Zona binding refers to the process where proteins on sperm plasma specifically bind to zona pellucida proteins on the oocyte. The zona pellucida consists of three glycoproteins - ZP1, ZP2, and ZP3. ZP3 acts as a receptor that binds to proteins on the sperm membrane. Sperm have two zona binding regions - the primary region responsible for adherence and the acrosome promoting ligand that initiates the acrosomal reaction upon binding to ZP3. Polyspermy block prevents the fertilization of an oocyte by multiple sperm and occurs through zona block and vitelline block. Zona block is achieved through cortical granule exocytosis

1. Zona binding
&
Polyspermy block
Prepared By
Subash Sapkota
VGO-M-05-2021
M.V.Sc (Theriogenology)
Agriculture and Forestry University (AFU), Rampur

2. • Process by which specific proteins on the surface of sperm
plasma bind specifically binds to the zona pellucida proteins is
called Zona Bindings.
• As, capacitation is completed spermatozoa undergoes
hyperactive motility which facilitate sperm-oocyte contact.
• Zona Pellucida of oocyte consist of three glycoproteins which
are named as Zona Protein 1(ZP1), Zona Protein 2(ZP2), Zona
protein 3(ZP3).
Zona Binding

3. • ZP1 & ZP2 are the structural proteins which provides structural
integrity of the Zona.
• ZP3 acts like the receptor of the hormones which binds to the
protein on spermatozoal membrane.
• Similarly, sperm plasma membrane contains two zona binding
sites i.e primary zona binding region & acrosome reaction
promoting ligand.
• Primary zona binding region is responsible for adherence of
spermatozoa to the zona pellucida.
• Acrosomal reaction promoting ligand initiates the acrosomal
reaction by signal transduction process as binding occurs between
this region and ZP3 molecule.

4. • Polyspermy is the fertilization of an oocyte by more than one
spermatozoan which results in embryo death.
• Extra sperm get succeed in entering the vitellus, inspite of
zona reaction and vitelline block are called supranumerary
sperm.
• Major disadvantage of polyspermy is it leads to the triploidy
which is the lethal condition.
• Polyspermy block helps to prevent such condition. Simply it
takes place by two process i.e. Zona Block & Vitelline Block.
Polyspermy Block

5. Prevents polyspermy.
Exocytosis of the cortical granules results in the zona block.
Cortical granules undergo exocytosis and their contents are
released into the perivitelline space after membrane fusion.
consist of mucopolysaccharides, proteases, plasminogen
activator, acid phosphatase and peroxidase.
small, dense granules called cortical granules move to the
periphery of the oocyte cytoplasm.
After membrane fusion, the oocyte undergoes a series of
changes that prepare it for early embryogenesis.
Polyspermy prevention by zona block………………..

6. Prevents Polyspermy
Results in Vitelline Block
Cortical reaction reduce the ability of the oocyte plasma
membrane to fuse with additional spermatozoa.
Similarly,
Polyspermy prevention by vitelline block………………..

7. THANK YOU!