Expression of N-cadherin, N-CAM, fibronectin and tenascin is stimulated byTGF-beta 1, beta 2, beta 3 and beta 5 during the formation of precartilagecondensations

Cell surface adhesion and extracellular matrix proteins are known to play a key role in the formation of cell condensations during skeletal developmen t, and their formation is crucial for the expression of cartilage-specific genes. However, little is known about the relationship between adhesion mol ecules (N-cadherin and N-CAM), extracellular matrix proteins (fibronectin a nd tenascin) and TGF-beta 1,TGF-beta 2 and TGF-beta 3 during in vitro preca rtilage condensations in mouse chondrogenesis. On these bases, we determine d the participation of mammalian TGF-beta 1, TGF-beta 2 and TFG-beta 3 and Xenopus TGF-beta 5 on the expression of cell surface adhesion and extracell ular matrix proteins during the formation of precartilage condensations. Al so, we characterized the effects of TGF-beta s on proteoglycan metabolism a t different cellular densities in mouse embryonic limb bud mesenchymal cell s. In TGF-beta 1 and TGF-beta 5-treated cultures, proteoglycan biosynthesis was higher than in controls, while there were no differences in proteoglyc an catabolism, which caused the accumulation of cartilage extracellular mat rix. When mesenchymal cells were seeded at three different cellular densiti es in the presence of TGF-beta s, only high density cultures presented incr eased stimulation of proteoglycan biosynthesis, compared to low and interme diate densities. To determine whether the effect of TGF-beta s on precartil age condensations is mediated through the expression of N-cadherin, N-CAM, fibronectin and tenascin, we evaluated their expression. Results showed tha t TGF-beta 1, TGF-beta 2, TGF-beta 3, and TGF-beta 5 differentially enhance d the expression of N-cadherin, N-CAM, fibronectin and tenascin in precarti lage condensations, suggesting that TGF-beta isoforms play an important rol e in the establishment of cell-cell and cell-extracellular matrix interacti ons during precartilage condensations.