Hyaluronan and mesenchymal stem cells: from germ layer to cartilage and bone.

A simple, linear polysaccharide with unique molecular functions, hyaluronan is a glycosaminoglycan whose biomechanical and hydrodynamic properties have been thoroughly characterized. However, the exact role the molecular mechanisms and signaling pathways of hyaluronan play in the regulation of stem cell fate, such as self-renewal and differentiation, remains to be determined. The abundance of hyaluronan in embryonic tissues indicates that it is highly important in developmental processes. Recent studies have focused on understanding the mechanisms of hydrated hyaluronan action and its interaction with neighboring substances. This review is an attempt to elucidate the complex role of hyaluronan signaling in the initialization and regulation of developmental processes, particularly in events dictating the fates of mesenchymal stem cells during the organogenetic phases of chondrogenesis and osteogenesis.