Lecture 3: Oogenesis

Question 1

In oogenesis, what do PCGs differentiate into?

Answer 1

oogonia (46, 2N)

Primary locates (46, 4N) —> remain dormant in prophase I (diplotene) until puberty
Secondary locate (23, 2N) —> arrests in metaphase II until just prior/at fertilization
Mature locate (23, N)

Question 2

What happens in meiosis I and prolonged Diplotene (prophase I)?

Answer 2

Metaphase I:
- some yolk accumulation
- cortical granule production
- accumulation of mRNA, rRNA
- crossing-over

Telephone I:
- all primary locates arrest in Diplotene until puberty

Question 3

What are the structures involved in the Female Productive System?

Answer 3

Fallopian tube
Ovary
Uterus
Cervix
- Internal os
- external os
Vagina
Labium minus

Question 4

What are the types of Uterus’ in species?

Answer 4

Simplex —> primate
Duplex —> rat, mouse, rabbit, gerbil
Bicornuate —> pig
Bipartite —> Mare, cat, dog, ewe

Question 5

Describe the pathway of both Oogenesis and Follicle development.

Answer 5

Question 6

Name the structure of the Ovary.

Answer 6

Question 7

What are Ovarian Follicles?

Answer 7

• contains a single oocyte
• periodically initiated to grow and develop, cumulate in ovulation
• consisted of granulosa cells and theca cells

Question 8

What are the types of follicles involved in Folliculogenesis?

Answer 8

Primordial follicle
Primary follicle
Secondary follicle
Mature follicle
Corpus Iuteum

Question 9

What is a Primordial follicle?

Answer 9

• one cell thick; squamous
• cells from the ovary surround the arrested primary oocyte
• Rise in GnRH stimulates rise in FSH —> causing 5-20 primordial follicles to develop

Question 10

What is a Primary Follicle?

Answer 10

• one cell thick; cuboidal
• by birth, primary oocytes have a complete layer of follicular cells
• Zona pellucida starts to form but not visible

Question 11

What is a Secondary Follicule?

Answer 11

• many cell layers; cuboidal
• oocyte secretes activin —> stimulate granulosa cells to proliferate (while secreting estrogen)
• after birth, follicular cells secrete meiotic inhibitory factor (MIF) —> causing first meiotic arrest in diplotene of prophase I until puberty
• FSH acts on granulosa cells —> enhancing activin action
• Zona pellucida well developed
• antrum visible
• theca forming

Question 12

What is the Mature Follicle?

Answer 12

• many layers; cuboidal
• at puberty. Follicle enlarges
• secondary oocyte arrested in metaphase II until fertilization
• antrum very large
• cumulus oophorus evident
• corona radiata surrounds mature secondary oocyte
• theca layers are prominent

Luteinizing hormone (LH) surge results in:
- MPF production
- release from MI arrest
- Progesterone production

Question 13

What is the Corpus Iuteum?

Answer 13

• ruptured and empty follicle (granulosa cells) left behind after ovulation
• lutein rxn converts cells to progesterone-producing cells

Question 14

What are the aspects involved in the process of the developing follicle surrounding the developing egg?

Answer 14

Cumulus oophorus: surrounds oocyte in follicle and after ovulation —> to protect, development, during fertilization
Corona radiata: part of the cumulus oophorus —> inner most layer closest to ZP
Zona pellucida: surrounds secondary oocyte and polar body —> binds spermatozoa, species-specific barriers

Question 15

Name the second messengers and hormones involved in Meiotic Arrest and Resumption?

Answer 15

Arrest:
- rise of cAMP inactivates MPF (maturation promoting factor)
- cGMP inhibits PDE3A

Resumption:
- LH surge
- closes gap junctions
- in effect decreases cAMP
- activate MPF

Question 16

What is Theca?

Answer 16

• cellular coverings from ovarian stroma developing around follicle, becoming 2 or 3 layers thick

Theca Folliculi:
1. Theca interna —> highly vascularized and glandular
2. Theca externa —> connective tissue-like outer capsule

Question 17

What are the major Hormonal Interactions taking place in Theca and Granulosa Cells?

Answer 17

FSH:
- pituitary gonadotropin
- acts on granulosa cells —> stimulating estrogen production

Estrogen:
- stimulates formation of LH receptors on granulosa cells

Activin:
- stimulate granulosa proliferation

Inhibin:
- secreted by granulosa cells of dominant secondary follicle
- inhibits secretion of FSH and LH by negative feedback —> atresia (degeneration of ovarian follicles) of other follicles

Question 18

Describe the Menstrual Cycle.

Answer 18

Proliferative Phase: Day 5-14
- GnRH stimulates the release of FSH and LH
- Secondary follicles secrete estrogen (act on reproductive tract)
- LH and FSH surge

Ovulation:
- result of LH surge
- Transforms ruptured follicle to corpus Iuteum (secretes progesterone)

Secretory Phase: Day 14-28
- progesterone helps ready the reproductive tract for implantation
- Inhibin production
- Endometrium sheds

Question 19

Overview process of Folliculogenesis.

Answer 19

Question 20

What are the 3 stages of Oogenesis?

Answer 20

1. Oocytogenesis
2. Ootidogenesis
3. Oogenesis

Question 21

What is the process to Oocytogenesis?

Answer 21

• oogonia —> Primary oocytes by mitosis
• process complete either before or shortly after birth
• primary oocytes reach max development at ~20 weeks of gestational age
• regularly 1-2 million primary oocytes at birth

Question 22

What is the process of Ootidogenesis?

Answer 22

• Primary oocyte —> secondary oocyte
• begins at prenatal age, stops in diplotene stage of prophase I of first meiotic division (dictyate)
• at puberty, some primary oocytes develop in each menstrual cycle, chromosomal cross-over occurs, meiosis I is completed, first polar body extruded

Question 23

What is the process of Oogenesis?

Answer 23

Haploid secondary oocyte initiates meiosis II and stops at metaphase II stage until fertilization —> occurs in ovarian duct, after ovulation

Question 24

Overview of Hormonal Control of Oogenesis/Folliculogenesis.

Answer 24

Question 25

What is the process of Oocyte cytoplasmic maturation?

Answer 25

Reorganization of organelle
- accumulation of mRNA, protein, substrates, and nutrients required to achieve the oocyte developmental competence that fosters embryonic developmental competence

Question 26

What are the changes that occur in Golgi fragmentation?

Answer 26

GV OOCYTES: Golgi apparatus dispersed throughout the ooplasm but it is slightly more concentrated in the interior than at the cortex

GVBD OOCYTES: Golgi apparatus undergoes fragmentation, as shown by an accumulation of dotted structures (light blue) in the central part of the oocyte

MI: Golgi apparatus is further fragmented and dispersed throughout the oocyte

MII: this distribution is maintained following extrusion of the first polar body