In vivo investigation of hyaluronan and hyaluronan synthase-2 function during cartilage and joint development

Hyaluronan (HA) is a major component of the extracellular and pericellular matrix. It is a simple, linear glycosaminoglycan composed of thousands of disaccharide repeats of glucuronic acid and N-acetylglucosamine [1].Initially isolated from the vitreous humor, this macromolecule can be found in numerous tissues and body fluids of vertebrates, as well as in some bacteria [1].In vertebrates, HA is synthesized by any one of three hyaluronan synthases (Has) designated Has1, Has2 and Has3, respectively [2,3]. During embryogenesis, large amounts of HA are synthesized by many cell types, particularly those that are proliferating and migrating. Through specific inactivation of the mouse Has2 gene [4], we have recently shown that HA is critical for embryogenesis and is required for the maintenance and possibly the creation of extracellular matrix-defined spaces throughout the embryo, in addition to the migration of endocardial cushion cells.