Lecture 3: Oogenesis Flashcards
Lecture 3
In oogenesis, what do PCGs differentiate into?
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)
What happens in meiosis I and prolonged Diplotene (prophase I)?
Metaphase I:
- some yolk accumulation
- cortical granule production
- accumulation of mRNA, rRNA
- crossing-over
Telephone I:
- all primary locates arrest in Diplotene until puberty
What are the structures involved in the Female Productive System?
Fallopian tube
Ovary
Uterus
Cervix
- Internal os
- external os
Vagina
Labium minus
What are the types of Uterus’ in species?
Simplex —> primate
Duplex —> rat, mouse, rabbit, gerbil
Bicornuate —> pig
Bipartite —> Mare, cat, dog, ewe
Describe the pathway of both Oogenesis and Follicle development.
Name the structure of the Ovary.
What are Ovarian Follicles?
- contains a single oocyte
- periodically initiated to grow and develop, cumulate in ovulation
- consisted of granulosa cells and theca cells
What are the types of follicles involved in Folliculogenesis?
Primordial follicle
Primary follicle
Secondary follicle
Mature follicle
Corpus Iuteum
What is a Primordial follicle?
- 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
What is a Primary Follicle?
- one cell thick; cuboidal
- by birth, primary oocytes have a complete layer of follicular cells
- Zona pellucida starts to form but not visible
What is a Secondary Follicule?
- 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
What is the Mature Follicle?
- 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
What is the Corpus Iuteum?
- ruptured and empty follicle (granulosa cells) left behind after ovulation
- lutein rxn converts cells to progesterone-producing cells
What are the aspects involved in the process of the developing follicle surrounding the developing egg?
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
Name the second messengers and hormones involved in Meiotic Arrest and Resumption?
Arrest:
- rise of cAMP inactivates MPF (maturation promoting factor)
- cGMP inhibits PDE3A
Resumption:
- LH surge
- closes gap junctions
- in effect decreases cAMP
- activate MPF
What is Theca?
- 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
What are the major Hormonal Interactions taking place in Theca and Granulosa Cells?
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
Describe the Menstrual Cycle.
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
Overview process of Folliculogenesis.
What are the 3 stages of Oogenesis?
- Oocytogenesis
- Ootidogenesis
- Oogenesis
What is the process to Oocytogenesis?
- 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
What is the process of Ootidogenesis?
- 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
What is the process of Oogenesis?
Haploid secondary oocyte initiates meiosis II and stops at metaphase II stage until fertilization —> occurs in ovarian duct, after ovulation
Overview of Hormonal Control of Oogenesis/Folliculogenesis.
What is the process of Oocyte cytoplasmic maturation?
Reorganization of organelle
- accumulation of mRNA, protein, substrates, and nutrients required to achieve the oocyte developmental competence that fosters embryonic developmental competence
What are the changes that occur in Golgi fragmentation?
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
