oocyte maturation

Mitosis

doubling genetic material

Meiosis 1

same concept as mitosis with crossing over

Meiosis 2

produce four daughter cells that have ½ the required genetic material

four phases of oocyte maturation

mitotic divisions of primordial germ cells → occurs during early prenatal development

nuclear arrest → dictyotene phase - longer stage during the diplotene phase

cytoplasmic growth → during progression from primordial to primary follicle

resumption of meiosis following LH surge

primordial germ cells (2n)

migrate to developing gonads

10-20 um

miotic divisions

• start with 20-100 primordial germ cells

• end up with millions

after mitotic stage

• DNA synthesis

Primary Oocyte (4n)

progress into 1st meiotic prophase

• in cattle: 75-80d post-conception

arrested in prophase 1

• pairing of homologous chromosomes, synapsis, and crossing over

• specific stage

  • dictyate which is part of diplotene

dictyate reached at 170d post conception in cattle

Primordial follicles

primary oocyte

single layer squamous epithelial cells

primordial resting pool

primary follicle

primary oocyte

single layer of 11-20 cuboidal granulosa cells

begin to see increase in organelles

• elongated mitochondria and diving mitochondria

• smooth and rough ER

Secondary Follicle

primary oocyte

second layer of granulosa cells

initial deposition of zona pellucida glycoproteins

cortical granules formed

oocyte begins RNA synthesis

zona pellucida

made of glycoproteins produced by the oocyte

designated zona protein (ZP) 1,2,3

sperm bind to ZP3

Early Tertiary Follicle

primary oocyte

follicle diameter: 2-3 um

oocyte (begins to grow, reaching 110 um, becomes transcriptionally active

tertiary follicle

primary oocyte

follicle diameter: 8-9 mm

oocyte stops growing, 120-130 um

perivitelline space appears

free smooth and rough ER decrease

hooded mitochondria appear

mitochondria, Golgi bodies, cortical granule clusters, and nucleus migrate to the periphery

dominant follicle

primary oocyte

follicle diameter: >14 mm | (swine = ~7 mm, mare = 35-55 mm)

increase in lipid content

decrease in size of Golgi bodies

cortical granules move closer to plasma membrane

LH surge causes what?

activates meiosis

cortical granules move to just inside oocyte plasma membrane

perivitelline place completely formed

further increase in lipid content and decrease in Golgi bodies

meiosis resumed

meiosis resumption

primary oocyte arrested in dictyate

with LH surge:

• progresses through meiosis 1

• arrested in metaphase 2

• first polar body

now a secondary oocyte

oocyte ready for ovulation