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Location
Folliculostellate (FS) cells are located within the anterior lobe of the pituitary gland. They are located along with 5 types of endocrine cells involved in functions such as growth, metabolism and regulation.

Histology
The characteristic features of FS cells are their star shape, hence the –stellate part of the name, and their ability to form follicles. Unlike the majority of cells in the anterior pituitary, they are non-endocrine and agranular. They typically have a large number of microvilli on their apical side, and lysosomes exist within them, perhaps suggesting phagocytotic activity. Markers for FS cells include the S-100 protein, the Glial Fibriliary acidic protein (GFAP) and a more recent discovery, green florescent protein (GFP) which was found in the anterior pituitary of transgenic rats. The S-100 protein can also be found in the cells of Rathke’s pouch, suggesting a similarity between these cells.

Ultrastructure
Usually found lining the lumen of small follicles situated within the pituitary gland. They have long, cytoplasmic processes which interlock to form a mesh, within which the endocrine cells reside. Upon electron microscopy, gap junctions can be seen between the FS cells and the adjacent endocrine cells. They are excitable cells, something which is unusual given the fact that they are agranular.