PP 18 Fertilization Chapter 12 pg 276283

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PP 18FertilizationChapter 12 pg 276-283
ANS 3319Dr. Michael J. FieldsUniversity of
Florida
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Capacitation

• Cellular changes that occur in sperm in the
  female reproductive tract giving sperm the
  capacity to fertilize.
• Completed in vitro with high ionic strength
  buffer via influx of Ca into sperm.
• Inhibited by secondary sex gland secretions in
  semen.
• Uterus dilutes out this inhibition and sperm cell
  undergoes maturation before fertilization.

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Capacitation

• Oxidative process
• Caused by presence of HCO3
• Regulated by G-protein

Activation Of Adenyl Cyclase
Cholesterol Efflux
Hyperpolarization
Release of HCO3
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Calnet, University of Bristol
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Sperm Transport to Uterus

• Within minutes, hundreds of sperm reach site of
  fertilization.
• Move by peristaltic actions of uterus, cervix and
  oviduct via oxytocin.
• PGF2? in semen causes contractions of uterus.
• Rapid phase of transport moves both dead and live
  sperm.

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Sperm Transport to Uterus

• Semen deposit site differs between species
• Vaginal primates, rabbits, sheep, cattle
• Intracervical horses
• Transcervical swine
• Only thousands of sperm penetrate cervix and
  reach uterus.
• Sperm concentrations
• Cattle 3000 x106 3 billion at deposit, very
  few reach ampulla
• Sheep 1000 x106 1 billion at deposit, 600-700
  reach ampulla
• Horse 10,000 x106 10 billion at deposit, very
  few reach ampulla
• Pig 8000 x106 8 billion at deposit, 1000 reach
  ampulla

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Egg Transport in Oviduct

• Ciliated epithelial cells of the fimbria pick up
  ovum (with cumulus mass).
• Fimbria of the infundibulum forms ovarian bursa
• Ostium is opening to ampulla.
• Cilia beat in direction of uterus and segmented
  peristaltic contractions move ovum to site of
  fertilization (Ampullary - Isthmus Junction).
• Under estrogen action beat towards ovary
• Under progesterone action beat towards uterus
• Egg travels to site of fertilization in less than
  2 hours.

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Egg Transport in Oviduct

• Estrogen causes retention of egg (estrus -
  fertilization).
• Day 1 (post ovulation)
• Favors sperm motility
• Progesterone hastens movement of egg (post
  ovulation, CL formation).
• Day 3 (post ovulation)
• Inhibits sperm motility
• Egg remains in oviduct 3 days (horse 5 days).
• Only 1 day in Isthmus before entering uterus in
  all species.
• Fluid peaks in Ampulla at day 3
• After peak, fluid steadily decreases

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Sperm Recognition Penetration

• Zona Pellucida receptors (ZP 1, 2 and 3) bind the
  sperm resulting in the Acrosomal Reaction.
• Acrosomal Reaction - fusion of acrosomal membrane
  and plasma membrane of sperm
• Releases acrosin, hyaluronidase, and other
  proteolytic enzymes for penetration of the zona
  pellucida.
• Causes loss of enzymatic components of acrosome

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Sperm Recognition Penetration

• Zona Reaction
• Sperm penetration of zona pellucida (glycoprotein
  membrane) with aid of Acrosin
• Sperm plasma membrane fuses with oocyte plasma
  membrane
• Oocyte Activation Cortical Reaction
• Release of calcium
• Na/H exchange
• Increase in pH of sperm after sperm egg plasma
  membrane fusion

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Mammalian sperm bind equatorial to zona
pellucida. Sea urchin sperm bind perpendicular.
Acrosomal membrane
Plasma membrane
Acrosome Reaction
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Calnet, University of Bristol
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www.nature.com
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www.miami.edu
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www.dushkin.com
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www.zoology.wisc.edu
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Blocks To Polyspermy

• Polyspermy fertilization by more than one sperm
• 1 2 mammals embryos are 3N (triploid),
  resulting from aged gametes (sperm 24 h, ovum 12
  h)
• Fast Block
• Slow Block

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Fast Block to Polyspermy

• Influx of sodium ions causes surface
  depolarization of membrane
• After first sperm binding
• Blocks further sperm binding
• Seen in sea urchins

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Vitelline BlockSlow Block - Mammals

• Cortical Granules migrate to vitelline membrane
  and fuse with it.
• Releases proteinases glycosidases.
• Hydrolysis of ZP3.
• Sperm head fuses with vitelline membrane
• Releases calcium from granules
• Granule contents released into perivitelline
  space.
• Makes zona refractory to other sperm
• Mucopolysaccarides of vitelline membrane crosslink

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Fertilization

• Second Polar Body is extruded after sperm
  penetration of vitelline membrane.
• Syngamy - joining of male and female Pronuclei.
• Zygote - one cell embryo following complete
  fertilization and first phase of embryonic
  growth.

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MovieOvulation and Egg Transport