Early molecular events in chondrogenesis

This paper reviews the molecular and cellular events during precartilage condensation and describes the application of a new retroviral gene transduction procedure. In micromass cultures, dissociated mesenchymal cells interact to form cartilage nodules. Cells first form small aggregates, then bigger clusters. Next, through rearrangement, they consolidate to form precartilage condensations which then differentiate into cartilage. We mapped molecular expression in these early stages and showed that the sequence of molecular expression was tenascin-C, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), and phos-phorylated CREB (PCREB) → neural cell adhesion molecules → integrin β1 and fibronectin → collagen II and Alcian blue. We then used a newly developed replication competent avian sarcoma (RCAS) mediated gene transduction procedure to alter the gene expression in micromass cultures. We showed that RCAS-(antisense NCAM) can suppress cartilage formation by forming smaller and fewer cartilage nodules. Sonic hedgehog directs mesenchymal cells to form novel nodules with characteristics of hypertrophic cartilage. The use of retroviral transduction, together with the addition of growth factors and Fab’ antibodies to the media, constitute powerful approaches to the analysis of the molecular cascade of chondrogenesis in micromass cultures. It also provides a means to engineer the fate of mesenchymal cells through modulation of adhesion molecules and transgene expression of signaling molecules.