] Omegasome is a Cell (biology), cell organelle consisting of

lipid bilayer The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many vir ...

membranes A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. Bi ...

enriched for

phosphatidylinositol 3-phosphate Phosphatidylinositol 3-phosphate (PtdIns3''P'') is a phospholipid found in cell membranes that helps to recruit a range of proteins, many of which are involved in protein trafficking, to the membranes. It is the product of both the class II and ...

(abbreviated PI(3)P or PtdIns3P), and related to a process of

autophagy Autophagy (or autophagocytosis; from the Ancient Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent re ...

. It is a subdomain of the

Endoplasmic Reticulum The endoplasmic reticulum (ER) is, in essence, the transportation system of the eukaryotic cell, and has many other important functions such as protein folding. It is a type of organelle made up of two subunits – rough endoplasmic reticulum ( ...

(ER), and has a

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

resembling the Greek capital letter

Omega Omega (; capital: Ω, lowercase: ω; Ancient Greek ὦ, later ὦ μέγα, Modern Greek ωμέγα) is the twenty-fourth and final letter in the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The wo ...

(Ω). Omegasomes are the sites from which phagophores (also called "isolation membranes") form, which are sack-like structures that mature into

autophagosomes An autophagosome is a spherical structure with double layer membranes. It is the key structure in macroautophagy, the intracellular degradation system for cytoplasmic contents (e.g., abnormal intracellular proteins, excess or damaged organelles, in ...

, and fuse with

lysosomes A lysosome () is a membrane-bound organelle found in many animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules. A lysosome has a specific composition, of both its membrane prote ...

in order to degrade the contents of the autophagosomes. The formation of omegasomes depends on various factors, however in general, formation of omegasomes is increased as a response to starvation, and in some biochemical situations the presence of PI(3)P leads to the formation of omegasomes.

Macroautophagy

Autophagy (from Greek words for “self” and “eating”) is a process of digesting or degrading cytoplasmic molecules (

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

lipids Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

sugars Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double s ...

and

organelles In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the ...

Macroautophagy Autophagy (or autophagocytosis; from the Ancient Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent re ...

is the main autophagic pathway, used primarily to eradicate damaged cell organelles such as

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

, ribosomes, etc., which helps in supplying amino acids and energy to the cells, and maintains longevity. Omegasomes positioned on the endoplasmic reticulum, are enriched with PI(3)P and PI(3)P-binding proteins, and responsible for the formation of phagophores. 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. Additionally, collections of thin tubules at the junction between omegasome and phagophore appear to be involved. Actin is also believed to be important. It has been observed that various pathogen infections that lead to the induction of autophagy display the formation of autophagosomes through omegasomes developed as an innate response to the infection.

Function

Omegasomes display significant functional roles in different biochemical pathways which assist in various autophagosome processes. Omegasomes attract the effectors needed to target PI3P, while also ensuring that the autophagosomal membranes fuse with the double membrane vesicles and promote autophagosome formation. Omegasomes act as progenitors of autophagosome formation during the autophagy pathway. There are various autophagosome mediators involved in autophagy, however it is the omegasome regulation of the pathway that provides a smooth transition of autophagosome formation, and enrichment of nutrients in the cells.

References

Membrane biology {{Cell-biology-stub