Cell context dependent Sonic hedgehog signaling

Abstract

Vagal NCC give rise to neuron and glia of the enteric nervous system (ENS). We have shown that Shh regulated the proliferation of NCC isolated from E11.5 mouse guts. The molecular mechanisms by which Shh regulates cellular behaviors are cell context dependent, and Shh could regulate the migration of NCC independently of Ptc-Smo-Gli pathway. In this study, we investigate the molecular mechanisms by which Shh regulate vagal NCC. Shh enhanced the proliferation of NCC, induced the expression of Gli1 and Ptc1, and prevented the production of Gli3 repressor. Purmorphamine exhibited similar inductions on NCC as Shh. Addition of cyclopamine abolished the Shh induction. Nmyc-1 and cyclin-D1 are upregulated by Shh in CNS progenitors. In contrast, Nmyc-1 and cyclin-D1 in NCC were not upregulated by Shh. Ptc1 deletion leads Smo derepression and constitutive active Shh signaling inducing Gli1 expression in many cell types including CNS progenitors. However, Ptc1 siRNA treatment did not induce Gli1 expression, and Ptc1 knockdown eliminated the Gli1 induction by Shh. Smo knockdown has no effect on the proliferation of NCC, and Shh induction of Gli1 expression in NCC was unaffected by Smo knockdown. Furthermore, conditional deletion of Smo in vagal NCC in mice was generated in our laboratory, and these mutant mice displayed no discernible ENS phenotype. Shh induced Klf4, which was abolished by Ptc1 knockdown. Klf4 knockdown reduced the proliferation of NCC. Our data suggest that Shh regulation of NCC may involve signaling cascades (e.g. Klf4) besides canonical Ptc-Smo-Gli pathway.