PG-M/Versican-like Proteoglycans Are Components of Large Disulfide-stabilized Complexes in the Axolotl Embryo

Large disulfide-stabilized proteoglycan complexes were previously shown to be synthesized by the epidermis of axolotl embryos during stages crucial to subepidermal migration of neural crest cells. We now show that the complexes contain PG-M/versican-like monomers in addition to some other component with low buoyant density. Metabolically 35S-labeled proteoglycans were extracted from epidermal explants and separated by size exclusion chromatography and density equilibrium gradient centrifugation. The complexes, which elute in the void volume on Sepharose CL-2B, were recovered at buoyant density 1.42 g/ml in CsCl gradients, whereas the monomer proteoglycans, which could only be liberated from the complexes by reduction, had a higher buoyant density (1.48 g/ml). The native complexes did not aggregate with hyaluronan. The purified complexes reacted with antibodies against a portion of a cloned PG-M/versican-like axolotl proteoglycan. These antibodies were found to stain the subepidermal matrix of axolotl embryos, suggesting that the proteoglycan complexes are encountered by neural crest cells during subepidermal migration. From Western blot analysis, the core protein of the PG-M/versican-like monomers was found to be of similar size (≈500 kDa) as those of PG-M/versican variants of other species. Another chondroitin sulfate proteoglycan that was present in small amounts in the epidermal extracts was found to be distinctly different from the similarly sized PG-M/versican-like monomers.