Fig. 4.
The induction of differentiation depends on the geometry of the microenvironment. (A) Phase contrast microscopic images of beads measuring either 5 (Left), 20 (Center), or 100 (Right) μm in diameter. Beads were coated with an antibody to an axonal protein (p75NTR) and then conjugated at high density along the length of axons. (B–D) Immunostaining of OPC-DRG cocultures five days after seeding a standard density of 200,000 OPCs and a high density of beads measuring either 5 (B), 20 (C), or 100 (D) μm in diameter. OPCs are induced to differentiate only in the presence of the 20-μm beads (C). Oligodendrocytes are identified by immunostaining for MBP (red). Axons are identified by immunostaining for NF (green). Nuclei are stained by using DAPI (blue). Beads are visualized by using DIC microscopy.