Cytochalasin D disrupts the restricted localization of N-CAM, but not of L1, at sites of Schwann cell-neurite and Schwann cell-Schwann cell contact in culture

The neural recognition molecules L1 and N-CAM have been shown to be prefere ntially localized at sites of Schwann cell-to-neurite and Schwann cell-to-S chwann cell contact in vitro. In the present study, we investigated the mec hanisms underlying the restricted expression of these molecules at the Schw ann cell surface, focusing on the possible role of actin filaments. Go-cult ures consisting of Schwann cells from newborn mice and explants of dorsal r oot ganglia from chicken embryos were maintained in the absence of presence of cytochalasin D, an agent disrupting actin filaments. Immunoelectron mic roscopy with mouse-specific antibodies was carried out to quantify the rest ricted localization of L1 and N-CAM at the Schwann cell surface in contact with neurites. After 2 days of co-culturing in the absence of cytochalasin D, approximately 65% of the cell-cell contacts showed a restricted immunore activity for L1 and N-CAM. The accumulation of L1 at contact sites was unch anged in cytochalasin D-treated co-cultures, while the agent strongly reduc ed the restricted localization of N-CAM to 20% of all cell-cell contacts. T he disruption of N-CAM accumulation appeared to be rapid and occurred withi n 5 h of cytochalasin D treatment. These results indicate that the restrict ed localization of N-CAM, but not of L1, is sensitive to cytochalasin D tre atment, suggesting a dependence on the integrity of the actin network. Thus , different mechanisms may regulate the subcellular distribution of cell ad hesion molecules in Schwann cells.