cell biology, 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 1 secretory vesicle.
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 cells, contain components which can lead to the lysis of neighboring cells. The granules of leukocytes are classified as azurophilic granules or specific granules. Leukocyte granules are released in response to immunological stimuli during a process known as degranulation.
The granules of
platelets are classified as dense granules and alpha granules.
In 1957, André and Rouiller first coined the term "
nuage". (French for "cloud"). Its 2 amorphous and fibrous structure occurred in drawings as early as in 1933 (Risley). Today, the nuage is accepted to represent a characteristic, electrondense germ plasm organelle encapsulating the cytoplasmic face of the nuclear envelope of the cells destined to the germline fate. The same granular material is also known under various synonyms: dense bodies, . Molecularly, the mitochondrial clouds, yolk nuclei, Balbiani bodies, perinuclear P granules in Caenorhabditis elegans, germinal granules in Xenopus laevis and chromatoid bodies in mouse and polar granules in Drosophila nuage is a tightly interwoven network of differentially localized RNA-binding proteins, which in turn localize specific mRNA species for differential storage, asymmetric segregation (as needed for asymmetric cell division), differential splicing and/or translational control. The germline granules appear to be ancestral and universally conserved in the germlines of all metazoan phyla.
^ " granule" at Dorland's Medical Dictionary
^ André J, Rouiller CH (1957) L'ultrastructure de la membrane nucléaire des ovocytes del l'araignée (Tegenaria domestica Clark). Proc European Conf Electron Microscopy, Stockholm 1956. Academic Press, New York, pp 162 164