Hyaluronan-mediated aggregation of limb bud mesenchyme and mesenchymal condensation during chondrogenesis

Cell condensations are the initial structures in the formation of proper cartilage and skeletal patterning in the developing vertebrate limb. Chondrogenic differentiation is dependent upon the cell-cell and/or cell-matrix interactions which take place during the condensation process. Coincident with the onset of condensation is the expression by limb mesenchyme of specific cell surface binding sites for the extracellular matrix macromolecule hyaluronan. The association of hyaluronan with the cell surface can influence the behavior of cells, especially cell aggregation. In this study the possible involvement of hyaluronan as an extracellular linker molecule in the cell-cell adhesion event during mesenchymal condensation was investigated in the avian limb model. Hyaluronan hexasaccharides were used to prevent the multivalent interactions that occur between native hyaluronan macromolecules and the cell surface. Our studies show that hyaluronan is required for early adhesive cell-cell interactions of limb bud mesenchyme and that perturbations of hyaluronan-cell interactions with hyaluronan hexasaccharides result in a delay in the formation of condensations as well as a delay in chondrogenic differentiation of mesenchymal cells in micromass cultures.