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Extracellular vesicles (EVs) are lipid bilayer-delimited particles [1] that are naturally released from almost all types of cells but, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unilamellar liposome (around 20-30 nanometers) to as large as 10 microns or more, although the vast majority of EVs are smaller than 200 nm.
There are three mechanisms which lead to release of vesicles into the extracellular space. First of these mechanisms is exocytosis from multivesicular bodies and the formation of exosomes. Another mechanism is budding of microvesicles directly from a plasma membrane. And the last one is cell death leading to apoptotic blebbing. These are all ...
Exosomes, ranging in size from 30 to 150 nanometers, [1] are membrane-bound extracellular vesicles (EVs) that are produced in the endosomal compartment of most eukaryotic cells. [ 2 ] [ 3 ] [ 4 ] In multicellular organisms , exosomes and other EVs are found in biological fluids including saliva , blood , urine and cerebrospinal fluid . [ 5 ]
The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.
Transient vesicle fusion is driven by SNARE proteins, resulting in release of vesicle contents into the extracellular space (or in case of neurons in the synaptic cleft). The merging of the donor and the acceptor membranes accomplishes three tasks: The surface of the plasma membrane increases (by the surface of the fused vesicle).
Vesicle contains proteins destined for extracellular release. After packaging, the vesicles bud off and immediately move towards the plasma membrane, where they fuse and release the contents into the extracellular space in a process known as constitutive secretion. Antibody release by activated plasma B cells Secretory vesicles (regulated)
The International Society for Extracellular Vesicles (ISEV) is an international scientific organization that focuses on advancing global extracellular vesicle (EV) research. [1] These membrane-bound particles are released from all known cells and include exosomes , ectosomes , exophers, oncosomes, and more.
Another proposed mechanism for release of vesicle contents into extracellular fluid is called kiss-and-run fusion. There is some indication that vesicles may only form a small pore in the presynaptic membrane allowing contents to be released by standard diffusion for a short while before retreating back into the presynaptic cell.