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Block I: Reproduction & Sexuality > Histology: Oocyte Development > Flashcards

Histology: Oocyte Development Flashcards

1
Q

6 stages of the life history of an oocyte

A
  1. Primordial germ cell
  2. Oogonium (mitotically active)
  3. Oocyte (entry into meiosis)
  4. Growth
  5. Meiotic maturation
  6. Ovulation and fertilization
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2
Q

What occurs to embryonic oocytes part-way through meiosis

A

They become arrested and complete meiosis at sexual maturity

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3
Q

Fate of meiotically arrested oocytes near the time of birth

A

Become enclosed in primordial follicles

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4
Q

Percentage of oocytes that die before puberty

A

>90%

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5
Q

4 steps of post-natal oogenesis

A
  1. Oocyte and follicle exit the primordial stage and initiate growth
  2. Oocyte grows; follicle enlarges by cell proliferation and follicular fluid
  3. Oocyte matures and is ovulated
  4. Empty folicle becomes corpus luteum, producing progesterone needed for implantationg and beyond
    • Embryo secretes factors required to maintain the corpus luteum
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6
Q

3 important genes involved in premature ovarian failure

A
  • Pten
  • Foxo3a
  • Tsc1/2

(Inhibitors of primordial follicular growth)

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7
Q

Genetic treatment for infertility

A

Hippo signalling disruption and Akt stimulation of ovarian follicles

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8
Q

Volume increase and time required for oocyte growth

A

Volume increase = ~100 fold

Requires 3 - 4 months

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9
Q

Where is the growing oocyte arrested?

A

Late G2 (prophase I, diplotene, diakinesis)

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10
Q

Why do oocytes grow?

A
  • To accumulate mRNAs, proteins, ribosomes, mitochondrias etc that the early embryo will need
  • To produce a giant cell that can be divided into many smaller cells during the cleavage divisions of early embryogenesis
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11
Q

Follicular cells required for the oocyte to grow

A

Granulosa cells (without them, there is no growth)

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12
Q

2 factors provided by the granulosa cells to the growing oocyte and how

A
  • Gja4 (gap junctions)
  • Kit ligand (secreted)
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13
Q

Without Gja4, what cannot occur in the oocyte?

A

Oocytes cannot undergo final stage of development

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14
Q

Define the zona pellucida

A

Barrier to oocyte-graulosa communication

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15
Q

What connects the granulosa to the oocyte?

A

Transzonal processes (TZPs)

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16
Q

Essential factor provided by the oocyte to the granulosa

A

Gdf9

17
Q

3 consequences of lacking Gdf9

A
  • Granulosa cells do not proliferate properly
  • Oocytes grow larger than normal
  • Oocytes cannot undergo final stage of development (meiotic maturation) –> infertility
18
Q

Describe the role of thecal and granulosa cells in the production of estradiol

A
  1. Thecal cells synthesize testosterone from cholesterol
  2. Granulosa cells convert testosterone to estradiol
19
Q

2 distinct populations of granulosa cells (different gene products)

A
  • Mural granulosa
  • Cumulus granulosa
20
Q

At what stage do most follicles become atretic?

A

After reaching the antral stage (although the oocytes are probably healthy)

21
Q

Substance that underlies follicular atresia

A

Limited supply of FSH

22
Q

Effect of injected FSH

A

Rescue subordinate future atretic) follicles to increase the number of eggs for assisted reproduction

23
Q

Physiological trigger of meiotic maturation of the oocyte

A

Luteinizing hormone (LH) (also triggers ovulation)

24
Q

When may meiotic maturation of the oocyte occur without LH?

A

When fully grown oocytes are removed from the follicle and places in culture (in vitro maturation)

25
Q

Two components of meiotic maturation of the oocyte

A
  • Nuclear maturation
  • Cytoplasmic maturation
26
Q

Events of nuclear maturation

A

Completion of the first meiotic division and progression to metaphase II

27
Q

Origin of maternally derived aneuploidy

A

Nuclear maturation

28
Q

5 essential processes of cytoplasmis maturation

A
  1. Translational activation of some mRNAs
  2. Degradation of many mRNAs (oocyte-to-embryo transition)
  3. Migration of cortical granules to cortex
  4. Reorganization of endoplasmic reticulum – facilitate Ca release at fertilization
  5. Redistribution of mitochondria – surround meiotic spindle
29
Q

3 steps from LH to oocyte maturation

A
  1. LH
  2. Mural granulosa LH receptors induced by FSH (note: not present on the cumulus granulosa cells or oocyte)
  3. EGF-related growth factors
  4. OGFR or mural and/or cumulus granulosa
  5. Oocyte maturation
30
Q

Event in the oocyte that triggers maturation

A

Decreased cyclic AMP within the oocyte

31
Q

Explain the way cAMP (and maturation) are regulated by LH

A

cGMP inhibition by EGFR to reduce cAMP production

Block I: Reproduction & Sexuality (23 decks)

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