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Circulating microvesicle


Circulating microvesicles (cMVs) are small membrane bound fragments of between 50 and 1,000 nanometers (nm) in diameter, found in many types of body fluids as well as the interstitial space between cells. Though initially dismissed as cellular debris, cMVs have a role in cell signaling and the process of molecular communication between cells, and are released by a number of cell types. Although a consistent and precise definition is lacking, cMVs are generally considered to be a heterogeneous population of exosomes (<100 nm) and shed microvesicles (100-1000 nm), which are similar but have distinct mechanisms of formation. Through these mechanisms, cMVs are released into the extracellular space and interact with specific target cells, delivering bioactive molecules. Changes in cMV levels are implicated in a variety of diseases, including cancer. These changes can be used as biomarkers in a variety of diagnostic assays.

Microvesicles and exosomes are formed and released by two slightly different mechanisms. These processes result in the release of intercellular signaling vesicles. Microvesicles are small, plasma membrane-derived particles that are released into the extracellular environment by the outward budding and fission of the plasma membrane. This budding process involves multiple signaling pathways including the elevation of intracellular calcium and reorganization of the cell's structural scaffolding. The formation and release of microvesicles involve contractile machinery that draws opposing membranes together before pinching off the membrane connection and launching the vesicle into the extracellular space.

Microvesicle budding takes place at unique locations on the cell membrane that are enriched with specific lipids and proteins reflecting their cellular origin. At these locations, proteins, lipids, and nucleic acids are selectively incorporated into microvesicles and released into the surrounding environment.

Exosomes are membrane-covered vesicles, formed intracellularly are considered to be smaller than 100 nm. In contrast to microvesicles, which are formed through a process of membrane budding, or exocytosis, exosomes are initially formed by endocytosis. Exosomes are formed by invagination within a cell to create an intracellular vesicle called an endosome, or an endocytic vesicle. In general, exosomes are formed by segregating the cargo (e.g., lipids, proteins, and nucleic acids) within the endosome. Once formed, the endosome combines with a structure known as a multivesicular body (MVB). The MVB containing segregated endosomes ultimately fuses with the plasma membrane, resulting in exocytosis of the exosomes.


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