To investigate the PG expression and GAG composition in Xenopus embryos, we microinjected [35S]sulfate into the blastocoel at stage 9 and analyzed the purified PGs at stage 22 after chemical and lyase treatment to degrade distinct GAG chains (Fig. 3). Nitrous acid at low pH was used to degrade HS (Shively and Conrad, 1976), and chondroitinases that are specific for DS (denoted Chase B) or both CS and DS (denoted Chase ABC) were used to degrade the DS or CS/DS chains, respectively. The size separation of the split products indicated that 56% of the total radioactivity corresponded to CS/DS PGs (Fig. 3A). SDS-PAGE analysis demonstrated two broad bands that were resistant to nitrous acid treatment and compatible with being biglycan (Bgn, 200-300 kDa, Moreno et al., 2005) and versican (Vcan, ∼1000 kDa) (Fig. 3B). Both bands disappeared following Chase ABC digestion and decreased following Chase B digestion to 71% (Bgn) and 65% (Vcan). We have previously demonstrated that CS/DS chains are present in Xenopus overexpressing Bgn (Hou et al., 2007). In post-neurula embryos, both Bgn (Fig. 3C,C′) and Vcan (Casini
