Histology: Oocyte Development Flashcards Preview

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

Flashcards in Histology: Oocyte Development Deck (31):
1

6 stages of the life history of an oocyte

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

2

What occurs to embryonic oocytes part-way through meiosis

They become arrested and complete meiosis at sexual maturity

3

Fate of meiotically arrested oocytes near the time of birth

Become enclosed in primordial follicles

4

Percentage of oocytes that die before puberty

>90%

5

4 steps of post-natal oogenesis

  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

6

3 important genes involved in premature ovarian failure

  • Pten
  • Foxo3a
  • Tsc1/2

(Inhibitors of primordial follicular growth)

7

Genetic treatment for infertility

Hippo signalling disruption and Akt stimulation of ovarian follicles

8

Volume increase and time required for oocyte growth

Volume increase = ~100 fold

Requires 3 - 4 months

9

Where is the growing oocyte arrested?

Late G2 (prophase I, diplotene, diakinesis)

10

Why do oocytes grow?

  • 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

11

Follicular cells required for the oocyte to grow

Granulosa cells (without them, there is no growth)

12

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

  • Gja4 (gap junctions)
  • Kit ligand (secreted)

13

Without Gja4, what cannot occur in the oocyte?

Oocytes cannot undergo final stage of development

14

Define the zona pellucida

Barrier to oocyte-graulosa communication

15

What connects the granulosa to the oocyte?

Transzonal processes (TZPs)

16

Essential factor provided by the oocyte to the granulosa

Gdf9

17

3 consequences of lacking Gdf9

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

18

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

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

19

2 distinct populations of granulosa cells (different gene products)

  • Mural granulosa
  • Cumulus granulosa

20

At what stage do most follicles become atretic?

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

21

Substance that underlies follicular atresia

Limited supply of FSH

22

Effect of injected FSH

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

23

Physiological trigger of meiotic maturation of the oocyte

Luteinizing hormone (LH) (also triggers ovulation)

24

When may meiotic maturation of the oocyte occur without LH?

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

25

Two components of meiotic maturation of the oocyte

  • Nuclear maturation
  • Cytoplasmic maturation

26

Events of nuclear maturation

Completion of the first meiotic division and progression to metaphase II

27

Origin of maternally derived aneuploidy

Nuclear maturation

28

5 essential processes of cytoplasmis maturation

  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

3 steps from LH to oocyte maturation

  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

Event in the oocyte that triggers maturation

Decreased cyclic AMP within the oocyte

31

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

cGMP inhibition by EGFR to reduce cAMP production