Fertilisation & Early Embryo Development Flashcards
How do sperm reach the oocyte?
Sperm navigate through the vagina, cervix, and uterus via rheotaxis, chemotaxis, and thermotaxis.
What is the role of PLCζ during fertilisation?
PLCζ from the sperm triggers intracellular calcium oscillations in the oocyte, initiating fertilization and embryogenesis and completes the egg’s final meiotic division
What is the maternal-to-zygote transition?
The embryo shifts from relying on maternal mRNA to activating its genome at the 2-cell stage.
What is the zona pellucida, and what is it’s role in fertilisation?
It is a glycoprotein matrix surrounding the oocyte that sperm must penetrate to fertilize the egg.
What are the key steps in sperm-oocyte fusion?
The sperm binds to the oocyte’s plasma membrane via IZUMO1-JUNO interaction, triggering egg activation through PLCζ.
What is the role of hyaluronic acid in the cumulus-oocyte complex transport?
It buffers the pH, interacts with oviduct cilia, and facilitates oocyte movement.
What are blastomeres and how do they form?
Blastomeres are cells formed during the cleavage of a zygote, dividing without increasing overall embryo size.
What is totipotency? and how does it differ from pluripotency?
Totipotent cells can form all somatic, germ cells and extra-embryonic tissues, while pluripotent cells cannot form extra embryonic cells
What is the significance of the acrosome reaction during fertilisation?
The acrosome reaction releases enzymes that digest the zona pellucida, allowing sperm to reach the oocyte.
What prevents polyspermy during fertilisation?
After the first sperm binds, cortical granules release enzymes that harden the zona pellucida, preventing additional sperm from entering.
What is the role of the inner cell mass (ICM) in the blastocyst?
The ICM develops into the embryo, while the surrounding trophectoderm forms the placenta.
How does embryonic compaction contribute to development?
Blastomeres form tight junctions, increasing cellular communication and preparing for differentiation into the ICM and trophectoderm.
How does the classical model of fertilisation describe zona penetration?
Sperm surface hyaluronidase breaks down the zona pellucida, allowing penetration and acrosome reaction.
How does the modern model explain sperm-egg interaction?
Progesterone activates CatSper channels, maintaining hypermotility, and IZUMO1 on sperm binds to JUNO on the oocyte for fusion.
What is the role of oviductal cilia in fertilisation?
Transiently bind to sperm and hold them in the isthmus.
They are then released in batches to ensure enough sperm reach the oocyte but not too many to prevent polyspermy
