egg plasma
  memb.
• Sperm-egg fusion is mediated by CD9 (tetraspanin)
  protein on egg plasma memb.
• Cell fusion causes rise in intracellular Ca
  (oscillations). (IP3 pathway)

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