oocyte maturation

immature vs mature oocytes

oocyte maturation

1. nuclear maturation

   1. before LH surge

   2. after LH surge

2. cytoplasmic maturation

MPF

• M-phase promoting factor

• mitosis promoting factor

• maturation promoting factor

• CDZ-cyclin complex

  • CDK

  • Cyclin B

• activity of CDK is also controlled by the pattern of phosphorylation

  • phosphorylation at one site (red) inactivates CDK

  • phosphorylation at another site (green) activates CDK

timeline of MPF activity

MPF

cAMP-mediated meiotic arrest

• what maintains elevated cAMP concentrations?

  • granulosa/cumulus-derived cGMP

  • granulosa-derived factor stimulation of adenylate cyclase (AC)

    • binding to G-protein receptor 3 (GPR3)

      • FSH

      • other hormones

  • phosphodiesterase 3A (PDE3A) block

resumption of meiosis

1. decreased g-coupled protein kinase receptor 3 (GPR3) signaling

2. increased PDE3A

3. decreased granulosa/cumulus cGMP

granulosa-cumulus cell maintenance of elevated cAMP levels

• NEED TO KNOW:

  • species differences exist

  • cumulus cell-derived cGMP

    • gap junctions

    • phosphodiesterase (PDE3A)

  • natriuretic peptide receptor 2 (NPR2)

    • receptor activity controlled by natriuretic peptides (NPP), and the expression of NPPs are influenced by various cumulus-granulosa factors

  • paracrine system

  • so, elevated cGMP, blocks PDE3A, and this maintains elevated cAMP levels

granulosa-cumulus cell mediation of meiosis resumption

1. LH-induced reduction in oocyte cAMP

   1. NO LH RECEPTORS ON OOCYTE — ACTS ON GRANULOSA CELLS

   2. LH increases granulosa cell cAMP

   3. increases PDE1 and PDE5

   4. decreases cGMP

   5. PDE3A block is released in oocyte

   6. conversion of cAMP to AMP

2. LH-mediated stimulation in EGF-like molecules (EGF-LP)

   1. A-Reg, E-Reg act through EGF receptor (EGFR) in granulosa/cumulus cell to reduce cGMP transport through the oocyte

   2. block NPR2

      1. blocks cGMP production

   3. block gap junctions

resumption of meiosis during in vitro fertilization (IVF)

simulated physiological oocyte maturation (SPOM)

cytoplasmic (ooplasmic) maturation

1. cortical granule expansion and redistribution

2. mitochondria expansion and cellular redistribution

3. protein and mRNA packaging

maternal mRNA storage

bovine transcripts associated with oocyte competency

oocyte-secreted factors

• soluble growth factors

  • growth-differentiation factor 9

  • bone morphogenetic protein 15

• modulate various cumulus and granulosa cell activities

fecundity genes in sheep

• inverdale sheep

• romney breed

• FecX mutation:

  • BMP15

  • single allele mutation = increased lamb #

    • increased twinning, triplets

  • double allele mutation = sterile

• several other Fec mutations have been discovered

  • all of them target BMP15 of GDF9

• Booroola Merino

• FecB mutation:

  • BMPR-1B

  • wildtype: 1-2 lambs/ewe

  • monoallelic FecB: 3-4 lambs/ewe

  • biallelic FecB: 5+ lambs/ewe

terminology

• fertility:

  • actual reproductive performance

  • number of offspring produced

• fecundity:

  • the potential for an individual to reproduce

  • the capacity to produce offspring

    • number of gametes

    • health

    • environment

    • evolutionary

fecundity genes in sheep: mechanism

picture…