RESUMEN
Chondroitin sulfate proteoglycans, cell surface and extracellular matrix molecules in both neural and non-neural tissues, are highly regulated during normal development. Entire proteoglycan molecules may be either up-regulated or down-regulated, or only the chondroitin sulfate glycosaminoglycan portions of these molecules may be modified. Subtle changes in the chemistries of chondroitin sulfate chains can now be identified through the use of a panel of anti-chondroitin sulfate monoclonal antibodies. Each of these antibodies recognizes specific chemical structures which are non-randomly dispersed along the lengths of chondroitin sulfate chains. The location of individual epitopes within defined domains in these chains is demonstrated through controlled treatments of aggrecan with chondroitinase ABC, whereby portions of these chains are removed from the non-reducing terminal ends and where the remainder of the chains remains covalently attached to the core protein. In these situations, some epitopes, such as those recognized by antibodies CS-56 and 6C3, can be removed without loss of other epitopes, such as that recognized by antibody 4C3. The independent expression of individual epitopes is demonstrated by immunocytochemical analyses of developing skin appendages in embryonic chicks and fetal humans. These are sites where highly patterned morphogenetic movements result from epithelial-mesenchymal interactions. In both chicks and humans, some epitopes are constitutively expressed while others are strictly regulated in the mesenchymal portions of the developing skin appendages. These data strongly suggest that chondroitin sulfate proteoglycans, including their chondroitin sulfate chains, have important roles in regulating these epithelial mesenchymal interactions. Furthermore, these data underscore the significance of the aforementioned observation that individual epitopes are located in specific domains within chondroitin sulfate chains. The highly organized expression of chondroitin sulfate proteoglycans in the development of the central nervous system strongly argues for a similar role for these molecules in the organs that comprise this system.