Abstract. The glia-derived J1 extracellular matrix glycoproteins have been referred to as Jl-160/Jl-180 (the developmentally late appearing lower molecular weight group) and J1-200/J1-220 (the developmentally early appearing higher molecular weight group immunochemically related to tenascin). Members of the two groups show distinct cross-reactivities. To characterize the structural and functional differences between these J1 glycoproteins, two monoclonal antibodies were generated which recognize only the members of the lower molecular weight group. The two antibodies detect immunochemical similarities among the members of the lower molecular weight group, but do not react with J1/tenascin. Jl-160 and Jl-180 are specifically expressed by differentiated oligodendrocytes in culture and by myelin of the central nervous system and have not been found in the peripheral nervous system nor in any other organ of the adult mice tested. Electron microscopic examination of rotary-shadowed Jl-160 and Jl-180 reveals, respectively, dimeric and trimeric (tribrachion) kink-armed rodlike structures, which are linked by disulfide bridges. Jl-160/Jl-180 are nonpermissive substrates for the attachment and spreading of early postnatal small cerebellar neurons, astrocytes, and fibroblasts. In a mixture with laminin, Jl-160/J1-180 are nonpermissive substrates for neurons, but not for astrocytes or fibroblasts. The repulsive effect toward neurons can be neutralized by one of the monoclonal antibodies, but not by the other. These observations are discussed in the context of cell interactions during regeneration in the mammalian nervous system.

Chondroitin sulfate proteoglycan (CS-PG) expression is increased in response to CNS injury and limits the capacity for axonal regeneration. Previously we have shown that neurocan is one of the CS-PGs that is upregulated (Asher et al., 2000). Here we show that another member of the aggrecan family, versican, is also upregulated in response to CNS injury. Labeling of frozen sections 7 d after a unilateral knife lesion to the cerebral cortex revealed a clear increase in versican immunoreactivity around the lesion. Western blot analysis of extracts prepared from injured and uninjured tissue also revealed considerably more versican in the injured tissue extract. In vitro studies revealed versican to be a product of oligodendrocyte lineage cells (OLCs). Labeling was seen between the late A2B5-positive stage and the O1-positive pre-oligodendrocyte stage. Neither immature, bipolar A2B5-positive cells, nor differentiated, myelin-forming oligodendrocytes were labeled. The amount of versican in conditioned medium increased as these cells differentiated. Versican and tenascin-R colocalized in OLCs, and coimmunoprecipitation indicated that the two exist as a complex in oligodendrocyte-conditioned medium. Treatment of pre-oligodendrocytes with hyaluronidase led to the release of versican, indicating that its retention at the cell surface is dependent on hyaluronate (HA). In rat brain, approximately half of the versican is bound to hyaluronate. We also provide evidence of a role for CS-PGs in the axon growth-inhibitory properties of oligodendrocytes. Because large numbers of OLCs are recruited to CNS lesions, these results suggest that OLC-derived versican contributes to the inhospitable environment of the injured CNS.

Janusin and tenascin are glia-derived, structurally related, extracellular matrix glycoproteins of the J1 family that are expressed in vivo at times and in locations where active neurite outgrowth occurs, but also when the formation or stabilization of cytoarchitectonic boundaries appears to be in operation. To resolve this apparent functional dichotomy, we have studied the behavioral response of growth cones, growing in culture on the permissive substrate laminin to janusin and tenascin, by video time lapse microscopy. When janusin and tenascin were offered as sharp substrate boundaries, dorsal root ganglion (DRG) and retinal ganglion neuron growth cones avoided growing on these molecules, but were not induced to collapse. On the other hand, when janusin and tenascin were offered, in a mixture with laminin, as uniform substrates, DRG growth cones displayed a collapsed morphology and were able to advance at a faster rate than on laminin alone. In contrast, the outgrowth of retinal ganglion neuron growth cones was completely inhibited under these conditions, underscoring a cell type specificity in the response of growth cones to these molecules. Using several monoclonal antibodies binding to distinct epitopes on the tenascin molecule, we have identified two domains responsible for growth cone repulsion, on epidermal growth factor (EGF)-like repeats 3-5 and fibronectin type III homologous repeats 4 and 5. These domains are different from the one previously recognized to be involved in neurite outgrowth on a uniform tenascin substrate. We conclude that both molecules may promote or retard growth cone advance, depending on the spatial expression pattern and the neuronal cell type.

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O4ϩ oligodendrocyte (OL) progenitors in the mammalian CNS are committed fully to terminal differentiation into myelinforming cells. In the absence of other cell types in vitro, OL differentiation reproduces the in vivo development with a correct timing, suggesting the existence of an intrinsic regulatory mechanism that presently is unknown. We have examined the effect of two isoforms of the extracellular matrix (ECM) molecule tenascin-R ( TN-R), which is expressed by OLs during the process of myelination, on the adhesion and maturation of OLs in vitro. Here we show that the substrate-bound molecules supported the adhesion of O4ϩ OLs independently of the CNS region or age from which they were derived. At the molecular level this process was mediated by protein binding to membrane surface sulfatides (Sulf ), as indicated by the interference of O4 antibody and Sulf with the attachment of OLs or other Sulf ϩ cells, erythrocytes, to TN-R substrates and by direct protein-glycolipid binding studies. In the absence of plateletderived growth factor (PDGF ), exogenous TN-R induced myelin gene expression and the upregulation of its own synthesis by cultured cells, resulting in a rapid terminal differentiation of O4 ϩ progenitors. Our findings strongly suggest that TN-R represents an intrinsic regulatory molecule that controls the timed OL differentiation by an autocrine mechanism and imply the relevance of TN-R for CNS myelination and remyelination. Key words: cell adhesion; extracellular matrix; glycosphingolipid; myelination; oligodendrocyte differentiation; sulfatide; tenascin-RIn the mammalian CNS the differentiation of oligodendrocytes (OLs) is characterized by the sequential expression of myelinspecific molecules, which finally leads to the formation of the myelin sheath. The earliest stages of macroglial development take place in the ventral regions of the neural tube (for spinal cord) and the ventricular zones of the neonatal mammalian forebrain, where the first OL progenitors characterized by simple morphology and the expression of the disialoganglioside GD3 and /or the O4 antigen(s) proliferate and migrate into the presumptive white matter