Expression of N-cadherin and alkaline phosphatase in chick limb bud mesenchymal cells: regulation by 1,25-dihydroxyvitamin D3 or TGF-beta 1.

When mesenchymal cells from the early chick limb bud (stage 23-24) are plated at high cell density they spontaneously undergo chondrogenesis implicating extensive cell-to-cell interactions. In the past it has been shown that TGF-beta and vitamin D can influence this process and can stimulate chondrogenesis. Given the importance of cell adhesion molecules during cellular interactions we decided to examine the effects of 1,25-dihydroxyvitamin D3 or TGF-beta on the expression of molecules involved in cell-to-cell adhesion (N-cadherin) or cell-substrate adhesion (alkaline phosphatase). Immunofluorescence demonstrated that N-cadherin was expressed in the mesenchymal cells and in the very early cartilage nodules but it was down-regulated in the older nodules. As shown by Western blotting, the expression of N-cadherin declined as chondrogenesis proceeded and was affected in cultures treated with 1,25-dihydroxyvitamin D3 and TGF-beta 1. Alkaline phosphatase was also expressed in the mesenchymal cells; these cells preferentially use an alternative transcript compared to the cartilage cells of the sternum. Thus, our data suggest that the involvement of 1,25-dihydroxyvitamin D3 in chondrogenesis could be mediated via regulation of cell adhesion.