Omegasome


Omegasome is a cell compartment consisting of lipid bilayer membranes enriched for phosphatidylinositol 3-phosphate and related to a process of autophagy. It is a subdomain of the endoplasmic reticulum membrane and has a morphology resembling Greek capital letter omega. Omegasomes are the sites from which phagophores form. Phagophores are sack-like structures that mature into autophagosomes that fuse with lysosomes in order to degrade the contents of the autophagosomes. The formation of omegasomes is increased as a response to starvation.

Macroautophagy

Autophagy is a process of digesting or degrading cytoplasmic molecules. Macroautophagy is the main autophagic pathway, used primarily to eradicate damaged cell organelles such as mitochondria, ribosomes, etc. The omegasome is present at the opening of the sack-like phagophore while items destined for degradation by macroautophagy are loaded into the phagophore. There are specific receptor proteins that recruit items to the phagophore. The phagophore expands to accommodate the items, until the omegasome is closed to produce the roughly spherical autophagosome. How autophagosomes are "detached" or "exit" from the omegasome is not clear, but autophagocytosis associated protein Atg3 and other proteins are required, and collections of thin tubules at the junction between omegasome and phagophore appear to be involved. Actin is also believed to be important.