Bleb (cell biology)
In cell biology, a bleb is an irregular bulge in the plasma membrane of a cell, caused by localized decoupling of the cytoskeleton from the plasma membrane. Blebbing or zeiosis is the formation of blebs.
During apoptosis (programmed cell death), the cell's cytoskeleton breaks up and causes the membrane to bulge outward. These bulges may separate from the cell, taking a portion of cytoplasm with them, to become known as apoptotic bodies. Phagocytic cells eventually consume these fragments and the components are recycled.
Blebbing also has important functions in other cellular processes, including cell locomotion, cell division, and physical or chemical stresses. The types of blebs vary greatly, including variations in bleb growth rates, size, contents, and actin content.
Prokaryotic gram-negative microbes also reveal membrane blebbing as a physiogical process and it has been a news to cell biologists. Physiological significance of membrane blebbing in gram negative microbes was first realized, when virulent Salmonella microbes were seen to produce numerous periplasmic protrusions (later referred to as invasosomes, virulence organelles and finally as periplasmic organelles) while closely encountering animal host ileal epithelial cell microvilli in vivo, under transmission electron microscope. A structural model of microbial bleb or periplasmic organelle has been proposed as expanded area containing a periplasmic bulge above bacterial inner membrane and peptidoglycan layer, externally bounded by lipopolysaccharide-rich bacterial outer membrane, and considered to be riveted at the base of the bulge with few Type3 secretory needle complex like rivet complexes. These periplasmic organelles were then shown to represent a preparative stage for release of bacterial outer membrane bounded nano-sized vesicles (outer membrane vesicles, OMVs), suggested to translocate bacterial signals to host/target cells, as a new mode of membrane vesicle trafficking at the host-pathogen interface, for many purposes, including invasion of host.
A chemical known as blebbistatin was shown, in 2004, to inhibit the formation of blebs. This agent was discovered in a screen for small molecule inhibitors of nonmuscle myosin IIA and was shown to lower the affinity of myosin with actin, thus altering the contractile forces that impinge on the cytoskeleton-membrane interface.
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