DSD-1-PG is a chondroitin sulfate proteoglycan (CSPG) expressed by glial cells that can promote neurite outgrowth from rat embryonic mesencephalic (E14) and hippocampal (E18) neurons, an activity that is associated with the CS glycosaminoglycans (GAGs). Further characterization of DSD-1-PG has included sequencing of peptides from the core protein and the cloning of the corresponding cDNA using polyclonal antisera against DSD-1-PG to screen phage expression libraries. On the basis of these studies we have identified DSD-1-PG as the mouse homolog of phosphacan, a neural rat CSPG. Monoclonal antibodies 3H1 and 3F8 against carbohydrate residues on rat phosphacan recognize these epitopes on DSD-1-PG. The epitopes of the antibodies, L2/HNK-1 and L5/Lewis-X, which have been implicated in functional interactions, are also found on DSD-1-PG. Although DSD-1-PG has previously been shown to promote neurite outgrowth, its upregulation after stab wounding of the CNS and its localization in regions that are considered boundaries to axonal extension suggested that it may also have inhibitory functions. Neonatal dorsal root ganglion (DRG) explants grown on a rich supportive substrate (laminin) with and without DSD-1-PG were strikingly inhibited by the proteoglycan. The inhibitory effects of DSD-1-PG on the DRG explants were not relieved by removal of the CS GAGs, indicating that this activity is associated with the core glycoprotein. The neurite outgrowth from embryonic hippocampal neurons on laminin was not affected by the addition of DSD-1-PG. This indicates that DSD-1-PG/mouse phosphacan can have opposing effects on the process of neurite outgrowth dependent on neuronal lineage.

Abstract. The glia-derived extracellular matrix glycoprotein tenascin-C (TN-C) is transiently expressed in the developing CNS and may mediate neuron-glia interactions. Perturbation experiments with specific monoclonal antibodies suggested that TN-C functions for neural cells are encoded by distinct sites of the glycoprotein (Faissner, A., A. Scholze, and B. GOtz. 1994. Tenascin glycoproteins in developing neural tissues--only decoration? Persp. Dev. Neurobiol. 2:53-66). To characterize these further, bacterially expressed recombinant domains were generated and used for functional studies. Several short-term-binding sites for mouse CNS neurons could be assigned to the fibronectin type III (FNIII) domains. Of these, the alternatively spliced insert TNfnA1,2,4,B,D supported initial attachment for both embryonic day 18 (El8) rat and postnatal day 6 (P6) mouse neurons. Only TNfnl-3 supported binding and growth of P6 mouse cerebellar neurons after 24 h, whereas attachment to the other domains proved reversible and resulted in cell detachment or aggregation. In choice assays on patterned substrates, repulsive properties could be attributed to the EGF-type repeats TNegf, and to TNfnA1,2,4. Finally, neurite outgrowth promoting properties for E18 rat hippocampal neurons and P0 mouse DRG explants could be assigned to TNfnB,D, TNfnD,6, and TNfn6. The epitope of mAb J1/ tn2 which abolishes the neurite outgrowth inducing effect of intact TN-C could be allocated to TNfuD. These observations suggest that TN-C harbors distinct cellbinding, repulsive, and neurite outgrowth promoting sites for neurons. Furthermore, the properties of isoform-specific TN-C domains suggest functional significance of the alternative splicing of TN-C glycoproteins.

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The use of monoclonal antibodies has led to much progress in the characterization of extracellular matrix components of the CNS. F1C3 is a monoclonal antibody raised against the astrocytic cell line, Neu7. Analysis by immunoprecipitation and Western blots of the F1C3 antigen in Neu7 cell lysates and conditioned medium reveals a recognition of several protein bands around 140 -230 kD. Internal peptide sequence data from these bands indicate that they are highly homologous to fibrillar collagens, and the F1C3 antigen is specifically digested by the collagenase I protease. Other glial cell lines show F1C3 antigen expression including A7, C6, and U373. Cultures of neonatal primary astrocytes also express F1C3 antigen, and Western blot analysis of rat brain extracts from different ages and parts of the brain confirm an in vivo expression of F1C3 protein. The significance of the expression of fibrillar collagenlike proteins by astrocytes is discussed together with its possible implication during developmental processes and in the context of CNS lesions and regeneration. GLIA 41: 382-392, 2003.

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