L7: Ovary 2: Oocyte and Ovulation Flashcards
What happens to oocyte during follicle development?
- it maintains meiotic arrest
- but at same time, it develops the competence to resume meiosis later
- it grows, and acquires more components as it grows
- it undergoes genomic imprinting
- around the time of ovulation, it resumes meiosis
- crucially, it acquires developmental competence (ability to support the development of a viable embryo and then healthy individual if fertilised)
What is germinal vesicle?
Simply the term for the nucleus of an oocyte
What is nuclear maturation of an oocyte?
only processes within germinal vesicle (GV)
What is cytoplasmic maturation of an oocyte?
Excludes processes within GV
What is zona pellucida?
Specialised ECM formed from secretion from the oocyte and surrounding granulosa cells (both cell types are needed!)
When is zona pellucida formed?
As follicles start to grow
What is zona pellucida made of?
Repeating dimers of ZP2 and ZP3 linked together by occasional cross-linking of ZP1
How is ZP3 important?
At fertilisation ZP3 is key - stops polyspermy
Why does oocyte accumulate mRNAs and organelles as it grows?
- the oocyte is in meiotic arrest, with an extra set of all chromosomes, and so has four copies of each chromosome.
- While meiosis is arrested, the chromosomes themselves are active, including mRNA production and transcription of proteins.
- Some proteins are used as the oocyte grows, other mRNAs and proteins are used only after fertilisation, providing a maternal source of RNAs that can support the embryo until its own genome is activated.
What are the cytoplasmic organelles of an oocyte?
- mitochondria
- lipids
- cortical granules
- vesicles
How is mitochondria important for an oocyte?
- site of energy production
- circular DNA, high mutation rate (particularly susceptible to reactive oxygen species - likely why mitochondria from sperm do not contribute to embryo)
- as mammals become older, mitochondria in oocytes become increasingly vacuolated - poor quality - and reduced in number
What is mitochondrial bottleneck?
Each oocyte inherits only a small proportion of a female’s mitochondria: has important implication in mitochondrial diseases, depending on the mitochondrial DNA that the oocyte receives –> depends the severity of the disease
That’s why three parent embryos created, also with mitochondrial DNA, so diseases not inherited
- As PGCs are dividing at each division you will only get a few mitochondria going into oocytes – bottleneck
How are cortical granules important for an oocyte?
secretory organelles produced by Golgi, needed to block polyspermy along with ZP3
How is the interaction between oocyte and granulosa cells important?
Now very clear that both cell types (granulosa and oocyte) are dependent on each other for their development.
Oocyte regulates:
- differentiation,
- follicle organization,
- steroidogenesis,
- proliferation,
- expansion.
Granulosa cells regulate:
- meiotic arrest,
- oocyte growth,
- metabolic substrates,
- meiotic maturation.
Without granulosa cells the oocyte doesn’t stay in meiotic arrest.
How do granulosa cells and oocyte communicate?
Via gap junctions - collections of intracellular channels