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Tuesday 1 November 2005

Thrombospondins were originally discovered as a secretory product of platelet alpha-granules in 1971. Since that time it has been detected as a product of a great variety of cells.

It is a multifunctional protein that contains binding sites for thrombin, fibrinogen, heparin, fibronectin, plasminogen, plasminogen activator, collagen, laminin, etc. It functions in many cell adhesion and migration events, including platelet aggregation. It also influences granule cell migration during histogenesis of the cerebellar cortex.In the developing mouse embryo, it is present as early as the 1- to 4-cell stage.

The thrombospondins are a family of 5 distinct gene products: thrombospondins I (THBS1), II (THBS2), III (THBS3), and IV (THBS4) and cartilage oligomeric matrix protein (COMP).

Thrombospondin I and thrombospondin II are almost identical in exon/intron organization. In the mouse, each gene encodes a protein chain of about 1,170 amino acids with sequences very similar in the carboxy-terminal two-thirds but differing considerably in the NH2-terminal regions. THBS3 is a developmentally regulated heparin binding protein.

The predicted translation product was a protein clearly homologous to THBS1 and THBS2 in its COOH-terminal domains but substantially different in its NH2-terminal region. This structure suggested functional properties for THBS3 that are unique, but also related to those of THBS1 and THBS2. The gene was located on mouse chromosome 3, immediately upstream of the gene for episialin (MIM.158340).