stocksteif encodes cyp26b1. (A) stocksteif was mapped to a narrow region on linkage group 7. Flanking SSLP markers are both located on BAC zC197C14. cyp26b1 appears to be the only gene present on the clone. (B) Schematic overview of cyp26b1 structure on the genomic level with nonsense (K46STOP or sstsa0002) and splice donor (sstsa0003) mutation indicated. Translated parts of the exons are shaded. (C,D) Alizarin Red bone staining of a cyp26b1+/+ embryo and a transheterozygous cyp26b1(sstsa0002/sstsa0003) embryo. (C′,D′,E-G) Double staining with Alcian Blue for cartilage and Alizarin Red for bone. (C′,D′) A cyp26b1+/+ embryo shows normal cartilage, whereas a transheterozygous cyp26b1(sstsa0002/sstsa0003) embryo shows missing tissue dorsal to the ethmoid plate (asterisk) and fusion of the ceratohyal with the basihyal (arrow). (E-G) Ventral views of a wild-type embryo (E), a homozygous sstt24295 mutant (F) and a homozygous sstsa0002 mutant (G). Note the reduced and misshaped ethmoid plate (asterisk) in the sstsa0002 mutant. (H-K) Expression of col10a1 is not changed in 4 dpf wild-type siblings (H,I) versus mutants (J,K). cl, cleithrum; en, entopterygoid; op, operculum; ps, parasphenoid.