Cell specific-chondroitin sulfate proteoglycan expression during CNS morphogenesis in the chick embryo

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There is increasing evidence that proteoglycans, particularly chondroitin sulfate proteoglycans (CSPGs), are integral components in the assembly of the extracellular matrix during early stages of histogenesis. The differential expression of several CSPGs in the developing CNS has raised questions on their origin, phenotype (chemical and structural characteristics), regulation of expression and function. The S103L monoclonal antibody has been an invaluable specific reagent to identify and study a large and abundant CSPG in embryonic chick brain. In the present study we demonstrate that during embryogenesis of the chick CNS, the S103L CSPG (B-aggrecan) is synthesized by neurons of all major neuronal cell types but not by astrocytes, is developmentally regulated, and is associated predominantly with neuronal somata, suggesting that neuronal-specific regulatory mechanisms control the expression of the S103L CSPG in culture. Neurons also exhibit differential expression of glycosaminoglycan type (i.e., KS) and sulfation patterns on different CSPGs when compared to astrocytes, meningial cells or chondrocytes, implying the existence of additional, cell type-specific modes of regulation of the final CSPG phenotype (chemical and structural posttranslational characteristics). A specific temporal pattern of expression of the S103L-CSPG was observed which may contribute to conditions that induce or stabilize specific cell phenotypes during CNS development. In contrast, the other major CSPG in the CNS recognized by the HNK-1 antibody, is synthesized by all cell types of different cell lineages over the entire embryonic period, suggesting a more global cell maintenance function for this CSPG.