NFIB and neuroblastoma: We then assessed the role of nf1 in suppressing RAS effector pathways in the neuroblastoma cells of wild-type fish overexpressing MYCN. By immunohistochemistry and measurement of the area of the diaminobenzidine-peroxidase (DAB)-stained tumor cells, we detected high levels of pERK, pAKT and pS6 in neuroblastomas from 6-week-old fish (Figure 6A,D,G and J), indicating activation of RAS effector pathways in the proliferating neuroblasts of wild-type nf1a+/+; nf1b+/+;MYCN fish that were blocked from terminal differentiation by overexpression of MYCN.