LARGE CHONDROITIN SULFATE PROTEOGLYCANS OF DEVELOPING CHICK CNS ARE EXPRESSED IN CEREBRAL HEMISPHERE NEURONAL CULTURES

Chondroitin sulfate proteoglycans (CSPG) of the extracellular matrix m ay play regulatory roles in central nervous system (CNS) development. We have examined the expression of two large CSPGs of the embryonic ch ick brain, which can be differentiated using the monoclonal antibodies HNK-1 and S103L, in cultures of embryonic day 6 chick cerebral hemisp here neurons. Western blot analysis following immunoprecipitation and endoglycosidase treatment revealed that these cultures produce S103L- and HNK-1-reactive proteoglycans which are biochemically indistinguish able from the CSPGs (previously) identified in homogenized chick embry o brain extracts. The HNK-1-reactive CSPG accumulated in the medium th roughout the course of cultures. In contrast, the S103L-reactive CSPG was found in a neuron-associated form during the period of aggregate e stablishment in culture, as well as in a soluble form secreted into th e medium. Immunocytochemical staining of cultures with the S103L antib ody localized reactivity to most neurons during the period of aggregat e formation, while neuronal processes and the few flat cells present ( presumably neuroblasts and early glia) were negative. Cell selection e xperiments confirmed that neurofilament-positive cells were the source of the S103L-reactive CSPG. The use of differential fixation techniqu es suggested that the cell-associated S103L reactivity may be intracel lular. Because of this pattern of expression and localization, we prop ose that the developmentally regulated S103L-reactive CSPG may play a role in neuronal migration arrest and organization of neurons into fun ctional aggregates.