Cells and Materials


Cartilage development, or chondrogenesis, is a process which involves the condensation of prechondrogenic mesenchymal cells, followed by the expression of the cartilage phenotype characterized by the biosynthesis of cartilage-specific, extracellular matrix components. We have previously shown that the cationic biopolymer, polylysine (PL), is able to stimulate chondrogenesis by embryonic limb bud mesenchymal cells in vitro. In this study, we have evaluated the chondrogenesis-stimulating activity of PL in vivo using an experimental system consisting of chick embryonic muscle explants, which were grafted onto the chorioallantoic membrane of chick embryos maintained in long-term shell-less culture. The muscle grafts were treated with PL by multiple direct injections of PL of 398 KO Mr. The phenotypic changes in the muscle grafts were assessed by histology, scanning electron microscopy, and analysis of the biosynthesis of extracellular matrix components. The microscopic observations revealed that a cartilage-like matrix was elaborated in the PL-treated grafts, as indicated by positive alcian blue staining and the presence of abundant matrix material morphologically similar to that in a typical cartilage. Cartilage matrix biosynthesis in the PL-treated grafts was further indicated by their increased [35S] sulfate incorporation and the apparent expression of collagen type II. Taken together, these findings indicate that PL acts to stimulate, or perhaps induce, chondrogenesis in the explanted muscle grafts. It is speculated that matrix molecules with PL-like, cationic domains may act in vivo to regulate chondrogenesis.