Versican knock-down compromises chondrogenesis in the embryonic chick limb

Mesenchymal cell aggregation is critical for cartilage formation in the vertebrate limb. The extracellular matrix (ECM) plays a critical role in governing cell behavior and cell phenotype in this tissue, and the hyalectin versican is highly expressed in the ECM of precartilage mesenchymal cells and developing synovial joints. Although several in vitro studies have been conducted in an attempt to address versican's role during limb mesenchymal condensation, factors such as differences in cell density in culture, variations between chondrogenic cell lines, and the inability to prolong the viability of limb explants have led to conflicting data, mandating an in vivo analysis. By using a morpholino directed strategy in ovo, we performed knock-down of versican expression in the presumptive ulnar region of the developing chick wing at time points critical to skeletogenesis. These data indicate that in ovo misexpression of versican compromised mesenchymal condensation with resulting ulnar cartilages reduced in length distally by an average of 53% relative to contralateral control limbs. In select versican morphants the olecranon process was also reduced in size proximally and failed to cup the humerus, likely impairing joint morphogenesis. This study represents the first report assessing the role of versican in the developing chick limb in ovo, further demonstrating the importance of versican proteoglycan expression during chondrogenesis and extending previous findings to suggest a role for versican during synovial joint development.