NOG and infection: Implantation of Noggin-soaked beads in the FnP mesenchyme at HH15/16 or infection of neural crest cells at HH10 with a replication-competent retrovirus encoding the Bmp antagonist Noggin (RCAS-Noggin) abolished Shh expression in the ventral domains of FEZ (Foppiano et al., 2007; Hu et al., 2015).