Figure 6. NRG1 Type III Induces Myelination as a Juxtacrine Signal from Axons.

(A) Schwann cells were grown with wt and NRG1 type III^−/− neurons in myelinating conditions for 14 days without (control) or with the addition of 1 nM or 10 nM of recombinant, soluble extracellular domain of type III (sECD). Cultures were fixed and stained for MBP (rhodamine) and cell nuclei (Hoechst, blue). Numerous myelin segments are present in wt cocultures but none in NRG1 type III^−/− cocultures, even when supplemented with sECD.

(B) Schwann cells were plated onto control CHO cells (Ba and Bb) or CHO cells that stably express NRG1 type III (Bc and Bd). After 14 days, Schwann cells were stained for S100 (fluorescein, [Ba and Bc]) and MBP (rhodamine, [Bb and Bd]). There was a marked increase in the number of Schwann cells grown on the CHO-III cell monolayer but no MBP expression was detected. Scale bars, 100 μm.