Transforming growth factor-β (TGF-β) plays crucial roles in controlling cell differentiation and maintaining tissue integrity. Previously we reported that TGF-β3 treatment decreased the mRNA expression of the gap junction pro-tein, connexin 43 as well as cell number, which lead to the inhibition of chondrogenic condensation in cultured chick leg bud mesenchymal cells. The present study demonstrates that TGF-β3 can induce cleavage in the ectodomain of neuronal cadherin (N-cadherin) at the initiation stage of chondrogenesis and reduce cell numbers, cellular adhesion and the expression level of connexin 43. Differential displayed PCR (DD-PCR) comparison of adherent- and non-adherent chick leg chondrogenic progenitor cells showed increased expression of the chick ras-responsive element binding transcription factor, cRREB-1, in adherent cells. In chick leg bud mesenchymal cells, cRREB-1 transcription was inhibited by TGF-β3 at the early stage of chondrogenesis. Small interfering RNA (siRNA)-mediated knockdown of cRREB-1 reduced cell numbers, cellular adhesion, and the expression level of connexin 43 resulting in the inhibition of precartilage condensation. Taken together, these findings indicate that TGF-β3 mediates the inhibitory signal necessary for precartilage condensation by stimulating N-cadherin shedding and reducing cRREB-1 expression levels.

Keywords: chondrogenesis, ectodomain shedding, N-cadherin, RREB-1, TGF-β3