N-cadherin expression and signaling in limb mesenchymal chondrogenesis: Stimulation by poly-L-lysine

Cellular condensation is a requisite step in the initiation of mesenchymal chondrogenesis in the embryonic limb bud. We have previously shown that cel lular condensation of limb chondroprogenitor mesenchymal cells is accompani ed by elevated expression of N-cadherin during chondrogenesis both in vivo and in vitro. N-Cadherin-mediated cell-cell interaction is also Functionall y required for proper mesenchymal chondrogenesis both in vivo and in vitro. In this report, we have further analyzed the functional importance of N-ca dherin in the cellular condensation-chondrogenesis pathway by examining N-c adherin expression and related activities in high density micromass culture s of chide limb mesenchymal cells in which chondrogenesis is being stimulat ed with the cationic polymer, poly-L-lysine (PL). The chondrogenesis-promot ing action of PL is thought to involve the clustering of cells via ionic cr oss-linking, perhaps mimicking the action of an endogenous matrix component . Immunohistochemistry, immunoblotting, and Northern blot analysis all show that PL treatment results in a time-dependent increase in N-cadherin expre ssion at both the protein and mRNA levels. In addition, inhibition of N-cad herin function with a neutralizing monoclonal antibody directed to its extr acellular domain inhibits the chondrogenesis-stimulating effect of FL. PL t reatment also alters the tyrosine-phosphorylation state of the N-cadherin a ssociated signaling protein, beta-catenin. These results suggest that N-cad herin-mediated cell adhesion is a requisite regulatory component of the lim b mesenchymal chondrogenic differentiation program, involving at least in p art beta-catenin tyrosine phosphorylation as a signaling step. (C) 1999 Wil ey-Liss, Inc.