Schwann cells fail to differentiate when co-cultured in contact with PC12 neurites

Schwann cells derived from mouse or rat dorsal root ganglia (DRG) were co-cultured with either DRG neurons or nerve growth factor (NGF)-responsive PC12 pheochromocytoma cells for up to 7 weeks. When Schwann cells were grown in the presence of DRG neurites, they displayed normal ensheathing behavior and produced basal laminae and small diameter collagen fibrils within 5-19 days in vitro. However, when Schwann cells were co-cultured in direct contact with PC12 cells and without DRG neurons, they largely failed to ensheath PC12 neurites, and failed to assemble either basal lamina or small diameter collagen fibrils at any point during 7 weeks. Schwann cell proliferation continued in the presence of PC12 neurites, indicating that PC12 cells produced a mitogenic activity for Schwann cells functionally similar to previously described neurite-associated activities. These results demonstrate that Schwann cell contact with PC12 cells does not elicit the final morphogenetic events in Schwann cells (ensheathment, basal lamina formation and collagen fibril assembly) that normally occur when Schwann cells are co-cultured in contact with DRG neurons.