SPECIFIC GLYCANFORMS OF TYPE-IX COLLAGEN ACCUMULATE IN EMBRYONIC CHICK STERNA AFTER 17 DAYS OF DEVELOPMENT

Type IX collagen is a key component of the extracellular matrix of car tilage where it occurs at the surfaces of type II collagen fibrils as a glycanated molecule. The function of the glycosaminoglycan (GAG) sid e chain of the molecule is, however, unknown. We have shown that type IX collagen in chicken sternal cartilage is synthesized with a unimoda l distribution of GAG chain size, but at post 17 days of development t hree predominant glycanforms of type IX collagen accumulate. Such accu mulation did not occur in sterna from day 15 embryos. In day 17 embryo s predominant glycanforms were found in the caudal region of the stern um, By day 19 of development the three predominant glycanforms are wid espread throughout the caudal and cephalic regions. The results indica te that developmental and anatomical changes occur to type IX collagen that depend on the size of the GAG chain attached to the alpha 2(IX) chain of the molecule.