Tissue variation of two large chondroitin sulfate proteoglycans (PG-M/versican and PG-H/aggrecan) in chick embryos

PG-M and PG-H, chick large chondroitin sulfate proteoglycans corresponding to versican (fibroblast-type proteoglycan) and aggrecan (cartilage-characteristic proteoglycan), respectively, which are found in mammals, have been characterized in various tissues of chick embryos. Their distribution and the compositions of the core molecules were analyzed by immunofluorescence staining and immunoblotting, respectively, using various monospecific antibodies. Molecules reactive to a monoclonal antibody to the PG-M core protein (designated MY-174) were distributed in various tissues, including aorta, lung, cornea, brain, skeletal muscle and dermis. Immunoblotting with MY-174 of the chondroitinase ABC-digested tissue extracts showed a tissue variation of MY-174-reactive core molecules (550-kD, 500-kD, 450-kD, and 350-300-kD). In contrast, PG-H, besides massive occurrence in cartilage, was only found in a few tissues such as aorta and brain. In addition, PG-H in aorta, cornea, and skin was atypical in structure, because it lacked keratan sulfate. The expression of PG-M in developing chick embryos was then examined. PG-M was found in some developmentally active areas, such as the perinotochordal mesenchyme between notochord and neural tube, the basement membranes facing neuroepithelial cells, and condensing mesenchymal cells in limb buds, suggesting some functions distinctive of the developing tissues.