The vitelline membrane or vitelline envelope is a structure surrounding the outer surface of the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

of an

ovum The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete i ...

(the oolemma) or, in some animals (e.g., birds), the extracellular

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example ...

and the oolemma. 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 The zona pellucida (plural zonae pellucidae, also egg coat or pellucid zone) is a specialized extracellular matrix that surrounds the plasma membrane of mammalian oocytes. It is a vital constitutive part of the oocyte. The zona pellucida first ap ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

s. Between the vitelline membrane and zona pellucida is a fluid-filled perivitelline space. As soon as the

spermatozoon A spermatozoon (; also spelled spermatozoön; ; ) 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. (A zygote is a single cell, with a complete set of chromosom ...

fuses with the

signal transduction Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...

occurs, resulting in an increase of cytoplasmic calcium ions. This itself triggers the

cortical reaction The cortical reaction is a process initiated during fertilization that prevents polyspermy, the fusion of multiple sperm with one egg. In contrast to the fast block of polyspermy which immediately but temporarily blocks additional sperm from fer ...

, which results in depositing several substances onto the vitelline membrane through

exocytosis Exocytosis () is a form of active transport and bulk transport in which a cell transports molecules (e.g., neurotransmitters and proteins) out of the cell ('' exo-'' + ''cytosis''). As an active transport mechanism, exocytosis requires the use ...

of the

cortical granules Cortex or cortical may refer to: Biology * Cortex (anatomy), the outermost layer of an organ ** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain'' *** Motor cortex, the regions of the cerebral cortex i ...

, 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. In insects, the vitelline membrane is called the vitelline envelope and is the inner lining of the chorion.

Structure and function

The vitelline membrane of the hen is made of two main protein layers that provide support for the yolk and separation from the

albumen Egg white is the clear liquid (also called the albumen or the glair/glaire) contained within an egg. In chickens it is formed from the layers of secretions of the anterior section of the hen's oviduct during the passage of the egg. It forms a ...

. The inner layer is known as the perivitelline lamina. It is a single layer that measures roughly 1 μm to 3.5 μm thick and is mainly composed of five glycoproteins that have been discovered to resemble glycoproteins of the

in mammals involved in maintaining structure. The outer layer, known as the extravitelline lamina, has multiple sublayers which results in thickness that ranges from 0.3 μm to 9 μm. It is primarily composed of proteins, such as

lysozyme Lysozyme (EC 3.2.1.17, muramidase, ''N''-acetylmuramide glycanhydrolase; systematic name peptidoglycan ''N''-acetylmuramoylhydrolase) is an antimicrobial enzyme produced by animals that forms part of the innate immune system. It is a glycoside ...

, ovomucin and vitelline outer membrane proteins that are responsible for constructing the network of dense, thin protein fibres that establish the foundation for further growth of the outer layer during embryonic development. The vitelline membrane is known to function as a barrier that allows for diffusion of water and selective nutrients between the albumen and the yolk.

Formation

In the adult hen, liver cells express the proteins required for initial formation of the inner layer. These proteins travel via the blood from the liver to the site of assembly in the

ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. ...

. Before ovulation occurs, the inner layer forms from follicular cells that surround the

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...

. After ovulation, fertilization of the egg proceeds with the formation of the outer layer that is secreted by infundibulum glands located along the first parts of the oviduct.

Sperm recognition and fertilization

After the sperm digests its way through the jelly layer, the acrosomal process of the sperm makes contact with the vitelline envelope. The vitelline envelope has glycoproteins and peptides that allow for species-specific sperm binding and recognition. For example, in the sea urchin species,

red sea urchin The red sea urchin (''Mesocentrotus franciscanus'') is a sea urchin found in the northeastern Pacific Ocean from Alaska to Baja California. It lives in shallow waters from the low-tide line to greater than deep, and is typically found on rocky ...

and

purple sea urchin ''Strongylocentrotus purpuratus'', the purple sea urchin, lives along the eastern edge of the Pacific Ocean extending from Ensenada, Mexico, to British Columbia, Canada. This sea urchin species is deep purple in color, and lives in lower int ...

, the vitelline membrane has bindin receptors for the bindin protein present on the sperm head. In the

African clawed frog The African clawed frog (''Xenopus laevis'', also known as the xenopus, African clawed toad, African claw-toed frog or the ''platanna'') is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws o ...

, it was found that the gp69/gp64 glycoprotein pair is involved in sperm recognition and binding.

Infections and diseases

The vitelline membrane serves a different purpose in chickens. In the chicken egg, the yolk is separated from the albumen by the vitelline membrane which acts as a barrier to microbial infection. Apart from the 13 proteins identified to make up the membrane, the proteins that are key to providing antimicrobial properties to the membrane are the vitelline outer membrane proteins (VMO) 1 and 2. A recent study reports that VMO 1 can be a potential diagnostic marker for

ovarian cancer Ovarian cancer is a cancerous tumor of an ovary. It may originate from the ovary itself or more commonly from communicating nearby structures such as fallopian tubes or the inner lining of the abdomen. The ovary is made up of three different ...

in hens due to its ability to regulate estrogen and target

microRNA MicroRNA (miRNA) are small, single-stranded, non-coding RNA molecules containing 21 to 23 nucleotides. Found in plants, animals and some viruses, miRNAs are involved in RNA silencing and post-transcriptional regulation of gene expression. mi ...

s in the chickens' oviduct. Another difference is that the vitelline membrane has two major layers: the inner layer that faces the yolk, intermediary and external outer layer that contacts the albumen.

Other animals

sea urchin Sea urchins () are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard shells (tests) o ...

s, the formation of the vitelline membrane comes directly after fertilization and later thickens to form the fertilization membrane. This process is completed in about a minute. The innermost membrane of all animal eggs except some

cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that ...

ns is called the vitelline membrane. Some

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordat ...

and some lower

chordate A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...

eggs are covered by this membrane only, while most have other membranes.

Frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

and

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

eggs have a very thin vitelline membrane which are surrounded by either a jelly layer (frogs) or other membranes (birds). In

s, the structure is called the

and is surrounded by a layer of support cells, called the corona radiata.

Additional images

File:Anatomy of an egg.svg, Vitelline membrane in a bird egg (7) File:Amphibian Egg Diagram.svg, Vitelline membrane in an amphibian egg (2) File:Fish Egg Diagram (1).jpg, Vitelline membrane in a fish egg (A) File:Fertilization envelope.png, Formation of Fertilization envelope from the Vitelline envelope File:Parasite160001-fig2 - Vitellogenesis in Crepidostomum metoecus (Digenea) TEM.png, Parasitism and the Vitelline Membrane

References

{{Portal bar, Anatomy Embryology Germ cell structures