Fig. 4. Cyp26b1 is expressed in mouse osteoblasts prior to osterix expression. (A-E) Cyp26b1 expression in mice. (A) At E14.5 Cyp26b1 mRNA is present in the brain, neural tube, craniofacial structures and in the pre-vertebrae regions. (B) Transversal section (E12.5) showing expression of Cyp26b1 in the cells of the condensing sclerotome (arrows) around the notochord. (C) Detail of sagittal section (E12.5) confirming the segmented pattern in the pre-vertebrae regions. (D-G) Consecutive sections showing expression of Cyp26b1 (D, enlargement in E) and osterix (F, enlargement in G) in the forming vertebrae. Expression is seen in exactly the same region, showing that Cyp26b1 is expressed in osteoblasts. Arrows in D indicate expression of Cyp26b1 in posterior vertebrae where osterix is not expressed yet.