Figure 4.
SPARC neurite outgrowth activity is dependent on Schwann cells, signaling via laminin. A, B, Representative montages of DAPI-positive nuclei in DRG explants grown in NGF alone (A) or NGF supplemented with 5 ng/ml rhSPARC (B). C, Representative image of S100β+ SCs underlying the DRG neurite carpet. D–I, Representative images of pure, dissociated DRG cultures (D, G) and dissociated DRGs cocultured with SCs in D, E, G, and H NGF alone (E, F, H, I) or NGF plus 5 ng/ml rhSPARC (F, I). J, DRG explants were grown in the presence of AraC for 2 d to eliminate dividing cells, after which explants were grown with or without SPARC for an additional 2 d. After AraC treatment, the neurite outgrowth activity stimulated by SPARC is no longer detected. Similarly, when DRG explants are grown on poly-l-lysine alone, with laminin removed from the substrate, the addition of SPARC fails to induce outgrowth above control (NGF/PLL) levels. K, Neurite outgrowth in pure, dissociated DRG cultures is unaffected by SPARC. Reintroduction of SCs to dissociated DRGs results in increased neurite outgrowth in NGF alone, and this is further enhanced in the presence of SPARC. *p < 0.05. Scale bars, 100 μm. NST, Neuron-specific tubulin.