Vitelline membrane
Encyclopedia
The vitelline membrane is a structure directly adjacent to the outer surface of the plasma membrane of an ovum
. It is composed mostly of protein fibers, with protein receptors needed for sperm binding which, in turn, are bound to sperm plasma membrane receptors. The species-specificity between these receptors contributes to prevention of breeding between different species.
It is called zona pellucida
in mammal
s.
As soon as the spermatozoon
fuses with the ovum
, signal transduction
occurs, resulting in an increase of cytoplasmic calcium ions. This itself triggers the cortical reaction
, which results in depositing several substances onto the vitelline membrane through exocytosis of the cortical granules, transforming it into a hard layer called the “fertilization membrane”, which serves as a barrier inaccessible to other spermatozoa. This phenomenon is the slow block to polyspermy.
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
. It is composed mostly of protein fibers, with protein receptors needed for sperm binding which, in turn, are bound to sperm plasma membrane receptors. The species-specificity between these receptors contributes to prevention of breeding between different species.
It is called zona pellucida
Zona pellucida
The zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...
in mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s.
As soon as the spermatozoon
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
fuses with the ovum
Ovum
An ovum is a haploid female reproductive cell or gamete. Both animals and embryophytes have ova. The term ovule is used for the young ovum of an animal, as well as the plant structure that carries the female gametophyte and egg cell and develops into a seed after fertilization...
, signal transduction
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...
occurs, resulting in an increase of cytoplasmic calcium ions. This itself triggers the cortical reaction
Cortical reaction
The cortical reaction occurs when a sperm cell unites with the egg's plasma membrane, modification of the zona pellucida that blocks polyspermy; enzymes released by cortical granules digest sperm receptor proteins ZP2 and ZP3 so that they can no longer bind sperm, in mammals.The cortical reaction...
, which results in depositing several substances onto the vitelline membrane through exocytosis of the cortical granules, transforming it into a hard layer called the “fertilization membrane”, which serves as a barrier inaccessible to other spermatozoa. This phenomenon is the slow block to polyspermy.
See also
- Zona pellucidaZona pellucidaThe zona pellucida is a glycoprotein membrane surrounding the plasma membrane of an oocyte. It is a vital constitutive part of the latter, external but of essential importance to it...
- Egg activation
- Cortical reactionCortical reactionThe cortical reaction occurs when a sperm cell unites with the egg's plasma membrane, modification of the zona pellucida that blocks polyspermy; enzymes released by cortical granules digest sperm receptor proteins ZP2 and ZP3 so that they can no longer bind sperm, in mammals.The cortical reaction...
- Perivitelline spacePerivitelline spaceThe perivitelline space is the space between the zona pellucida and the cell membrane of an oocyte or fertilized ovum. In the slow block to polyspermy, the cortical granules released from the ovum are deposited in the perivitelline space. Polysaccharides released in the granules cause the space...