A neuroectoderm-associated ganglioside participates in fibronectin receptor-mediated adhesion of germinal cells to fibronectin

Previous studies with a rat neural cell line have shown that the D1.1 ganglioside, an O-acetylated derivative of GD3, is involved in cellular adhesion to fibronectin. In vivo, D1.1 is present on germinal cells of the developing rat central nervous system, but not on postmitotic cells that migrate away from the germinal zones. These observations suggest that D1.1 could participate in adhesive interactions with germinal zones and that the loss of D1.1 could be involved in the decision to being migration. In support of this hypothesis, immunofluorescence histochemistry shows that both fibronectin and fibronectin receptor are colocalized with D1.1 in the ventricular zones of the embryonic rat brain and in the external granule cell layer of the postnatal cerebellum. Dishes coated with monoclonal antibody against D1.1 were used to isolate D1.1-positive germinal cells from Embryonic Day 14 cerebrum and from Postnatal Day 6 cerebellum. These cells are able to adhere to fibronectin-coated dishes by a mechanism that is inhibitable by a synthetic hexapeptide containing the arg-gly-asp cell recognition sequence of fibronectin. Adhesion is also partially inhibited by antibody against fibronectin receptor and is slowed by anti-D1.1 antibody, implicating both the receptor and the ganglioside in the adhesion process. During 3 days in culture these D1.1-positive, fibronectin receptor-positive cells exhibit a neuronal phenotype, as judged by morphology and staining with tetanus toxin. This further confirms the neuroepithelial origin of the cells. The cells do not synthesize detectable amounts of fibronectin, thus leaving unidentified the source of the fibronectin seen in the germinal zones in tissue sections. Immunoprecipitation experiments show that the fibronectin receptors present on these cells are heterodimers. Under nonreducing conditions, the immunoprecipitates contain an alpha-subunit of 150-160 kDa and a beta-subunit of 115-125 kDa.