A new heparan sulfate proteoglycan in the extracellular matrix of the developing chick embryo

A new heparan sulfate proteoglycan was identified by two monoclonal antibodies. The antibodies (hybridoma clones 6C4 and 1B11) were generated from mice immunized with inner limiting membranes of the embryonic chick retina. The proteoglycan had an apparent molecular weight of 250 kDa with a core protein of 180 kDa. Antibodies to perlecan and to a recently identified brain-derived heparan sulfate proteoglycan did not cross-react with purified 6C4/1B11 antigen, confirming that the three proteoglycans are not related. The 6C4/1B11 proteoglycan was abundant in basal laminae, such as the inner limiting membrane of the retina, the lens capsule, the epidermal, the pial, and the muscle basal laminae, and the vitreous body. The distribution and developmental expression of the 6C4/1B11 proteoglycan was different than that of perlecan and the brain-derived heparan sulfate proteoglycan. When used as a substrate for embryonic retinal explants, the proteoglycan did not support axonal outgrowth in vitro. The data present a new heparan sulfate proteoglycan and demonstrate the existence of at least three different heparan sulfate proteoglycans in the developing chick embryo with partially overlapping distribution.