Effect of 4-methylumbelliferyl-β-d-xyloside on collagen synthesis in chick limb bud mesenchymal cell cultures

Previous studies showed that cultures of chick limb bud mesenchymal cells plated at high density, to maximize chondrogenic expression, had a much reduced extracellular matrix around chondrocytes when exposed to 4-methyl-, umbelliferyl-β-d-xyloside. The majority of newly synthesized chondroitin sulfate chains were found in the culture medium presumably bound to the xyloside as opposed to their normal deposition on the core protein of proteoglycan. The question remained open as to whether the development of an abnormal matrix affected the synthesis of extracellular deposition of other cartilage-specific macromolecules. We have analyzed, both morphologically and biochemically, the synthesis and deposition of Type I and Type II collagen by β-d-xyloside-treated cultures of limb mesenchymal cells. While the rate of collagen synthesis per plate and its extracellular accumulation after 8 days in culture were reduced to some extent, the ratios of Type II to Type I collagen and the morphological distribution of these macromolecules were not affected by exposure to β-d-xyloside. We conclude that the expression of the cartilage-specific Type II collagen during chondrogenic differentiation is, although reduced, qualitatively not dependent on the amount of extracellular chondroitin sulfate chains attached to matrix-associated proteoglycan core protein. However, prolonged exposure of limb bud cells to xylosides leads to the formation of a chondroitin sulfate- and collagen-deficient matrix which, in turn, reduces the capacity of limb bud cells to synthesize Types I and II collagen.