SSR, August 1, 97

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PP17 Oocyte Maturation Oogenesis Chapter 8 pg
182-187
ANS 3319Dr. Michael J. FieldsUniversity of
Florida
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OogenesisOogonium Maturation

• Oogonium undergoes Mitotic division in utero.
• Mitosis ceases at birth.
• Arrested at Meiosis I.

Mitosis
2N
2N
Pregnancy
Birth
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MovieCell Division
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OogenesisPrimary OocyteMaturation

• Oocyte arrested in Prophase of Meiosis I.
• Day 75-80 post conception (cattle)
• Corona Radiata
• 2 or 3 layers of follicular cells that surrounds
  oocyte.
• Produces cAMP that inhibits maturation of oocyte.

Meiosis I cAMP Inhibition
2N
2N
Oocyte
Puberty
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Primary Oocytes
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Primary Oocyte
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Primary Oocyte
Cumulus
Zona Pellucida
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OogenesisFormation of Secondary Oocyte
Extrusion of First Polar Body 1 copy of
chromosomes
1N
Meiosis I cAMP Inhibition
2N
1N
2N
LH Surge
Secondary Oocyte
Primary Oocyte
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OogenesisFormation of Secondary Oocyte

• Cumulus expansion in follicle
• Hyaluronic Acid aids in expansion
• Corona Radiata withdraws from oocyte.
• LH surge loosens gap junctions between granulosa
  cells
• Decrease in cAMP production

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OogenesisFormation of Secondary Oocyte

• Escape from Meiotic I block results in 1st Polar
  Body extrusion.
• Activation of Maturation Promoting Factor (MPF)
• MPF Cyclin
• Required for meiosis

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Oogenesis Formation of Secondary Oocyte

• Germinal Vesicle Breakdown (GVBD)
• Cortical Granules
• Lysosomal-like granules that prep oocyte for
  fertilization
• Migrate from germinal vesicle to vitelline
  membrane
• Luteinization starts, resulting from LH surge.

1st Polar Body
1N
cAMP Inhibition
2N
1N
2N
LH Surge
2o Oocyte
1o Oocyte
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Zona Pellucida
Secondary Oocyte
First Polar Body
Perivitelline Space
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Red cortical granules Blue oocyte
DNA www.colostate.edu
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OogenesisOvulation/Fertilization

• Secondary oocyte released from follicle.
• Oocyte arrested at Meiosis II Metaphase II until
  sperm entry.
• Fertilization activates Ca influx, resulting
  in resumption of Meiosis II and 2nd Polar Body
  extrusion.

2nd Polar Body
1N
2nd Oocyte
Zygote
1N
1N
2N
Ovulation
Syngamy
Fertilization
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OogenesisOvulation/Fertilization

• Ovulation not a pressure-built burst, but a
  proteolytic degradation of follicular and ovarian
  cell layers
• Ex matrix metalloproteinases (MMPs)
• Degradation of follicular connective tissue at
  apex of follicle
• Dissolution of granulosal basement membrane
• Stimulated by pre-ovulatory LH surge

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Ruptured follicle
Oocyte
encarta.msn.com
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Secondary Oocyte
Pronuclei Sperm Penetration
Cumulus Cells
Zona Pellucida
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OogenesisFertilization

• Sperm binds to plasma membrane of oocyte.
• Cortical granules migrate into perivitelline
  space and blocks additional sperm entry (prevent
  polyspermy).
• Male and female Pronuclei migrate to form single
  diploid nucleus (Syngamy).
• Zygote is diploid.

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Oogenesis
Zygote 2nd Polar Body
2o Oocyte 1st Polar Body
1o Oocyte
2N
1N
2N
2N
LH Surge
Syngamy
Ovulation
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MovieFertilization and Syngamy