Hyaluronates in developing skeletal tissues

Hyaluronic acid (HA) is present in the extracellular matrix (ECM) as early as the time of gastrulation. At these early stages, HA is thought to organize the ECM into a hydrated, open lattice and thereby support cell movements. At later stages, when specialized tissues appear, hyaluronidase activity increases. A correlation between elevated hyaluronidase activity and deposition of cartilage-type ECM is now well established. Differentiation of cartilage may be accompanied by changes in molecular forms of HA; however, the synthesis of HA is not understood well enough to permit firm generalizations to be drawn. There is also a lack of evidence regarding specificity of the hyaluronidase that appears at the onset of chondrogenesis. Thus, while HA is a ubiquitous ECM component and its appearance has been well studied during embryogenesis, there remain large gaps in the present knowledge regarding the means by which HA interacts with embryonic cells, tissues, and other ECM components.