Regulation of Sox-2 by Krox-20 and c-Jun. (A–D) Immunolabeling of teased newborn sciatic nerve. Nuclear c-Jun is in premyelinating cells (Parkinson et al., 2004), most of which also express Sox-2 (overlay). (E) db-cAMP down-regulates Sox-2 protein. Western blot of control untreated cells (Con) and cells treated with 1 mM db-cAMP for 3 d (cAMP) is shown. Note down-regulation of c-Jun and Sox-2 and increase in Oct-6 and Krox-20. (F) Krox-20 down-regulates Sox-2 and c-Jun. Western blot of cells 3 d after infection with either GFP control (GFP) or Krox-20 (K20) adenoviruses. (G–N) c-Jun and Sox-2 are coexpressed after nerve injury. Double immunolabeling of a teased uncut nerve (G–J) and of the distal stump of a nerve 3 d after transection (K–N). Note that neither c-Jun nor Sox-2 are expressed in intact nerve, whereas both factors are activated by injury and found in the same nuclei (arrows). Bars, 15 μm. (O) Sox-2 protein is reduced in c-Jun–null cells. Western blot of mouse Jun^fl/fl Schwann cells infected with either GFP control (GFP) or CRE-recombinase (CRE) adenoviruses. Note reduced levels of Sox-2 in CRE recombined cells. (P) Inhibition of JNK reduces Sox-2 protein levels. Western blot for Sox-2 in control cells (Con) and cells treated for 2 d with 30 μM SP600125 JNK inhibitor (+SP6). (Q) Western blot showing that enforced Krox-20 expression suppresses residual Sox-2 in c-Jun–null cells. Control cells (Con) and c-Jun–negative cells (CRE) were infected with control adenovirus (GFP) or adenovirus expressing Krox-20 (K20). Note the two-step reduction in Sox-2, first by removing c-Jun alone (GFP and CRE) and second by expressing Krox-20 from c-Jun–null cells (K20 and CRE).