[Hyaluronan, embryogenesis and morphogenesis].

Hyaluronan is a major carbohydrate component of the extracellular matrix. Besides its structural role, it also appears to regulate cell transformation and migration during embryogenesis in vertebrates. Hyaluronan is synthesized by hyaluronan synthetases, transmembrane proteins expressed at several embryonic stages, as early as gastrulation. Inactivation or upregulation of hyaluronan synthetases elicits cardiac or skeletal development anomalies (atrioventricular septal defects caused by abnormal endocardial cushion formation, impaired chondrogenesis). Hyaluronidases degrade hyaluronan and interact with cell surface receptors involved in cell activation. Hyluronan binds not only extracellular matrix glycoproteins, but also cell surface receptors (CD44, RHAMM) also involved in cell signalling, differentiation and proliferation pathways. It facilitates migration and transformation and decreases contact inhibition. Hence, hyaluronan has a central regulating role during embryogenesis.