Granule (cell biology)
In cell biology
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

, a granule is a small particle. It can be any structure barely visible by light microscopy. The term is most often used to describe a secretory
Secretory pathway
The secretory pathway is a series of steps a cell uses to move proteins out of the cell; a process known as secretion. The path of a protein destined for secretion has its origins in the rough endoplasmic reticulum, a membrane-bound compartment in the cell...

Vesicle (biology)
A vesicle is a bubble of liquid within another liquid, a supramolecular assembly made up of many different molecules. More technically, a vesicle is a small membrane-enclosed sack that can store or transport substances. Vesicles can form naturally because of the properties of lipid membranes , or...



A group of leukocytes called granulocytes contain granules and play an important role in the immune system. The granules of certain cells, such as natural killer cell
Natural killer cell
Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...

s, contain components which can lead to the lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....

 of neighboring cells. The granules of leukocytes are classified as azurophilic granules or specific granules
Specific granules
Specific granules are secretory vesicles found exclusively in cells of the immune system called granulocytes. They are also known as secondary granules....

Leukocyte granules are released in response to immunological stimuli during a process known as degranulation
Degranulation is a cellular process that releases antimicrobial cytotoxic molecules from secretory vesicles called granules found inside some cells...



The granules of platelets are classified as dense granule
Dense granule
Dense granules are specialized secretory organelles.-In unicellular organisms:They are found in animals and in unicellular organisms including Apicomplexa protozoans....

s and alpha granule
Platelet alpha-granule
In platelets, the term "alpha granules" is used to describe granules containing several growth factors.-Contents:Contents include insulin-like growth factor 1, platelet-derived growth factor, TGFβ, platelet factor 4 and other clotting proteins In platelets, the term "alpha granules" is used to...


Germline Granules

In 1957, André and Rouiller first coined the term "nuage
Nuage is a specific term for Drosophila melanogaster germline granules. Nuage are the hallmark of Drosophila melanogaster germline cells, which have an electron-dense perinuclear structure and can silence the selfish genetic elements in Drosophila melanogaster...

". (French for "cloud"). Its amorphous and fibrous structure occurred in drawings as early as in 1933 (Risley 1933). Today, the nuage is accepted to represent a characteristic, electrondense
Electron density
Electron density is the measure of the probability of an electron being present at a specific location.In molecules, regions of electron density are usually found around the atom, and its bonds...

 germ plasm
Germ plasm
Germ plasm or polar plasm is a zone found in the cytoplasm of the egg cells of some model organisms , which contains determinants that will give rise to the germ cell lineage. As the zygote undergoes mitotic divisions the germ plasm is ultimately restricted to a few cells of the embryo...

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid bilayer....

 encapsulating the cytoplasmic face of the nuclear envelope
Nuclear envelope
A nuclear envelope is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus from the cytosol...

 of the cells destined to the germline
In biology and genetics, the germline of a mature or developing individual is the line of germ cells that have genetic material that may be passed to a child.For example, gametes such as the sperm or the egg, are part of the germline...

 fate. The same granular material is also known under various synonyms: dense bodies, mitochondrial clouds, yolk nuclei, Balbiani bodies, perinuclear P granules in Caenorhabditis elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...

, germinal granules in Xenopus laevis and chromatoidal bodies
Chromatoidal bodies
Chromatoidal bodies are aggregations of ribosomes found in cysts of some amoebae including Entamoeba histolytica and Entamoeba coli....

 in mouse and polar granules in Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

. Molecularly, the nuage is a tightly interwoven network of differentially localized RNA-binding protein
RNA-binding protein
RNA-binding proteins are proteins that bind to RNA. They bind to either double-strand or single-strand RNAs through RNA recognition motif . RNA-binding proteins may regulate the translation of RNA, and post-transcriptional events, such as RNA splicing, editing.They are cytoplasmic and nuclear...

s, which in turn localize specific mRNA species for differential storage, asymmetric segregation (as needed for asymmetric cell division
Asymmetric cell division
An asymmetric cell division produces two daughter cells with different cellular fates. This is in contrast to normal, symmetric, cell divisions, which give rise to daughter cells of equivalent fates...

), differential splicing and/or translational control. The germline
In biology and genetics, the germline of a mature or developing individual is the line of germ cells that have genetic material that may be passed to a child.For example, gametes such as the sperm or the egg, are part of the germline...

 granules appear to be ancestral and universally conserved in the germlines of all metazoan phyla
Phyla, the plural of phylum, may refer to:* Phylum, a biological taxon between Kingdom and Class* Phylum , in linguistics, a large division of possibly related languagesPhyla, as a singular, may refer to:...

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