A role for rhoB in the delamination of neural crest cells from the dorsal neural tube

The differentiation of neural crest cells from progenitors located in the d orsal neural tube appears to involve three sequential steps: the specificat ion of premigratory neural crest cell fate, the delamination of these cells from the neural epithelium and the migration of neural crest cells in the periphery. BMP signaling has been implicated in the specification of neural crest cell fate but the mechanisms that control the emergence of neural cr est cells from the neural tube remain poorly understood. To identify molecu les that might function at early steps of neural crest differentiation, we performed a PCR-based screen for genes induced by BMPs in chick neural plat e cells. We describe the cloning and characterization of one gene obtained from this screen, rhoB, a member of the rho family GTP-binding proteins. rh oB is expressed in the dorsal neural tube and its expression persists trans iently in migrating neural crest cells. BMPs induce the neural expression o f rhoB but not the more widely expressed rho family member, rhoA. Inhibitio n of rho activity by C3 exotoxin prevents the delamination of neural crest cells from neural tube explants but has little effect on the initial specif ication of premigratory neural crest cell fate or on the later migration of neural crest cells. These results suggest that rhoB has a role in the dela mination of neural crest cells from the dorsal neural tube.