Plasticity in mouse neural crest cells reveals a new patterning role for cranial mesoderm

The anteroposterior identity of cranial neural crest cells is thought to be preprogrammed before these cells emigrate from the neural tube. Here we te st this assumption by developing techniques for transposing cells in the hi ndbrain of mouse embryos, using small numbers of cells in combination with genetic and lineage markers. This technique has uncovered a surprising degr ee of plasticity with respect to the expression of Hox genes, which can be used as markers of different hindbrain segments and cells, in both hindbrai n tissue and cranial neural crest cells. Our analysis shows that the patter ning of cranial neural crest cells relies on a balance between permissive a nd instructive signals, and underscores the importance of cell-community ef fects. These results reveal a new role for the cranial mesoderm in patterni ng facial tissues. Furthermore, our findings argue against a permanently fi xed prepatterning of the cranial neural crest that is maintained by passive transfer of positional information from the hindbrain to the periphery.