Immunochemical and biochemical comparisons between embryonic chick bone marrow and epiphyseal cartilage chondroitin/dermatan sulphate proteoglycans.
Chrondroitin sulphate proteoglycans obtained from embryonic chick bone marrow and epiphyseal cartilage were compared using immunochemical and biochemical analyses. Proteoglycans from each tissue, separated on CsCl density gradients, under dissociative conditions, into high (1.6 g ml-1), medium (1.5 g ml-1) and low (1.4 g ml-1) buoyant density fractions, were immunochemically analysed, using a panel of monoclonal antibodies that specifically recognize chondroitin 4-/dermatan sulphates, chondroitin 6-sulphate, keratan sulphate, the hyaluronate binding region present on connective tissue proteoglycans, and link protein. The same antibodies were used in Western blot analyses to detect intact proteoglycan monomers and core proteins that had been fractionated by agarose-polyacrylamide and by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Specific differences between marrow and cartilage proteoglycans were detected. In CsCl gradients, marrow proteoglycans displayed a higher degree of heterogeneity in terms of buoyant densities and hexuronate distribution. Keratan sulphate chains were constituents of the majority of 'large' proteoglycans in the marrow; however, a portion of the large proteoglycans in marrow middle buoyant density fraction either lacked keratan sulphate chains or were substituted with a form different from that found on cartilage proteoglycans. Marrow lacked 'small' chondroitin/dermatan sulphate proteoglycans that were present in cartilage and contained a more heterogeneous population of proteoglycans, particularly in the lower buoyant density fractions. Both marrow and cartilage were similar in that they contained, as their major components, large, aggregating proteoglycans and link proteins that were immunochemically and biochemically identical. The significance of these differences between marrow and cartilage proteoglycans remains to be determined, but they may, in part, be responsible for imparting unique characteristics to the haematopoietic extracellular matrices.