CDNA Cloning of PG-M, a Large Chondroitin Sulfate Proteoglycan Expressed During Chondrogenesis in Chick Limb Buds. Alternative Spliced Multiforms of PG-M and Their Relationships to Versican

We have isolated cDNA clones encoding the core protein of PG-M, a large chondroitin sulfate proteoglycan that has been shown to be expressed in the prechondrogenic condensation area of the developing chick limb buds (Shinomura T., Jensen, K. L., Yamagata, M., Kimata, K., and Solursh, M. (1990) Anat. Embryol. 181, 227-233). The amino acid sequence deduced from the cDNA analysis revealed the presence of a hyaluronic acid binding domain at the amino-terminal side and two epidermal growth factor-like domains, a lectin-like domain, and a complement regulatory protein-like domain at the carboxyl-terminal side. These domains show an extremely high homology to corresponding domains of a human fibroblast large chondroitin sulfate proteoglycan, versican. Such evolutionally conserved structures in the PG-M core protein might be involved in important biological functions of this molecule. On the other hand, the chondroitin sulfate attachment domain at the middle region of the PG-M core protein shows no significant amino acid sequence homology to the corresponding domain of the versican core protein. Further, the chondroitin sulfate attachment domain of PG-M core protein is about 100 kDa larger than that of versican core protein. The finding of alternatively spliced forms of the PG-M core protein suggests that versican might be one of the multiple forms of PG-M.