The BMP antagonists Nog2, chrd, fsta, and grem2b were found to be expressed in or adjacent to the ANP, and an induction of the BMP ligand bmp4 at 8.5 hpf was sufficient to hamper ANP splitting, which resulted in a severe form of HPE and anophthalmia (Bulk et al. This evidence concerns the gene NPPA and holoprosencephaly.