Two Chondroitin Sulfate Proteoglycans Differentially Expressed in the Developing Chick Visual System

Two monoclonal antibodies, 2B9 and 9BA12, were used to identify and characterize two different chondroitin sulfate proteoglycans (CSPGs) associated with the embryonic chick visual system. Monoclonal antibody 2B9 recognizes a carbohydrate epitope of collagen type IX proteoglycan. Immunohistochemistry showed that collagen type IX proteoglycan was abundant in the vitreous body and meninges, but absent in brain and retina. In developing trunk regions, collagen type IX proteoglycan is segmentally distributed in the somites, appearing only in the posterior sclerotome. Monoclonal antibody 9BA12 recognizes collagen type IX proteoglycan from vitreous body and an unidentified chondroitin sulfate proteoglycan in retina and brain, herein referred to as 9BA12 CSPG. Immunohistochemistry showed that 9BA12 CSPG is present in the optic fiber layer of the retina, coinciding temporally and spatially with the onset and cessation of ganglion cell axon growth. In the trunk region, 9BA12 immunostaining appears in the developing spinal cord and throughout the sclerotome. In culture, neither the collagen type IX proteoglycan nor the brain-derived 9BA12 CSPG were able to support neurite outgrowth from retinal ganglion cell explants. In combination with basal lamina proteins, collagen type IX proteoglycan slightly inhibited neurite outgrowth and led to a stronger fasciculation of retinal axons. In contrast, 9BA12 CSPG had no inhibitory effect on the outgrowth of retinal axons and had no effect on their fasciculation. Our study demonstrates the existence of two chondroitin sulfate proteoglycans in the developing visual system of the chick. Based on the developmental expression and the results from neurite outgrowth experiments, it was concluded that the 9BA12 CSPG does not operate as a neurite outgrowth inhibitor for retinal axons.