Anuradha Housnur: What is Oocyte Activation?
Anuradha Housnur, Head-Training in Clinical Embryology and Chief Embryologist at Seeds of Innocens IVF and Fertility Centres, shared a post on LinkedIn:
”What is Oocyte Activation?
Oocyte activation is the series of cellular events that begins after a sperm successfully enters the oocyte and triggers the oocyte to resume and complete meiosis, ultimately preparing it for embryo development.
In simple words:
Sperm entry – oocyte activation – completion of meiosis – pronuclei formation – embryo development
What happens during oocyte activation?
The key event is a rise in intracellular calcium (Ca²⁺) inside the oocyte.
- Sperm enters the oocyte
- The sperm factor PLCζ (phospholipase C zeta) triggers calcium oscillations.
- Repeated Ca²⁺ oscillations activate the oocyte.
The oocyte completes meiosis II and extrudes the second polar body.
Cortical granules release their contents, modifying the zona pellucida and helping prevent polyspermy.
The male and female pronuclei form.
The zygote proceeds toward syngamy and cleavage.
Why is it important in IVF/ICSI?
In ICSI, sperm is mechanically introduced into the oocyte, but sperm entry alone doesn’t guarantee normal activation.
If appropriate calcium signaling does not occur, the oocyte may fail to activate, resulting in fertilization failure.
This is why artificial oocyte activation (AOA) can sometimes be considered in selected cases of recurrent or complete fertilization failure after ICSI. AOA attempts to mimic the calcium-signaling events that normally occur following sperm-oocyte interaction.”
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